GRB 250807B
GCN Circular 41333
Subject
GRB 250807B: Swift-BAT refined analysis
Date
2025-08-12T19:39:29Z (13 days ago)
From
Mike Moss at NASA GSFC <mikejmoss3@gmail.com>
Via
Web form
S. D. Barthelmy (GSFC), R. Gupta (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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250807B (trigger #1340561)
(Klingler, et al., GCN Circ. 41268). The BAT ground-calculated position is
RA, Dec = 15.611, -59.098 deg which is
RA(J2000) = 01h 02m 26.7s
Dec(J2000) = -59d 05' 52.2"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 64%.
The mask-weighted light curve displays a complex structure with several pulses.
The T90 (15-350 keV) is 104.17 +- 29.17 sec (estimated error including systematics).
The time-averaged spectrum from T-51.00 to T+85.16 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.72 +- 0.12. The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-48.59 sec in the 15-150 keV band
is 0.9 +- 0.3 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/1340561
GCN Circular 41312
Subject
GRB 250807B: SVOM/VT optical observation
Date
2025-08-10T08:51:43Z (16 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 250807B detected by Swift/BAT (Klingler et al., GCN 41268). The observation began at 2025-08-09T19:37:17 UTC, 51.903 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical counterpart (Klingler et al., GCN 41268; Goad et al., GCN 41272; van Dalen et al., GCN 41278; Giudice et al., GCN 41289; Freeberg et al., GCN 41293; Shilling et al,. GCN 41294) was detected in both VT_R and VT_B. The magnitudes are:
Mid-time (h) | exposure time (s) | band | mag (AB) | mag err
---------------|-------------------|------|----------|--------
53.83 | 24*70 | VT_B | 23.7 | 0.3
53.84 | 24*70 | VT_R | 22.9 | 0.3
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 41294
Subject
GRB 250807B: Swift/UVOT Detection
Date
2025-08-08T16:47:22Z (17 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 250807B
154 s after the BAT trigger (Klingler et al., GCN Circ. 41268).
A source consistent with the enhanced XRT position
(Goad et al., GCN Circ. 41272) is detected in the initial UVOT exposures.
Preliminary detections 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 154 303 147 16.30 +/- 0.03
u_FC 313 339 26 15.05 +/- 0.06
u 50186 50647 450 19.86 +/- 0.28
v_FC 134 145 10 >17.31
v 61831 61845 14 >17.45
w1 38723 39497 761 19.64 +/- 0.20
w2 60924 61824 886 >20.8
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.016 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 41293
Subject
GRB 250807B: Kilonova-Catcher optical afterglow detection
Date
2025-08-08T16:35:39Z (17 days ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), M. Mašek (Institute of Physics, Prague, FZU, CZ), M. Molham (NRIAG), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 250807B (Klingler et al., GCN 41268) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 telescope operated by M. Freeberg. Our observations started at T0+11.9hr.
In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect a faint uncatalogued optical source inside the Swift/XRT position (Klingler et al., GCN 41268; Goad et al., GCN 41272) and consistent with the Swift/UVOT (Klingler et al., GCN 41268), NTT (van Dalen et al., GCN 41278) and the VLT/X-shooter (Giudice et al., GCN41289) optical afterglow .
We report our follow-up results in the table below:
+---------------+-----------+-----------+----------------+--------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+===========+===========+================+==============+
| 12.4 | 11 x 300s | Rc (Vega) | 20.37 +/- 0.25 | iT72 |
+---------------+-----------+-----------+----------------+--------------+
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 41289
Subject
GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522
Date
2025-08-08T14:30:18Z (18 days ago)
From
Ines Francesca Giudice <ines.giudice@inaf.it>
Via
Web form
I. F. Giudice (INAF/OACn), M. Garnichey (LUX-Paris Obs.), A. L. Thakur (INAF-IAPS), A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn & DARK/NBI), A. Martin-Carrillo (UCD), M. De Pasquale (U.Messina), N. R. Tanvir (U. Leicester), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud Univ.), report on behalf of the Stargate collaboration:
We observed the optical counterpart (Kingler et al., GCN 41268; van Dalen et al., GCN 41278) of GRB 250807B detected by Swift with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 A, and consist of 4 exposures of 600 s each. Observation started on 2025-08-08 at 08:42:42 UTC (17 hours after trigger).
In a preliminary reduction of the spectra, we identify several absorption features, which we interpret as Fe II, the Mg II doublet, and Mg I, from which we derive a redshift of z = 1.522. We notice the absence of emission or fine-structure lines. The presence of a continuum in the UVB arm supports the interpretation that this could be the GRB redshift.
The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
We acknowledge excellent support from the ESO observing staff in Paranal.
GCN Circular 41280
Subject
GRB 250807B: Swift-XRT refined Analysis
Date
2025-08-08T09:17:21Z (18 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Ferro
(INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea
(PSU), D.N. Burrows (PSU), M.A. Williams (PSU) and P.A. Evans report on
behalf of the Swift-XRT team:
We have analysed 6.3 ks of XRT data for GRB 250807B, from 133 s to 50.6
ks after the trigger. The data comprise 188 s in Windowed Timing (WT)
mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+3.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.16 (+0.14, -0.13).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.96 (+/-0.07). The
best-fitting absorption column is 4.2 (+1.5, -1.4) x 10^20 cm^-2, in
excess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.97 (+0.21, -0.19)
and a best-fitting absorption column of 5.8 (+4.7, -4.0) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.4 x 10^-11 (3.8 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 5.8 (+4.7, -4.0) x 10^20 cm^-2
Galactic foreground: 1.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.97 (+0.21, -0.19)
If the light curve continues to decay with a power-law decay index of
1.16, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x
10^-13 (2.4 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01340561.
This circular is an official product of the Swift-XRT team.
GCN Circular 41278
Subject
GRB 250807B: NTT optical observations
Date
2025-08-08T08:10:05Z (18 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), L. Cotter (UCD), M. Fraser (UCD), A. Martin-Carrillo (UCD), L. Galbany (IEEC-CSIC), T. Petrushevska (Nova Gorica), S. Srivastav (Oxford), L. Izzo (INAF/OAC and DARK/NBI), P. D'Avanzo (INAF/OAB), J. Anderson (ESO), T. Müller Bravo (Southampton), T.-W. Chen (NCU), M. Gromadzki (Warsaw), C. Inserra (Cardiff), E. Kankare (Turku), M. Nicholl (QUB), O. Yaron (Weizmann), D. Young (QUB), E. Zimmerman (Weizmann) report on behalf of the ePESSTO+ collaboration:
We observed the optical counterpart of the Swift GRB 250807B (Klingler et al., GCN 41268) using the ESO NTT located in La Silla (Chile), equipped with the EFOSC2 camera. A total of 600 s imaging was secured in each of the Gunn r and g bands, with mean epoch 2025 Aug 8.15 UT (11.9 hr after the trigger).
The optical afterglow is well detected in both filters. We measure the following J2000 coordinates (~0.3" error):
RA = 01:02:33.04
Dec = -59:07:09.1
The object has a magnitude r = 20.4 +- 0.2 AB (calibrated against nearby stars from the SkyMapper catalog, and not corrected for Galactic extinction), where the error mostly stems from calibrators scatter.
We acknowledge expert support from the NTT operator, Duncan Castex.
GCN Circular 41272
Subject
GRB 250807B: Enhanced Swift-XRT position
Date
2025-08-07T19:34:25Z (18 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1712 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 250807B, 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 = 15.63710, -59.11896 which is equivalent
to:
RA (J2000): 01h 02m 32.90s
Dec (J2000): -59d 07' 08.3"
with an uncertainty of 2.4 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 41268
Subject
GRB 250807B: Swift detection of a burst with an optical counterpart.
Date
2025-08-07T15:59:34Z (18 days ago)
From
noelklin@umbc.edu
Via
email
N. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB),
J. J. DeLaunay (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC),
S. Lanava (PSU), M. J. Moss (GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), C. Salvaggio (INAF-OAB) and M. A. Williams (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 15:43:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250807B (trigger=1340561). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 15.585, -59.094 which is
RA(J2000) = 01h 02m 21s
Dec(J2000) = -59d 05' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows complex activity
during the slew that immediately preceded this trigger, with a total
observed duration of about 100 sec. The peak count rate
was ~1200 counts/sec (15-350 keV), at ~15 sec after the trigger.
The XRT began observing the field at 15:45:32.3 UT, 144.5 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 15.6378, -59.1186 which is equivalent to:
RA(J2000) = 01h 02m 33.07s
Dec(J2000) = -59d 07' 07.0"
with an uncertainty of 5.6 arcseconds (radius, 90% containment). This
location is 131 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 153 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 01:02:32.98 = 15.63741
DEC(J2000) = -59:07:07.9 = -59.11887
with a 90%-confidence error radius of about 0.75 arc sec. This position is 1.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.31 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.016.
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/)