Gamma-ray Burst 251028A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 28 Oct 25 03:27:01 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     783314796
GRB_RA:          146.100d {+09h 44m 24s} (J2000),
                 146.464d {+09h 45m 51s} (current),
                 145.394d {+09h 41m 34s} (1950)
GRB_DEC:         +22.717d {+22d 43' 00"} (J2000),
                 +22.597d {+22d 35' 50"} (current),
                 +22.947d {+22d 56' 49"} (1950)
GRB_ERROR:       25.72 [deg radius, statistical plus systematic]
GRB_INTEN:       75 [cnts/sec]
DATA_SIGNIF:     4.70 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        20976 TJD;   301 DOY;   25/10/28
GRB_TIME:        12391.86 SOD {03:26:31.86} UT
GRB_PHI:          87.00 [deg]
GRB_THETA:        55.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.37
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       1,0,0, 0,0,0, 0,0,1, 0,0,0, 0,0,
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.17d {-13d 10' 25"}
SUN_DIST:         74.04 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
MOON_POSTN:      289.59d {+19h 18m 22s}  -26.68d {-26d 40' 46"}
MOON_DIST:       146.35 [deg]
MOON_ILLUM:      35 [%]
GAL_COORDS:      208.21, 47.60 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      140.75,  8.61 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 72.78,14.43 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 28 Oct 25 03:27:10 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     783314796
GRB_RA:          147.467d {+09h 49m 52s} (J2000),
                 147.822d {+09h 51m 17s} (current),
                 146.778d {+09h 47m 07s} (1950)
GRB_DEC:         +17.483d {+17d 28' 60"} (J2000),
                 +17.362d {+17d 21' 43"} (current),
                 +17.717d {+17d 43' 02"} (1950)
GRB_ERROR:       5.25 [deg radius, statistical plus systematic]
GRB_INTEN:       466 [cnts/sec]
DATA_SIGNIF:     44.10 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20976 TJD;   301 DOY;   25/10/28
GRB_TIME:        12391.86 SOD {03:26:31.86} UT
GRB_PHI:          85.00 [deg]
GRB_THETA:        50.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.63
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       1,0,0, 0,0,0, 0,0,1, 0,0,0, 0,0,
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.17d {-13d 10' 25"}
SUN_DIST:         70.93 [deg]   Sun_angle= 4.3 [hr] (West of Sun)
MOON_POSTN:      289.59d {+19h 18m 22s}  -26.68d {-26d 40' 45"}
MOON_DIST:       143.50 [deg]
MOON_ILLUM:      35 [%]
GAL_COORDS:      216.14, 47.15 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      143.73,  4.11 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 72.78,14.43 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 28 Oct 25 03:27:20 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     783314796
GRB_RA:          150.910d {+10h 03m 38s} (J2000),
                 151.265d {+10h 05m 04s} (current),
                 150.222d {+10h 00m 53s} (1950)
GRB_DEC:         +19.150d {+19d 08' 60"} (J2000),
                 +19.024d {+19d 01' 27"} (current),
                 +19.392d {+19d 23' 33"} (1950)
GRB_ERROR:       1.72 [deg radius, statistical only]
DATA_SIGNIF:     21.90 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        20976 TJD;   301 DOY;   25/10/28
GRB_TIME:        12391.86 SOD {03:26:31.86} UT
GRB_PHI:          81.00 [deg]
GRB_THETA:        52.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.17d {-13d 10' 25"}
SUN_DIST:         68.52 [deg]   Sun_angle= 4.1 [hr] (West of Sun)
MOON_POSTN:      289.59d {+19h 18m 22s}  -26.68d {-26d 40' 44"}
MOON_DIST:       141.02 [deg]
MOON_ILLUM:      35 [%]
GAL_COORDS:      215.51, 50.79 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      146.24,  6.79 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_783314796.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 28 Oct 25 03:28:28 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      4
TRIGGER_NUM:     783314796
GRB_RA:          152.130d {+10h 08m 31s} (J2000),
                 152.486d {+10h 09m 57s} (current),
                 151.439d {+10h 05m 45s} (1950)
GRB_DEC:         +20.970d {+20d 58' 12"} (J2000),
                 +20.843d {+20d 50' 34"} (current),
                 +21.215d {+21d 12' 55"} (1950)
GRB_ERROR:       1.64 [deg radius, statistical only]
DATA_SIGNIF:     57.00 [sigma]
DATA_INTERVAL:   17.408 [sec]
GRB_DATE:        20976 TJD;   301 DOY;   25/10/28
GRB_TIME:        12391.86 SOD {03:26:31.86} UT
GRB_PHI:          80.00 [deg]
GRB_THETA:        54.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.17d {-13d 10' 26"}
SUN_DIST:         68.21 [deg]   Sun_angle= 4.0 [hr] (West of Sun)
MOON_POSTN:      289.60d {+19h 18m 25s}  -26.68d {-26d 40' 38"}
MOON_DIST:       140.50 [deg]
MOON_ILLUM:      35 [%]
GAL_COORDS:      213.32, 52.46 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      146.67,  8.90 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_783314796.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 28 Oct 25 03:28:39 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      5
TRIGGER_NUM:     783314796
GRB_RA:          152.160d {+10h 08m 38s} (J2000),
                 152.516d {+10h 10m 04s} (current),
                 151.469d {+10h 05m 53s} (1950)
GRB_DEC:         +20.940d {+20d 56' 24"} (J2000),
                 +20.813d {+20d 48' 46"} (current),
                 +21.185d {+21d 11' 07"} (1950)
GRB_ERROR:       1.14 [deg radius, statistical only]
DATA_SIGNIF:     65.30 [sigma]
DATA_INTERVAL:   21.504 [sec]
GRB_DATE:        20976 TJD;   301 DOY;   25/10/28
GRB_TIME:        12391.86 SOD {03:26:31.86} UT
GRB_PHI:          80.00 [deg]
GRB_THETA:        54.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.17d {-13d 10' 26"}
SUN_DIST:         68.17 [deg]   Sun_angle= 4.0 [hr] (West of Sun)
MOON_POSTN:      289.61d {+19h 18m 25s}  -26.68d {-26d 40' 37"}
MOON_DIST:       140.47 [deg]
MOON_ILLUM:      35 [%]
GAL_COORDS:      213.38, 52.48 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      146.71,  8.88 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_783314796.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 28 Oct 25 03:35:41 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     783314796
GRB_RA:          149.540d {+09h 58m 10s} (J2000),
                 149.898d {+09h 59m 35s} (current),
                 148.847d {+09h 55m 23s} (1950)
GRB_DEC:         +20.250d {+20d 15' 00"} (J2000),
                 +20.126d {+20d 07' 33"} (current),
                 +20.489d {+20d 29' 21"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
GRB_DATE:        20976 TJD;   301 DOY;   25/10/28
GRB_TIME:        12391.86 SOD {03:26:31.86} UT
GRB_PHI:          83.00 [deg]
GRB_THETA:        53.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       212.69d {+14h 10m 45s}  -13.18d {-13d 10' 32"}
SUN_DIST:         70.15 [deg]   Sun_angle= 4.2 [hr] (West of Sun)
MOON_POSTN:      289.67d {+19h 18m 41s}  -26.67d {-26d 39' 58"}
MOON_DIST:       142.66 [deg]
MOON_ILLUM:      35 [%]
GAL_COORDS:      213.22, 49.93 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      144.63,  7.38 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_locplot_all_bn251028143.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.

GCN Circular #42497
The Fermi GBM team reports the detection of a likely LONG GRB
At 03:26:31 UT on 28 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028A (trigger 783314796.860488 / 251028143).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 149.5, Dec = 20.2 (J2000 degrees, equivalent to J2000 09h 58m, 20d 11'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 53.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_skymap_all_bn251028143.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/bn251028143/quicklook/glg_healpix_all_bn251028143.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/quicklook/glg_lc_medres34_bn251028143.gif
GCN Circular #42498
H. Sugai (Chuo U.), Y. Kawakubo, M. Serino (AGU), H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 03:27:06 UT on October 28, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (149.003 deg, 17.518 deg) = (09 56 00, +17 31 04) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.27 deg and 0.21 deg, respectively. The roll angle of long axis from the north direction is 49.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 267 +- 43 mCrab (4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners:
```
(148.423, 18.362) deg = (09 53 41, +18 21 43) (J2000)
(148.075, 17.954) deg = (09 52 17, +17 57 14) (J2000)
(149.164, 17.109) deg = (09 56 39, +17 06 32) (J2000)
(149.513, 17.514) deg = (09 58 03, +17 30 50) (J2000)
```
There was no significant excess flux in the previous transit at 02:15 UT with an upper limit of 20 mCrab.
GCN Circular #42499
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 783314796 at 03:26:31 on 28 Oct. 2025 were automatically 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) = 145.7 deg
Decl.(2000.0) = 16.8 deg
```
The 1 sigma statistical error radius is 2.1 deg. We estimate an additional systematic error of 2 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB251028143/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251028143/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251028143/json
GCN Circular #42506
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 251028A, which was also detected by Fermi/GBM (GCN 42497, 42499) and MAXI/GSC (GCN 42498).
Using an adaptive window with a resolution of 32-ms, and taking the GBM-reported T0 (2025-10-28 03:26:31 UT), the burst onset is determined to be T0+22.48s with a duration of 2.0 s and a total significance of about 7.5 sigma. The single peak observed by Glowbug corresponds to the maximum in the Fermi/GBM light curve (GCN 42497). Additional lower-level emission from ~T0+5s to T0+20s may be present in the Glowbug light curve at low significance.
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 #42520
P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 03:26:31.86 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028A (trigger 783314796/251028143) which was also detected by MAXI (Negoro et al. 2025, GCN 42498) and Glowbug (Cheung et al. 2025, GCN 42506). The Fermi GBM on-ground location is consistent with the MAXI position.
The angle from the Fermi LAT boresight is 50 degrees.
The GBM light curve consists of multiple overlapping pulses with a duration (T90) of about 30 s (50-300 keV). The time-averaged spectrum from T0 to T0+39.9 s is best fit by a Band function with Epeak = 244 +/- 14 keV, alpha = -0.91 +/- 0.03, and beta = -2.4 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is (3.13 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+24 s in the 10-1000 keV band is 10.8 +/- 0.3 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 #42522
SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Zheng-Hang Yu, Chao Zheng,, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)SVOM/ECLAIRs team: Report on behalf of the SVOM team:
SVOM/ECLAIRs team: Sebastien Guillot (IRAP)
SVOM/GRM was triggered in-flight by a burst GRB 251028A (SVOM trigger reference: sb25102801) at 2025-10-28T03:26:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498) and Glowbug (C.C. Cheung et al., GCN#42506).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple peaks with a T90 of 31.0 +6.5/-3.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251028A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 149.5, DEC= 20.2, GCN#42497), is located at about 157 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs due to the reflection of the Earth atmosphere.
With this localization, the time-averaged spectrum from T0-10 to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.31 +0.14/-0.16 and the cutoff energy, parameterized as Epeak, is 345 +107/-64 keV. The event fluence (10-1000 keV) in this time interval is (4.56 +0.24/-0.27)E-5 erg/cm^2.
The localization of GRB 251028A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251028A_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: Hao-Xuan Guo (IHEP)(guohx@ihep.ac.cn)
GCN Circular #42523
Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by a long burst, GRB 251028A, at 2025-10-28T03:26:40.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498), Glowbug (C.C. Cheung et al., GCN#42506) and SVOM/GRM (SVOM/GRM team, SVOM/ECLAIRs team, GCN#42522).
According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 38 +4/-5 s. shi The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251028A.png
The time-averaged spectrum from T0-10 s to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.05 +0.11/-0.11 and the cutoff energy, parameterized as Epeak, is 259 +38/-25 keV. The event fluence (10-1000 keV) in this time interval is (3.12 +0.20/-0.17)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 251028A is shown at: https://www.bursthub.cn//admin/static/gecambgrb251028A_amati.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular #42527
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 251028A (Ferm-GBM detection: The Fermi GBM team, GCN 42497; Veres and Meegan, GCN 42520; BALROG localization: Preis & Greiner, GCN 42499; MAXI-GSC detection: Sugai et al., GCN 42498; Glowbug detection: Cheung et al., GCN 42506; SVOM-GRM detection: Guo et al., GCN 42522; GECAM-B detection: Guo et al., GCN 42523) triggered Konus-Wind at T0=12396.343 s UT (03:26:36.343).
The burst light curve starts with a possible rise of a weak emission at ~T0-67 s, which, at ~T0-5.5 s, evolves into the main multi-peaked emission episode with a duration of ~38 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/GRB251028_T12396/
As observed by Konus-Wind, the burst had the total fluence of 3.95(-0.25,+0.27)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+19.568 s, of 3.17(-0.62,+0.64)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the main episode (measured from T0 to T0+33.024 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 = -0.70(-0.12,+0.13), the high energy photon index beta = -2.81(-0.39,+0.22), the peak energy Ep = 229(-15,+16) keV (chi2 = 92/97 dof).
The spectrum near the maximum count rate (measured from T0+16.640 to T0+24.832 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 = -0.31(-0.20,+0.22), the high energy photon index beta = -3.22(-1.23,+0.42), the peak energy Ep = 217(-15,+17) keV (chi2 = 77/82 dof).
All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.
GCN Circular #42580
Hao-Xuan Guo, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team:
At 2025-10-28T03:26:40.000 (T0), Insight-HXMT/HE detected a long burst, GRB 251028A, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498), Glowbug (C.C. Cheung et al., GCN#42506), SVOM/GRM (SVOM/GRM team, SVOM/ECLAIRs team, GCN#42522), GECAM-B (GECAM team, GCN#42523), and Konus-Wind (Konus-Wind team, GCN#42527).
The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 80 +21/-30 s. The 1s peak rate, measured from T0-4.5 s, is 450 cnts/sec. Insight-HXMT/HE detected a total of 9154 counts from this burst.
The Insight-HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251028A.png
All measurements above are made with the CsI detectors of Insight-HXMT/HE 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

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Jochen Greiner, last update: 04-Nov-2025 [Disclaimer]