GRB 250919A, EP250919a
GCN Circular 42177
Subject
GRB 250919A: TERI gamma-ray detection
Date
2025-10-09T21:09:21Z (3 days ago)
Edited On
2025-10-10T04:59:46Z (2 days ago)
From
Daniel Shy <danielshy@danielshy.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Daniel Shy <danielshy@danielshy.com>
Via
Web form
Daniel Shy (a), C.C. Cheung (a), Bernard Phlips (a), Michael Streicher (b), James Mason (b), Douglas M. Groves (b), Feng Zhang (b), Willy Kaye (b)
(a) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375
(b) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA
The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 250919A, which was also detected by Fermi/GBM, SVOM/GRM, EP/WXT, NuSTAR, Glowbug, Insight-HXMT, and Konus-Wind (Fermi GBM team, GCN 41874; Wang et al., GCN 41882; Liang et al., GCN 41879; Waratkar & Grefenstette, GCN 41888; Cheung et al., GCN 41891, Wang et al., GCN 41900; Frederiks et al., GCN 41905)
Using 1 Hz binning, and adopting T0 = 2025-09-19 00:28:52.28, we observe the three dominant peaks seen in the Fermi/GBM lightcurve (GCN 41874) at ~T0+24s, ~T0+26s, and ~T0+29s with respective peak excess count rates of roughly 57, 171, and 104 counts per second (cps) above the 27-cps baseline rate observed in nearby off-source intervals.
The analysis results presented here are preliminary and currently lack a detailed response function.
TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program’s STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module.
[1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559).
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 41996
Subject
GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
Date
2025-09-26T06:58:48Z (16 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni., Argentina);
N.Tiurina, E.Gorbovskoy, V.Lipunov, A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, Yu. Tselik, A. Sosnovskiy, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU, SAI, Moscow),
D.Buckley, (SAAO, South Africa)
O.Gress, N.Budnev (ISU, Irkutsk),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,
L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
The MASTER-OAFA robotic wide-field camera, located in Argentina (OAFA observatory of San Juan National University [1], during a regular survey, obtained an image of the region of the sky containing the point with coordinates MASTER OT J195412.89-485016.4 (GCN 41893) and source (Li et al., GCN 41877) before, during and after the Fermi trigger moment (GBM GCN 41874, GCN 41876, GCN 41890; LAT GCN 41884, Ttrigger=00:28:52) of GRB 250919A .
Very bright optical counterpart MASTER OT J195412.89-485016.4
promptly detected at the agnitude ~ 9 m.
This transient was first publishied as EP250919a optical counterpart by Las
Cumbres observatory (GCN 41877, t_detection=03:02:52.800 UTC)
and as Fermi GRB 250919A/EP250919a optical counterpart by Gemini-South (LEvan et
al. GCN 41883) with reshift detection z = 1.145
X-ray counterpart was also detected by Swift (Osborne et al. GCN 41885) with OT afterglow detection by UVOT (Oates et
al. GCN 41886), NuSTAR (GCN 41888) and Svom (41882).
The full 4 nights light curve is currently being processed.
[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#625
GCN Circular 41961
Subject
GRB 250919A / EP250919a: further LCO optical observation
Date
2025-09-24T11:30:34Z (18 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA/Irfu), Z. Q. Wang (GXU), Y. F. Liang (PMO), report on behalf of the SVOM mission team:
We re-observed the field of GRB 250919A / EP250919a (Fermi GBM Team, GCN 41874; Liang et al., GCN 41879; Wang et al., GCN 41882; Holzmann Airasca et al., GCN 41884; Waratkar et al., GCN 41888; Cheung et al., GCN 41891; Wang et al. GCN 41900; Frederiks et al. GCN 41905) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument.
We obtained 3x200 s exposures in the SDSS r filter. The optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893; Ma et al. GCN 41894, Saccardi et al., GCN 41906) is still clearly detected in our subtracted image (using the Legacy Survey DR10 image template) with the following magnitude (calibrated against the SkyMApper DR4 catalogued stars, not corrected for Galactic extinction):
r = 20.67 +/- 0.08 (AB), at a mid-time of 4.47 days after the trigger.
Compared to our first epoch (Saccardi et al., GCN 41906), the afterglow is fading as a power law decay with alpha ~ 1.1 with no evidence of any late break so far.
Further observations are planned.
This project is funded by the SVOM collaboration.
GCN Circular 41906
Subject
GRB 250919A / EP250919a: LCO optical observation
Date
2025-09-20T16:06:37Z (22 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), J. T. Palmerio (CEA/Irfu), Z. Q. Wang (GXU), Y. F. Liang (PMO), report on behalf of the SVOM mission team:
We observed the field of GRB 250919A / EP250919a detected by Fermi/GBM (Fermi GBM Team, GCN 41874), EP/WXT (Liang et al., GCN 41879), SVOM/GRM (Wang et al., GCN 41882), Fermi/LAT (Holzmann Airasca et al., GCN 41884), NuSTAR (Waratkar et al., GCN 41888), Glowbug (Cheung et al., GCN 41891), Insight-HXMT (Wang et al. GCN 41900), Konus-Wind (Frederiks et al. GCN 41905), with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument.
We obtained 3x200 s exposures in each of the SDSS g, r and i filters. The optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893; Ma et al. GCN 41894) is clearly detected in our subtracted image (using the Legacy Survey DR10 image template) with the following magnitudes (calibrated against the SkyMApper DR4 catalogued stars, not corrected for Galactic extinction):
g = 19.49 +/- 0.02 (AB), at a mid-time of 32.7 hr after the trigger;
r = 19.19 +/- 0.03 (AB), at a mid-time of 32.5 hr after the trigger;
i = 18.98 +/- 0.04 (AB), at a mid-time of 32.5 hr after the trigger.
Further observations are planned.
This project is funded by the SVOM collaboration.
GCN Circular 41905
Subject
Konus-Wind detection of GRB 250919A
Date
2025-09-20T15:50:37Z (22 days ago)
Edited On
2025-09-22T01:49:07Z (20 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Dmitry Frederiks at Ioffe Institute <ddfrederiks@gmail.com>
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 GRB 250919A (Fermi-GBM detection:
The Fermi GBM team, GCN 41874; Mukherjee & Meegan, GCN 41890;
EP-WXT detection: Liang et al., GCN 41879;
SVOM-GRM observaion: Wang et al., GCN 41882),
Fermi-LAT detection: Holzmann Airasca et al., GCN 41884;
Glowbug detection: Cheung et al., GCN 41891)
triggered Konus-Wind (KW) at T0=1741.403 s UT (00:29:01.403).
The burst consists of two separated emission pulses
and had the total duration of ~240 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250919_T01741/
As observed by Konus-Wind, the burst had
a fluence of (4.24 ± 0.25)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 23.168 s,
of (1.33 ± 0.09)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+218 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -0.94 (-0.05,+0.05),
the high energy photon index beta = -2.32 (-0.17,+0.11),
the peak energy Ep = 452 (-33,+39) keV,
chi2 = 101/97 dof.
The spectrum near the peak count rate (measured from T0+23.04 to T0+23.296 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -0.07 (-0.09,+0.10),
the high energy photon index beta = -2.15 (-0.07,+0.06),
the peak energy Ep = 515 (-38,+42) keV,
chi2 = 63/62 dof.
Assuming the redshift z=1.145 (Levan et al., GCN 41883)
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 (1.53 ± 0.09)x10^54 erg,
the isotropic peak luminosity L_iso to (1.03 ± 0.07)x10^54 erg/s, and
the rest-frame peak spectral energy Ep,z to (970 ± 80) keV.
With the obtained estimates, GRB 250919A is consistent with 68% prediction bands
of both '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/GRB250919_T01741/GRB250919A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 41900
Subject
GRB 250919A / EP250919a: Insight-HXMT detection
Date
2025-09-20T13:01:19Z (22 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Shao-Lin Xiong, Shi-Jie Zheng, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2025-09-19T00:29:15.000 (T0), Insight-HXMT/HE detected the burst GRB 250919A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41874), SVOM/GRM (Wang et al., GCN#41882), Fermi/LAT (A. Holzmann Airasca, GCN#41884), NuSTAR (G. Waratkar et al., GCN#41888), Glowbug (C.C. Cheung et al., GCN#41891), associated with EP250919a detected by EP/WXT (Liang et al., GCN Circ. 41879).
The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 117.0 +4.5/-3.0 s. The 1s peak rate, measured from T0+10.250 s, is 14624 cnts/sec. The total counts from this burst is 98750 counts. However, the HE detector was suffered from saturation from T0+6 s to T0+8 s and T0+10 s to T0+11 s due to the high-brightness.
The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250919A.png
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.
GCN Circular 41894
Subject
GRB 250919A/EP250919a: SVOM/VT optical observation
Date
2025-09-20T02:42:26Z (22 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, 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 GRB 250919A/EP250919a detected by Fermi/GBM, SVOM/GRM, EP/WXT, NuSTAR, and Glowbug (Fermi GBM team GCN 41874; Wang et al., GCN 41882; Liang et al., GCN 41879; Waratkar & Grefenstette, GCN 41888; Cheung et al., GCN 41891). SVOM/VT began observing the field at 2025-09-19T14:24:05 UTC, 13.92 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 (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893) was clearly detected in both VT_B and VT_R bands. The magnitudes are:
mid time (h) | exposure time (s) | band | mag (AB) | mag err
-------------|-------------------|------|----------|--------
14.240 | 47*50 | VT_B | 18.55 | 0.02
14.247 | 46*50 | VT_R | 18.13 | 0.02
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 41893
Subject
GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
Date
2025-09-20T00:38:17Z (22 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.M.Lipunov (Lomonosov MSU, Moscow),
R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA),
A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, E.Gorbovskoy, N.Tiurina,
M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU),
D.Buckley, (SAAO, South Africa)
O.Gress, N.Budnev (ISU, Irkutsk),
A.Sosnovskij (Crao RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,
L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
MASTER Global robotic Net (Lipunov et al. 2010) started Fermi GRB 250919A
(GBM GCN 41874, GCN 41876, GCN 41890; LAT GCN 41884, Ttrigger=00:28:52)
observation in alert mode (Lipunov et al. GCN 41875)
at MASTER-OAFA and continued as EP GRB 250919 (GCN 41879) since its notice time (Lipunov et al. 41880)
Bright optical counterpart MASTER OT J195412.89-485016.4 was detected with peak structure light curve.
24h after GRB detection (GCN 41874) this optical counterpart has unfiltered m_OT~18.3
MASTER observations will be continued
This transient was first publishied as EP250919a optical counterpart by Las Cumbres observatory (GCN 41877, t_detection=03:02:52.800 UTC)
and as Fermi GRB 250919A/EP250919a optical counterpart by Gemini-South (LEvan et al. GCN 41883)
with reshift detection z = 1.145
X-ray counterpart was also detected by
Swift (Osborne et al. GCN 41885) with OT afterglow detection by UVOT (Oates et al. GCN 41886), .
NuSTAR (GCN 41888) and Svom (41882).
GCN Circular 41891
Subject
GRB 250919A: Glowbug gamma-ray detection
Date
2025-09-19T18:58:32Z (23 days ago)
From
C.C. Cheung at Naval Research Lab <Teddy.Cheung@nrl.navy.mil>
Via
Web form
C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 250919A, which was also detected by Fermi/GBM (GCN 41874, 41881, 41890), SVOM/GRM (GCN 41882), and NuSTAR (GCN 41888), and associated with the Einstein Probe transient EP250919a (GCN 41879).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-19 00:28:56.288 with a duration of 32.1 s and a total significance of about 14.5 sigma. The burst originated toward the Nadir side of Glowbug and was detected despite passing through the passive material from the H9 pallet and internal passive material/shielding within Glowbug. The observed light curve comprises two primary peaks at ~T0+24s and ~T0+28s. Note that data from ~T0+30s to +38s suffered from deadtime in various detectors.
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12.
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 41890
Subject
GRB 250919A: Fermi GBM Observation
Date
2025-09-19T18:56:13Z (23 days 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 00:28:52.28 UT on 19 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250919A (trigger 779934537/250919020)
which was also detected by Fermi-LAT ( A. Holzmann Airasca et al. 2025, GCN 41884),
SVOM-GRM (Chen-Wei Wang et al. 2025, GCN 41882),
Swift-XRT (J.P. Osborne et al., 2025, GCN 41885),
EP-WXT (Y.F. Liang et al. 2025, GCN 41879),
Swift-UVOT (S.R. Oates et al. 2025, GCN 41886),
Gemini/GMOS-S spectroscopic redshift z = 1.145 (A. J. Levan et al. 2025, GCN 41883)
The Fermi GBM on-ground location is consistent with the position measured by other instruments.
The angle from the Fermi LAT boresight is 56 degrees.
The GBM light curve consists of a very bright emission episode,
followed by a fainter second emission episode, with a total duration (T90)
of about 129.3 s (50-300 keV). The time-averaged spectrum
from T0+3 to T0+190 s is best fit by
a Band function with Epeak = 476 +/- 6 keV,
alpha = -0.88 +/- 0.01, and beta = -2.39 +/- 0.04.
The event fluence (10-1000 keV) in this time interval is
(4.36 +/- 0.002)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+33 s in the 10-1000 keV band is 115.2 +/- 0.7 ph/s/cm^2.
The time-averaged spectrum of the main pulse
from T0+3 to T0+58 s is best fit by
a Band function with Epeak = 475 +/- 5 keV,
alpha = -0.7 +/- 0.01, and beta = -2.38 +/- 0.03.
The event fluence (10-1000 keV) in this time interval is
(2.56 +/- 0.01)E-04 erg/cm^2.
The time-averaged spectrum of the second pulse
from T0+111 to T0+190 s is best fit by
a Band function with Epeak = 220 +/- 12 keV,
alpha = -1.12 +/- 0.02, and beta = -1.93 +/- 0.03.
The event fluence (10-1000 keV) in this time interval is
(5.77 +/- 0.05)E-05 erg/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 41888
Subject
GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
Date
2025-09-19T18:19:52Z (23 days ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:
The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 250919A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm triggered at 2025-09-19T00:29:12.000 (with a resolution ~5-seconds). This is consistent with the detections of GRB 250919A by Fermi/GBM (Fermi GBM Team, GCN Circ. 41874), SVOM/GRM (Wang et al., GCN Circ. 41882), associated with EP250919a detected by EP/WXT (Liang et al., GCN Circ. 41879).
The NuSTAR CsI shield data are recorded at 1 Hz. The burst appears to be composed of a very bright peak lasting for ~20-s, followed 75-s later by a relatively fainter burst episode lasting for ~50-s. The peak count rate is ~9000-cps over a baseline rate of ~1,000-cps during this time period. We also see clear evidence in the signal above 100 keV in the CdZnTe detectors for the first episode.
The localization from the counterpart candidate (Li et al., GCN Circ. 41877; Levan et al., GCN Circ. 41883; Airasca et al., GCN Circ. 41884; Osborne et al., GCN Circ. 41885, Oates et al., GCN Circ. 41886) at RA = 298.52, Dec = -48.83 implies an offset from the NuSTAR boresight of 33-deg and the offset from the geocenter of 74-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250919A/
Information on NuSTAR SINGS can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/
NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.
GCN Circular 41886
Subject
GRB 250919A/EP250919A: Swift/UVOT afterglow detection
Date
2025-09-19T16:03:30Z (23 days ago)
From
Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>
Via
email
S. R. Oates (Lancaster U.) and R. Gupta (GSFC) report on behalf of the Swift/UVOT team:
Swift/UVOT has performed follow-up observations of GRB 250919A/EP250919a (Fermi GBM team GCN 41874;
Liang et al., GCN 41879, Wang et al., GCN 41882). Swift/UVOT began observations in the
u band 21.4ks after the detection by Fermi/GBM (Fermi GBM team GCN 41874).
A source is detected consistent with the optical counterpart reported by Li et al., (GCN 41877).
The preliminary detection magnitude reported below is calculated using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).
Filter T_start(s) T_stop(s) Exp(s) Mag
u 21418 23150 1705 17.14+\-0.03
The magnitude in the table is not corrected for the Galactic extinction due to the
reddening of E(B-V) = 0.057 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 41885
Subject
GRB 250919A: Swift-XRT afterglow detection
Date
2025-09-19T14:03:29Z (23 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Ferro
(INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Lanava
(PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U.
Leicester) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of GRB
250919A/EP250919a. We searched for X-ray sources in 1.7 ks of Photon
Counting (PC) mode data. The total exposure at the position of the
afterglow (see below) is 1.7 ks, obtained between T0+21.4 ks and
T0+23.1 ks, taking T0 as the Fermi trigger time.
An uncatalogued X-ray source is detected within the estimated 3-sigma
Einstein Probe/WXT error region (35 arcsec), also consistent with the
Fermi-LAT error region, and is above the RASS 3-sigma upper limit at
this position, and is therefore likely the GRB afterglow. Using 1732 s
of PC mode data and 1 UVOT image, we find an enhanced XRT position
(using the XRT-UVOT alignment and matching UVOT field sources to the
USNO-B1 catalogue): RA, Dec = 298.55415, -48.83775 which is equivalent
to:
RA (J2000): 19h 54m 13.00s
Dec(J2000): -48d 50' 15.9"
with an uncertainty of 2.5 arcsec (radius, 90% confidence). The light
curve is consistent with a constant source of mean count rate 2.3e+00
ct/sec. A power-law fit gives an index of 1.0 (+1.9, -1.0). However,
given the position of this X-ray saource is consistent with the optical
counterpart with a measured redshift of 1.145 (GCN 41883), as well as
being above the RASS 3-sigma upper limit, we believe this to be the
X-ray afterglow.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.52 (+0.13, -0.11). The
best-fitting absorption column is 6.7 (+4.1, -1.6) x 10^20 cm^-2,
consistent with the Galactic value of 5.1 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 4.5 x 10^-11 (4.8 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 6.7 (+4.1, -1.6) x 10^20 cm^-2
Galactic foreground: 5.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.52 (+0.13, -0.11)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/03000101.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/EP/EP_FIELD00075.
This circular is an official product of the Swift-XRT team.
GCN Circular 41884
Subject
GRB 250919A: Fermi-LAT detection
Date
2025-09-19T09:21:09Z (23 days ago)
From
A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it>
Via
Web form
A. Holzmann Airasca (UniTrento and INFN Bari), N. Di Lalla (Stanford Univ.), E. Bissaldi (Politecnico and INFN Bari), S. Lopez (CNRS / IN2P3), D. Depalo (Politecnico and INFN Bari), T. Khalil (Johannesburg Univ), R. Gupta (NASA/GSFC) and F. Longo (University and INFN, Trieste) report on behalf of the Fermi-LAT Collaboration:
On September 19, 2025, Fermi-LAT detected high-energy emission from GRB 250919A, which was also detected by Fermi-GBM (trigger 779934537 / 250919020, GCN 41876), EP (GCN 41879) spatially coincident but temporally offset by 1.77 hours, SVOM/GRB (GCN 41882) and Gemini/GMOS-S (GCN 41883).
The best LAT on-ground location is found to be:
RA, Dec = 298.52, -48.83 (J2000)
with an error radius of 0.08 deg (90 % containment, statistical error only).
This was 56 deg from the LAT boresight at the time of the GBM trigger (T0 = 00:28:52.28 UT).
The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 1.7 ks after the GBM trigger is (1.03 ± 0.14) E-5 ph/cm2/s. The estimated photon index above 100 MeV is -1.84 ± 0.09.
The highest-energy photon is a 7 GeV event which is observed ~ 980 seconds after the GBM trigger.
The Fermi-LAT point of contact for this burst is Oscar Wistemar (wistemar@kth.se).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 41883
Subject
EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
Date
2025-09-19T08:07:27Z (23 days ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Via
Web form
A. J. Levan (Radboud and Warwick), J. N. D. van Dalen (Radboud), G. Corcoran (UCD), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), J. A. Quirola-Vasquez (Radboud), F. E. Bauer (SSI and UTA), A. Martin-Carrillo (UCD) report on behalf of a larger collaboration:
We obtained spectroscopic observations of the optical counterpart (Li et al., GCN 41877) of EP250919a (Liang et al., 41879), probably connected to GRB 250919A (Fermi GBM team, GCN 41874; Wang et al., GCN 41882; as also indicated by the consistency with the Fermi/LAT GRB localization; https://gcn.gsfc.nasa.gov/fermi_grbs.html). Observations were secured at the Gemini-South Telescope equipped with the GMOS spectrograph using grating B480, and began at 05:30 UT, approximately 3.25 hr (5 hr) after the EP (Fermi and SVOM) triggers. At this point we obtained 4x200 s observations covering the spectral range 3800-8000 AA.
In the acquisition image, the optical counterpart is clearly detected with an AB magnitude r = 17.52 +- 0.02 (calibrated against nearby objects from the SkyMapper catalog, not corrected for Galactic extinction).
The spectral trace is extremely bright and reveals multiple absorption features from Mg II, Mg I, Fe II, Al III, all at a common redshift of z = 1.145. We therefore suggest this is the redshift of EP250919a / GRB 250919A.
We thank the staff of Gemini, in particular Karleyne Silva for the rapid execution of these observations.
GCN Circular 41882
Subject
GRB 250919A: SVOM/GRM observation of a very bright GRB
Date
2025-09-19T07:33:19Z (23 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a very bright burst GRB 250919A (SVOM trigger reference: sb25091901) at 2025-09-19T00:29:15.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41874).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 158.0 +/-6.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250919A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 303.5, DEC= 49.8, GCN#41874), is located at about 84 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs through the shield due to the high brightness.
With this localization, the time-averaged spectrum from T0-25 to T0+270 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.14 +0.03/-0.02 and the cutoff energy, parameterized as Epeak, is 610 +52/-46 keV. The event fluence (10-1000 keV) in this time interval is (3.01 +/-0.05)E-04 erg/cm^2.
The localization of GRB 250919A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb250919A_amati.png
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.
The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
GCN Circular 41881
Subject
GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
Date
2025-09-19T05:41:12Z (23 days ago)
From
Jochen Greiner at MPE <jcgrog@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
779934537 at 00:28:52 on 19 Sept. 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) = 300.5 deg
Decl.(2000.0) = -49.1 deg
The 1 sigma statistical error radius is 0.3 deg.
We estimate an additional systematic error of 2 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB250919020/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB250919020/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB250919020/json
GCN Circular 41880
Subject
EP250919a: Global MASTER-Net observations report
Date
2025-09-19T04:54:19Z (23 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-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 EP250919a ( EP Team et al., GCN 41879) errorbox 1286 sec after trigger time at 2025-09-19 02:36:21 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 28 deg. The sun altitude is -50.4 deg.
MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the EP250919a errorbox 2640 sec after trigger time at 2025-09-19 02:58:55 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 85 deg. The sun altitude is -20.6 deg.
The galactic latitude b = -31 deg., longitude l = 350 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2994829
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
1317 | 2025-09-19 02:36:21 | MASTER-OAFA | (20h 01m 51.73s , -50d 10m 08.0s) | C | 60 | 20.4 |
1393 | 2025-09-19 02:37:38 | MASTER-OAFA | (20h 01m 45.42s , -50d 11m 06.5s) | C | 60 | 20.4 |
1468 | 2025-09-19 02:38:53 | MASTER-OAFA | (20h 01m 51.69s , -50d 11m 05.3s) | C | 60 | 20.4 |
1771 | 2025-09-19 02:43:56 | MASTER-OAFA | (20h 02m 12.87s , -48d 15m 58.0s) | C | 60 | 20.3 |
1848 | 2025-09-19 02:45:13 | MASTER-OAFA | (20h 02m 12.38s , -48d 14m 56.9s) | C | 60 | 20.3 |
1923 | 2025-09-19 02:46:28 | MASTER-OAFA | (20h 02m 18.99s , -48d 15m 56.3s) | C | 60 | 20.3 |
2652 | 2025-09-19 02:58:37 | MASTER-OAFA | (19h 53m 50.03s , -48d 54m 47.0s) | C | 60 | 20.1 |
2671 | 2025-09-19 02:58:55 | MASTER-SAAO | (19h 53m 22.97s , -48d 53m 39.0s) | C | 60 | 17.3 |
2731 | 2025-09-19 02:58:55 | MASTER-SAAO | (19h 53m 23.03s , -48d 53m 39.6s) | C | 180 | 17.7 | Coadd
2718 | 2025-09-19 02:59:42 | MASTER-OAFA | (19h 53m 50.12s , -48d 54m 46.3s) | C | 60 | 20.2 |
2750 | 2025-09-19 03:00:14 | MASTER-SAAO | (19h 53m 22.90s , -48d 53m 35.3s) | C | 60 | 17.2 |
2783 | 2025-09-19 03:00:48 | MASTER-OAFA | (19h 53m 50.30s , -48d 54m 45.8s) | C | 60 | 20.2 |
2829 | 2025-09-19 03:01:33 | MASTER-SAAO | (19h 53m 22.92s , -48d 53m 29.8s) | C | 60 | 16.4 |
2849 | 2025-09-19 03:01:54 | MASTER-OAFA | (19h 53m 50.44s , -48d 54m 45.2s) | C | 60 | 20.2 |
2908 | 2025-09-19 03:02:52 | MASTER-SAAO | (19h 53m 22.65s , -48d 53m 20.6s) | C | 60 | 17.0 |
2915 | 2025-09-19 03:02:59 | MASTER-OAFA | (19h 53m 50.57s , -48d 54m 44.6s) | C | 60 | 20.3 |
2980 | 2025-09-19 03:04:05 | MASTER-OAFA | (19h 53m 50.70s , -48d 54m 43.9s) | C | 60 | 20.3 |
3047 | 2025-09-19 03:05:11 | MASTER-OAFA | (19h 53m 50.85s , -48d 54m 43.5s) | C | 60 | 20.3 |
3112 | 2025-09-19 03:06:17 | MASTER-OAFA | (19h 53m 51.00s , -48d 54m 43.3s) | C | 60 | 20.2 |
3178 | 2025-09-19 03:07:22 | MASTER-OAFA | (19h 53m 51.10s , -48d 54m 42.9s) | C | 60 | 20.2 |
3244 | 2025-09-19 03:08:29 | MASTER-OAFA | (19h 53m 51.26s , -48d 54m 42.6s) | C | 60 | 20.2 |
3310 | 2025-09-19 03:09:34 | MASTER-OAFA | (19h 53m 51.38s , -48d 54m 42.1s) | C | 60 | 20.3 |
3375 | 2025-09-19 03:10:39 | MASTER-OAFA | (19h 53m 51.55s , -48d 54m 41.6s) | C | 60 | 20.2 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41879
Subject
EP250919a: Einstein Probe detection of an X-ray transient
Date
2025-09-19T04:34:49Z (23 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. F. Liang (PMO), R. D. Liang, C. L. Guo, W. J. Hu, Z. X. Ling (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 EP250919a. The transient triggered EP-WXT (ID: 01709243841).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. At 2025-09-19T02:14:55 (UTC), an uncatalogued X-ray source was detected at R.A. = 298.5520 deg, DEC = -48.8395 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). An uncataloged optical source was detected within FXT error circle (GCN 41877, 41878). EP250919a is located within the 1-sigma error region of GRB 250919A (GCN 41874). However, the temporal offset exceeds 2 hours, and thus we cannot rule out the possibility of a chance spatial coincidence.
Further information will be updated when the telemetry data is received. Further follow-up observations are encouraged.
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 41877
Subject
The EP-WXT trigger 01709243841: Las Cumbres discovery of the optical counterpart
Date
2025-09-19T03:28:55Z (23 days ago)
Edited On
2025-09-29T13:37:02Z (13 days ago)
From
Wenxiong Li at NAOC <liwenxiong1992@gmail.com>
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
Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona)
We observed the position of EP-WXT trigger 01709243841 with a Las Cumbres 1m telescope at Cerro Tololo Inter-American Observatory 0.8 hours after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band. We find an uncataloged source at RA=298.55383, Dec=-48.8378 within the EP/WXT error circle and measure the following preliminary photometry calibrated to the r band:
MJD 60937.127 Mag 17.0
Additional followup is encouraged.
GCN Circular 41875
Subject
Fermi GRB 250919A: Global MASTER-Net observations report
Date
2025-09-19T01:30:59Z (23 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) started inspect of the Fermi GRB 250919A ( Fermi GBM team, GCN 41874) errorbox 557 sec after notice time and 592 sec after trigger time at 2025-09-19 00:38:44 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 63 deg. The sun altitude is -47.5 deg.
MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250919A errorbox 658 sec after notice time and 693 sec after trigger time at 2025-09-19 00:40:26 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 19 deg. The sun altitude is -28.7 deg.
The galactic latitude b = -34 deg., longitude l = 350 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2994728
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
622 | 2025-09-19 00:38:44 | MASTER-SAAO | (20h 12m 52.30s , -49d 54m 57.2s) | C | 60 | 19.3 |
622 | 2025-09-19 00:38:44 | MASTER-SAAO | (20h 10m 02.82s , -49d 39m 38.7s) | C | 60 | 19.2 |
764 | 2025-09-19 00:40:26 | MASTER-OAFA | (20h 13m 10.49s , -49d 55m 27.8s) | C | 140 | 20.2 |
925 | 2025-09-19 00:42:52 | MASTER-OAFA | (20h 13m 10.79s , -49d 55m 23.7s) | C | 170 | 20.3 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41874
Subject
GRB 250919A: Fermi GBM Final Real-time Localization
Date
2025-09-19T00:39:24Z (23 days 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 00:28:52 UT on 19 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250919A (trigger 779934537.284108 / 250919020).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 303.5, Dec = -49.8 (J2000 degrees, equivalent to J2000 20h 14m, -49d 47'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 57.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/quicklook/glg_skymap_all_bn250919020.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/bn250919020/quicklook/glg_healpix_all_bn250919020.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/quicklook/glg_lc_medres34_bn250919020.gif