Gamma-ray Burst 251011B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:08:46 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1403191,   Seg_Num: 0
GRB_RA:           13.287d {+00h 53m 09s} (J2000),
                  13.555d {+00h 54m 13s} (current),
                  12.766d {+00h 51m 04s} (1950)
GRB_DEC:         -62.032d {-62d 01' 55"} (J2000),
                 -61.893d {-61d 53' 33"} (current),
                 -62.304d {-62d 18' 12"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       3209 [cnts]    Image_Peak=214 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   139     E_range: 15-50 keV
BKG_INTEN:       18608 [cnts]
BKG_TIME:        25683.51 SOD {07:08:03.51} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20959 TJD;   284 DOY;   25/10/11
GRB_TIME:        25702.33 SOD {07:08:22.33} UT
GRB_PHI:         -85.66 [deg]
GRB_THETA:        28.35 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     32.14 [sigma]
IMAGE_SIGNIF:    10.44 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +1  +0  +0  +0 +35  +0 
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 41"}
SUN_DIST:        110.92 [deg]   Sun_angle= -11.8 [hr] (East of Sun)
MOON_POSTN:       73.85d {+04h 55m 24s}  +27.82d {+27d 49' 14"}
MOON_DIST:       101.84 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      302.58,-55.09 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      331.05,-58.56 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 276.67,15.24 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=781859306).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:08:52 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     781859306
GRB_RA:          359.450d {+23h 57m 48s} (J2000),
                 359.782d {+23h 59m 08s} (current),
                 358.803d {+23h 55m 13s} (1950)
GRB_DEC:         -57.617d {-57d 37' 00"} (J2000),
                 -57.473d {-57d 28' 23"} (current),
                 -57.895d {-57d 53' 41"} (1950)
GRB_ERROR:       15.38 [deg radius, statistical plus systematic]
GRB_INTEN:       105 [cnts/sec]
DATA_SIGNIF:     7.60 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        20959 TJD;   284 DOY;   25/10/11
GRB_TIME:        25701.91 SOD {07:08:21.91} UT
GRB_PHI:         115.00 [deg]
GRB_THETA:        75.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      1.58
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      84%  GRB
2nd_MOST_LIKELY:  13%  Generic SGR
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 1,1,0, 0,0,
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 41"}
SUN_DIST:        113.91 [deg]   Sun_angle= -10.9 [hr] (East of Sun)
MOON_POSTN:       73.85d {+04h 55m 24s}  +27.82d {+27d 49' 14"}
MOON_DIST:       105.25 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      316.52,-58.07 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      327.54,-50.60 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_lc_medres34_bn251011297.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 165.53,8.02 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1403191).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:09:09 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     781859306
GRB_RA:            0.860d {+00h 03m 26s} (J2000),
                   1.187d {+00h 04m 45s} (current),
                   0.223d {+00h 00m 54s} (1950)
GRB_DEC:         -53.890d {-53d 53' 23"} (J2000),
                 -53.747d {-53d 44' 46"} (current),
                 -54.168d {-54d 10' 05"} (1950)
GRB_ERROR:       6.88 [deg radius, statistical only]
DATA_SIGNIF:     9.00 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20959 TJD;   284 DOY;   25/10/11
GRB_TIME:        25701.91 SOD {07:08:21.91} UT
GRB_PHI:         119.00 [deg]
GRB_THETA:        75.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 42"}
SUN_DIST:        117.70 [deg]   Sun_angle= -11.0 [hr] (East of Sun)
MOON_POSTN:       73.85d {+04h 55m 25s}  +27.82d {+27d 49' 15"}
MOON_DIST:       102.74 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      317.97,-61.81 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      332.01,-48.14 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_lc_medres34_bn251011297.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_781859306.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
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.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1403191).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:17:49 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     781859306
GRB_RA:            5.330d {+00h 21m 19s} (J2000),
                   5.640d {+00h 22m 34s} (current),
                   4.726d {+00h 18m 54s} (1950)
GRB_DEC:         -56.110d {-56d 06' 35"} (J2000),
                 -55.967d {-55d 58' 01"} (current),
                 -56.387d {-56d 23' 13"} (1950)
GRB_ERROR:       5.26 [deg radius, statistical only]
GRB_DATE:        20959 TJD;   284 DOY;   25/10/11
GRB_TIME:        25701.91 SOD {07:08:21.91} UT
GRB_PHI:         117.00 [deg]
GRB_THETA:        78.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       196.82d {+13h 07m 16s}   -7.15d {-07d 08' 50"}
SUN_DIST:        116.21 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       73.95d {+04h 55m 49s}  +27.83d {+27d 49' 53"}
MOON_DIST:       101.77 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      311.47,-60.52 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      333.02,-51.46 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_lc_medres34_bn251011297.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_locplot_all_bn251011297.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:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1403191).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:09:52 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     781859306
GRB_RA:            0.810d {+00h 03m 14s} (J2000),
                   1.137d {+00h 04m 33s} (current),
                   0.173d {+00h 00m 41s} (1950)
GRB_DEC:         -53.870d {-53d 52' 11"} (J2000),
                 -53.727d {-53d 43' 34"} (current),
                 -54.148d {-54d 08' 53"} (1950)
GRB_ERROR:       4.13 [deg radius, statistical only]
DATA_SIGNIF:     11.30 [sigma]
DATA_INTERVAL:   11.264 [sec]
GRB_DATE:        20959 TJD;   284 DOY;   25/10/11
GRB_TIME:        25701.91 SOD {07:08:21.91} UT
GRB_PHI:         119.00 [deg]
GRB_THETA:        75.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 42"}
SUN_DIST:        117.71 [deg]   Sun_angle= -11.0 [hr] (East of Sun)
MOON_POSTN:       73.86d {+04h 55m 27s}  +27.82d {+27d 49' 19"}
MOON_DIST:       102.76 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      318.04,-61.82 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      331.99,-48.10 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_lc_medres34_bn251011297.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_781859306.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
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.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1403191).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:10:33 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1403191,   Seg_Num: 0
GRB_RA:           13.2358d {+00h 52m 56.5s} (J2000),
                  13.5038d {+00h 54m 00.9s} (current),
                  12.7137d {+00h 50m 51.2s} (1950)
GRB_DEC:         -62.0326d {-62d 01' 57.3"} (J2000),
                 -61.8930d {-61d 53' 34.7"} (current),
                 -62.3039d {-62d 18' 14.0"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       75 [cnts]
IMG_START_DATE:  20959 TJD;   284 DOY;   25/10/11
IMG_START_TIME:  25798.80 SOD {07:09:58.80} UT,   96.5 [sec] since BAT Trigger Time
CENTROID_X:      342.81,  raw= 343  [pixels]
CENTROID_Y:      263.26,  raw= 263  [pixels]
ROLL:            183.75 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -83.53
GRB_POS_XRT_Z:   73.57
IMAGE_URL:       sw01403191000msxps_rw.img
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 43"}
SUN_DIST:        110.91 [deg]   Sun_angle= -11.8 [hr] (East of Sun)
MOON_POSTN:       73.87d {+04h 55m 29s}  +27.82d {+27d 49' 22"}
MOON_DIST:       101.87 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      302.62,-55.09 [deg] galactic lon,lat of the burst
ECL_COORDS:      331.02,-58.54 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:10:35 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1403191,   Seg_Num: 0
GRB_RA:           13.2358d {+00h 52m 56.5s} (J2000),
                  13.5038d {+00h 54m 00.9s} (current),
                  12.7137d {+00h 50m 51.2s} (1950)
GRB_DEC:         -62.0326d {-62d 01' 57.3"} (J2000),
                 -61.8930d {-61d 53' 34.7"} (current),
                 -62.3039d {-62d 18' 14.0"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       75 [cnts]
IMG_START_DATE:  20959 TJD;   284 DOY;   25/10/11
IMG_START_TIME:  25798.80 SOD {07:09:58.80} UT,   96.5 [sec] since BAT Trigger Time
CENTROID_X:      342.81,  raw= 343  [pixels]
CENTROID_Y:      263.26,  raw= 263  [pixels]
ROLL:            183.75 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -83.53
GRB_POS_XRT_Z:   73.57
IMAGE_URL:       sw01403191000msxps_rw.img
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 43"}
SUN_DIST:        110.91 [deg]   Sun_angle= -11.8 [hr] (East of Sun)
MOON_POSTN:       73.87d {+04h 55m 29s}  +27.82d {+27d 49' 22"}
MOON_DIST:       101.87 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      302.62,-55.09 [deg] galactic lon,lat of the burst
ECL_COORDS:      331.02,-58.54 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Oct 25 07:10:23 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1403191,   Seg_Num: 0
GRB_RA:           13.2358d {+00h 52m 56.59s} (J2000),
                  13.5038d {+00h 54m 00.90s} (current),
                  12.7137d {+00h 50m 51.28s} (1950)
GRB_DEC:         -62.0326d {-62d 01' 57.3"} (J2000),
                 -61.8930d {-61d 53' 34.7"} (current),
                 -62.3039d {-62d 18' 14.0"} (1950)
GRB_ERROR:       5.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.95e-09 [erg/cm2/sec]
GRB_SIGNIF:      8.66 [sigma]
IMG_START_DATE:  20959 TJD;   284 DOY;   25/10/11
IMG_START_TIME:  25798.80 SOD {07:09:58.80} UT,   96.5 [sec] since BAT Trigger Time
TAM[0-3]:        327.61 237.19 261.51 243.82
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       196.81d {+13h 07m 15s}   -7.15d {-07d 08' 43"}
SUN_DIST:        110.91 [deg]   Sun_angle= -11.8 [hr] (East of Sun)
MOON_POSTN:       73.87d {+04h 55m 28s}  +27.82d {+27d 49' 21"}
MOON_DIST:       101.87 [deg]
MOON_ILLUM:      77 [%]
GAL_COORDS:      302.62,-55.09 [deg] galactic lon,lat of the burst
ECL_COORDS:      331.02,-58.54 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.45 arcmin from the BAT position.

GCN Circular #42196
The Fermi GBM team reports the detection of a likely LONG GRB
At 07:08:21 UT on 11 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251011B (trigger 781859306.91454 / 251011297).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 5.3, Dec = -56.1 (J2000 degrees, equivalent to J2000 00h 21m, -56d 06'), with a statistical uncertainty of 5.3 degrees.
The angle from the Fermi LAT boresight is 78.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_skymap_all_bn251011297.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/bn251011297/quicklook/glg_healpix_all_bn251011297.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251011297/quicklook/glg_lc_medres34_bn251011297.gif
GCN Circular #42197
A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Melandri (INAF-OAR), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 07:08:22.33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251011B (trigger=1403191). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 13.287, -62.032 which is
```
   RA(J2000) = 00h 53m 09s
   Dec(J2000) = -62d 01' 55"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 150 seconds. The peak count rate was ~3000 counts/sec (15-350 keV) at ~0 sec after the trigger.
The XRT began observing the field at 07:09:58.8 UT, 96.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 13.23523, -62.03269 which is equivalent to:
```
   RA(J2000)  = 00h 52m 56.46s
   Dec(J2000) = -62d 01' 57.7"
```
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 87 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.68 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.5 (+3.47/-2.92) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 1.95e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT data are unavailable at this time.
Burst Advocate for this burst is A. D'Ai (antonino.dai AT inaf.it). 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/)
GCN Circular #42201
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 243 s of XRT Photon Counting mode data and 1 UVOT images for GRB 251011B, 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 = 13.23469, -62.03340 which is equivalent to:
```
RA (J2000): 00h 52m 56.33s
Dec (J2000): -62d 02' 00.2"
```
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 https://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 #42203
P.Balanutsa, V.Lipunov, A.Kuznetsov, G.Antipov, I.Panchenko, K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, M.Shilova, A.Chasovnikov, V.Topolev, V.Senik, D.Vlasenko, Yu.Tselik, E.Gorbovskoy(Lomonosov MSU), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A. Sosnovskiy (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
The MASTER-OAFA robotic telescope of the MASTER Global Robotic Net [1,2,3,4] started GRB 251011B (Fermi GCN 42196, Swift: D'Ai et al. GCN 42197, XRT Evans et al. GCN 42201, Ttrigger=2025-10-11 07:08:22UT XRT RA,Dec(2000)=00h 52m 56.33s,-62d 02' 00.2") at 2025-10-11 07:09:27 with 10s expositions at 48 deg.altitude There is no optical counterpart on a single images Observations and reduction will be continued.

Tstart(+exp), UT        RADec(2000) of MASTERsquarecent. Exp,s mlim
2025-10-11 07:09:07	00h 53m 53.80s -61d 58m 00.8s 	10	18.0
2025-10-11 07:09:23	00h 53m 53.92s -61d 58m 00.0s 	10	18.0
2025-10-11 07:09:39	00h 53m 53.86s -61d 58m 00.6s 	20	18.6
2025-10-11 07:10:05	00h 53m 53.91s -61d 58m 00.5s 	20	18.9
2025-10-11 07:10:31	00h 53m 54.05s -61d 57m 59.3s 	30	18.0
2025-10-11 07:11:06	00h 53m 54.18s -61d 57m 59.2s 	30	18.0
2025-10-11 07:11:43	00h 53m 54.30s -61d 57m 59.1s 	40	18.3
2025-10-11 07:12:29	00h 53m 54.50s -61d 57m 58.5s 	50	18.8
2025-10-11 07:13:25	00h 53m 54.74s -61d 57m 58.3s 	60	19.2
2025-10-11 07:14:32	00h 53m 55.02s -61d 57m 57.6s 	70	19.6
2025-10-11 07:15:47	00h 53m 55.39s -61d 57m 57.1s 	90	19.6
2025-10-11 07:17:23	00h 53m 55.79s -61d 57m 56.7s 	110	19.6
2025-10-11 07:19:19	00h 53m 56.33s -61d 57m 55.8s 	130	19.6
2025-10-11 07:21:35	00h 53m 57.00s -61d 57m 55.1s 	160	19.6

up to 2025-10-11 09:17:08.

[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A.
 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics,
Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625

GCN Circular #42204
O. Mukherjee (USRA), C. Meegan (UAH), U. Pathak (IIT Bombay) and L. Scotton (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 07:08:21.91 UT on 11 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251011B (trigger 781859306/251011297). which was also detected by Swift BAT (A. D'Ai et al. 2025, GCN 42197), and Swift XRT (P.A. Evans et al. 2025, GCN 42201). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 81.8 degrees.
The GBM light curve consists of a single pulse with a duration (T90) of about 35 s (50-300 keV). The time-averaged spectrum from T0-8.0 to T0+26.5 s is best fit by a Band function with Epeak = 36 +/- 5 keV, alpha = 0.4 +/- 0.7, and beta = -2.2 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is (3.3 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.58 s in the 10-1000 keV band is 3 +/- 0.2 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 #42205
B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Ferro (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 5.1 ks of XRT data for GRB 251011B, from 85 s to 61.7 ks after the trigger. The data comprise 112 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 light curve can be modelled with an initial power-law decay with an index of alpha=3.12 (+/-0.08), followed by a break at T+579 s to an alpha of 0.57 (+0.07, -0.20).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.15 (+/-0.12). The best-fitting absorption column is 1.8 (+0.4, -0.3) x 10^21 cm^-2, in excess of the Galactic value of 1.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
```
Total column:	     1.8 (+0.4, -0.3) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 8.4 sigma
Photon index:	     2.15 (+/-0.12)
```
If the light curve continues to decay with a power-law decay index of 0.57, the count rate at T+24 hours will be 0.013 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.0 x 10^-13 (5.7 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01403191.
This circular is an official product of the Swift-XRT team.
GCN Circular #42206
SVOM/GRM team: Xue-Yuan Zao, Zheng-Hang Yu, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Sebastien Guillot (IRAP), Stéphane Schanne (CEA), Nicolas Dagoneau
Report on behalf of the SVOM team:
SVOM/GRM detected the burst GRB 251011B at 2025-10-11T07:08:22.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42196) and Swift/BAT (A. D'Ai et al., GCN #42197).
With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 251011B. The GRM light curve shows that this burst consists of a single pulse with a T90 of 48 +9/-10 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251011B.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 5.3, DEC= -56.1, GCN#42196), is located at about 85.17 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-15 to T0+30 s is best fitted by a power law function. The power law index is 2.22 +0.23/-0.19. The event fluence (10-1000 keV) in this time interval is (3.56 +0.56/-0.82)E-06 erg/cm^2.
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/GRM point of contact for this burst is: Xue-Yuan Zao (IHEP) (zaoxy@ihep.ac.cn)
GCN Circular #42209
M. H. Siegel (PSU) and A. D'Ai (INAF-IASFPA) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251011B 107 s after the BAT trigger (D'Ai et al., GCN Circ. 42197). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 42201) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           107          257          147         >20.9
white              107          257          147         >20.9
u                  320          463          141         >20.4
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.017 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #42211
Ya.Kechin, V.Lipunov, P.Balanutsa, A.Kuznetsov, G.Antipov, I.Panchenko, K.Zhirkov, E.Gorbovskoy, N.Tiurina, A.Sankovich, Ya.Kechin, M.Shilova, A.Chasovnikov, V.Topolev, V.Senik, D.Vlasenko, Yu.Tselik (Lomonosov MSU), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A. Sosnovskiy (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
The MASTER-OAFA robotic telescope of the MASTER Global Robotic Net [1,2,3,4] started Swift GRB 251011B (Ttrigger=2025-10-11 07:08:22UT; XRT RA,Dec(2000)=00h 52m 56.33s,-62d 02'00.2" GCN 42197, GCN 42201) alert observations at 2025-10-11 07:09:27 and observed it up to sunrise (Balanutsa et al. GCN 42203).
Next night MASTER automatic planner continued Fermi error-box (GCN 32196) inspection as independent alert
MASTER OT J011025.98-583210.6 discovery
MASTER-OAFA auto-detection system of MASTER Global Robotic Net [1,2,3,4] during Fermi GRB 251011B (GCN42204, also detected by Swift (GCN42197) and observed by MASTER in alert mode (GCN 42203)) inspection discovered OT source at (RA, Dec) = 01h 10m 25.98s -58d 32m 10.6s on 2025-10-12.16208 UT with light curve, that is typical for gamma-ray bursts optical counterpart.
The OT unfiltered magnitud m=17.8 (first image) at 2025-10-12 03:53:24UT (mlim=19.3 at single image). The OT is seen in 8 images with typical GRB counterpart decay. There is no minor planet at this place. We have reference image on 2025-09-16.19346 UT with unfiltered mlim=20.3m.
So as the Ttrigger for GRB 251011B was 19h earlier our discovery time (2025-10-11 07:08:22.33UT) and Swift error-box center was at 00h 52m 56.33s -62d 02' 00.2" (Swift GCN 42197, GCN 42201) MASTER OT looks not connected with just GRB 251011B, but can be the orphan one [5].
Spectral observations and deep photometry are required.
```
[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A.
 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625
[5] Lipunov et al. 2022, MNRAS, 516, 4980 https://ui.adsabs.harvard.edu/abs/2022MNRAS.516.4980L/abstract
```
GCN Circular #42282
Y. N. Ma, H. L. Li, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, 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, D. H. Zhao (NAOC), J. Palmerio (CEA), Y. H. Cheng (YNU), Y. Wang (PMO) report on behalf of the SVOM/VT team.
SVOM performed a Target of Opportunity observation of GRB 251011B detected by Swift/BAT, Fermi/GBM, and SVOM/GRM (D'Ai et al., GCN 42197; Fermi GBM team, GCN 42196; Evans et al., GCN 42201; Mukherjee et al., GCN 42204; Sbarufatti et al., GCN 42205; Zao et al., GCN 42206). SVOM/VT began observing the field at 2025-10-11 09:06:00 UTC, 1.961 hours after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No uncatalogued sources, compared to Legacy Survey, were detected in our single or stacked images within the error box provided by Swift/XRT position (D'Ai et al., GCN 42197; Evans et al., GCN 42201), the three sigma limits are:
```
mid-time  | exposure time   | band  | upper limit (AB) 
----------|-----------------|-------|----------------- 
  2.3 h   |    44*50 sec    | VT_B  |   > 23.2 mag
  2.3 h   |    41*50 sec    | VT_R  |   > 23.3 mag
```
Our results are consistent with MASTER (Balanutsa et al., GCN 42203) and Swift/UVOT (Siegel & D'Ai, GCN 42209).
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.

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Jochen Greiner, last update: 15-Oct-2025 [Disclaimer]