EP250512a, GRB 250512B
GCN Circular 40437
Subject
EP250512a: Einstein Probe detection of an X-ray transient
Date
2025-05-12T12:13:33Z (19 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
D. H. Zhao, M. J. Liu, J. W. Hu, H. W. Pan (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 EP250512a. The transient triggered EP-WXT (ID: 01709175718) at 2025-05-12T11:22:08 (UTC). The WXT position of the source is R.A. = 215.216 deg, DEC = -10.092 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. = 215.2023 deg, DEC = -10.0988 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.
The contact TA of EP250512a is D. H. Zhao, please contact her via the email zhaodh@bao.ac.cn if needed.
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 40439
Subject
GRB 250512B: SVOM detection of a burst
Date
2025-05-12T14:40:03Z (19 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Pierre Maggi (ObAS), Yinuo Ma (NAOC), Nicolas Dagoneau (CEA), Ulysse Jacob (LUPM), Miguel Moita (CEA) report on behalf of the SVOM mission team:
SVOM/ECLAIRs triggered and located GRB 250512B (SVOM burst-id sb25051203) starting at 2025-05-12T11:20:08 (Tb), also detected by Einstein Probe (labelled as EP250512a, Zhao et al. GCN 40437).
The following trigger information was received after data download through the X-band ground station.
The burst was detected onboard both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 16 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 25.26 in the 8-120 keV energy band over a time window of 20.40 seconds starting at Tb.
The localization of the best alert is R.A., Dec. 215.22, -10.1086 degrees with a 90% confidence level (C.L.) radius of 3.65 arcmin (including systematic error of 2 arcmin added in quadrature).
The ECLAIRs light curve in the 4-120 keV energy band shows a single broad peak structure with a T90 duration of 23.76 (-2.50/+0.48) seconds.
SVOM slewed to the burst.
MXT began observing the field at 2025-05-12T11:22:58.718 UTC, 160 seconds after Tb.
Using the X-band data we found an uncatalogued X-ray source located at R.A., Dec. 215.200, -10.1128 degrees:
R.A. (J2000) = 14h20m48.1s
Dec. (J2000) = -10d06m46.16s
with a 90% C.L. radius of 40 arcseconds including 35 arcseconds added in quadrature.
This location is 1.2 arcminutes from the ECLAIRs onboard position and 50 arcseconds from the EP/FXT one.
The MXT source is rapidly fading and is not detected in the second orbit starting 1.5 hours after slew.
VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this burst is Pierre Maggi: pierre.maggi@astro.unistra.fr.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN Circular 40443
Subject
GRB 250512B/EP250512a：SVOM/VT bright optical counterpart
Date
2025-05-12T15:15:31Z (19 days ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, 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), P. Maggi (ObAS), Y. N. Ma, D. H. Zhao(NAOC) report on behalf of the SVOM/VT Instrument Team:
GRB 250512B (sb25051203), triggered both by SVOM/Eclairs (Maggi et al., GCN 40439) and Einstein Probe(EP/WXT) (labeled as EP250512a, Zhao et al., GCN 40437), was observed by on-board SVOM/VT after the automatic slew of the satellite. The VT conducted observations in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
With the downlinked X-band data, the optical counterpart was clearly detected within the error box of EP/FXT(Zhao et al., GCN 40437) in both VT_B and VT_R bands. The earliest observation started on 2025-05-12T11:23:21 UTC (i.e. 193 seconds after the SVOM trigger time).
The position of the counterpart is RA=215.20368 deg, DEC= -10.10071 deg, which is equivalent to:
R.A.=14:20:48.88,
DEC.=-10:06:02.56,
J2000,
Error=0.5 arcseconds
The light curves show a brightening with a peak of 19.3+/-0.1 mag in VT_R and 21.0+/-0.2 mag in VT_B at 668 seconds after the burst. The photometry is in the AB system and is not corrected for Galactic extinction.
Given the color of VT_B-VT_R~1.7 mag, it might be a low or intermediate redshift GRB (Wang et al., 2020).
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 40444
Subject
GRB 250512B/EP250512a: SVOM/VT optical fading
Date
2025-05-12T16:37:10Z (19 days ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, 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), S. D. Vergani (CNRS, Obs. Paris/LUX), P. Maggi (ObAS), Y. N. Ma, D. H. Zhao (NAOC) report on behalf of the SVOM/VT Instrument Team:
The analysis with more downlinked X-band data shows that the optical counterpart (Li et al., GCN 40443) of GRB 250512B/EP250512a (Maggi et al., GCN 40439, Zhao et al., GCN 40437) has been fading to about 21.5+/-0.2 (AB) mag in VT_R mag at the mid time of 1.6 hours after the burst, with an effective time of 12*50 seconds. The decay slop is about -1.0 after the peak time (Li et al., GCN 40443).
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 40446
Subject
EP250512a: Global MASTER-Net observations report
Date
2025-05-12T20:45:41Z (19 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the EP250512a ( EP Team et al., GCN 40437) errorbox 28318 sec after notice time and 31541 sec after trigger time at 2025-05-12 20:07:49 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 30 deg. The sun altitude is -54.2 deg.
The galactic latitude b = 46 deg., longitude l = 337 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2868623
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
31571 | 2025-05-12 20:07:49 | MASTER-SAAO | (14h 19m 12.13s , -10d 13m 30.1s) | C | 60 | 17.2 |
31631 | 2025-05-12 20:07:49 | MASTER-SAAO | (14h 19m 12.13s , -10d 13m 30.1s) | C | 180 | 17.7 | Coadd
31650 | 2025-05-12 20:09:08 | MASTER-SAAO | (14h 19m 06.91s , -10d 14m 28.5s) | C | 60 | 17.1 |
31730 | 2025-05-12 20:10:27 | MASTER-SAAO | (14h 19m 12.41s , -10d 13m 58.2s) | C | 60 | 17.2 |
31809 | 2025-05-12 20:11:47 | MASTER-SAAO | (14h 19m 09.57s , -10d 12m 28.8s) | C | 60 | 17.2 |
31869 | 2025-05-12 20:11:47 | MASTER-SAAO | (14h 19m 09.57s , -10d 12m 28.8s) | C | 180 | 17.6 | Coadd
31889 | 2025-05-12 20:13:06 | MASTER-SAAO | (14h 19m 09.61s , -10d 13m 58.7s) | C | 60 | 17.0 |
31968 | 2025-05-12 20:14:25 | MASTER-SAAO | (14h 19m 12.16s , -10d 12m 34.3s) | C | 60 | 17.0 |
32047 | 2025-05-12 20:15:44 | MASTER-SAAO | (14h 19m 07.13s , -10d 13m 22.0s) | C | 60 | 17.0 |
32107 | 2025-05-12 20:15:44 | MASTER-SAAO | (14h 19m 07.14s , -10d 13m 22.0s) | C | 180 | 17.6 | Coadd
32126 | 2025-05-12 20:17:04 | MASTER-SAAO | (14h 19m 05.72s , -10d 12m 20.9s) | C | 60 | 17.1 |
32206 | 2025-05-12 20:18:24 | MASTER-SAAO | (14h 19m 12.92s , -10d 13m 20.0s) | C | 60 | 17.2 |
32286 | 2025-05-12 20:19:43 | MASTER-SAAO | (14h 19m 06.56s , -10d 14m 18.8s) | C | 60 | 17.0 |
32346 | 2025-05-12 20:19:43 | MASTER-SAAO | (14h 19m 06.56s , -10d 14m 18.8s) | C | 180 | 17.5 | Coadd
32366 | 2025-05-12 20:21:04 | MASTER-SAAO | (14h 19m 13.61s , -10d 14m 04.5s) | C | 60 | 16.9 |
32446 | 2025-05-12 20:22:23 | MASTER-SAAO | (14h 19m 11.06s , -10d 12m 36.7s) | C | 60 | 17.0 |
32943 | 2025-05-12 20:30:40 | MASTER-SAAO | (14h 19m 12.88s , -10d 12m 10.3s) | C | 60 | 16.9 |
33003 | 2025-05-12 20:30:40 | MASTER-SAAO | (14h 19m 12.88s , -10d 12m 10.3s) | C | 180 | 17.4 | Coadd
33022 | 2025-05-12 20:32:00 | MASTER-SAAO | (14h 19m 18.93s , -10d 13m 09.3s) | C | 60 | 16.8 |
33102 | 2025-05-12 20:33:19 | MASTER-SAAO | (14h 19m 14.64s , -10d 14m 08.2s) | C | 60 | 16.8 |
33181 | 2025-05-12 20:34:39 | MASTER-SAAO | (14h 19m 21.08s , -10d 14m 06.4s) | C | 60 | 16.9 |
33241 | 2025-05-12 20:34:39 | MASTER-SAAO | (14h 19m 21.08s , -10d 14m 06.4s) | C | 180 | 17.5 | Coadd
33260 | 2025-05-12 20:35:58 | MASTER-SAAO | (14h 19m 18.22s , -10d 12m 20.5s) | C | 60 | 16.9 |
33340 | 2025-05-12 20:37:17 | MASTER-SAAO | (14h 19m 18.96s , -10d 14m 01.5s) | C | 60 | 16.8 |
33419 | 2025-05-12 20:38:37 | MASTER-SAAO | (14h 19m 22.19s , -10d 12m 23.8s) | C | 60 | 16.9 |
33499 | 2025-05-12 20:39:56 | MASTER-SAAO | (14h 19m 16.86s , -10d 13m 02.6s) | C | 60 | 16.8 |
33578 | 2025-05-12 20:41:16 | MASTER-SAAO | (14h 19m 18.30s , -10d 12m 01.7s) | C | 60 | 16.8 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 40447
Subject
EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart
Date
2025-05-13T03:20:43Z (19 days ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report:
We observed the couterpart of EP250512a/GRB 250512B (Zhao et al., GCN 40437; Maggi et al., GCN 40437; Li et al., GCN 40443; Xin et al., GCN 40444; Lipunov et al., GCN 40446) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-05-12T21:43:13 UT (0.43 days after the trigger). We only detect the counterpart in the J band at
J = (21.6 +/- 0.3) mag.
The 3 sigma upper limits for the r and i band are
r > 21.9 mag
i > 21.2 mag.
The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction.
We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations.
GCN Circular 40448
Subject
EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
Date
2025-05-13T07:02:52Z (19 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H.N. Yang, D. H. Zhao (NAO, CAS), Y. L. Hua (PMO, CAS), Y. J. Zhang (THU), M. J. Liu, J. W. Hu, H. W. Pan, Y. Liu (NAO, CAS), on behalf of the Einstein Probe (EP) team:
The X-ray transient EP250512a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (D. H. Zhao et al. GCN 40437). It was also detected by SVOM/ECLAIRs (Pierre Maggi et al. GCN 40439), and followed up by several telescopes ( H. L. Li et al. GCN 40443; L. P. Xin et al. GCN 40444; V.Lipunov et al. GCN 40446; Malte Busmann et al. GCN 40447). Refined analysis of the WXT data shows that the event started at T0 = 2025-05-12T11:20:03 (UTC) and lasted for about 360 s (T90). The peak flux is about 4.2 x 10^(-9) erg/s/cm^2 (T0+135 s). The averaged 0.5-4 keV spectrum of T90 can be fitted by an absorbed power law model with a Galactic hydrogen column density of 5.7 x 10^20 cm^-2 and a photon index of 1.31 (-0.17/+0.18). The derived average unabsorbed 0.5-4 keV flux is 1.13 (-0.13/+0.14) x 10^(-9) erg/s/cm^2. The uncertainties are quoted at the 90% confidence level for the above parameters.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 4 min after T0, starting at 2025-05-12T11:23:44 (UTC). Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 215.2043, DEC = -10.1009 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). During the observation a decline in the source flux lasting for a few hundred seconds is observed from the beginning. The averaged 0.5-10 keV FXT spectrum (from T0+291 s to T0+7094 s, with a total exposure time of 4,095 s) can be fitted by an absorbed power law model with a Galactic hydrogen column density of 5.7 x 10^20 cm^-2 and a photon index of 1.45 (+/-0.05). The derived average unabsorbed 0.5-10 keV flux is 3.78 (-0.18/+0.19) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
EP-FXT will continue monitoring this source. More follow-up observations are encouraged. The contact TAs of EP250512a are D. H. Zhao and H. N. Yang. Please contact them via email zhaodh@bao.ac.cn, hnyang@nao.cas.cn if needed.
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 40452
Subject
EP250512a/GRB 250512B: REM optical/NIR observations
Date
2025-05-13T10:28:43Z (18 days 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 EP250512a/GRB 250512B detected by EP/WXT (Zhao et al., GCN 40437) and SVOM/ECLAIRs (Maggi et al., GCN 40439) 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 May 12 at 22:52:55 UT (i.e. 11.5 hr after the burst), and lasted for about 1 hour.
From preliminary inspection, we do not detect any possible counterpart consistent with the afterglow (Li et al., GCN 40443; Xin et al., GCN 40444; Busmann et al., GCN 40447) down to the following 3sigma limits:
r > 18.9 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 12.0 hr after the trigger;
H > 16.2 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 11.9 hr after the trigger.
GCN Circular 40460
Subject
Konus-Wind detection of GRB 250512B / EP250512a
Date
2025-05-15T11:03:14Z (16 days ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A.Lysenko, A. Ridnaia, A. Tsvetkova,
M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long-duration GRB 250512B / EP250512a
(EP-WXT detection: Zhao et al., GCN 40437;
Yang et al., GCN 40448;
SVOM-ECLAIRs detection: Maggi et al., GCN 40439)
was detected by Konus-Wind (KW) in the waiting mode
at about T0 = T0(EP) = 40803 s UT (11:20:03).
A Bayesian block analysis of the KW waiting mode data in
the 20-400 keV band reveals a ~8 sigma count-rate increase in
the interval from T0+7.4 s to T0+113.3 s.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB250512B/
The total burst fluence is 6.68(-2.23,+1.59)x10^-6 erg/cm^2,
and the 2.944 s peak energy flux, measured from T0+10.309 s,
is 3.08(-1.14,+0.89)x10^-7 erg/cm^2.
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst,
measured from T0+7.4 s to T0+113.3 s,
can be described by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha > -1.82 and Ep = 114(-37,+57) keV.
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 40465
Subject
GRB 250512B / EP250512a: SVOM/GRM analysis
Date
2025-05-16T13:34:45Z (15 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Nicolas Dagoneau, Stéphane Schanne (CEA)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by the burst GRB 250512B (SVOM trigger reference: sb sb25051203) at 2025-05-12T11:20:08 UTC (T0), which is also detected by SVOM/ECLAIRs (Pierre Maggi et al., GCN #40439) , Einstein Probe (Zhao et al. GCN 40437) and Konus-Wind (D. Svinkin et al., GCN #40460).
With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250512B. The GRM light curve shows that this burst consists of multi-episodes with a T90 of 179 +19/-7 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250512B.png
With the localization of ECLAIRs (RA=215.22, DEC=-10.1086), the time-averaged spectrum from T0-3 to T0+50 s (the main episode before the slew) is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.23 +0.42/-0.44 and the cutoff energy, parameterized as Epeak, is 70 +9/-6 keV. The event fluence (10-1000 keV) in this time interval is (3.1 +0.3/-0.2)E-06 erg/cm^2.
We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later.
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.