GRB 251028B
GCN Circular 42509
C. Malacaria (INAF-OAR) report
on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 07:48:06.71 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251028B (trigger 783330491/251028325),
which was also detected by the Glowbug (Woolf et al. 2025, GCN 42507)
and Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 42508).
A final Fermi/GBM localization correction was issued in GCN 42502.
The GBM light curve consists of two main pulses with a duration (T90)
of about 14 s (50-300 keV). The time-averaged spectrum from T0-0.3 s to T0+12.0 s
is best fit by a power law function with an exponential high-energy cutoff.
The power law index is -0.77 +/- 0.10 and the cutoff energy, parameterized as
Epeak, is 125 +/- 8 keV.
The event fluence (10-1000 keV) in this time interval is
(3.9 +/- 0.2)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+8.9 s in the 10-1000 keV band
is 6.4 +/- 0.4 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak = 113 +/- 11 keV,
alpha = -0.68 +/- 0.14 and beta = -2.8 +/- 0.4.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 42508
James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report:
Swift/BAT did not localize GRB 251028B onboard (T0: 2025-10-28T07:48:06.71 UTC, Fermi Trig 783330491, CALET Trig 1445672396, Glowbug GCN 42507)
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 12.3 in a 1.024 s analysis time bin, starting at T0 + 8.704 s.
Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)
The 90% credible area is 6,959 deg2 and the 50% credible area is 1,123 deg2. The integrated probability inside the coded field of view is 1%.
The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 42502). The combined Fermi/GBM+NITRATES 90% credible area is 436 deg2 and the 50% credible area is 92 deg2.
A plot of the probability skymap can be viewed here:
The probability skymap and joint skymap files can be downloaded from the links here
Instructions on how to read and manipulate this map can be found here:
https://guano.swift.psu.edu/documentation
More details about this burst can be found on the trigger report page here:
https://guano.swift.psu.edu/trigger_report?id=783330523
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular 42507
R. Woolf, C.C. Cheung, 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 251028B, which was also detected by Fermi GBM (GCN 42502) and CALET (GCN 42505).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-28 07:48:04.672 with a duration of 22.5 s and a total significance of about 30.5 sigma. The light curve comprises two primary peaks.
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 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 42505
Y. Akaike (Waseda U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii,
K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The long GRB 251028B (Fermi GBM Final Localization Correction: Fermi GBM team,
GCN Circ. 42502) triggered the CALET Gamma-ray Burst Monitor (CGBM) at
07:48:06.24 UTC on 28 October 2025
(https://cgbm.calet.jp/cgbm_trigger/flight/1445672396/index.html).
The burst signal was seen by all CGBM detectors.
The burst light curve shows a multi-peaked structure that starts
at T-0.5 sec, peaks at T+9.9 sec, and ends at T+11.5 sec.
The T90 and T50 durations measured by the SGM data are 11.3 +/- 0.4 sec
and 8.5 +/- 0.3 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1445672396/
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 42504
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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 251028B ( Fermi GBM team, GCN 42502) errorbox 19936 sec after notice time and 19967 sec after trigger time at 2025-10-28 13:20:54 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 6 deg. The sun altitude is -33.5 deg.
The galactic latitude b = -10 deg., longitude l = 99 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3025691
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
19998 | 2025-10-28 13:20:54 | MASTER-Tunka | (22h 31m 44.47s , +45d 04m 55.7s) | C | 60 | 18.6 |
19998 | 2025-10-28 13:20:54 | MASTER- | (22h 30m 56.32s , +45d 13m 01.0s) | C | 60 | 18.3 |
20070 | 2025-10-28 13:22:06 | MASTER-Tunka | (22h 34m 25.03s , +46d 58m 00.3s) | C | 60 | 17.5 |
20070 | 2025-10-28 13:22:06 | MASTER- | (22h 33m 35.14s , +47d 06m 10.6s) | C | 60 | 17.3 |
20146 | 2025-10-28 13:23:22 | MASTER-Tunka | (22h 30m 48.12s , +43d 08m 44.4s) | C | 60 | 13.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 42502
The Fermi GBM team reports the detection of a likely LONG GRB
"At 07:48:06.71 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251028B (trigger 783330491/251028325).
This trigger was initially classified as Distant Particles by the flight software,
but is in fact a GRB.
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 337.82, Dec = 45.75 (J2000 degrees, equivalent to J2000 22h 31m, +45d 45'),
with a statistical uncertainty of 3.69 degrees.
The angle from the Fermi LAT boresight is 119 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028325/quicklook/glg_skymap_all_bn251028325.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/bn251028325/quicklook/glg_healpix_all_bn251028325.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028325/quicklook/glg_lc_medres34_bn251028325.gif"