Gamma-ray Burst 251023A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 23 Oct 25 05:58:03 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     782891868
GRB_RA:           37.783d {+02h 31m 08s} (J2000),
                  38.112d {+02h 32m 27s} (current),
                  37.147d {+02h 28m 35s} (1950)
GRB_DEC:          -1.167d {-01d 10' 00"} (J2000),
                  -1.053d {-01d 03' 11"} (current),
                  -1.388d {-01d 23' 15"} (1950)
GRB_ERROR:       19.45 [deg radius, statistical plus systematic]
GRB_INTEN:       118 [cnts/sec]
DATA_SIGNIF:     6.30 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        20971 TJD;   296 DOY;   25/10/23
GRB_TIME:        21463.66 SOD {05:57:43.66} UT
GRB_PHI:         172.00 [deg]
GRB_THETA:        85.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.45
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      49%  Distant Particles
2nd_MOST_LIKELY:  46%  GRB
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 0,1,1, 0,0,
SUN_POSTN:       207.99d {+13h 51m 58s}  -11.50d {-11d 29' 56"}
SUN_DIST:        163.91 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
MOON_POSTN:      225.27d {+15h 01m 04s}  -21.82d {-21d 49' 06"}
MOON_DIST:       156.09 [deg]
MOON_ILLUM:      3 [%]
GAL_COORDS:      169.76,-54.71 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       35.03,-15.21 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/quicklook/glg_lc_medres34_bn251023248.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 189.90,-25.53 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 23 Oct 25 05:58:12 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     782891868
GRB_RA:           34.617d {+02h 18m 28s} (J2000),
                  34.953d {+02h 19m 49s} (current),
                  33.967d {+02h 15m 52s} (1950)
GRB_DEC:          +3.517d {+03d 31' 00"} (J2000),
                  +3.635d {+03d 38' 05"} (current),
                  +3.287d {+03d 17' 12"} (1950)
GRB_ERROR:       12.25 [deg radius, statistical plus systematic]
GRB_INTEN:       125 [cnts/sec]
DATA_SIGNIF:     13.30 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20971 TJD;   296 DOY;   25/10/23
GRB_TIME:        21463.66 SOD {05:57:43.66} UT
GRB_PHI:         175.00 [deg]
GRB_THETA:        80.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.47
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      53%  Distant Particles
2nd_MOST_LIKELY:  44%  GRB
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 0,1,1, 0,0,
SUN_POSTN:       207.99d {+13h 51m 58s}  -11.50d {-11d 29' 56"}
SUN_DIST:        169.54 [deg]   Sun_angle= 11.5 [hr] (West of Sun)
MOON_POSTN:      225.27d {+15h 01m 04s}  -21.82d {-21d 49' 08"}
MOON_DIST:       159.24 [deg]
MOON_ILLUM:      3 [%]
GAL_COORDS:      160.71,-52.85 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       33.55, -9.75 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/quicklook/glg_lc_medres34_bn251023248.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 189.90,-25.53 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 23 Oct 25 06:52:22 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     782891868
GRB_RA:           39.870d {+02h 39m 29s} (J2000),
                  40.190d {+02h 40m 46s} (current),
                  39.250d {+02h 37m 00s} (1950)
GRB_DEC:          -6.530d {-06d 31' 47"} (J2000),
                  -6.420d {-06d 25' 11"} (current),
                  -6.745d {-06d 44' 39"} (1950)
GRB_ERROR:       3.12 [deg radius, statistical only]
GRB_DATE:        20971 TJD;   296 DOY;   25/10/23
GRB_TIME:        21463.66 SOD {05:57:43.66} UT
GRB_PHI:         168.00 [deg]
GRB_THETA:        89.17 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:       208.03d {+13h 52m 06s}  -11.51d {-11d 30' 43"}
SUN_DIST:        158.37 [deg]   Sun_angle= 11.2 [hr] (West of Sun)
MOON_POSTN:      225.72d {+15h 02m 53s}  -21.96d {-21d 57' 42"}
MOON_DIST:       151.11 [deg]
MOON_ILLUM:      3 [%]
GAL_COORDS:      179.10,-57.10 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       35.26,-20.96 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/quicklook/glg_lc_medres34_bn251023248.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/quicklook/glg_locplot_all_bn251023248.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 has human-in-the-loop processing.

GCN Circular #42385
The Fermi GBM team reports the detection of a likely LONG GRB
"At 05:57:43.66 UT on 23 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251023A (trigger 782891868/251023248). 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 = 39.87, Dec = -6.53 (J2000 degrees, equivalent to J2000 02h 39m, -06d 31'), with a statistical uncertainty of 3.12 degrees.
The angle from the Fermi LAT boresight is 89 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/quicklook/glg_skymap_all_bn251023248.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/bn251023248/quicklook/glg_healpix_all_bn251023248.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/quicklook/glg_lc_medres34_bn251023248.gif"
GCN Circular #42408
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 251023A, which was also detected by Fermi/GBM (GCN 42385).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-23 05:57:43.480 with a duration of 4.1 s and a total significance of about 9.1 sigma. The light curve comprises a single peak. Note that data from ~T0-1s to T0+1s suffered from deadtime in various detectors.
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 #42451
SVOM/GRM team: Chen-Wei Wang, Zheng-Hang Yu, Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Feliu Lacreu (IAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a burst GRB 251023A (SVOM trigger reference: sb25102301) at 2025-10-23T05:57:44.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42385) and Glowbug (R. Woolf, GCN#42408).
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 63.5 +19.5/-5.5 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251023A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 39.87, DEC= -6.53, GCN#42385), is located at about 51 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-2 to T0+70 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.45 +0.25/-0.26 and the cutoff energy, parameterized as Epeak, is 143 +26/-19 keV. The event fluence (10-1000 keV) in this time interval is (5.47 +0.55/-0.56)E-6 erg/cm^2.
The localization of GRB 251023A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251023A_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 #42590
H. Yang, M. Brunet, O. Godet (IRAP)
report on behalf of the SVOM team:
The SVOM/ECLAIRs telescope detected GRB 251023A, starting at 2025-10-23T05:57:42.44 UTC (T0), through an offline targeted search with the event-by-event data downloaded through the X-band ground station, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42385), Glowbug (R. Woolf, GCN#42408), and SVOM/GRM (C. Wang, GCN#42451).
The burst was detected within several timescales and energy ranges. The best detection is obtained by the image trigger with a signal-to-noise ratio of 6.5 within 8-120 keV over a time window of 40.96 seconds starting at T0.
The localization of the source is RA, Dec = 31.661,-7.617 degrees:
```
RA (J2000) = 02h06m26.66s     
Dec (J2000) = -07d37m01.20s
```
with a 90% C.L. radius of 13.0 arcmin (including systematic error of 6 arcmin added in quadrature). This position is roughly consistent with that measured by Fermi/GBM, with an angular separation of 8.2 degrees.
The time-averaged spectrum from T0 to T0+40.96 s in the energy range 5-120 keV is well fitted by a power law. The powerlaw index is 0.8 +/-0.3, consistent with that measured by SVOM/GRM. With this model, the total fluence in 4-120 keV is (1.86 +0.08/-1.00)e-6 erg/cm^2.
All quoted errors are at the 68% confidence level.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP.
The SVOM/ECLAIRs point of contact for this event is : Hui Yang (hui.yang@irap.omp.eu)
Please contact him by email if you require additional information regarding the SVOM follow-up of this burst.

Back to JG's homepage

Jochen Greiner, last update: 30-Nov-2025 [Disclaimer]