GRB 250807A
GCN Circular 41318
Subject
GRB 250807A: Swift-BAT refined analysis
Date
2025-08-11T14:04:39Z (16 days ago)
Edited On
2025-08-12T14:56:23Z (15 days ago)
From
Mike Moss at NASA GSFC <mikejmoss3@gmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Mike Moss at NASA GSFC <mikejmoss3@gmail.com>
Via
Web form
R. Gupta (GSFC), S. D. Barthelmy (GSFC),
N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+520 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250807A (trigger #1340514)
(Klingler, et al., GCN Circ. 41262). The BAT ground-calculated position is
RA, Dec = 51.435, -47.882 deg which is
RA(J2000) = 03h 25m 44.4s
Dec(J2000) = -47d 52' 54.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 72%.
The mask-weighted light curve displays a complex structure with several pulses.
T90 (15-350 keV) is 75.46 +- 2.19 sec (estimated error including systematics).
The time-averaged spectrum from T-20.35 to T+119.49 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.32 +- 0.03. The fluence in the 15-150 keV band is 2.5 +- 0.0 x 10^-05 erg/cm2.
The 1-sec peak photon flux measured from T+33.82 sec in the 15-150 keV band
is 16.7 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340514
GCN Circular 41299
Subject
GRB 250807A: SVOM/VT optical continued observation
Date
2025-08-09T09:00:02Z (18 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, Z. H. Yao, L. P. Xin, 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/VT conducted continued observations of GRB 250807A detected by Swift/BAT（Klingler et al., GCN 41262), AstroSat-CZTI (Salunke et al., GCN 41281), SVOM/GRM (Wang et al,. GCN 41283) and Konus-Wind (Svinkin et al,. GCN 41295).
The magnitude of the optical afterglow (Klingler et al., GCN 41262; Ma et al., GCN 41274; Shilling et al., GCN 41291) is:
mid time | exposure time (s) | band | mag (AB) | mag err
-----------|-------------------|------|----------|--------
18.25h | 31*70 | VT_R | 21.59 | 0.08
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 Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 41295
Subject
Konus-Wind detection of GRB 250807A
Date
2025-08-08T18:25:17Z (19 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 250807A
(Swift-BAT detection: Klingler et al., GCN 41262;
AstroSat-CZTI detection: Salunke et al., GCN 41281;
SVOM-GRM detection: Wang et al., GCN 41283)
triggered Konus-Wind at T0=38766.990 s UT (10:46:06.990).
The burst light curve shows a multipeaked structure
which starts at ~T0-2.3 s and has a total duration of ~79 s.
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250807_T38766/
As observed by Konus-Wind, the burst
had the total fluence of 1.03(-0.09,+0.08)x10^-4 erg/cm2,
and the 64-ms peak flux, measured from T0+35.904 s,
of 1.11(-0.10,+0.10)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+79.104 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.04(-0.04,+0.04),
the high energy photon index beta = -2.74(-0.66,+0.26),
the peak energy Ep = 369(-26,+26) keV
(chi2 = 132/97 dof).
The spectrum near the maximum count rate
(measured from T0+29.952 to T0+38.144 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.04(-0.05,+0.05)
and Ep = 390(-25,+28) keV (chi2 = 105/86 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.5
(chi2 = 105/85 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN Circular 41291
Subject
GRB 250807A: Swift/UVOT Detection
Date
2025-08-08T16:24:35Z (19 days ago)
From
s.shilling@lancaster.ac.uk
Via
Web form
S. P. R. Shilling (Lancaster U.) and N. J. Klingler (GSFC/UMBC/CRESSTII)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250807A
111 s after the BAT trigger (Klingler et al., GCN Circ. 41262).
A source consistent with the enhanced XRT position
(Evans et al., GCN Circ. 41270) is detected in the initial UVOT exposures.
Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 111 261 147 18.00 +/- 0.04
v 653 1769 136 >18.8
b 579 1695 117 >19.5
u 323 1840 361 19.88 +/- 0.31
w1 702 1818 117 >19.0
w2 801 821 19 >17.7
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.011 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 41290
Subject
GRB 250807A: Swift-XRT refined Analysis
Date
2025-08-08T15:31:42Z (19 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai
(INAF-IASFPA), S. Campana (INAF-OAB), D.N. Burrows (PSU), M.A. Williams
(PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:
We have analysed 4.6 ks of XRT data for GRB 250807A, from 93 s to 91.2
ks after the trigger. The data comprise 1.2 ks in Windowed Timing
(WT) mode (the first 5 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+6.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.75 (+0.11, -0.10).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.96 (+/-0.03). The
best-fitting absorption column is 1.90 (+/-0.11) x 10^21 cm^-2, in
excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.85 (+0.11, -0.10)
and a best-fitting absorption column of 1.8 (+0.4, -0.3) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.9 x 10^-11 (4.9 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.8 (+0.4, -0.3) x 10^21 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: 8.0 sigma
Photon index: 1.85 (+0.11, -0.10)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01340514.
This circular is an official product of the Swift-XRT team.
GCN Circular 41283
Subject
GRB 250807A: SVOM/GRM observation
Date
2025-08-08T11:07:22Z (19 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: Sebastien Guillot (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250807A (SVOM trigger reference: sb25080702) at 2025-08-07T10:46:06.700 UTC (T0), which is also detected by Swift/BAT (N. J. Klingler et al., GCN #41262), AstroSat (S.Salunke et al., GCN #41281) and Konus-Wind.
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 71.0 +4.5/-7.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250807A.png
In addition, the position of this burst, as determined by Swift/BAT (RA= 51.420, DEC= -47.877, GCN #41064), is located at about 69 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nonetheless, the burst is seen (via analysis of X-band data) in the ECLAIRs data above 50 keV at the T0 given by GRM, likely through the ECLAIRs shielding.
With this localization, the time-averaged spectrum from T0-15 to T0+130 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.19 +/-0.03 and the cutoff energy, parameterized as Epeak, is 547 +52/-45 keV. The event fluence (10-1000 keV) in this time interval is (1.00 +/-0.10)E-04 erg/cm^2. Thus GRB 250807A is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/grb250807A_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 41281
Subject
GRB 250807A: AstroSat CZTI detection of bright long burst
Date
2025-08-08T09:48:16Z (19 days ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
S.Salunke (IUCAA), 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 a bright long-duration GRB 250807A which was also detected by Swift/BAT (N. J. Klingler et.al, GCN Circ. 41262), and Konus-Wind (reported through GCN Notices).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-08-07 10:46:42.50 UTC. The measured peak count rate associated with the burst is 535 (+49, -47) counts/s above the background in the combined data of all quadrants, with a total of 6218 (+449, -269) counts. The local mean background count rate was 275 (+1, -4) counts/s. Using cumulative rates, we measure a T90 of 44 (+2, -3) s. In the preliminary analysis, we find 630 Compton events associated with this event.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-08-07 10:46:42.27 UTC. The measured peak count rate associated with the burst is 3662 (+110, -125) counts/s above the background in the combined data of all quadrants, with a total of 36237 (+1153, -1203) counts. The local mean background count rate was 1239 (+5, -6) counts/s. We measure a T90 of 48 (+1, -3) 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 41274
Subject
GRB 250807A: SVOM/VT optical observation
Date
2025-08-08T03:38:37Z (20 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, Z. H. Yao, L. P. Xin, 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/VT performed a Target of Opportunity observation of GRB 250807A detected by Swift-BAT（Klingler et al., GCN 41262; Evans et al., GCN 41270). The observation began at 2025-08-07T11:21:39.516 UTC, 35.52 minutes after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical afterglow (Evans et al., GCN 41262) is detected in both VT_R and VT_B using VT X-band data at R.A. = 51.448126 , DEC = -47.887663 degrees:
RA (J2000) = 3:25:47.55
Dec (J2000) = -47:53:15.58
with an uncertainty of 0.5 arcsec.
The magnitudes are:
mid time (sec) | exposure time (s) | band | mag (AB) | mag err
---------------|-------------------|------|----------|--------
2236 | 70 | VT_B | 20.52 | 0.08
14319 | 70 | VT_B | 21.07 | 0.10
2236 | 70 | VT_R | 18.98 | 0.03
14319 | 70 | VT_R | 19.29 | 0.03
Our photometry was not corrected for Galactic extinction.
During our observations, the light curves exhibit an initial brightening followed by a decay phase.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 41270
Subject
GRB 250807A: Enhanced Swift-XRT position
Date
2025-08-07T16:14:45Z (20 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 769 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 250807A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 51.44795, -47.88761 which is equivalent
to:
RA (J2000): 03h 25m 47.51s
Dec (J2000): -47d 53' 15.4"
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 41262
Subject
GRB 250807A: Swift detection of a burst with an optical counterpart
Date
2025-08-07T11:03:36Z (20 days ago)
From
noelklin@umbc.edu
Via
email
N. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB),
J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU),
K. L. Page (U Leicester) and C. Salvaggio (INAF-OAB) report on behalf
of the Neil Gehrels Swift Observatory Team:
At 10:46:08.44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250807A (trigger=1340514). Swift slewed immediately to the burst.
The BAT on-board calculated location is RA, Dec 51.420, -47.877 which is
RA(J2000) = 03h 25m 41s
Dec(J2000) = -47d 52' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a complex structure
with a duration of about 80 sec. The peak count rate
was ~19000 counts/sec (15-350 keV), at ~35 sec after the trigger.
The XRT began observing the field at 10:47:49.5 UT, 101.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 51.4478, -47.8880 which is equivalent to:
RA(J2000) = 03h 25m 47.47s
Dec(J2000) = -47d 53' 16.8"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 77 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 111 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 03:25:47.59 = 51.44829
DEC(J2000) = -47:53:16.2 = -47.88782
with a 90%-confidence error radius of about 0.75 arc sec. This position is 1.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.98 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.011.
Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)