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EP250404a, GRB 250404A

GCN Circular 41787

Subject
GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
Date
2025-09-11T09:25:59Z (2 months ago)
Edited On
2025-09-11T13:36:52Z (2 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
Web form
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) and D. B. Malesani (DAWN/NBI and Radboud) report:

We carried out a full reduction of the spectrum of GRB 250404A / EP250404a observed with the GMG-2.4m telescope (Li et al., GCN 40084) using the most up-to-date calibrations and complete pipeline procedures.

A Ly-alpha absorption feature at ~4400 AA was reported by the Xinglong-2.16 m telescope (Zhu et al., GCN 40061).

In the GMG spectrum, the region around ~4400 AA exhibits a smooth continuum, and no typical Ly-alpha absorption feature is identified. However, we identified multiple metal absorption features, including Si IV at 1394 AA, Si IV at 1403 AA, Si II at 1527 AA, C IV at 1549 AA, Fe II at 1608 AA, Al II at 1671 AA, Al III at 1855 AA, Al III at 1863 AA, Zn II/Cr II at 2026 AA, Zn II/Cr II at 2062 AA, Fe II at 2344 AA, Fe II at 2374 AA, and Fe II at 2383 AA. These features consistently indicate a redshift of z = 1.88.

In summary, we conclude that the redshift of the transient is z = 1.88 (see Figure B1 of Yin et al., 2025; doi:10.3847/2041-8213/adf552).

We are grateful to D. B. Malesani for kindly pointing out the issue with the redshift determination.
 
We apologize for any confusion that our preliminary report may have caused.

GCN Circular 40236

Subject
GRB 250404A / EP250404a: GRBAlpha detection
Date
2025-04-24T15:03:18Z (6 months ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
Via
Web form
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal,  A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory),  T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.

The long-duration GRB 250404A / EP250404a (Fermi/GBM detection: GCN 40050; EP/WXT detection: GCN 40051; Wind/Konus detection: GCN 40087) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract).

The detection was confirmed at the peak time 2025-04-04 14:20:37.4 UTC. The T90 duration measured by GRBAlpha is 67 s and the overall significance during T90 reaches 19 sigma.

The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250404A_GCN.pdf

All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/
GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.

GCN Circular 40141

Subject
EP250404a: Nanshan 0.43m Telescope optical observatios
Date
2025-04-13T13:41:02Z (7 months ago)
From
Abdusamatjan Iskandar at XAO,CAS <abudu@xao.ac.cn>
Via
Web form
S. Yaqup, J.Z. Liu, A. Iskandar, Y. Zhang, A. Esamdin, C.H. Bai, T.H. Zhong (XAO) report on behalf of optical group of the XAO:

We observed the field of the EP250404a (Einstein Probe mission, Trigger ID 01709133918) with the 0.43m telescope at Nanshan Station of Xinjiang Astronomical Observatory (XAO). The observations were started at 2025-04-04T14:54:21(UTC), and obtained a series of gri band images.

The optical afterglow (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; 
Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al, GCN 40064;  He et al., GCN 40069; 
Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al, GCN 40073; 
Taguchi et al., GCN 40074; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., 
GCN 40083; Li et al., GCN 40084; Yin et al., GCN 40085; Pankov et al., GCN 40086; Chu Chen et al., 
GCN 40088  and Chen et al., GCN 40089) was clearly detected at position R.A. = 125.0606 deg, DEC = 35.5282 deg J2000.

The preliminary photometric magnitudes are below: 

Observation Start-Time	    T-T0(hr)   Exposure	    Filter  Mag.	Err.
2025-04-04 14:54:21	    0.583      060s	    g	    16.914	0.106
2025-04-04 14:55:56	    0.604      060s	    r	    16.067	0.076
2025-04-04 14:57:12	    0.626      060s	    i	    15.610	0.080
2025-04-04 14:58:29	    0.648      060s	    g	    17.090	0.108
2025-04-04 14:59:48	    0.669      060s	    r	    16.294	0.072
2025-04-04 15:01:05	    0.690      060s	    i	    15.940	0.105
2025-04-04 15:02:22	    0.712      060s	    g	    17.484	0.108
2025-04-04 15:03:41	    0.734      060s	    r	    16.398	0.071
2025-04-04 15:04:58	    0.755      060s	    i	    15.965	0.099
2025-04-04 15:11:08	    0.858      120s	    i	    16.388	0.067
2025-04-04 15:13:25	    0.897      120s	    g	    17.690	0.106
2025-04-04 15:15:44	    0.934      120s	    r	    17.066	0.077
2025-04-04 15:18:01	    0.972      120s	    i	    16.496	0.074
2025-04-04 15:20:19	    1.011      120s	    g	    17.735	0.096
2025-04-04 15:22:38	    1.049      120s	    r	    17.030	0.059
2025-04-04 15:24:54	    1.087      120s	    i	    16.736	0.061
2025-04-04 15:27:12	    1.126      120s	    g	    18.184	0.105
2025-04-04 15:29:31	    1.164      120s	    r	    17.407	0.070
2025-04-04 15:31:48	    1.202      120s	    i	    17.033	0.067
2025-04-04 15:34:27	    1.247      200s	    g	    18.252	0.090
2025-04-04 15:52:56	    1.554      200s	    r	    17.719	0.085
2025-04-04 15:56:33	    1.615      200s	    i	    17.332	0.088
2025-04-05 16:00:10	    1.676      200s	    g	    18.508	0.116
2025-04-05 16:03:50	    1.736      200s	    r	    18.121	0.087
2025-04-05 16:07:27	    1.796      200s	    i	    17.742	0.101
2025-04-05 16:11:04	    1.857      200s	    g	    18.335	0.093
2025-04-05 16:14:43	    1.917      200s	    r	    17.924	0.070
2025-04-05 16:18:19	    1.978      200s	    i	    17.569	0.090
2025-04-05 16:25:36	    2.099      200s	    r	    18.261	0.081
2025-04-05 16:36:30	    2.280      200s	    r	    18.681	0.117
2025-04-05 16:40:06	    2.341      200s	    i	    18.319	0.136
2025-04-05 16:43:45	    2.402      200s	    g	    18.815	0.129
2025-04-05 16:47:42	    2.467      300s	    g	    18.713	0.123
2025-04-05 16:52:59	    2.555      300s	    r	    18.799	0.132
2025-04-05 16:58:16	    2.643      300s	    i	    17.798	0.094
2025-04-05 17:03:34	    2.732      300s	    g	    19.368	0.188
2025-04-05 17:08:52	    2.820      300s	    r	    18.608	0.111

The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction.

GCN Circular 40097

Subject
EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
Date
2025-04-06T19:33:24Z (7 months ago)
Edited On
2025-04-07T13:44:45Z (7 months ago)
From
qiang xi <xiqiang051@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of qiang xi <xiqiang051@gmail.com>
Via
Web form

Qiang-Xi (UCAS), Yiming-Mao (NAOC), Xinxiang-Sun (NAOC), Ningchen-Sun (NAOC), Junjie-Jin (NAOC), Min-He (NAOC) report:

We detected an optical counterpart for the field of EP 250404A using two independent facilities: the 70 cm telescope UCAS-70 and the 35 cm telescope XL-C14. The optical counterpart was observed at the coordinates:

RA = 08h20m14.54s, Dec = +35°31′42.2″.

Stacked imaging of the field has revealed a clear optical transient. The photometric measurements derived from the stacked images are summarized below. In our analysis, the photometry in the Johnson band was calibrated from APASS data converted using the Lupton (2005) equations, while the SDSS band data were calibrated against the SDSS star catalog. The observation time reported corresponds to the median of the individual exposure times.

Median Time (UT)TelescopeExposure (s)FilterMagnitudeErr
2025-04-04 15:42:35.500UCAS-706×180B18.730.24
2025-04-04 15:45:44.199UCAS-706×180V17.890.12
2025-04-04 15:48:52.780UCAS-706×180R17.180.14
2025-04-04 15:52:01.952UCAS-706×180I16.760.13
2025-04-04 16:04:43.721XL-C1411×120g>18.71( 3-sigma limit)
2025-04-04 16:17:19.682XL-C1413×120r17.590.19
2025-04-04 16:15:12.716XL-C1413×120i17.150.20
2025-04-04 15:58:22.729XL-C148×120z>17.41( 3-sigma limit)

This measurement has not been corrected for galaxy extinction.

Our observations are consistent with other already reported Jiang et al. (GCN 40052

Loading...
 
 
), Perez-Garcia et al. (GCN 40053), Du et al. (GCN 40058), Zhu et al. (GCN 40061), Konno et al. (GCN 40063), Odeh et al. (GCN 40064), Lipunov et al. (GCN 40066), Min-He et al. (GCN 40069), Lipunov et al. (GCN 40070), Perez-Fournon et al. (GCN 40071), Jelinek et al. (GCN 40072), Rakotondrainibe et al. (GCN 40073), Taguchi et al. (GCN 40074), Brivio et al. (GCN 40075), Ruocco (GCN 40076), Martin-Carrillo et al. (GCN 40080), Pavoni et al. (GCN 40083), Li et al. (GCN 40084), Yin et al. (GCN 40085), Pankov et al. (GCN 40086), Chen et al. (GCN 40088), Chen et al. (GCN 40089), Pankov et al. (GCN 40090), Leonini et al. (GCN 40093), Leonini et al(GCN40095).

GCN Circular 40095

Subject
GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
Date
2025-04-06T17:44:24Z (7 months ago)
From
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai@tiscali.it>
Via
Web form
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy 
Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. 

Report:

We observed the field of GRB 250404A detected by Fermi Gamma-ray Burst Monitor (GBM team, GCN 40050) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. 
  
The observations were started at 2025-04-04 22:45 UT (approximately 8.42 hours after burst) stacking a set of unfiltered CCD image. The observations were made with modest visibility conditions: passing clouds and Moon (illumin. 48%, dist. 19°)

The OT was detected at the following position (+/- 0.3 arcsec):

RA    (J2000.0)  08h 20m 14.59s   
Decl. (J2000.0) +35° 31' 41.5" 

Photometry was obtained using nearby PanSTARRS stars as follows: 

Observation    Mid-Time    T-T0 (hr)      Exposure        Filter      Mag.      Err.
2025-04-04   23:27:00 UT    9.12           82x60s          CR        20.16     +/-0.2

Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. 
No correction for galactic dust extinction was applied.

Our observations are consistent with other already reported Jiang et al. (GCN 40052), Perez-Garcia et al. (GCN 40053), Du et al. (GCN 40058), Zhu et al. (GCN 40061), Konno et al. (GCN 40063), Odeh et al. (GCN 40064), Lipunov et al. (GCN 40066), Min-He et al. (GCN 40069), Lipunov et al. (GCN 40070), Perez-Fournon et al. (GCN 40071), Jelinek et al. (GCN 40072), Rakotondrainibe et al. (GCN 40073), Taguchi et al. (GCN 40074), Brivio et al. (GCN 40075), Ruocco (GCN 40076), Martin-Carrillo et al. (GCN 40080), Pavoni et al. (GCN 40083), Li et al. (GCN 40084), Yin et al. (GCN 40085), Pankov et al. (GCN 40086), Chen et al. (GCN 40088), Chen et al. (GCN 40089), Pankov et al. (GCN 40090), Leonini et al. (GCN 40093).

The message may be cited.

GCN Circular 40093

Subject
EP250404a / GRB 250404A: Montarrenti Observatory optical observations
Date
2025-04-06T13:49:11Z (7 months ago)
From
Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini@iol.it>
Via
Web form
S. Leonini, A. Lorini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:

we observed the field of the X-ray transient EP250404a (Einstein Probe mission, Trigger ID 01709133918) probably associated with GRB 250404A (Fermi team, GCN 40050) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).

The observations were started at 2025-04-04 18:36:04 UT (approximately 4 hours after burst) ending at 2025-04-04 22:00:50 UT stacking a set of  Rc-band CCD images.  Observations were performed under thin cloud cover in the second part of the night. 

The optical afterglow (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al, GCN 40064;  He et al., GCN 40069; Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al, GCN 40073; Taguchi et al., GCN 40074; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Yin et al., GCN 40085; Pankov et al., GCN 40086; Chu Chen et al., GCN 40088  and Chen et al., GCN 40089) was clearly detected at the following position:

RA    (J2000.0)  08h 20m 14.57s  +/-0.06 
Decl. (J2000.0) +35° 31' 42.0"   +/-0.04

Preliminary photometry was obtained using nearby PanSTARRS stars as follows: 

Observation Mid-Time    T-T0 (hr)        Exposure        Filter       Mag.        Err.        
2025-04-04  18:36:24 UT   4.27            50x40s           Rc        19.60       +/-0.10    
2025-04-04  19:11:30 UT   4.85            50x40s           Rc        19.67       +/-0.10
2025-04-04  19:46:31 UT   5.43            50x40s           Rc        19.81       +/-0.15
2025-04-04  20:21:33 UT   6.02            54x40s           Rc        20.25       +/-0.20
2025-04-04  21:07:10 UT   6.78            78x40s           Rc        20.16       +/-0.12

Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.
  
Along the span of our observations and within our uncertainties, the afterglow evolves in agreement with a power-law decay with a rate alpha ~1.40.

GCN Circular 40090

Subject
GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
Date
2025-04-06T13:05:06Z (7 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
 N. Pankov (HSE), A.N. Tarasenkov (INASAN), A. Pozanenko (IKI) report on
behalf of IKI GRB-FuN:

We observed GRB 250404A / EP250404a (Fermi GBM team, GCN 40050; Hu et al.,
GCN 40051; Frederiks et al., GCN 40087) with RC500 telescope of the
INASAN-Kislovodsk observatory. The optical counterpart (Jiang et al., GCN
40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al.,
GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN
40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072;
Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et
al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN
40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Yin et al., GCN
40085; Pankov et al., GCN 40086; Chen et al., GCN 40088;) is not detected
starting on 2025-04-04 (UT) 21:10:11. Preliminary upper limit of the
stacked image is the following

Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)

2025-04-04 21:10:11 0.33362 R 70*120 n/d n/d 20.1

The photometry is based on nearby USNO-B1.0 stars.

GCN Circular 40089

Subject
GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
Date
2025-04-06T12:27:20Z (7 months ago)
From
Chen Liang-Jun at Guangxi University <chenlj@st.gxu.edu.cn>
Via
Web form
L. J. Chen(GXU), L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan,  W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM follow-up team:


We observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A (Fermi team, GCN 40050), with the GWAC-F50A and GWAC-F60 at Xinglong Observatory, China. F50 started observing at 2025-04-04T14:25:34 UTC and lasted until 2025-04-04T15:36:36 with 9 frames in R-band and 15 frames in I-band. F60A started observing at 2025-04-04T14:24:56 UTC and lasted until 2025-04-04T15:24:21 with 25 frames in R-band. F60B started observing at 2025-04-04T14:25:05 UTC and lasted until 2025-04-04T15:24:28 with 25 frames in R-band.

The optical counterpart of GRB 250404A / EP250404a (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Pankov et al., GCN 40086), was clearly detected in our images.

The afterglow shows a first brightening and then a single decay with a peak magnitude of R~14.3 mag, calibrated to the USNO B1.0 catalog, at about 1000 sec after the burst.

Two 60cm GWAC-F60(A/B) are operated by Guangxi University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 19*19 arcmin.  The 50cm telescope (F50A) is operated by Huaibei Normal University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 27*27 arcmin.

GCN Circular 40088

Subject
EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
Date
2025-04-06T12:26:24Z (7 months ago)
From
Chun Chen at Sun Yat-sen University, SYSU 80cm telescope team <chench386@mail2.sysu.edu.cn>
Via
Web form
Chun Chen, Xia Li, Zhong-Nan Dong, Jia-Qi Lin, Wei-Sen Huang, Jin-Ji Li, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Hao-Yuan Zheng, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team:

We observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB250404A (Fermi GBM team, GCN40050; Fermi GBM team, GCN40067), using the Sun Yat-sen University 80cm infrared telescope with 183 x 20 s exposures in J band. The calculated position is R.A. = 125.0575 deg, DEC = 35.5305 deg J2000, from EP/FXT observation. Our observations began at 2025-4-4 15:25:20 UTC, 1.09 hours after the EP trigger. 

We detected a counterpart at the position of the optical afterglow (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al. GCN 40063; Odeh et al., GCN 40064; Lipunov et al., GCN 40066; He et al., GCN 40069; Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074;  Ruocco, GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084) in the stacked images. The preliminary photometric magnitudes in J band are below:

Start Time (UTC)    |Band | Exp   | Mag (Vega)
--------------------|-----|-------|------------------
2025/4/4 15:25:20   | J   | 200s  | 15.30+/-0.08
2025/4/4 15:28:40   | J   | 200s  | 15.28+/-0.09
2025/4/4 15:32:20   | J   | 200s  | 15.47+/-0.10
2025/4/4 15:35:40   | J   | 200s  | 15.76+/-0.11
2025/4/4 15:39:00   | J   | 360s  | 15.83+/-0.10
2025/4/4 15:50:20   | J   | 400s  | 16.05+/-0.12
2025/4/4 15:57:00   | J   | 400s  | 15.99+/-0.12
2025/4/4 16:03:40   | J   | 400s  | 15.99+/-0.12
2025/4/4 16:10:40   | J   | 400s  | 16.29+/-0.15
2025/4/4 16:17:40   | J   | 1100s | 16.21+/-0.11

The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitudes are not corrected for Galactic extinction.

GCN Circular 40087

Subject
Konus-Wind detection of GRB 250404A / EP250404a
Date
2025-04-06T12:08:53Z (7 months ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 250404A (Fermi-GBM detection:
The Fermi GBM team, GCN 40050; Mukherjee & Meegan, GCN 40067),
coincident with the X-ray transient EP250404a (Hu et al., GCN 40051),
triggered Konus-Wind (KW) at T0=51605.773 s UT (14:20:05.773).

The burst light curve shows a multi-peaked structure
which starts at ~T0-21 s and has a total duration of ~105 s.
The emission is seen up to ~1 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250404_T51605/

As observed by Konus-Wind, the burst had
a fluence of (2.83 ± 0.09)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 0.832 s,
of (1.78 ± 0.22)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+81.186 s)
is best fit in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.38(-0.13,+0.14) and Ep = 56(-5,+4) keV (chi2 = 76/98 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -3.5 (chi2 = 76/97 dof).

The spectrum near the peak count rate(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a CPL
with  alpha = -1.16(-0.17,+0.19) and Ep = 68(-9,+8) keV (chi2 = 90/96 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -4.2 (chi2 = 90/95 dof).

Assuming the redshift z ~ 2.627 ( Li et al., GCN 40084) and a standard cosmology
with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the burst isotropic energy release E_iso to (4.60 ± 0.14)x10^53 erg,
the isotropic peak luminosity L_iso to (1.05 ± 0.13)x10^53 erg/s,
the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (203 ± 18) keV,
and the rest-frame peak energy at the peak of the emission Ep,p,z to (247 ± 30) keV.
With the obtained estimates, GRB 250404A lies at the lower edge, but is consistent
with 90% prediction bands of the 'Amati' and 'Yonetoku' relations
for the sample of >300 long KW GRBs with known redshifts
(Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB250404_T51605/GRB250404A_rest_frame.pdf

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.

GCN Circular 40086

Subject
GRB 250404A / EP250404a: Mondy optical observations
Date
2025-04-06T11:27:55Z (7 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
 N. Pankov (HSE), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of
IKI GRB-FuN:

We observed GRB 250404A / EP250404a (Fermi GBM team, GCN 40050; Hu et al.,
GCN 40051). The optical counterpart (Jiang et al., GCN 40052; Perez-Garcia
et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et
al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon
et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN
40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al.,
GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li
et al., GCN 40084; Yin et al., GCN 40085) is early detected on 2025-04-04
and was observed between (UT) 14:50:52 and 17:09:01. We obtained an upper
limit on 2025-04-05. Preliminary photometry of some stacked images is the
following

Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)

2025-04-04 14:50:52 0.04244 R 40*90 16.53 0.02 22.4
2025-04-04 16:01:21 0.08999 R 28*120 17.96 0.03 22.2
2025-04-05 15:08:33 1.05611 R 42*90 n/d n/d 21.5

The photometry is based on nearby USNO-B1.0 stars.

GCN Circular 40085

Subject
EP250404a: refined analysis of the EP-WXT and EP-FXT observations
Date
2025-04-06T09:45:07Z (7 months ago)
Edited On
2025-04-07T13:45:15Z (7 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (NJU), J. W. Hu (NAO, CAS), Y. L. Hua (PMO, CAS), Q. C. Liu (THU), B. B. Zhang (BNU), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:

The X-ray transient EP250404a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 40051), and followed up by several telescopes (Jiang et al, GCN 40052, Perez-Garcia et al, GCN 40053, Du et al, GCN 40058, Zhu et al, GCN 40061, Konno et al, GCN 40063, Odeh et al, GCN 40064, Lipunov et al, GCN 40066, He et al, GCN 40069, Pérez-Fournon et al, GCN 40071, Jelinek et al, GCN 40072, Rakotondrainibe et al, GCN 40073, Taguchi et al, GCN 40074, Brivio et al, GCN 40075, Ruocco et al, GCN 70076, Martin-Carrillo et al, GCN 40080, Pavoni et al, GCN 40083, Li et al, GCN 40084), with an optical counterpart detected at a redshift of 2.63 (Zhu et al, GCN 40061, Li et al, GCN 40084). Refined analysis of the WXT data shows that the event started at T0=2025-04-04T14:19:45 (UTC) and lasted for about 16 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.41 (-0.28/+0.26). The absorption is fixed at the best-fit values from FXT spectral fitting with a Galactic hydrogen column density of 6.00 x 10^20 cm^-2 and an intrinsic hydrogen column density of 4.89 x 10^22 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 5.9 (-1.6/+2.2) x 10^(-8) erg/s/cm^2. The data recovered from the slew process shows that the transient event lasted for about 300 seconds.

The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 1 min after T0, starting at 2025-04-04T14:20:46 (UTC). Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 125.0601, DEC = 35.5284 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is also consistent with the position of the optical counterpart. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 6.00 x 10^20 cm^-2 and an intrinsic hydrogen column density of 4.89 (-0.45/+0.33) x 10^22 cm^-2. The photon index is 2.18 (-0.03/+0.03). The derived average unabsorbed 0.5-10 keV flux is 9.00 (-0.25/+0.19) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).

GCN Circular 40084

Subject
GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
Date
2025-04-06T03:57:18Z (7 months ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
Web form
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report:

GRB 250404A / EP250404a was detected by Fermi GBM (Fermi GBM team, GCN 40050) and by EP/WXT (Hu et al., GCN 40051). We observed the optical counterpart of GRB 250404A / EP250404a (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083). 

The spectroscopic observation was conducted using the GMG-2.4m telescope with Grism #14, which provides a wavelength coverage of 3600–7460 AA. A single 1800s spectrum was obtained, with exposure beginning at 2025-04-04T15:18:24, about 0.98 hours after the Fermi/GBM and EP/WXT trigger (Fermi GBM team, GCN 40050; Hu et al., GCN 40051).

Two absorption systems were identified in the spectrum. 

For the first absorption system, we detected multiple metal absorption features, including Si II at 1527 AA, Al II at 1671 AA, Al III at 1855 AA and 1863 AA, Zn II/Cr II at 2026 AA and 2062 AA, and Fe II at 2344 AA, 2374 AA, and 2383 AA. These features consistently indicate a redshift of z ~ 1.881. 

For the second absorption system, the spectrum shows multiple metal absorption lines from Si II/S II at 1260 AA, O I/Si II at 1303 AA, C II at 1335 AA, Si IV at 1394 AA, Si II at 1527 AA, Fe II at 1608 AA, and Al III at 1863 AA. These absorption features correspond to a redshift of z ~ 2.627. 

These results support a redshift of z ~ 2.627 for the transient, consistent with the measurement reported by Xinglong-2.16m (Zhu et al., GCN 40061).

We thank the staff at the Lijiang Observatory for their support in conducting the observation.

GCN Circular 40083

Subject
GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
Date
2025-04-05T22:56:51Z (7 months ago)
From
leavittob@gmail.com
Via
Web form
E. Pavoni,  L. Moretti (Leavitt Observatory, Italy)

Members of:
GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani
ATA - Associazione Tuscolana di Astronomia

In a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
report:

We observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A (Fermi team, GCN 40050), with our RC telescope (D=250 mm, F/D=8) of Leavitt Observatory, Manciano, Italy. 
Median moon illumination of 47% was present.

The observations started approximately 5.1 hours after the trigger time, stacking a series of R-Cousins filtered exposures, for a total integration time of approximately 88 minutes. All images were processed using the astropy package (Astropy Collaboration et al., 2022ApJ...935..167A).

We detected the optical counterpart (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al. GCN 40063; Odeh et al., GCN 40064; Lipunov et al., GCN 40066; He et al., GCN 40069; Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074;  Ruocco, GCN 40076; Martin-Carrillo et al., GCN 40080) in the stacked image at the following coordinates +/- 2 arcsec:

R.A. (J2000) =  08:20:14:59
Dec. (J2000) = +35:31:41:75

with the following photometry: 

Date UT at mid-exposure: 2025-04-04 20:24:18 UTC
Mag (R Cousins) 19.47 
Error +/- 0.2

Magnitudes were estimated with the Pan-STARRS cat. and converted using Lupton (2005) equations. No corrected for galactic dust extinction.

The message may be cited.


Reference:
https://leavittobservatory.altervista.org

GCN Circular 40080

Subject
GRB 250404A / EP250404a: NOT optical observations
Date
2025-04-05T15:27:15Z (7 months ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
A. Martin-Carrillo (UCD), B. Schneider (LAM), A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. An (NAOC), D. Xu (NAOC), G. Corcoran (UCD), Dimple (U. Birmingham), M. A. Diaz Teodori (NOT and Turku Univ.), report on behalf of a larger collaboration:

We observed the field of EP250404a (Hu et al., GCN 40051), likely associated with GRB 250404A detected by Fermi/GBM (Fermi GBM team, GCN 40050; Mukherjee & Meegan, GCN 40067) using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained exposures in the SDSS-r (3x180 s) and SDSS-z (2x180 s) bands, starting at 22:09:17 UT on 2025-04-04 (7.82 hr after the EP trigger).

The optical counterpart reported by Jiang et al. (GCN. 40052), Perez-Garcia et al. (GCN 40053), Du et al. (GCN 40058), Zhu et al. (GCN 40061), Konno et al. (GCN 40063), Odeh et al. (GCN 40064), He et al. (GCN 40069), Pérez-Fournon et al. (GCN 40071), Jelinek et al. (GCN 40072), Rakotondrainibe et al. (GCN 40073), Taguchi et al. (GCN 40074), Ruocco et al. (GCN 40076) is well detected in the stacked images, with the following preliminary magnitudes:

r = 20.43 +/- 0.05  (7.90 hr after trigger);
z = 19.79 +/- 0.06  (8.04 hr after trigger).

The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction.

GCN Circular 40076

Subject
EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
Date
2025-04-05T10:05:39Z (7 months ago)
From
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy - MPC Code C82 <osservatorionastroverde@gmail.com>
Via
Web form
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:
 
Following the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission  triggered EP-WXT (ID: 01709133918) (GCN Circular 40051 J. W. Hu (NAO, CAS), Q. C. Liu (THU), B. B. Zhang (BNU), Y. L. Hua (PMO, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team), I pointed at the coordinates RA(J2000)= 08:20:14.59 : Dec(J2000)= +35:31:42.3 and started observations with telescope of Nastro Verde Observatory - Sorrento (Naples), Italy.
Member of: 
AAVSO - American Association of Variable Star Observers.
GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.

Clear sky but moon presence at about 20 degrees from the target.
The observations started at 20:36 UT of 2025/04/04, after about 6 hours after the GRB trigger, with clear sky, with principal telescope  SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME
I took 22 unfiltered images of 120 sec . 
   Start                 End               Rlim
20:36:23 UT            21:22:15 UT         20.5

All images, calibrated with masterdark and masterflat have been measured with Thycho Tracker software
We have detected a faint source at the enhanced position reported by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission AT following position

RA (J2000.0)   08 20 15.95
Dec (J2000.0) +35 31 48.3  

with the following photometry and astrometry:


EP250404a 08 20 15.95 +35 31 48.3         19.0       C82




Magnitudes were estimated with the ATLAS cat. and are not corrected for galactic dust extinction.



The message may be cited.

GCN Circular 40075

Subject
EP250404a: REM optical/NIR observations
Date
2025-04-05T09:32:41Z (7 months ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:

We observed the field of EP250404a (Hu et al., GCN 40051), likely associated with GRB 250404A detected by Fermi/GBM (Fermi GBM team, GCN 40050) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 04 at 23:26:12 UT (i.e. 9.1 hr after the burst), and lasted for about 1 hour.

From preliminary inspection, we do not detect any counterpart at the position of the optical afterglow (Jiang et al., GCN. 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074) down to the following 3sigma limits:

r > 19.7 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 9.6 hours after the trigger;

H > 16.3 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 9.5 hours after the trigger.

GCN Circular 40074

Subject
EP250404a: Seimei/TriCCS optical counterpart detection
Date
2025-04-05T09:09:53Z (7 months ago)
From
Kenta Taguchi <kentagch@kusastro.kyoto-u.ac.jp>
Via
Web form
Kenta Taguchi, Keiichi Maeda (Kyoto U.), Masaomi Tanaka (Tohoku U.) report on behalf of a larger collaboration:

We observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051) using the Tricolor CMOS Camera and Spectrograph (TriCCS) on the 3.8-m Seimei telescope. Observations started at 15:27:48 UT on 2025-04-04  (MJD = 60769.64). We detected a counterpart at a position consistent with the source detected by Jiang et al. (GCN 40052, also reported by Perez-Garcia et al. GCN 40053, Du et al. GCN 40058, Konno et al. GCN 40063, Odeh et al. GCN 40064, He et al. GCN 40069, Pérez-Fournon et al. GCN 40071, Jelinek et al. GCN 40072, Rakotondrainibe et al. GCN 40073).

Preliminary analysis gives the following magnitudes of the source:
g = 18.20 +- 0.05
r = 17.46 +- 0.04
i = 17.10 +- 0.03

GCN Circular 40072

Subject
EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
Date
2025-04-05T03:49:34Z (7 months ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov) report:We observed the field of EP250404a detected by EP (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A (Fermi team, GCN 40050; Mukherjee et al., GCN 40067), using the D50 telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. Our observations started at 15:50 UT on 2025-04-04, approximately 5.5 hours after the trigger. We performed a series of 120s exposures in the SDSS i' filter. The optical counterpart, previously reported by several teams (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071), is detected in our combined image of 25x120s exposures. The PanSTARRS-calibrated magnitude of the source is i' = 19.5 +/- 0.1, not corrected for Galactic extinction.

GCN Circular 40071

Subject
EP250404a: LCO optical counterpart detection
Date
2025-04-05T00:52:37Z (7 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), D. Aguado, A. López-Oramas, D. Nespral (IAC and ULL), N.C. Sun (UCAS), W. Li, Y. Wang, and Z. Niu (NAOC)

We report on Las Cumbres Observatory Global Telescope network (LCOGT) observations of the X-ray transient EP250404a (Hu et al., GCN circ. 40051), that is temporally and spatially consistent with the likely long GRB 250404A, detected by Fermi/GBM (Fermi GBM team, GCN 40050; and Mukherjee et al., GCN circ. 40067).

We observed the field of EP250404a with the two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Teide Observatory (Tenerife, Spain) in the SDSS i, g, and r filters,
starting at 2025-04-04 20:27:26 UTC, about 6.12 hours after the EP trigger. An uncatalogued source is clearly detected in the three images at the position of the optical counterpart first reported by 
Jiang et al. (GCN circ. 40052) and also detected by Perez-Garcia et al. (GCN circ. 40053), Du et al.  (GCN circ. 40058), Zhu et al. (GCN circ. 40061), Konno et al. (GCN circ. 40063), Odeh et al. (GCN circ. 40064), and He et al. (GCN circ. 40069). A redshift of z = 2.63 has been reported by Zhu et al. (GCN circ. 40061).

We measure the following preliminary magnitudes, calibrated against Pan-STARRS DR2 stars, that are not corrected for Galactic extinction:


Date       |  UT start |  mag  | error | filter | exposure time (sec)
---------------------------------------------------------------------
2025-04-04   20:27:26    20.11   0.22      i             300
2025-04-04   22:01:01    20.65   0.16      g             300
2025-04-04   22:05:55    20.38   0.11      r             300

 
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).

GCN Circular 40070

Subject
Fermi GRB 250404A: Global MASTER-Net observations report
Date
2025-04-05T00:17:01Z (7 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-Tunka robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250404A ( Fermi GBM team, GCN 40050) errorbox  16599 sec after notice time and 16639 sec after trigger time at 2025-04-04 18:57:05 UT, with upper limit up to  19.5 mag. The observations began at zenith distance = 66 deg. The sun  altitude  is -28.6 deg. 

MASTER-OAFA robotic telescope  located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250404A errorbox  31880 sec after notice time and 31919 sec after trigger time at 2025-04-04 23:11:46 UT, with upper limit up to  19.3 mag. Observations started at twilight.  The observations began at zenith distance = 67 deg. The sun  altitude  is -10.4 deg. 

The galactic latitude b = 32 deg., longitude l = 188 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2832903

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   16669 | 2025-04-04 18:57:05 |        MASTER-Tunka | (08h 19m 51.88s , +36d 00m 34.0s) |   C |    60 | 18.6 |        
   16729 | 2025-04-04 18:57:05 |        MASTER-Tunka | (08h 19m 51.88s , +36d 00m 34.0s) |   C |   180 | 19.3 |  Coadd 
   16740 | 2025-04-04 18:58:16 |        MASTER-Tunka | (08h 19m 58.07s , +36d 00m 34.7s) |   C |    60 | 18.6 |        
   16812 | 2025-04-04 18:59:28 |        MASTER-Tunka | (08h 19m 55.11s , +36d 02m 04.0s) |   C |    60 | 18.6 |        
   16885 | 2025-04-04 19:00:41 |        MASTER-Tunka | (08h 19m 55.07s , +36d 00m 32.5s) |   C |    60 | 18.7 |        
   16945 | 2025-04-04 19:00:41 |        MASTER-Tunka | (08h 19m 55.07s , +36d 00m 32.5s) |   C |   180 | 19.4 |  Coadd 
   16962 | 2025-04-04 19:01:58 |        MASTER-Tunka | (08h 19m 57.66s , +36d 02m 04.7s) |   C |    60 | 18.6 |        
   17033 | 2025-04-04 19:03:09 |        MASTER-Tunka | (08h 19m 52.37s , +36d 01m 15.7s) |   C |    60 | 18.7 |        
   17108 | 2025-04-04 19:04:24 |        MASTER-Tunka | (08h 19m 51.30s , +36d 02m 12.7s) |   C |    60 | 18.7 |        
   17168 | 2025-04-04 19:04:24 |        MASTER-Tunka | (08h 19m 51.30s , +36d 02m 12.8s) |   C |   180 | 19.5 |  Coadd 
   17393 | 2025-04-04 19:09:09 |        MASTER-Tunka | (08h 19m 52.28s , +35d 59m 59.8s) |   C |    60 | 18.7 |        
   17466 | 2025-04-04 19:10:22 |        MASTER-Tunka | (08h 19m 58.20s , +36d 00m 10.2s) |   C |    60 | 18.7 |        
   17540 | 2025-04-04 19:11:35 |        MASTER-Tunka | (08h 19m 54.28s , +36d 01m 24.3s) |   C |    60 | 18.7 |        
   17600 | 2025-04-04 19:11:35 |        MASTER-Tunka | (08h 19m 54.28s , +36d 01m 24.2s) |   C |   180 | 19.4 |  Coadd 
   17612 | 2025-04-04 19:12:48 |        MASTER-Tunka | (08h 19m 54.27s , +35d 59m 56.4s) |   C |    60 | 18.6 |        
   17683 | 2025-04-04 19:13:59 |        MASTER-Tunka | (08h 19m 57.20s , +36d 01m 34.1s) |   C |    60 | 18.6 |        
   17756 | 2025-04-04 19:15:12 |        MASTER-Tunka | (08h 19m 51.23s , +36d 00m 41.3s) |   C |    60 | 18.5 |        
   17816 | 2025-04-04 19:15:12 |        MASTER-Tunka | (08h 19m 51.23s , +36d 00m 41.3s) |   C |   180 | 19.3 |  Coadd 
   17829 | 2025-04-04 19:16:24 |        MASTER-Tunka | (08h 19m 51.76s , +36d 01m 37.4s) |   C |    60 | 18.6 |        
   17903 | 2025-04-04 19:17:39 |        MASTER-Tunka | (08h 19m 57.64s , +36d 00m 34.5s) |   C |    60 | 18.7 |        
   17975 | 2025-04-04 19:18:51 |        MASTER-Tunka | (08h 19m 51.82s , +35d 59m 30.3s) |   C |    60 | 18.6 |        
   18035 | 2025-04-04 19:18:51 |        MASTER-Tunka | (08h 19m 51.82s , +35d 59m 30.3s) |   C |   180 | 19.4 |  Coadd 
   18048 | 2025-04-04 19:20:04 |        MASTER-Tunka | (08h 19m 57.26s , +35d 59m 42.1s) |   C |    60 | 18.6 |        
   18120 | 2025-04-04 19:21:16 |        MASTER-Tunka | (08h 19m 53.77s , +36d 01m 07.0s) |   C |    60 | 18.5 |        
   18192 | 2025-04-04 19:22:28 |        MASTER-Tunka | (08h 19m 53.78s , +35d 59m 24.2s) |   C |    60 | 18.6 |        
   18252 | 2025-04-04 19:22:28 |        MASTER-Tunka | (08h 19m 53.78s , +35d 59m 24.1s) |   C |   180 | 19.4 |  Coadd 
   18263 | 2025-04-04 19:23:39 |        MASTER-Tunka | (08h 19m 57.55s , +36d 00m 59.3s) |   C |    60 | 18.7 |        
   18337 | 2025-04-04 19:24:53 |        MASTER-Tunka | (08h 19m 50.49s , +36d 00m 11.6s) |   C |    60 | 18.6 |        
   31925 | 2025-04-04 23:11:46 |         MASTER-OAFA | (08h 08m 19.47s , +34d 59m 12.3s) |   C |    10 | 14.9 |        
   31925 | 2025-04-04 23:11:46 |         MASTER-OAFA | (08h 19m 21.81s , +35d 21m 51.8s) |   C |    10 | 16.5 |        
   31967 | 2025-04-04 23:12:28 |         MASTER-OAFA | (08h 08m 15.18s , +35d 00m 30.7s) |   C |    10 | 14.9 |        
   31967 | 2025-04-04 23:12:28 |         MASTER-OAFA | (08h 19m 17.72s , +35d 23m 08.7s) |   C |    10 | 16.6 |        
   32005 | 2025-04-04 23:13:06 |         MASTER-OAFA | (08h 08m 15.01s , +34d 58m 38.5s) |   C |    10 | 14.9 |        
   32005 | 2025-04-04 23:13:06 |         MASTER-OAFA | (08h 19m 17.32s , +35d 21m 15.2s) |   C |    10 | 16.7 |        
   32044 | 2025-04-04 23:13:45 |         MASTER-OAFA | (08h 08m 17.35s , +35d 00m 09.4s) |   C |    10 | 15.1 |        
   32044 | 2025-04-04 23:13:45 |         MASTER-OAFA | (08h 19m 19.90s , +35d 22m 45.2s) |   C |    10 | 16.8 |        
   32086 | 2025-04-04 23:14:27 |         MASTER-OAFA | (08h 08m 10.02s , +34d 59m 29.2s) |   C |    10 | 15.2 |        
   32086 | 2025-04-04 23:14:27 |         MASTER-OAFA | (08h 19m 12.52s , +35d 22m 04.1s) |   C |    10 | 16.8 |        
   32127 | 2025-04-04 23:15:08 |         MASTER-OAFA | (08h 08m 11.16s , +35d 00m 25.4s) |   C |    10 | 15.2 |        
   32127 | 2025-04-04 23:15:08 |         MASTER-OAFA | (08h 19m 13.83s , +35d 22m 59.5s) |   C |    10 | 16.8 |        
   32165 | 2025-04-04 23:15:45 |         MASTER-OAFA | (08h 08m 16.58s , +34d 59m 22.6s) |   C |    10 | 15.3 |        
   32165 | 2025-04-04 23:15:46 |         MASTER-OAFA | (08h 19m 19.15s , +35d 21m 56.2s) |   C |    10 | 17.0 |        
   32204 | 2025-04-04 23:16:24 |         MASTER-OAFA | (08h 08m 09.70s , +34d 58m 17.6s) |   C |    10 | 15.3 |        
   32204 | 2025-04-04 23:16:25 |         MASTER-OAFA | (08h 19m 12.12s , +35d 20m 50.5s) |   C |    10 | 16.9 |        
   32241 | 2025-04-04 23:17:02 |         MASTER-OAFA | (08h 08m 15.41s , +34d 58m 44.1s) |   C |    10 | 15.3 |        
   32241 | 2025-04-04 23:17:02 |         MASTER-OAFA | (08h 19m 17.91s , +35d 21m 16.7s) |   C |    10 | 17.0 |        
   32280 | 2025-04-04 23:17:41 |         MASTER-OAFA | (08h 08m 11.54s , +35d 00m 01.8s) |   C |    10 | 15.3 |        
   32280 | 2025-04-04 23:17:41 |         MASTER-OAFA | (08h 19m 14.23s , +35d 22m 33.8s) |   C |    10 | 17.0 |        
   32318 | 2025-04-04 23:18:19 |         MASTER-OAFA | (08h 08m 11.34s , +34d 58m 27.0s) |   C |    10 | 15.3 |        
   32318 | 2025-04-04 23:18:19 |         MASTER-OAFA | (08h 19m 13.81s , +35d 20m 58.4s) |   C |    10 | 17.1 |        
   32356 | 2025-04-04 23:18:57 |         MASTER-OAFA | (08h 08m 13.99s , +34d 59m 41.3s) |   C |    10 | 15.4 |        
   32357 | 2025-04-04 23:18:57 |         MASTER-OAFA | (08h 19m 16.67s , +35d 22m 12.7s) |   C |    10 | 17.2 |        
   33140 | 2025-04-04 23:32:01 |         MASTER-OAFA | (08h 07m 59.46s , +34d 58m 26.5s) |   C |    10 | 15.7 |        
   33150 | 2025-04-04 23:32:01 |         MASTER-OAFA | (08h 19m 01.71s , +35d 21m 07.7s) |   C |    30 | 18.4 |        
   33186 | 2025-04-04 23:32:47 |         MASTER-OAFA | (08h 07m 58.57s , +34d 59m 30.7s) |   C |    10 | 15.8 |        
   33197 | 2025-04-04 23:32:47 |         MASTER-OAFA | (08h 19m 01.06s , +35d 22m 10.1s) |   C |    30 | 18.4 |        
   33235 | 2025-04-04 23:33:35 |         MASTER-OAFA | (08h 08m 03.56s , +34d 58m 34.6s) |   C |    10 | 15.8 |        
   33245 | 2025-04-04 23:33:36 |         MASTER-OAFA | (08h 19m 05.95s , +35d 21m 12.1s) |   C |    30 | 18.5 |        
   33280 | 2025-04-04 23:34:21 |         MASTER-OAFA | (08h 07m 56.35s , +34d 57m 37.5s) |   C |    10 | 15.8 |        
   33290 | 2025-04-04 23:34:21 |         MASTER-OAFA | (08h 18m 58.65s , +35d 20m 14.0s) |   C |    30 | 18.4 |        
   33328 | 2025-04-04 23:35:09 |         MASTER-OAFA | (08h 08m 02.36s , +34d 58m 09.7s) |   C |    10 | 15.9 |        
   33338 | 2025-04-04 23:35:09 |         MASTER-OAFA | (08h 19m 04.81s , +35d 20m 45.1s) |   C |    30 | 18.6 |        
   33373 | 2025-04-04 23:35:54 |         MASTER-OAFA | (08h 07m 58.28s , +34d 59m 32.8s) |   C |    10 | 15.8 |        
   33384 | 2025-04-04 23:35:54 |         MASTER-OAFA | (08h 19m 00.96s , +35d 22m 07.7s) |   C |    30 | 18.5 |        
   33424 | 2025-04-04 23:36:45 |         MASTER-OAFA | (08h 07m 57.86s , +34d 58m 00.1s) |   C |    10 | 15.8 |        
   33434 | 2025-04-04 23:36:45 |         MASTER-OAFA | (08h 19m 00.34s , +35d 20m 33.9s) |   C |    30 | 18.5 |        
   33464 | 2025-04-04 23:36:45 |         MASTER-OAFA | (08h 19m 00.33s , +35d 20m 33.8s) |   C |    90 | 19.3 |  Coadd 
   33471 | 2025-04-04 23:37:32 |         MASTER-OAFA | (08h 08m 01.00s , +34d 59m 22.3s) |   C |    10 | 15.8 |        
   33481 | 2025-04-04 23:37:32 |         MASTER-OAFA | (08h 19m 03.70s , +35d 21m 55.5s) |   C |    30 | 18.5 |        
   33519 | 2025-04-04 23:38:20 |         MASTER-OAFA | (08h 07m 54.12s , +34d 58m 51.0s) |   C |    10 | 15.9 |        
   33529 | 2025-04-04 23:38:20 |         MASTER-OAFA | (08h 18m 56.76s , +35d 21m 23.8s) |   C |    30 | 18.5 |        
   33566 | 2025-04-04 23:39:07 |         MASTER-OAFA | (08h 07m 52.92s , +34d 59m 53.3s) |   C |    10 | 15.9 |        
   33576 | 2025-04-04 23:39:07 |         MASTER-OAFA | (08h 18m 55.71s , +35d 22m 25.5s) |   C |    30 | 18.5 |        
   33606 | 2025-04-04 23:39:07 |         MASTER-OAFA | (08h 18m 55.72s , +35d 22m 25.5s) |   C |    90 | 19.3 |  Coadd 
   33613 | 2025-04-04 23:39:54 |         MASTER-OAFA | (08h 07m 58.66s , +34d 58m 55.1s) |   C |    10 | 15.9 |        
   33624 | 2025-04-04 23:39:54 |         MASTER-OAFA | (08h 19m 01.35s , +35d 21m 27.0s) |   C |    30 | 18.5 |        
   33659 | 2025-04-04 23:40:40 |         MASTER-OAFA | (08h 07m 51.06s , +34d 57m 56.5s) |   C |    10 | 15.9 |        
   33669 | 2025-04-04 23:40:40 |         MASTER-OAFA | (08h 18m 53.65s , +35d 20m 28.1s) |   C |    30 | 18.4 |        
   33721 | 2025-04-04 23:41:27 |         MASTER-OAFA | (08h 07m 56.45s , +34d 58m 08.6s) |   C |    40 | 16.6 |        
   33731 | 2025-04-04 23:41:27 |         MASTER-OAFA | (08h 18m 59.04s , +35d 20m 38.8s) |   C |    60 | 18.4 |        
   33799 | 2025-04-04 23:42:45 |         MASTER-OAFA | (08h 07m 52.46s , +34d 59m 53.5s) |   C |    40 | 16.6 |        
   33809 | 2025-04-04 23:42:45 |         MASTER-OAFA | (08h 18m 55.24s , +35d 22m 22.0s) |   C |    60 | 18.6 |        
   33874 | 2025-04-04 23:44:00 |         MASTER-OAFA | (08h 07m 51.72s , +34d 58m 08.4s) |   C |    40 | 16.5 |        
   33885 | 2025-04-04 23:44:00 |         MASTER-OAFA | (08h 18m 54.29s , +35d 20m 36.9s) |   C |    60 | 18.6 |        
   33950 | 2025-04-04 23:45:16 |         MASTER-OAFA | (08h 07m 52.58s , +34d 59m 42.2s) |   C |    40 | 16.6 |        
   33961 | 2025-04-04 23:45:16 |         MASTER-OAFA | (08h 18m 55.38s , +35d 22m 10.2s) |   C |    60 | 18.6 |        
   34029 | 2025-04-04 23:46:35 |         MASTER-OAFA | (08h 07m 46.04s , +34d 59m 09.7s) |   C |    40 | 16.5 |        
   34039 | 2025-04-04 23:46:35 |         MASTER-OAFA | (08h 18m 48.79s , +35d 21m 37.5s) |   C |    60 | 18.6 |        
   34105 | 2025-04-04 23:47:51 |         MASTER-OAFA | (08h 07m 44.23s , +35d 00m 11.7s) |   C |    40 | 16.6 |        
   34116 | 2025-04-04 23:47:51 |         MASTER-OAFA | (08h 18m 47.13s , +35d 22m 39.2s) |   C |    60 | 18.6 |        
   34183 | 2025-04-04 23:49:09 |         MASTER-OAFA | (08h 07m 50.81s , +34d 59m 13.6s) |   C |    40 | 16.6 |        
   34193 | 2025-04-04 23:49:09 |         MASTER-OAFA | (08h 18m 53.60s , +35d 21m 41.4s) |   C |    60 | 18.6 |        
   34258 | 2025-04-04 23:50:24 |         MASTER-OAFA | (08h 07m 43.46s , +34d 58m 15.9s) |   C |    40 | 16.7 |        
   34268 | 2025-04-04 23:50:24 |         MASTER-OAFA | (08h 18m 46.23s , +35d 20m 43.3s) |   C |    60 | 18.9 |        
   34334 | 2025-04-04 23:51:40 |         MASTER-OAFA | (08h 07m 49.53s , +34d 58m 37.1s) |   C |    40 | 16.7 |        
   34344 | 2025-04-04 23:51:40 |         MASTER-OAFA | (08h 18m 52.40s , +35d 21m 04.5s) |   C |    60 | 19.0 |        
   34412 | 2025-04-04 23:52:58 |         MASTER-OAFA | (08h 07m 45.63s , +34d 59m 52.0s) |   C |    40 | 16.7 |        
   34422 | 2025-04-04 23:52:58 |         MASTER-OAFA | (08h 18m 48.68s , +35d 22m 19.3s) |   C |    60 | 19.0 |        
   34490 | 2025-04-04 23:54:16 |         MASTER-OAFA | (08h 07m 45.61s , +34d 58m 24.1s) |   C |    40 | 16.7 |        
   34500 | 2025-04-04 23:54:16 |         MASTER-OAFA | (08h 18m 48.48s , +35d 20m 51.3s) |   C |    60 | 19.0 |        
   34568 | 2025-04-04 23:55:34 |         MASTER-OAFA | (08h 07m 47.51s , +34d 59m 56.5s) |   C |    40 | 16.7 |        
   34578 | 2025-04-04 23:55:34 |         MASTER-OAFA | (08h 18m 50.62s , +35d 22m 23.7s) |   C |    60 | 19.0 |        
   34694 | 2025-04-04 23:57:00 |         MASTER-OAFA | (08h 18m 44.27s , +35d 21m 54.2s) |   C |   120 | 19.3 |        
   34823 | 2025-04-04 23:59:19 |         MASTER-OAFA | (08h 07m 41.05s , +35d 00m 30.6s) |   C |   100 | 16.9 |        
   34833 | 2025-04-04 23:59:19 |         MASTER-OAFA | (08h 18m 44.29s , +35d 22m 57.6s) |   C |   120 | 19.3 |        
   34970 | 2025-04-05 00:01:46 |         MASTER-OAFA | (08h 07m 46.89s , +34d 59m 33.9s) |   C |   100 | 17.1 |        
   34981 | 2025-04-05 00:01:46 |         MASTER-OAFA | (08h 18m 50.01s , +35d 22m 01.1s) |   C |   120 | 19.3 |        
   35095 | 2025-04-05 00:04:06 |         MASTER-OAFA | (08h 07m 41.46s , +34d 58m 36.8s) |   C |    70 | 16.9 |        
   35105 | 2025-04-05 00:04:06 |         MASTER-OAFA | (08h 18m 44.44s , +35d 21m 04.0s) |   C |    90 | 19.1 |        
   35202 | 2025-04-05 00:05:53 |         MASTER-OAFA | (08h 07m 45.68s , +34d 58m 59.5s) |   C |    70 | 17.0 |        
   35212 | 2025-04-05 00:05:53 |         MASTER-OAFA | (08h 18m 48.74s , +35d 21m 26.6s) |   C |    90 | 19.1 |        
   35308 | 2025-04-05 00:07:39 |         MASTER-OAFA | (08h 07m 42.99s , +35d 00m 18.1s) |   C |    70 | 16.9 |        
   35319 | 2025-04-05 00:07:39 |         MASTER-OAFA | (08h 18m 46.22s , +35d 22m 44.9s) |   C |    90 | 19.1 |        
   35398 | 2025-04-05 00:09:24 |         MASTER-OAFA | (08h 07m 42.93s , +34d 59m 00.1s) |   C |    40 | 16.7 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

GCN Circular 40069

Subject
EP250404a: Xinglong decaying optical counterpart
Date
2025-04-04T22:17:12Z (7 months ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Min-He (NAOC), Yiming-Mao (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Jinlei-Zhang (NAOC), Junjun-Jia (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report:

We observed the field of the X-ray transient, EP 250404a, detected by EP/WXT using the Xinglong 0.8-m, 2.16-m telescope located at Xinglong, Hebei,  China. We obtained 6 x 300 s g'-band frames for 0.8-m telescope, 5 * 300s clear-band frames for 2.16-m telescope during the time between 2025-04-04T14:32:21.91 and  2025-04-04T17:08:42 as soon as the EP trigger. We have found the optical counterpart of EP 250404a in these images, and the light of this object had been decreased rapidly. The magnitude of this object firstly be ~ 15.68+/- 0.014 at 2025-04-04T14:32:21.91 with 0.8-m telescope in g'-band, and then decrease to ~ 19.7+/-0.102 with 2.16-m telescope at a median time of 2025-04-04T17:03:42, which measured by a stacked clear-band image and calibrated with the Pan-STARRS r' band field.  The stacked clear-band image using the 2.16-m telescope has a 5-sigma limiting magnitude of ~21.64 mag, calibrated with the Pan-STARRS r'-band field. 
Within the 20 arcsec error circle of the FXT, we identified an optical transient (OT) localized at R. A. = 08:20:11.41 , Dec. = 35:31:27.68 (J2000).

We summarize our observation results as follows:
Obs. No. | Start Time (UTC) | End Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) |Telescope Name
1 | 2025-04-04 14:32:21.91 | 2025-04-04 14:37:21.91 | 300s | g' | 15.681 +/- 0.014 | Xinglong 0.8-m Telescope.
2 | 2025-04-04 14:37:27.81 | 2025-04-04 14:42:27.81 | 300s | g' | 15.717 +/- 0.013 | Xinglong 0.8-m Telescope.
3 | 2025-04-04 14:42:33.76 | 2025-04-04 14:47:33.76 | 300s | g' | 16.124 +/- 0.019 | Xinglong 0.8-m Telescope.
4 | 2025-04-04 15:11:06.35 | 2025-04-04 15:16:06.35 | 300s | g' | 17.864 +/- 0.070 | Xinglong 0.8-m Telescope.
5 | 2025-04-04 15:16:12.26 | 2025-04-04 15:21:12.26 | 300s | g' | 18.149 +/- 0.088 | Xinglong 0.8-m Telescope.
6 | 2025-04-04 15:21:18.16 | 2025-04-04 15:26:18.16 | 300s | g' | 19.015 +/- 0.112 | Xinglong 0.8-m Telescope.
7 | 2025-04-04 14:37:24    | 2025-04-04 14:42:24    | 300s |clear| 14.882 +/- 0.001 (calibrated to r') | Xinglong 2.16-m Telescope.
8 | 2025-04-04 14:42:32    | 2025-04-04 14:47:32    | 300s |clear| 15.363 +/- 0.002 (calibrated to r')| Xinglong 2.16-m Telescope.
9 | 2025-04-04 16:58:22    | 2025-04-04 17:13:42    | 3x300s |clear| 19.703 +/- 0.102 (calibrated to r')| Xinglong 2.16-m Telescope 
Further observations are encouraged.

GCN Circular 40067

Subject
GRB 250404A: Fermi GBM Detection
Date
2025-04-04T19:52:20Z (7 months ago)
From
oindabimukherjee@gmail.com
Via
Web form
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 14:19:46.35 UT on 04 April 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250404A (trigger 765469191/250404597).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 123.37, Dec = 34.10 (J2000 degrees, equivalent to
J2000 8h 13m, +34d 6'), with a statistical uncertainty of 1.20 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 42 degrees.

The GBM light curve consists of multiple peaks with a duration (T90)
of about 91.4 s (50-300 keV). The time-averaged spectrum
from T0-3.6 to T0+124.4 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.10 +/- 0.02 and the cutoff energy,
parameterized as Epeak, is 55.7 +/- 0.5 keV.

The event fluence (10-1000 keV) in this time interval is
(3.33 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+21 s in the 10-1000 keV band is 12.9 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

GCN Circular 40066

Subject
EP250404a: Global MASTER-Net observations report
Date
2025-04-04T19:27:39Z (7 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-Tunka robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP250404a ( EP Team et al., GCN 40051) errorbox  13675 sec after notice time and 16626 sec after trigger time at 2025-04-04 18:57:05 UT, with upper limit up to  19.5 mag. The observations began at zenith distance = 66 deg. The sun  altitude  is -28.6 deg. 

The galactic latitude b = 33 deg., longitude l = 187 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2832935

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   16657 | 2025-04-04 18:57:05 |        MASTER-Tunka | (08h 19m 51.88s , +36d 00m 34.0s) |   C |    60 | 18.6 |        
   16717 | 2025-04-04 18:57:05 |        MASTER-Tunka | (08h 19m 51.88s , +36d 00m 34.0s) |   C |   180 | 19.3 |  Coadd 
   16728 | 2025-04-04 18:58:16 |        MASTER-Tunka | (08h 19m 58.07s , +36d 00m 34.7s) |   C |    60 | 18.6 |        
   16800 | 2025-04-04 18:59:28 |        MASTER-Tunka | (08h 19m 55.11s , +36d 02m 04.0s) |   C |    60 | 18.6 |        
   16872 | 2025-04-04 19:00:41 |        MASTER-Tunka | (08h 19m 55.07s , +36d 00m 32.5s) |   C |    60 | 18.7 |        
   16932 | 2025-04-04 19:00:41 |        MASTER-Tunka | (08h 19m 55.07s , +36d 00m 32.5s) |   C |   180 | 19.4 |  Coadd 
   16950 | 2025-04-04 19:01:58 |        MASTER-Tunka | (08h 19m 57.66s , +36d 02m 04.7s) |   C |    60 | 18.6 |        
   17021 | 2025-04-04 19:03:09 |        MASTER-Tunka | (08h 19m 52.37s , +36d 01m 15.7s) |   C |    60 | 18.7 |        
   17095 | 2025-04-04 19:04:24 |        MASTER-Tunka | (08h 19m 51.30s , +36d 02m 12.7s) |   C |    60 | 18.7 |        
   17155 | 2025-04-04 19:04:24 |        MASTER-Tunka | (08h 19m 51.30s , +36d 02m 12.8s) |   C |   180 | 19.5 |  Coadd 
   17381 | 2025-04-04 19:09:09 |        MASTER-Tunka | (08h 19m 52.28s , +35d 59m 59.8s) |   C |    60 | 18.7 |        
   17454 | 2025-04-04 19:10:22 |        MASTER-Tunka | (08h 19m 58.20s , +36d 00m 10.2s) |   C |    60 | 18.7 |        
   17527 | 2025-04-04 19:11:35 |        MASTER-Tunka | (08h 19m 54.28s , +36d 01m 24.3s) |   C |    60 | 18.7 |        
   17587 | 2025-04-04 19:11:35 |        MASTER-Tunka | (08h 19m 54.28s , +36d 01m 24.2s) |   C |   180 | 19.4 |  Coadd 
   17599 | 2025-04-04 19:12:48 |        MASTER-Tunka | (08h 19m 54.27s , +35d 59m 56.4s) |   C |    60 | 18.6 |        
   17670 | 2025-04-04 19:13:59 |        MASTER-Tunka | (08h 19m 57.20s , +36d 01m 34.1s) |   C |    60 | 18.6 |        
   17743 | 2025-04-04 19:15:12 |        MASTER-Tunka | (08h 19m 51.23s , +36d 00m 41.3s) |   C |    60 | 18.5 |        
   17803 | 2025-04-04 19:15:12 |        MASTER-Tunka | (08h 19m 51.23s , +36d 00m 41.3s) |   C |   180 | 19.3 |  Coadd 
   17816 | 2025-04-04 19:16:24 |        MASTER-Tunka | (08h 19m 51.76s , +36d 01m 37.4s) |   C |    60 | 18.6 |        
   17890 | 2025-04-04 19:17:39 |        MASTER-Tunka | (08h 19m 57.64s , +36d 00m 34.5s) |   C |    60 | 18.7 |        
   17962 | 2025-04-04 19:18:51 |        MASTER-Tunka | (08h 19m 51.82s , +35d 59m 30.3s) |   C |    60 | 18.6 |        
   18035 | 2025-04-04 19:20:04 |        MASTER-Tunka | (08h 19m 57.26s , +35d 59m 42.1s) |   C |    60 | 18.6 |        
   18108 | 2025-04-04 19:21:16 |        MASTER-Tunka | (08h 19m 53.77s , +36d 01m 07.0s) |   C |    60 | 18.5 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

GCN Circular 40064

Subject
EP250404a: AKO Optical Afterglow Detection
Date
2025-04-04T18:35:28Z (7 months ago)
From
Mohammad Odeh at Al Khatim Observatory M44 <mshodeh@gmail.com>
Via
email
Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International
Astronomical Center in Abu Dhabi, UAE), and Shaikha Alshamsi and Nidhal
Guessoum (American University of Sharjah, UAE), report:

We observed the field of EP250404a detected by EP (Hu et al., GCN 40051),
using our 0.36m f/7.7 robotic telescope. The observation session began on 04
April 2025 at 15:47 UT and continued until 16:56 UT, with a midpoint at
16:22 UT, approximately 2 hours after the trigger.

 

We obtained multiple 180-second exposures using the Ic filter. The optical
afterglow was clearly detected at:

R.A. (J2000): 08:20:14.59 

Dec. (J2000): +35:31:42.3

 

Our detection is consistent with the results of (Jiang et al., GCN 40052;
Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Konno et al., GCN
40063).

 

The following observation was calculated using the Atlas catalogue as a
reference:

----------------------------------------------------------------------------
-

ObsTime (mid), Exposure (sec), Filter, Mag

----------------------------------------------------------------------------
-

2025-04-04T16:21:38Z, 20 x 180s (stacked), Ic, 17.5 +/- 0.35

----------------------------------------------------------------------------
-

The magnitude is not corrected for galactic extinction.

GCN Circular 40063

Subject
EP250404a: LAST detection of optical counterpart
Date
2025-04-04T18:17:33Z (7 months ago)
From
Ruslan Konno at Weizmann Institute of Science <ruslan.konno@desy.de>
Via
Web form
R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), P. Chen (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), S. Spitzer (WIS), and K. Rybicki (WIS) on behalf of the LAST Collaboration

We report observations of the X-ray transient EP250404a (Hu et al., GCN 40051), detected by Einstein Probe, with the Large Array Survey Telescope (LAST; Ofek et al. 2023 PASP 135, 5001; Ben-Ami et al. 2023 PASP 135, 5002).

We observe the field of EP250404a using 4 parallel telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20 images with each of 20s exposure, and the limiting magnitude of a single coadd is around 20.5 (AB mag). We clearly detect the optical counterpart reported by Jiang et al. (GCN 40052), Perez-Garcia et al. (GCN 40053), and Du et al. (GCN 40058). The earliest detection with a 20x20s exposure image is confirmed at 2025-04-04 17:01:04 UTC (T-T0=2.68h) at an AB magnitude of 19.31 +/- 0.07. LAST is scheduled to continue observations of the source, and additional analysis will follow.

LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).

GCN Circular 40061

Subject
EP250404a: Xinglong-2.16m spectroscopic redshift
Date
2025-04-04T18:05:48Z (7 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, J.J. Jin, Z. Fan, D. Xu (NAOC), S.Y. Fu (HUST), report on behalf of a large collaboration:

We carried out spectroscopy of the optical counterpart (e.g., Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058) of EP250404a (Hu et al., GCN 40051), likely the identical event to GRB 250404A (GBM team, GCN 40050), using the 2.16-m telescope equipped with the BFOSC instrument, located at Xinglong, Hebei, China. Our spectra cover the wavelength range 3800 - 9000 AA, and consist of 2 exposures of 1800 s each. 

The continuum is throughout the spectrum. From the detection of a broad Lya absorption feature at ~ 4400 AA and relatively weak absorption features, which interpreted as being due to Si IV and Al III, we infer a common redshift of z = 2.63. We conclude this is the likely redshift of the event.

An intervening system is also detected with absorption features, interpreted as being due to Mg II and Fe II, we inferred its redshift of z = 1.88. 

We acknowledge the expert support from the Xinglong-2.16m staff, in particular Junjun Jia and Jie Zheng.

GCN Circular 40058

Subject
EP250404a: Mephisto multi-band optical detection
Date
2025-04-04T16:19:08Z (7 months ago)
Edited On
2025-04-04T16:25:57Z (7 months ago)
From
Chenxu Liu at Mephisto Team <cxliu@ynu.edu.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Chenxu Liu at Mephisto Team <cxliu@ynu.edu.cn>
Via
Web form
Guowang Du, Ziwei Li, Chenxu Liu, Dezi Liu, Yaosong Yu, Chenxi Shang, Jinghua Zhang, Yuan Fang, Xufeng Zhu, Tao Wang, Xinlei Chen, Xingzhu Zou, Yu Pan, Brajesh Kumar, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU)  report on behalf of the Mephisto Team:

We performed simultaneous multi-band photometric observations of EP250404a (EP-WXT ID: 01709133918) detected by EP (Hu et al., GCN 40051) and by Fermi/GBM (Fermi team, GCN 40050) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at the Lijiang Observatory. The observations were initiated at 14:32:03UTC2025-04-04 (i.e., 723s after the EP/WXT trigger) and are still ongoing at the time of this report. Multiple frames were obtained in uvgriz- bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is listed below:

UT start            |Band | Exp   | Mag (AB)
--------------------|-----|-------|----------|--------------------------
2025/4/4 14:32:03   | u   | 180s  | 18.65+/-0.08
2025/4/4 14:39:20   | v   | 180s  | 16.91+/-0.02
2025/4/4 14:32:05   | g   |  50s  | 15.72+/-0.01
2025/4/4 14:39:22   | r   |  50s  | 14.83+/-0.01
2025/4/4 14:32:04   | i   |  79s  | 14.60+/-0.01
2025/4/4 14:39:21   | z   |  79s  | 14.03+/-0.01

Our results echo the detection from Nanshan/HMT (Jiang et al., GCN 40052) and BOOTES-4/MET (I. Perez-Garcia et al., GCN 40053). 
----------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
----------------------------------------------------------

GCN Circular 40053

Subject
EP250404a: BOOTES-4/JGT optical afterglow detection
Date
2025-04-04T15:31:24Z (7 months ago)
Edited On
2025-04-04T18:46:21Z (7 months ago)
From
I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>
Via
Web form

I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M. D. Caballero-Garcia, G. Garcia-Segura, S. Guziy, R. Sanchez-Ramirez and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. de Malaga), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), and D. R. Xiong, J. M. Bai, Y. F. Fan, C. J. Wang, Y. X. Xin, X. H. Zhao, J. R. Mao, B. K. Lun, K. Ye (Yunnan Observatories/CAS, Kunming) on behalf of a larger collaboration, report:

Following the detection of EP250404a by Einstein Probe (Hu et al. GCNC 40051), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this X-ray transient starting on 2025-04-04 14:39:39UT (20 min after detection and 15 after notification). Series of images in clear filter were gathered and we detect and uncatalogud source constistent with position reported by Jiang et al. (GCN 40052). Using GaiaDR3 Gmag as reference we measure an initial magnitude of 14.8 +/- 0.03. Within 20 minutes, the source faded to magnitude 16.1. Further analysis of the additional images is ongoing.

We thank the staff at Lijiang observatory for their excellent support.

GCN Circular 40052

Subject
EP250404a: Nanshan/HMT optical counterpart detection
Date
2025-04-04T15:12:14Z (7 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of EP250404a detected by EP (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A detected by Fermi/GBM (GBM team, GCN 40050), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 14:24:59 UT on 2025-04-04, i.e., 300 s after the EP/WXT trigger time, and a series of unfiltered frames with different exposures were obtained.

An uncatalogued and varying optical source is detected within the EP/FXT error circle at coordinates:

R.A.(J2000) =  08:20:14.54
Dec.(J2000) = +35:31:41.57

with an uncertainty of ~0.5 arcsec. The source has R ~ 16.1 mag in the first image, calibrated with the nearby Pan-STARRS field and not corrected for Galactic extinction.

Observations are still ongoing.

GCN Circular 40051

Subject
EP250404a: Einstein Probe detection of an X-ray transient
Date
2025-04-04T15:03:49Z (7 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. W. Hu (NAO, CAS), Q. C. Liu (THU), B. B. Zhang (BNU), Y. L. Hua (PMO, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:

We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250404a. The transient triggered EP-WXT (ID: 01709133918) at 2025-04-04T14:19:59 (UTC). The WXT position of the source is R.A. = 125.064 deg, DEC = 35.511 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 125.0575 deg, DEC = 35.5305 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). It is noted that EP250404a is temporally and spatially coincident with GRB 250404A (Fermi team, GCN Circ. 40050).

Further information will be updated when the telemetry data is received.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).

GCN Circular 40050

Subject
GRB 250404A: Fermi GBM Final Real-time Localization
Date
2025-04-04T14:30:25Z (7 months ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB

At 14:19:46 UT on 4 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250404A (trigger 765469191.347644 / 250404597).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 123.4, Dec = 34.1 (J2000 degrees, equivalent to J2000 08h 13m, 34d 06'), with a statistical uncertainty of 1.2 degrees.

The angle from the Fermi LAT boresight is 42.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250404597/quicklook/glg_skymap_all_bn250404597.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250404597/quicklook/glg_healpix_all_bn250404597.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250404597/quicklook/glg_lc_medres34_bn250404597.gif
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