TITLE: GCN CIRCULAR
NUMBER: 41940
SUBJECT: IPN triangulation of GRB 250920A (long/bright)
DATE: 25/09/22 16:39:14 GMT
FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru>
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 250920A
(Ferm-GBM detection: The Fermi GBM team, GCN 41895;
Sonawane and Smith, GCN 41918;
BALROG localization: Preis and Greiner, GCN 41896
AstroSat-CZTI detection: Harsha et al., GCN 41899;
SVOM-GRM detection: Wang et al., GCN 41912;
NuSTAR-detection: Waratkar et al., GCN 41926)
was detected by Fermi (GBM trigger 780029651), SVOM (GRM),
AstroSat (CZTI), NuSTAR, Konus-Wind, and Mars-Odyssey (HEND),
at about 10447 s UT (02:54:07).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
176.909 (11h 47m 38s) +54.466 (+54d 27' 56")
Corners:
177.868 (11h 51m 28s) +54.769 (+54d 46' 07")
177.751 (11h 51m 00s) +54.775 (+54d 46' 28")
175.963 (11h 43m 51s) +54.152 (+54d 09' 06")
176.079 (11h 44m 19s) +54.148 (+54d 08' 54")
---------------------------------------------
The error box area is 168 sq. arcmin, and its maximum
dimension is 1.27 deg (the minimum one is 2.3 arcmin).
The Sun distance was 53 deg.
This localization may be improved.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250920_T10444/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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41940.
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TITLE: GCN CIRCULAR
NUMBER: 41939
SUBJECT: Konus-Wind detection of GRB 250911A
DATE: 25/09/22 16:37:08 GMT
FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com>
V. Panteleeva, 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-duration GRB 250911A
(Swift-BAT detection: Klingler et al., GCN 41781;
Palmer et al., GCN 41812;
GECAM-B detection: Zhang et al., GCN 41813;
Insight-HXMT detection: Wang et al., GCN 41827)
triggered Konus-Wind at T0=05370.240 s UT (01:29:30.240).
The burst light curve shows a multipeaked structure
which starts at ~T0-2.3 s and has a total duration of ~57 s.
The weak precursor that triggered Swift-BAT is seen at ~T0-100 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/GRB250911_T05370/
As observed by Konus-Wind, the burst
had the total fluence of 4.54(-0.29,+0.30)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+1.440 s,
of 5.15(-0.88,+0.90)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+41.216 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 = -0.85(-0.11,+0.12),
the high energy photon index beta = -2.58(-0.19,+0.14),
the peak energy Ep = 196(-13,+14) keV
(chi2 = 102/97 dof).
The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 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 = -0.92(-0.11,+0.12),
the high energy photon index beta = -2.44(-0.19,+0.14),
the peak energy Ep = 257(-25,+26) keV
(chi2 = 88/84 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41939.
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TITLE: GCN CIRCULAR
NUMBER: 41938
SUBJECT: GRB 250916A: Swift/UVOT Detection
DATE: 25/09/22 15:32:00 GMT
FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk>
A. A. Breeveld (UCL-MSSL) and R. Caputo (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of the Fermi/GBM detected burst GRB 250916A 102120s after the trigger (Fermi GBM team, GCN Circ. 41839).
The optical counterpart detected by Belkin et al., GCN Circ. 41847; Mohan et al., GCN Circ. 41858; Moskvitin et al., GCN Circ. 41859; Burkhonov et al., GCN Circ. 41860; de Ugarte Postigo et al., GCN Circ. 41863; Moskvitin et al., GCN Circ. 41870; Zheng and Filippenko, GCN Circ. 41873; Pankov et al., GCN Circ. 41892; Hall et al., GCN Circ. 41921 and Moskvitin et al., GCN Circ. 41934, is detected in the initial white and u-band UVOT exposures.
Preliminary magnitudes and upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 102120 107275 968 20.5 ± 0.2
white 102446 102767 316 21.1 ± 0.3
v 102774 103051 273 >19.4
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.051 in the direction of the burst (Schlegel et al. 1998).
View this GCN Circular online at https://gcn.nasa.gov/circulars/41938.
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TITLE: GCN CIRCULAR
NUMBER: 41937
SUBJECT: GRB 250920B: Glowbug gamma-ray detection
DATE: 25/09/22 14:59:17 GMT
FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil>
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 250920B, which was also detected by Fermi/GBM (GCN 41897, 41919) and Swift/BAT (GCN 41898, 41923).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-20 08:46:28.344 with a duration of 129.5 s and a total significance of over 30 sigma. The observed light curve comprises an initial multi-peaked structure from ~T0 to T0+7.5s, followed by peaks at ~T0+76s, ~T0+107s, and ~T0+128s.
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41937.
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TITLE: GCN CIRCULAR
NUMBER: 41936
SUBJECT: GRB 250916A: CrAO ZTSh R-band optical observations
DATE: 25/09/22 11:24:20 GMT
FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com>
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO)
report on behalf of IKI-GRB-FuN.
We observed the field of the GRB 250916A (The Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al., GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, GCN 41876) with the Shajn 2.65m telescope of CrAO, equipped with CCD-photometer. The observations in the R-filter were carried out on epochs 2025-09-19, 2025-09-20, and 2025-09-21. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870; Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; Hall et al., GCN 41921; Moskvitin et. al, GCN 41934) is clearly detected in the stacked images taken on each epoch. Preliminary results of our observations are given below:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (n*s) (3sigma)
2025-09-19 21:40:39 3.42451 120*120 R 21.45 0.02 25.0
2025-09-20 23:47:56 4.48374 78*120 R 21.89 0.03 24.7
2025-09-21 22:21:48 5.44545 109*120 R 22.72 0.05 24.8
Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted via Lupton 2005 transformations) and not corrected for the Galactic extinction.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41936.
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TITLE: GCN CIRCULAR
NUMBER: 41935
SUBJECT: GRB 250920C: Swift-XRT refined Analysis
DATE: 25/09/22 10:15:36 GMT
FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk>
A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR),
J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore
(U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on
behalf of the Swift-XRT team:
We have analysed 5.1 ks of XRT data for GRB 250920C, from 110 s to
131.0 ks after the trigger. The data comprise 64 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+7.1 ks) can be modelled with a
power-law decay with a decay index of alpha=1.53 (+/-0.09).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.94 (+/-0.10). The
best-fitting absorption column is 4.8 (+2.1, -2.0) x 10^20 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 1.89 (+0.16, -0.15)
and a best-fitting absorption column of 6.7 (+4.0, -3.5) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 6.7 (+4.0, -3.5) x 10^20 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index: 1.89 (+0.16, -0.15)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01351039.
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41935.
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TITLE: GCN CIRCULAR
NUMBER: 41934
SUBJECT: GRB 250916A: SAO RAS Zeiss-1000 optical observations
DATE: 25/09/22 09:39:39 GMT
FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru>
A. Moskvitin, O. Spiridonova (SAO), N. Pankov (HSE), A. Pozanenko
(IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg),
Tao An and Yuanqi Liu (Shanghai Astronomical Observatory)
report on behalf of GRB follow-up collaboration and IKI-GRB-FuN.
We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839;
Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al.,
GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan,
GCN 41876) with the 1-m SAO RAS telescope Zeiss-1000 equipped
with the CCD-photometer. We obtained 9 x 300 sec. images Rc band
on September 21, 23:36:57 -- September 22, 00:47:22 UT
(t_mid - T0 = 5.44639 days).
The optical transient (Belkin et al., GCN 41847; Mohan et al.,
GCN 41858; Moskvitin et al., GCN 41859; Burkhonov et al., GCN 41860;
de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870;
Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892;
Hall et al., GCN 41921) is clearly detected in the stacked frame
with the brightness of R = 22.6 +/- 0.1.
Date UT start t-T0 Exp. Filter OT Err. UL (3sigma)
(mid, d) (s)
2025.09.21 23:36:57 5.44639 9 x 300 Rc 22.6 +/- 0.1 23.3
Preliminary photometry is based on the nearby objects from PanSTARRS
(magnitudes converted with Lupton 2005 equations)
and has not corrected for the Galactic extinction.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41934.
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TITLE: GCN CIRCULAR
NUMBER: 41932
SUBJECT: GRB 250920B: Asiago optical observations
DATE: 25/09/21 17:57:22 GMT
FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk>
A. Reguitti (INAF/OAPd), L. Tomasella (INAF/OAPd), D. B. Malesani
(DAWN/NBI and Radboud) report on behalf of a larger collaboration:
We observed the field of GRB 250920B (Gupta et al., GCN 41898; Sonawane
& Meegan, GCN 41919) using the 67/92 Schmidt Telescope located at the
Asiago observatory (Italy). Observations were carried out using a clear
filter, which covers roughly the r and i bands.
The optical counterpart (Gupta et al., GCN 41898; Wu et al., GCN 41908;
Hall et al., GCN 41914; Kuin & Gupta, GCN 41915) is well detected in our
frames. At a mean epoch 2025 Sep 20.771 UT (9.74 hr after the GRB), we
measure an AB magnitude r = 18.62 +- 0.06 (calibrated directly against
r-band magnitudes from the Pan-STARRS catalog).
Considering the filter difference, our measurement is consistent with
the nearly simultaneous observation by Hall et al. (GCN 41914).
View this GCN Circular online at https://gcn.nasa.gov/circulars/41932.
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TITLE: GCN CIRCULAR
NUMBER: 41931
SUBJECT: GRB 250920B: Kitab-ISON optical upper limit
DATE: 25/09/21 17:38:23 GMT
FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com>
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Novichonok (Petrozavodsk State University, KIAM) report on behalf of GRB-IKI-FuN:
We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the RC-36 telescope of Kitab-ISON. The series of unfiltered 325x15 sec exposures was obtained starting on 2025-09-20 at 14:31 UT, i.e. ~0.26 days since Fermi/GBM trigger. The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914) is not visible in our stacked image of 298x15 sec. Preliminary results of our observations provided below:
Date UTstart Exptime t-T0 Filter OT Err. UL
(nxs) (mid, days) (3sigma)
2025-09-20 14:31:30 298x15 0.26550 Clear n/d n/d 15.4
The photometry was calibrated against nearby USNO-B1.0 stars (R2 mags) and not corrected for the Galactic extinction.
Ref. stars
USNO-B1.0
RA Dec R2
187.73536 47.71878 13.75
187.52490 47.74643 13.74
View this GCN Circular online at https://gcn.nasa.gov/circulars/41931.
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