EP250730a
GCN Circular 41226
Subject
EP250730a: SVOM/VT optical upper limit
Date
2025-08-04T09:37:30Z (a month ago)
From
zhyao@bao.ac.cn
Via
Web form
Z. H. Yao, H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Y. N. Ma, 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), B. T. Wang (YNAO) report on behalf of the SVOM/VT team.
SVOM performed a Target of Opportunity observation of EP250730a detected by EP/WXT (Wang et al., GCN 41207). SVOM/VT began observing the field at 2025-07-31T10:36:57.506 UTC, 28.5 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No uncataloged candidates were detected in our single or stacked images within the error box provided by EP/WXT (Wang et al., GCN 41207), the three sigma limits are:
mid-time (UTC) | exposure time (s) | band | upper limit (AB)
--------------------|-------------------------|------|-----------------
2025-07-31T11:47:09 | 19*100 | VT_B | 23.5
2025-07-31T11:47:09 | 19*100 | VT_R | 23.0
Our results are consistent with COLIBRÍ (Magnani et al., GCN 41209) and Global MASTER-Net (Lipunov et al., GCN 41210).
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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 41210
Subject
EP250730a: Global MASTER-Net observations report
Date
2025-07-31T08:45:26Z (a month 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250730a ( EP Team et al., GCN 41207) errorbox 762 sec after notice time and 79097 sec after trigger time at 2025-07-31 04:04:26 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 28 deg. The sun altitude is -74.8 deg.
The galactic latitude b = -30 deg., longitude l = 44 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2953990
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
79128 | 2025-07-31 04:04:26 | MASTER-OAFA | (20h 48m 25.83s , -04d 35m 50.0s) | C | 60 | 19.5 |
79204 | 2025-07-31 04:05:42 | MASTER-OAFA | (20h 56m 28.38s , -04d 37m 17.4s) | C | 60 | 19.9 |
79264 | 2025-07-31 04:05:42 | MASTER-OAFA | (20h 56m 28.38s , -04d 37m 17.3s) | C | 180 | 20.0 | Coadd
79380 | 2025-07-31 04:08:39 | MASTER-OAFA | (20h 48m 21.81s , -04d 36m 50.2s) | C | 60 | 19.6 |
80221 | 2025-07-31 04:22:39 | MASTER-OAFA | (20h 56m 21.95s , -04d 36m 17.7s) | C | 60 | 19.4 |
80384 | 2025-07-31 04:25:22 | MASTER-OAFA | (20h 48m 19.67s , -04d 38m 26.9s) | C | 60 | 19.3 |
80459 | 2025-07-31 04:26:37 | MASTER-OAFA | (20h 56m 28.18s , -04d 38m 08.1s) | C | 60 | 19.0 |
82546 | 2025-07-31 05:01:24 | MASTER-OAFA | (20h 48m 14.53s , -04d 39m 59.5s) | C | 60 | 19.6 |
82622 | 2025-07-31 05:02:41 | MASTER-OAFA | (20h 56m 20.98s , -04d 38m 21.8s) | C | 60 | 19.7 |
82682 | 2025-07-31 05:02:41 | MASTER-OAFA | (20h 56m 20.99s , -04d 38m 21.9s) | C | 180 | 19.8 | Coadd
82805 | 2025-07-31 05:05:44 | MASTER-OAFA | (20h 48m 09.69s , -04d 38m 26.0s) | C | 60 | 19.0 |
82880 | 2025-07-31 05:06:59 | MASTER-OAFA | (20h 56m 18.72s , -04d 39m 15.7s) | C | 60 | 19.2 |
83049 | 2025-07-31 05:09:47 | MASTER-OAFA | (20h 48m 15.74s , -04d 40m 36.9s) | C | 60 | 18.0 |
83139 | 2025-07-31 05:11:17 | MASTER-OAFA | (20h 56m 15.54s , -04d 38m 36.4s) | C | 60 | 18.4 |
85345 | 2025-07-31 05:48:03 | MASTER-OAFA | (20h 48m 01.89s , -04d 41m 11.2s) | C | 60 | 16.5 |
85423 | 2025-07-31 05:49:21 | MASTER-OAFA | (20h 56m 09.03s , -04d 41m 53.1s) | C | 60 | 14.9 |
85586 | 2025-07-31 05:52:05 | MASTER-OAFA | (20h 48m 05.61s , -04d 43m 03.1s) | C | 60 | 14.1 |
85696 | 2025-07-31 05:53:54 | MASTER-OAFA | (20h 56m 05.97s , -04d 41m 44.0s) | C | 60 | 14.0 |
85861 | 2025-07-31 05:56:40 | MASTER-OAFA | (20h 48m 04.15s , -04d 42m 01.5s) | C | 60 | 15.2 |
85937 | 2025-07-31 05:57:56 | MASTER-OAFA | (20h 56m 01.37s , -04d 42m 30.3s) | C | 60 | 15.1 |
94065 | 2025-07-31 08:13:23 | MASTER-OAFA | (20h 52m 50.00s , -04d 44m 13.9s) | C | 60 | 15.7 |
94143 | 2025-07-31 08:14:41 | MASTER-OAFA | (20h 52m 44.60s , -04d 45m 13.2s) | C | 60 | 16.9 |
94224 | 2025-07-31 08:16:02 | MASTER-OAFA | (20h 52m 50.40s , -04d 45m 05.9s) | C | 60 | 18.6 |
94299 | 2025-07-31 08:17:17 | MASTER-OAFA | (20h 52m 46.84s , -04d 43m 27.0s) | C | 60 | 19.1 |
94359 | 2025-07-31 08:17:17 | MASTER-OAFA | (20h 52m 46.84s , -04d 43m 27.0s) | C | 180 | 19.5 | Coadd
94374 | 2025-07-31 08:18:33 | MASTER-OAFA | (20h 52m 46.83s , -04d 44m 55.5s) | C | 60 | 18.0 |
94452 | 2025-07-31 08:19:50 | MASTER-OAFA | (20h 52m 49.75s , -04d 43m 42.7s) | C | 60 | 19.5 |
94559 | 2025-07-31 08:21:07 | MASTER-OAFA | (20h 52m 44.72s , -04d 44m 13.2s) | C | 120 | 19.7 |
95484 | 2025-07-31 08:36:32 | MASTER-OAFA | (20h 52m 44.73s , -04d 43m 16.8s) | C | 120 | 19.2 |
95621 | 2025-07-31 08:38:50 | MASTER-OAFA | (20h 52m 50.14s , -04d 44m 17.2s) | C | 120 | 19.6 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41209
Subject
EP250730a: COLIBRÍ optical upper limit
Date
2025-07-31T07:03:35Z (a month ago)
From
Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>
Via
Web form
Francesco Magnani (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (U Roma), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), and Ny Avo Rakotondrainibe (LAM):
We imaged the field the EP250730a (Wang et al., GCN Circ. 41207) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-07-31 04:13 to 05:35 UTC (from 22.1 to 23.5 hours after the trigger, starting 23 min after the report by Wang et al., GCN Circ. 41207) and obtained 64 minutes of exposure in the i filter.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 our stacked image, we do not detect any new source within the EP/WXT uncertainty region (Wang et al., GCN Circ. 41207) to a 5-sigma upper limit of:
i > 23.1
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 41207
Subject
EP250730a: Einstein Probe detection of an X-ray transient
Date
2025-07-31T03:50:45Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
B.-T. Wang (YNAO, CAS), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC), X.P. Xu, W. Yuan (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by EP-WXT through ground data analysis, designated EP250730a (ObsID:11900327297). The transient was detected at 2025-07-30T06:06:09 (UTC).
The WXT position of the source is R.A. = 313.264 deg, DEC = -4.648 deg (J2000) with an uncertainty of 2.1 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 250 seconds.
The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with nH fixed at the Galactic value of 6.0 x 10^20 cm^-2 and a photon index of 1.84 (-0.38, +0.41). The unabsorbed average 0.5-4 keV flux is estimated to be 1.93 (-0.39, +0.48)e-10 erg/s/cm2. The peak flux is about 2e-9 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters.
Further FXT observations are scheduled.
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).