GRB 250821B
GCN Circular 41537
Subject
GRB 250821B: AstroSat CZTI detection
Date
2025-08-25T09:32:36Z (4 hours ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
M. Tembhurnikar (IUCAA), A. Arya (IITB), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 250821B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 41473 and 41477), SVOM/GRM (SVOM team, GCN Circ. 41486), Konus-Wind (Frederiks et al., GCN Circ. 41508), and Insight-HXMT (Wang et al., GCN Circ. 41533).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-08-21 16:07:47.95 UTC. The measured peak count rate associated with the burst is 343 (+153, -46) counts/s above the background in the combined data of all quadrants, with a total of 218 (+60, -62) counts. The local mean background count rate was 252 (+10, -12) counts/s. Using cumulative rates, we measure a T90 of 1.2 (+0.2, -0.5) s.
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-08-21 16:07:47.16 UTC. The measured peak count rate associated with the burst is 1724 (+84, -94) counts/s above the background in the combined data of all quadrants, with a total of 2373 (+175, -194) counts. The local mean background count rate was 1175 (+9, -11) counts/s. We measure a T90 of 1.9 (+1.0, -0.2) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 41533
Subject
GRB 250821B: Insight-HXMT detection
Date
2025-08-25T03:30:20Z (10 hours ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Wen-Jun Tan, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2025-08-21T16:07:47.500 (T0), Insight-HXMT/HE detected the bright intermedium duration burst GRB 250821B, which is also detected by Fermi/GBM (Fermi GBM team., GCN #41473), SVOM/GRM (Tan et al., GCN #41486) and Konus-Wind (D. Frederiks et al., GCN #41508).
The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 2.05 +1.70/-0.45 s. The 1s peak rate, measured from T0-0.075 s, is 11927 cnts/sec. The total counts from this burst is 15817 counts.
The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250821B.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 41508
Subject
Konus-Wind detection of GRB 250821B
Date
2025-08-23T16:06:36Z (2 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
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 bright, long-duration GRB 250821B (Ferm-GBM detection:
The Fermi GBM team, GCN 41473; Smith and Meegan, GCN 41477;
SVOM-GRM detection: Tan et al., GCN 41486;
IPN localization Kozyrev et al., GCN 41498)
triggered Konus-Wind (KW) at T0=58069.135 s UT (16:07:49.135).
The burst light curve shows a single emission pulse with a total duration of ~2.5 s.
The emission is seen up to ~5 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250821_T58069/
As observed by Konus-Wind, the burst had
a fluence of (1.34 ± 0.13)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 0.512 s,
of (1.77 ± 0.17)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+8.448 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 = -0.60 (-0.14,+0.15),
the high energy photon index beta = -2.24 (-0.13,+0.10),
the peak energy Ep = 193(-18,+21) keV,
chi2 = 70/96 dof.
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 41498
Subject
IPN triangulation of GRB 250821B (long/bright)
Date
2025-08-22T15:46:04Z (3 days ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The bright, long-duration GRB 250821B
(Ferm-GBM detection: The Fermi GBM team, GCN 41473;
Smith and Meegan, GCN 41477;
BALROG localization: Preis and Greiner, GCN 41475;
SVOM-GRM detection: Tan et al., GCN 41486)
was detected by Fermi (GBM trigger 777485272), SVOM (GRM),
Konus-Wind, and Mars-Odyssey (HEND), at about 58067 s UT (16:07:47).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
29.373 (01h 57m 30s) -82.081 (-82d 04' 51")
Corners:
26.171 (01h 44m 41s) -82.255 (-82d 15' 19")
32.420 (02h 09m 41s) -81.925 (-81d 55' 30")
32.427 (02h 09m 42s) -81.883 (-81d 52' 58")
26.212 (01h 44m 51s) -82.213 (-82d 12' 48")
---------------------------------------------
The error box area is 127 sq. arcmin, and its maximum
dimension is 56 arcmin (the minimum one is 2 arcmin).
The Sun distance was 106 deg.
This localization may be improved.
The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM (GCN 41473) and BALROG (GCN 41475) localizations.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250821_T58069/IPN
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.
The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.
GCN Circular 41486
Subject
GRB 250821B: SVOM/GRM observation
Date
2025-08-22T06:53:40Z (3 days ago)
From
tanwj@ihep.ac.cn
Via
Web form
SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Frédéric Daigne (IAP), Stéphane Schanne (CEA) and Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250821B (SVOM burst-id sb25082109) at 2025-08-21T16:07:47.500 UTC (T0), which is also detected by FERMI/GBM (GBM team, GCN #41473 and GCN #41477).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 2.5 +0.3/-0.2 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250821B.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 39.95, Dec = -77.13, GCN #41473), is located at about 65 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. However, ECLAIRs detected this burst above 50 keV, through the shield.
With this localization given by FERMI/GBM, the time-averaged spectrum from T0-0.5 to T0+3.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.89 +/-0.05 and the cutoff energy, parameterized as Epeak, is 289 +37/-31 keV. The event fluence (10-1000 keV) in this time interval is (1.1 +/-0.1)E-05 erg/cm^2.
The localization of GRB 250821B in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/grb250821B_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: Wen-Jun Tan (IHEP)(tanwj@ihep.ac.cn)
GCN Circular 41484
Subject
Fermi GRB 250821B: Global MASTER-Net observations report
Date
2025-08-22T02:45:40Z (3 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) started inspect of the Fermi GRB 250821B ( Fermi GBM team, GCN 41473) errorbox 26834 sec after notice time and 35938 sec after trigger time at 2025-08-22 02:06:45 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 63 deg. The sun altitude is -50.3 deg.
The galactic latitude b = -39 deg., longitude l = 295 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2974796
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
35953 | 2025-08-22 02:06:45 | MASTER-OAFA | (02h 39m 51.65s , -77d 15m 11.6s) | C | 30 | 18.2 |
36003 | 2025-08-22 02:07:35 | MASTER-OAFA | (02h 39m 51.48s , -77d 14m 09.1s) | C | 30 | 18.2 |
36081 | 2025-08-22 02:08:38 | MASTER-OAFA | (02h 39m 55.46s , -77d 15m 05.3s) | C | 60 | 18.5 |
36162 | 2025-08-22 02:09:59 | MASTER-OAFA | (02h 39m 48.90s , -77d 16m 01.7s) | C | 60 | 18.4 |
36246 | 2025-08-22 02:11:23 | MASTER-OAFA | (02h 39m 55.59s , -77d 15m 36.4s) | C | 60 | 18.4 |
36370 | 2025-08-22 02:13:27 | MASTER-OAFA | (02h 39m 50.79s , -77d 14m 15.1s) | C | 60 | 18.6 |
36494 | 2025-08-22 02:15:31 | MASTER-OAFA | (02h 39m 49.56s , -77d 15m 45.5s) | C | 60 | 18.2 |
36592 | 2025-08-22 02:17:09 | MASTER-OAFA | (02h 39m 51.22s , -77d 13m 46.7s) | C | 60 | 18.7 |
36673 | 2025-08-22 02:18:30 | MASTER-OAFA | (02h 39m 44.40s , -77d 14m 42.5s) | C | 60 | 18.8 |
36749 | 2025-08-22 02:19:46 | MASTER-OAFA | (02h 39m 43.93s , -77d 13m 40.2s) | C | 60 | 18.5 |
36829 | 2025-08-22 02:21:06 | MASTER-OAFA | (02h 39m 50.13s , -77d 14m 36.9s) | C | 60 | 18.8 |
36918 | 2025-08-22 02:22:34 | MASTER-OAFA | (02h 39m 43.66s , -77d 15m 33.3s) | C | 60 | 17.7 |
37024 | 2025-08-22 02:24:21 | MASTER-OAFA | (02h 39m 46.86s , -77d 15m 02.4s) | C | 60 | 17.9 |
37132 | 2025-08-22 02:26:09 | MASTER-OAFA | (02h 39m 43.59s , -77d 13m 42.4s) | C | 60 | 17.9 |
37229 | 2025-08-22 02:27:46 | MASTER-OAFA | (02h 39m 42.71s , -77d 15m 06.5s) | C | 60 | 17.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41477
Subject
GRB 250821B: Fermi GBM Detection
Date
2025-08-21T21:02:40Z (4 days ago)
From
Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>
Via
Web form
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
At 16:07:47.46 UT on 21 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250821B (trigger 777485272/250821672).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 39.95, Dec = -77.13 (J2000 degrees, equivalent to
J2000 2h 39m, -77d 7'), with a statistical uncertainty of 1.00 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a systematic error
which we have characterized as a core-plus-tail model, with 90% of GRBs having a
3.7 deg error and a small tail suffering a larger than 10 deg systematic error
[Connaughton et al. 2015, ApJS, 216, 32]).
The angle from the Fermi LAT boresight is 67 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 2.3 s (50-300 keV). The time-averaged spectrum
from T0-0.06 to T0+2.62 s is best fit by
a Band function with Epeak = 250 +/- 10 keV,
alpha = -0.67 +/- 0.03, and beta = -2.24 +/- 0.06.
The event fluence (10-1000 keV) in this time interval is
(1.19 +/- 0.01)E-05 erg/cm^2. The 0.064-sec peak photon flux measured
starting from T0+0.576 s in the 10-1000 keV band is 58 +/- 1.9 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 41475
Subject
GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
Date
2025-08-21T19:57:25Z (4 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
at 16:07:47 on 21 Aug. 2025 were manually 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) = 60.0 deg
Decl.(2000.0) = -84.7 deg
The 1 sigma statistical error radius is 2.0 deg.
We estimate an additional systematic error of 2 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB250821672/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB250821672/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB250821672/json
GCN Circular 41473
Subject
GRB 250821B: Fermi GBM Final Localization of a Bright Burst
Date
2025-08-21T19:00:29Z (4 days ago)
From
Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>
Via
Web form
The Fermi GBM team reports the detection of a likely LONG GRB
"At 16:07:47.46 UT on 21 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250821B (trigger 777485272/250821672).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 39.95, Dec = -77.13 (J2000 degrees, equivalent to J2000 2h 39m, -77d 7'),
with a statistical uncertainty of 1.00 degrees.
The angle from the Fermi LAT boresight is 67 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821672/quicklook/glg_skymap_all_bn250821672.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/bn250821672/quicklook/glg_healpix_all_bn250821672.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821672/quicklook/glg_lc_medres34_bn250821672.gif"