EP250612a, GRB 250612B
GCN Circular 40700
Subject
EP250612a: Einstein Probe detection of an X-ray transient
Date
2025-06-12T13:03:13Z (13 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. L. Hua (PMO, CAS), T. Zhao, Y. J. Song, J. W. Hu , W. Yuan (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 EP250612a. The transient triggered EP-WXT (ID: 01709178580) at 2025-06-12T12:28:05 (UTC). The WXT position of the source is R.A. = 229.654 deg, DEC = -26.757 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. = 229.6503 deg, DEC = -26.7661 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 EP250612a is Y. L. Hua, please contact him via email ylhua@pmo.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 40701
Subject
GRB 250612B: BALROG localization (Fermi Trigger 771424081 / GRB 250612519)
Date
2025-06-12T13:17:08Z (13 days ago)
Edited On
2025-06-12T14:03:14Z (13 days ago)
From
Jochen Greiner at MPE <jcgrog@mpe.mpg.de>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Jochen Greiner at MPE <jcg@mpe.mpg.de>
Via
email
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
771424081 at 12:27:56 on 12 June 2025 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).
The best-fit position is:
RA(2000.0) = 226.1 deg
Decl.(2000.0) = -28.9 deg
The 1 sigma statistical error radius is 2.4 deg.
We estimate an additional systematic error of 1 deg.
This is consistent in time and position with the Einstein Probe detection of the X-ray transient EP 250612a (GCN 40700).
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB250612519/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB250612519/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB250612519/json
GCN Circular 40702
Subject
GRB 250612B (250612519/771424081): Fermi GBM Final Localization
Date
2025-06-12T14:23:44Z (13 days ago)
From
eliza.neights@gmail.com
Via
Web form
The Fermi GBM team reports the detection of a likely LONG GRB
"At 12:27:56.19 UT on 12 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250612B (trigger 771424081/250612519).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 231.28, Dec = -29.05 (J2000 degrees, equivalent to J2000 15h 25m, -29d 03'),
with a statistical uncertainty of 2.0 degrees.
The angle from the Fermi LAT boresight is 71.04 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612519/quicklook/glg_skymap_all_bn250612519.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/bn250612519/quicklook/glg_healpix_all_bn250612519.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612519/quicklook/glg_lc_medres34_bn250612519.gif"
GCN Circular 40709
Subject
EP 250612a: AST3-3 Yaoan Optical Observation
Date
2025-06-12T16:49:28Z (13 days ago)
From
ylhua@pmo.ac.cn
Via
Web form
Yan-Long Hua, Tian-Rui Sun, Lei Hu, Jin-Jun Geng, Xue-Feng Wu (PMO, CAS), report on behalf the AST3 Team:
Following the detection of EP 250612a detected by Einstein Probe (Hua et al., GCN 40700), and its potential gamma-ray counterpart by Fermi (Fermi GBM team, GCN 40702), we use Antarctic Survey Telescope 3-3 at Yaoan Astronomy Observation (China, Yunnan) to follow up for the afterglow.
We observed the target position with 30 x 180s exposure in g-band starting from 2025-06-12T13:12:59.95 about 0.75 hours after the burst.
No new optical source was detected within the error box (Hua et al., GCN 40700) down to 20.27 mag in the coadd image (total 30x180s, g-band).
GCN Circular 40710
Subject
EP250612a/GRB 250612B: JinShan optical upper limit
Date
2025-06-12T17:24:35Z (12 days ago)
From
liuxing@nao.cas.cn
Via
Web form
X. Liu, Z.P. Zhu, J. An, S.Q. Jiang, D. Xu (NAOC), S.Y. Fu(HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP250612a detected by EP/WXT (Hua et al., GCN 40700), which is very likely GRB 250612B by Fermi/GBM (Preis & Greiner, GCN 40701; Fermi GBM tea, GCN 40702), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 15:45:13 UT on 2025-06-12, i.e., 3.29 hr after the EP trigger, and 18 x 200 s frames were obtained in the Sloan i-band.
No new optical source is detected within the EP/FXT error circle (Hua et al., GCN 40700), down to a 3-sigma upper limit of i ~ 20.2 mag (AB), calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction.
We acknowledge the excellent support from T.Q. Chen for enabling these observations.
GCN Circular 40714
Subject
EP250612a: Global MASTER-Net observations report
Date
2025-06-12T22:36:21Z (12 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 EP250612a ( EP Team et al., GCN 40700) errorbox 33238 sec after notice time and 35413 sec after trigger time at 2025-06-12 22:18:18 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 24 deg. The sun altitude is -80.1 deg.
The galactic latitude b = 25 deg., longitude l = 340 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2901165
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
35444 | 2025-06-12 22:18:18 | MASTER-SAAO | (15h 17m 45.90s , -26d 51m 07.4s) | C | 60 | 18.5 |
35444 | 2025-06-12 22:18:18 | MASTER-SAAO | (15h 15m 46.32s , -26d 35m 46.7s) | C | 60 | 18.8 |
35635 | 2025-06-12 22:21:29 | MASTER-SAAO | (15h 17m 42.75s , -26d 50m 04.0s) | C | 60 | 18.6 |
35635 | 2025-06-12 22:21:29 | MASTER-SAAO | (15h 15m 43.63s , -26d 34m 41.7s) | C | 60 | 18.9 |
35828 | 2025-06-12 22:24:42 | MASTER-SAAO | (15h 17m 49.62s , -26d 49m 56.6s) | C | 60 | 18.6 |
35828 | 2025-06-12 22:24:42 | MASTER-SAAO | (15h 15m 50.50s , -26d 34m 33.7s) | C | 60 | 18.8 |
36019 | 2025-06-12 22:27:53 | MASTER-SAAO | (15h 17m 48.24s , -26d 50m 30.1s) | C | 60 | 18.6 |
36019 | 2025-06-12 22:27:53 | MASTER-SAAO | (15h 15m 49.05s , -26d 35m 06.7s) | C | 60 | 18.8 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 40716
Subject
EP250612a: SVOM/VT optical candidate
Date
2025-06-13T02:45:04Z (12 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, 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), Y. L. Hua (PMO, CAS), T. Zhao, Y. J. Song, J. W. Hu , W. Yuan (NAO, CAS) report on behalf of the SVOM and EP Teams:
SVOM/VT observed the field of EP250612a (Hua et al., GCN 40700) in ToO mode
in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The observation started at 2025-06-12T21:08:02 UT, about 8.67 hours after the trigger time.
One uncatalogued source, compared to Legacy Survey, was detected within FXT error circle (Hua et al., GCN 40700), RA = 229.65265, DEC = -26.76771, corresponding to:
R. A. (J2000) = 15:18:36.6
DEC. (J2000) = -26:46:03.8
Error = 0.5 arcseconds
The brightness of the candidate is derived as below :
mid-time band mag(AB) exposure
9.45 hour VT_B 22.3+/-0.1 20*70 sec
9.46 hour VT_R 21.8+/-0.1 19*70 sec
Our photometry was derived in AB magnitude and 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 40717
Subject
GRB 250612B: Fermi GBM Observation
Date
2025-06-13T06:34:50Z (12 days ago)
From
Rushikesh Sonawane at IISER, TVM <rushikesh23@iisertvm.ac.in>
Via
Web form
R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 12:27:56.19 UT on 12 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250612B (trigger 771424081/250612519).
which was also detected by EP-WXT (Hua et al. 2025, GCN 40700).
The Fermi GBM on-ground location is consistent with the EP-WXT position.
The angle from the Fermi LAT boresight is 68 degrees.
The GBM light curve consists of single emission episode with a duration (T90)
of about 10.8 s (50-300 keV). The time-averaged spectrum
from T0-4.4 to T0+18.2 s is best fit by
a Band function with Epeak = 47.80 +/- 1.53 keV,
alpha = -0.92 +/- 0.09, and beta = -3.47 +/- 0.39.
A Comp model fits the spectrum equally well, with a power-law index = –0.98 +/- 0.07
and cutoff energy parameterized as Epeak = 49.14 +/- 1.26 keV.
The event fluence (10-1000 keV) in this time interval is
(5.2 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.9 s in the 10-1000 keV band is 12.1 +/- 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 40720
Subject
EP250612a: refined analysis of the EP-WXT and EP-FXT observations
Date
2025-06-13T14:07:36Z (12 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.L.Hua (PMO, CAS), J. W. Hu, T. Zhao, Y. J. Song ,W. Yuan(NAO, CAS) report on behalf of the Einstein Probe team:
The fast X-ray transient EP250612a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hua et al., GCN 40700), and followed up by several optical and X-ray telescopes (Hua et al., GCN 40709, Li et al., GCN 40716). Refined analysis of the WXT data shows that the event started at T0=2025-06-12T12:27:38 (UTC) and lasted for about 35s before the interruption by the autonomous follow-up observation. The peak flux (0.5-4 keV) is estimated to be 3.9 x 10^-8 erg/s/cm^2. The averaged 0.5-4 keV spectrum can be fitted with an absorbed power-law with a Galactic hydrogen column density of 4.3 x 10^21 cm^-2(-2.1, +2.4) and a photon index of 1.01 (-0.1, +0.1). The derived average unabsorbed 0.5-4 keV flux is 3.67 (-0.74, +1.10) x 10^-9 erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2025-06-12 12:30:08, about 3 minutes after T0, with an exposure time of 5858 seconds. Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 229.6534, DEC = -26.7673 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is spatially consistent with the candidate X-ray counterpart detected by Fermi(Fermi GBM team., GCN 40702). The averaged 0.5-10 keV FXT spectrum can be fitted with an absorbed power-law with a Galactic hydrogen column density of 1.49 x 10^21 cm^-2 and a photon index of 2.2 (-0.045, +0.045). The derived unabsorbed 0.5-10 keV flux is 1.37 (-0.03, +0.04) x 10^-11 erg/s/cm^2. The uncertainties are at the 90% confidence level for all the above parameters.
EP-FXT will continue monitoring the source in the forthcoming days. Multi-band follow-up observations are encouraged. The contact TA of EP250612a is Y.L.Hua, please contact him via the email ylhua@pmo.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 40727
Subject
EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
Date
2025-06-14T08:29:34Z (11 days ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), L. Cotter (UCD), B. P. Gompertz (U. Birmingham), A. A. Djupvik (NOT), L. Fuglsang (NOT), report on behalf of a larger collaboration.
We observed the field of EP250612a / GRB 250612B detected by EP (Hua et al., GCN 40700) and Fermi (Fermi GBM team, GCN 40702), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 12x100 s exposures in the SDSS r-band, starting at 23:19 UT on 2025-05-13 (1.952 days after the EP trigger).
At J2000 coordinates RA:15:18:36.667, DEC: -26:46:03.624 (error 0.5”), consistent with those by Li et al. (GCN 40716), the optical counterpart is detected in our stacked image with a preliminary magnitude:
r = 23.59 +/- 0.22 (AB).
The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction.