EP251130a
GCN Circular 43061
Subject
EP251130a: Mondy and AbAO optical observations
Date
2025-12-10T09:19:25Z (4 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. A. Volnova (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), N. S. Pankov (HSE, IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We continued observations of the field of the X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915), also detected by Swift/XRT (Evans et al., GCN 42908) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy), and the AS-32 0.7m telescope of Abastumani Observatory (AbAO) taking several frames in R-band. Further observations at AZT-33IK started on Dec. 01 at 20:11 (~1.4 days after the trigger), then followed by AbAO on Dec. 3 starting at 23:01 UT (~3.5 days after the trigger). The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921; Volnova et al., GCN 42922; Ma et al., GCN 42940; Corcoran et al., GCN 42951; Tundidor Rodríguez et al., GCN 42963; Abidkhanov et al., GCN 42969; Fu et al., GCN 42990) is seen in the stacked AZT-33IK frame and is not detected in the stacked frame from AS-32. The photometry and observational details are the following:
Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum
(mid,days) (n*s) (3sigma)
2025-12-01 20:11:34 1.40888 45*120 R 21.83 0.15 22.5 Mondy/AZT-33IK
2025-12-03 23:01:52 3.56284 285*30 R n/d n/d 21.0 AbAO/AS-32
The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.
Our observations together with other published magnitudes confirm the steep decay (Tundidor Rodríguez et al., GCN 42963) after the re-brightening: the R-band light curve slope changed from ~1.3 at 0.06-0.19 days to ~4 at 0.9-1.4 days in the observer frame.
GCN Circular 42990
Subject
EP251130a: JinShan near-infrared observations
Date
2025-12-04T16:38:15Z (9 days ago)
From
syfu@nao.cas.cn
Via
Web form
S.Y. Fu (HUST), L.B. He (NAOC), A.D. Zhu, L. Lei, H.Z. Wu, W.H. Lei (HUST), J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO)
We continued monitoring the optical counterpart of EP251130a (Wu et al., GCN 42903) using the 100C telescope, equipped with the INS-BIue SWIR camera, of the JinShan project, located at Altay, Xinjiang, China. Observation started at 2025-12-01 16:29:07 UT, i.e., 1.22 days post-burst, and a series of J-band frames were obtained.
The previously reported optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; Dalen et al. GCN 42918; Moskvitin
& Spiridonova, GCN 42919; Aryan et al. GCN 42921; Volnova et al. GCN 42922; Ma et al. GCN 42940; Corcoran et al. GCN 42951; Rodríguez et al. GCN 42963; Abidkhanov et al. GCN 42969) was detected in our stacked J-band frame with magnitude J = 19.19 +/- 0.12 (Vega) at a mid-time 1.32 days post-burst. The magnitude was calibrated with the nearby 2MASS catalog and without the Galactic extinction correction.
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.
GCN Circular 42969
Subject
EP251130a: MAO/AZT-22 optical observations
Date
2025-12-03T12:42:19Z (11 days ago)
From
Yodgor Rajabov at UBAI <rajabov@astrin.uz>
Via
Web form
B.Abidkhanov, Y. Rajabov, O. Burkhonov, S. Ehgamberdiev, Y. Tillayev (UBAI), T. Boyqobilov, A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team.
We observed the field of EP transient EP251130a (Wu et al., GCN 42903 Zhang et al., GCN 42915), also detected by Swift/XRT (Evans et al., GCN 42908), with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2025-12-01 at 20:31:41 UT. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010).
The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921; Volnova et al., GCN 42922; Ma et al., GCN 42940; Corcoran et al., GCN 42951; and Rodríguez et. al., GCN 42963) is detected in the stacked frame. Preliminary photometry is the following:
Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope
(nxs) (mid, days)
2025-12-01 20:47:55 6x300 1.40284 R 21.25 0.07 22.59 MAO/AZT-22
van Dalen et al. (GCN Circ. 42918) have reported a redshift of z = 4.035 using GTC OSIRIS+.
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022).
Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog.
The data has not corrected for the Galactic extinction.
Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical
Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/).
GCN Circular 42963
Subject
EP251130a: ULL-ASTRO-MASTER late detection of the optical afterglow with LCO 1-m telescope at Teide Observatory
Date
2025-12-02T19:57:57Z (11 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
T. Tundidor Rodríguez, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL).
We report on observations of the optical counterpart of the X-ray transient EP251130a, detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wu et al., GCN Circ. 42903) and with detections of Swift-XRT (Evans et al., GCN Circ. 42908) and of the EP Follow-up X-ray Telescope (FXT) (Zhang et al., GCN Circ. 42915).
We observed the field of EP251130a with one of the two Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Teide Observatory, Tenerife, Canary Islands, Spain. The observation, a single exposure of 500 sec in the SDSS i' filter, started on 2025-12-01 at 23:31:37 UT, about 36.40 hours after the EP-WXT trigger. The optical counterpart first reported by Dornic et al. (GCN Circ. 42904) is clearly detected in our image with a magnitude of i' = 20.68 +/- 0.14 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical observations (Lipunov et al., GCN Circ. 42906; He et al., GCN Circ. 42914; Gupta et al., GCN Circ. 42916; Zheng et al., GCN Circ. 42917; van Dalen et al., GCN Circ. 42918; Moskvitin and Spiridonova, GCN Circ. 42919; Aryan et al., GCN Circ. 42921; Volnova et al., GCN Circ. 42922; Ma et al., GCN Circ. 42940; and Corcoran et al., GCN Circ. 42951).
van Dalen et al. (GCN Circ. 42918) have reported a redshift of z = 4.035 using GTC OSIRIS+.
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).
This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).
GCN Circular 42951
Subject
EP251130a: continued NOT optical observations indicate steep fading phase
Date
2025-12-02T15:26:45Z (11 days ago)
From
Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>
Via
Web form
G. Corcoran (UCD), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), R. H. Rasmussen (NOT and Aarhus) report on behalf of a larger collaboration.
We continued the monitoring of the optical counterpart (Dornic et al., GCN 42904; Evans et al., GCN 42908; He et al., GCN 42914; Gupta et al., GCN 42916; Zheng et al., GCN 42917; van Dalen et al., GCN 42918; Moskvitin et al., GCN 42919; Aryan et al., GCN 42921; Volnova et al., GCN 42922; Ma et al., GCN 42940) of EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.
Observations consisted of two epochs, the first consisting of 3 x 300 s exposures in SDSS-i and 5 x 200 s exposures in SDSS-z starting at 2025-12-01T23:32:00, with the second epoch being a repeat of the first i-band observation starting at 2025-12-02T05:56:48. The source was detected in all stacked images. We calibrated our photometry using nearby stars from the Pan-STARRS catalog and did not correct for Galactic extinction. We obtain the following i-band photometry:
epoch 1: i = 20.84 +/- 0.07 (mid time: 2025-12-01T23:42:39, ~1.52 days post trigger);
epoch 2: i = 21.23 +/- 0.04 (mid time: 2025-12-02T06:07:27, ~1.79 days post trigger).
These measurements show that the re-brightening reported by Zheng et al. (GCN 42917), van Dalen et al. (GCN 42918) and Moskvitin et al. (GCN 42919) seems to have finished and the light curve is fading quickly with a power-law decay index of ~2.2.
Further observations are planned and encouraged.
GCN Circular 42940
Subject
EP251130a: SVOM/VT optical observation
Date
2025-12-02T06:52:47Z (12 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, Y. L. Qiu, C. Wu, H. L. Li, L. P. Xin, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM performed a Target of Opportunity observation of EP251130a detected by EP/WXT (Wu et al., GCN 42903). SVOM/VT began observing the field at 2025-12-01T16:10:37 UTC, 29.05 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (Dornic et al., GCN 42904; Lipunov et al., GCN 42906; He et al., GCN 42914; Gupta et al., GCN 42916; Zheng et al., GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921; Volnova et al., GCN 42922) was detected within EP/FXT and Swift/XRT errorbox (Zhang et al., GCN 42915; Evans et al., GCN 42908) in both VT_B and VT_R bands. The magnitudes are:
mid time (h) | exposure time (s) | band | mag (AB) | mag err
-------------|-------------------|------|----------|--------
29.61 | 23*50 | VT_B | 22.8 | 0.3
29.61 | 23*50 | VT_R | 20.54 | 0.08
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 42922
Subject
EP251130a: Mondy optical observations
Date
2025-12-01T15:00:28Z (12 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. A. Volnova (IKI), A. S. Pozanenko (IKI), E. Klunko (ISTP), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN:
We observed the field of the X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915), also detected by Swift/XRT (Evans et al., GCN 42908) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting on 2025-11-30 (UT) 15:06:18 in R filter. The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921) is detected in the stacked frame. Preliminary photometry is the following:
Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum
(mid,days) (n*s) (3sigma)
2025-11-30 15:06:18 0.18716 60*120 R 21.76 0.20 22.1 Mondy/AZT-33IK
The photometry is calibrated using USNO-B1.0 stars from Moskvitin and Spiridonova, GCN 42919, and is not corrected for the Galactic extinction.
GCN Circular 42921
Subject
EP251130a: Optical detections with Kinder observations
Date
2025-12-01T14:51:58Z (12 days ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan, T.-W. Chen, H.-Y. Hsiao, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915) using the 1m LOT and 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first epoch of r-band LOT observations began at 16:49 UTC on November 30, 2025 (MJD 61009.701), 5.70 hours after the EP-WXT trigger.
We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. We clearly detected the optical counterpart (Dornic et al., GCN 42904; He et al., GCN 42914; Gupta et al., GCN 42916; Zheng et al., GCN 42917; van Dalen et al., GCN 42918; Moskvitin et al., GCN 42919). The optical counterpart lies within the Swift-XRT (Evans et al., GCN 42908) and the refined EP-FXT (Zhang et al., GCN 42915) localizations. Moreover, we utilized AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on stacked images. The details of the observations and the measured magnitudes (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 61009.701 | 5.70 | 300 * 6 | 21.97 +/- 0.08 | 1".16 | 1.03
SLT | i | 61009.703 | 5.74 | 300 * 7 | 20.87 +/- 0.09 | 1".78 | 1.03
We plan to continue following the FXT on a few subsequent days. The presented magnitudes are calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al., 2018, ApJ, 867, 105) and are not corrected for the expected Galactic foreground extinction of A_r = 0.26 mag and A_i = 0.19 in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission can be found in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
GCN Circular 42919
Subject
EP251130a: SAO RAS optical observations
Date
2025-12-01T14:03:05Z (13 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin and O. I. Spiridonova (SAO RAS)
report on behalf of GRB follow-up team.
We observed the field of the X-ray transient EP251130a (Wu et al.,
GCN 42903; Zhang et al., GCN 42915), also detected by Swift-XRT
(Evans et al., GCN 42908) with the Zeiss-1000 1m telescope
of the SAO RAS on December 1, 01:29:21--03:08:47 UT
(t_mid - T0 = 0.63281 days). We obtained 11 * 300 images in Rc band
under mediocre weather conditions.
The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914;
Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al.,
GCN 42918) is clearly detected in our stacked image
with the brightness of R = 20.11 +/- 0.07 (R_lim = 21.8).
This preliminary photometry is based on nearby stars from the USNO-B1
catalogue (R2 magnitudes) and is not corrected for the Galactic
extinction.
USNO-B1 star RA DEC R2
1173-00161316 101.000000 +27.372589 16.26
1173-00161485 101.071981 +27.375787 16.76
1173-00161417 101.045348 +27.394953 16.04
In comparison with the OT brightness from 1.3m DFOT data
(Gupta et al., GCN 42916) we noted a brightening between
two epochs (also reported by Zheng et al. GCN 42917
and van Dalen et al., GCN 42918).
GCN Circular 42918
Subject
EP251130a: GTC OSIRIS+ redshift z = 4.035 and rebrightening
Date
2025-12-01T09:30:53Z (13 days ago)
Edited On
2025-12-01T14:38:07Z (13 days ago)
From
Agnes van Hoof at Radboud University <agnes.vanhoof@ru.nl>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Agnes van Hoof at Radboud University <agnes.vanhoof@ru.nl>
Via
Web form
J. N. D. van Dalen (Radboud), A. P. C. van Hoof (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), D. Mata-Sanchez (IAC and ULL), N.C. Rodríguez (GTC), A. Cabrera-Lavers (GTC), C. Hernandez (GTC), D. Gonzalez (GTC) report on behalf of a larger collaboration:
We observed the counterpart (Dornic et al., GCN 42904; Evans et al., GCN 42908; He et al., GCN 42914; Gupta et al., GCN 42916; Zheng et al., GCN 42917) of EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915) with the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. Three 1200 s exposures were obtained using the R1000R grating and a 1 arcsec slit. Observations began on 2025 Dec 1 at 01:28 UT, approximately 0.6 days after the EP trigger time.
From the 60 s acquisition image taken in the i band, we measure a magnitude of i = 19.54+/-0.03 AB (calibrated against nearby Pan-STARRS objects). We find a rebrightening of the optical counterpart by ~1 mag in ~10 hr as compared to He et al. (GCN 42914).
In the spectrum, a broad trough centered around 6120 AA is detected, which we interpret as due to a DLA. Several metal absorption lines are also detected on top of the bright continuum, which match Si II, Si II*, O I, C II, Si IV, C IV, Fe II, Al II, all at a common redshift of z = 4.035.
GCN Circular 42917
Subject
EP251130a: KAIT optical observations
Date
2025-12-01T09:16:17Z (13 days ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, automatically responded to EP251130a (Wu et al.,
GCN 42903) starting at 11:21:40 UT, 831 seconds after the burst.
A set of 10x20s, 10x40s, 60x60s clear (roughly R) filter images
were obtained. We clearly detected the optical afterglow (Dornic
et al., GCN 42904, He et al., GCN 42914; Gupta et al., GCN 42916)
in our coadd image. We measure its brightness decreased from 19.6
+/- 0.1 mag (Vega; mid time 16.45 min) to 20.2 +/- 0.2 mag (mid
time of 91.03 min) with a decay index of 0.46.
Additional 30x60s clear filter images were obtained the following
night at a mid time of 0.89 days after the burst. The OT is still
detected at 19.7 +/- 0.1 mag, indicating the OT has brightened.
More follow-up observations are encouraged.
GCN Circular 42916
Subject
EP251130A: Optical observation from 1.3m DFOT
Date
2025-12-01T08:45:09Z (13 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Pankaj Pawar, Debalina Kar, Dhruv Jain, and Kuntal Misra (ARIES) report:
We observed the field of EP251130A detected by Einstein Probe (Wu et al. 2025, GCN 42903)
with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 22025-11-30 at 19:21:24 UT, i.e., ~8.22 hours after the EP trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect the optical counterpart in our stacked image within the error box of Swift-XRT (Evans et al. 2025, GCN 42908). We obtain the following preliminary magnitude in the stacked image:
Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude
======================================================================
2025-11-30 19:21:24 ~8.22 R 300*12 22.20+/- 0.09
Our detection is consistent with Dornic et al. 2025 (GCN 42904); Lipunov et al. 2025 (GCN 42906); He et al. 2025 (GCN 42914).
The magnitude is not corrected for the Galactic extinction in the direction of the burst.
Photometric calibration is performed using the standard stars from the USNO-B1 catalog.
GCN Circular 42915
Subject
EP251130a: refined analysis of the EP-WXT and EP-FXT observations
Date
2025-12-01T08:40:25Z (13 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
W. J. Zhang (NAO, CAS), H. C. Ding, T. Wu (AHNU), Y. H. Jiang, Y. Wu (NJU), Y. Wang (PMO), Y. Liu (NAO, CAS), on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP251130a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wu et al., GCN 42903), and was followed by several telescopes (Dornic et al., GCN 42904, Lipunov et al., GCN 42906 and Evans et al., GCN 42908). The refined analysis of the WXT data shows that the event started at T0=2025-11-30T11:04:00 (UTC) and lasted for ~230 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 fixed Galactic hydrogen column density of 1.40 x 10^21 cm^-2 and a photon index of 1.54 (-0.63/+0.70). The derived average unabsorbed 0.5-4 keV flux is 2.46 (-0.77/+1.06) x 10^(-10) erg/s/cm^2.
A follow-up observation of EP251130a with the Follow-up X-ray Telescope (FXT) was performed automatically at 2025-11-30T11:11:12 (UTC), about 7 minutes after T0, with an exposure time of 4,200 s. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 101.0210 deg, Dec. = 27.3840 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). This position is ~1.6 arcsec from the reported optical counterpart (Dornic et al., GCN 42904). The average FXT 0.5-10 keV spectrum of the observation can be fitted with an absorbed power law, with a hydrogen column density of 1.39 (-0.81/+0.86) x 10^21 cm^-2 and a photon index of 2.12 (-0.32/+0.34). The derived average unabsorbed 0.5-10 keV flux is 3.32 (-0.31/+0.32) x 10^(-12) erg/s/cm^2.
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 42914
Subject
EP251130a: JinShan optical observations
Date
2025-12-01T06:43:09Z (13 days ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP251130a (Wu et al., GCN 42903) using the 100B telescope of the JinShan project, located at Altay, Xinjiang, China. Obervations started at 2025-11-30 14:13:38 UT, i. e. 3.1 hrs post-burst, and a series of frames in g, r and i bands were obtained.
The previously reported optical counterpart candidate (Dornic et al., GCN 42904) was detected in our stacked i-band frame with a magnitude i = 20.60 +/- 0.18 at a mid-time 4.67 hrs post-burst. The magnitude was callibrated with nearby PanSTARRS1 dr2 catalog and without the Galactic extinction correction.
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.
GCN Circular 42908
Subject
EP251130a: Swift-XRT counterpart detection
Date
2025-11-30T19:00:56Z (13 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected
source EP251130a, collecting 2.0 ks of Photon Counting (PC) mode data between T0+5.8
ks and T0+11 ks after the trigger. A likely counterpart has been found. The details
of this source are:
Source 1 (SWIFT J064404.8+272302):
==================================
RA (J2000.0): 101.0203 = 06 44 04.87
Dec (J2000.0): +27.3839 = +27 23 02.0
Error: 3.9 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 75 arcsec from the Einstein Probe/WXT position.
Mean rate: 0.0618 [+0.0070, -0.0068] ct s^-1
Mean flux: (2.21 [+0.25, -0.24])e-12 erg cm^-2 s^-1
Peak rate: 0.139 +/- 0.031 ct s^-1
Peak flux: (5.0 +/- 1.1)e-12 erg cm^-2 s^-1
ECF: 3.57e-11 erg cm^-2 ct^-1
assuming NH=1.80e+21 cm^-2, gamma=1.97
determined from a spectral fit.
XMM UL: 3.5e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 1.4-sigma above this 3-sigma upper limit.
The source may be fading, at the 2.6-sigma level. This position is consistent
with the candidate optical counterpart reported by COLIBRI (GCN 42904).
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/EP/EP_FIELD00085.
This circular is an official product of the Swift-XRT team.
GCN Circular 42906
Subject
EP251130a: Global MASTER-Net observations report
Date
2025-11-30T16:45:38Z (13 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO),
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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251130a ( EP Team et al., GCN 42903) errorbox 16211 sec after notice time and 19018 sec after trigger time at 2025-11-30 16:24:47 UT, with upper limit up to 15.3 mag. The observations began at zenith distance = 80 deg. The sun altitude is -30.0 deg.
The galactic latitude b = 11 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=3055832
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
19048 | 2025-11-30 16:24:47 | MASTER-Kislovodsk | (06h 42m 49.31s , +27d 04m 35.5s) | C | 60 | 13.6 |
19048 | 2025-11-30 16:24:47 | MASTER-Kislovodsk | (06h 42m 50.47s , +27d 27m 17.4s) | C | 60 | 15.3 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 42904
Subject
EP251130a: COLIBRÍ optical counterpart candidate
Date
2025-11-30T15:18:49Z (13 days ago)
Edited On
2025-12-01T18:10:24Z (12 days ago)
From
Damien Dornic <ddornic@km3net.de>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
Damien Dornic (CPPM), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), William H. Lee (UNAM), Kin Ramandeep Gill (UNAM), Noémie Globus (UNAM), Ocelotl López (UNAM), Diego López-Cámara (UNAM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the EP251130a (Wu et al., GCN 42903) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-11-30T12:09:17 to 12:28 UTC (from 1.02 to 1.34 hours after the trigger) and obtained 16 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we detect an uncatalogued source at the coordinates: RA = 101.0205 deg, Dec = 27.3840 deg with an uncertainty of 0.5 arcsec, compatible with the EP/FXT position (Wu et al., GCN 42903), at preliminary magnitudes of:
r = 20.69 +/- 0.03
z = 19.45 +/- 0.03
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 42903
Subject
EP251130a: Einstein Probe detection of an X-ray transient
Date
2025-11-30T11:51:35Z (14 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
T. Wu, H. C. Ding (AHNU), Y. H. Jiang, Y. Wu (NJU), Y. Wang (PMO), W. J. Zhang, 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 EP251130a. The transient triggered EP-WXT (ID: 01709249022) at 2025-11-30T11:07:49 (UTC). The WXT position of the source is R.A. = 101.041 deg, DEC = 27.394 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. = 101.0242 deg, DEC = 27.3824 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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).