Gamma-ray Burst 251125B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 25 Nov 25 20:24:15 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     785795030
GRB_RA:          208.683d {+13h 54m 44s} (J2000),
                 208.859d {+13h 55m 26s} (current),
                 208.345d {+13h 53m 23s} (1950)
GRB_DEC:         +66.150d {+66d 09' 00"} (J2000),
                 +66.024d {+66d 01' 25"} (current),
                 +66.395d {+66d 23' 41"} (1950)
GRB_ERROR:       10.35 [deg radius, statistical plus systematic]
GRB_INTEN:       198 [cnts/sec]
DATA_SIGNIF:     9.10 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         267.00 [deg]
GRB_THETA:        55.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      1.32
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      72%  GRB
2nd_MOST_LIKELY:  26%  Distant Particles
DETECTORS:       0,0,0, 1,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       241.82d {+16h 07m 17s}  -20.91d {-20d 54' 39"}
SUN_DIST:         90.44 [deg]   Sun_angle= 2.2 [hr] (West of Sun)
MOON_POSTN:      308.50d {+20h 33m 59s}  -22.01d {-22d 00' 29"}
MOON_DIST:       113.92 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:      113.11, 49.75 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      152.36, 66.40 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 288.05,21.45 [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 25 Nov 25 20:24:24 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     785795030
GRB_RA:          237.300d {+15h 49m 12s} (J2000),
                 237.430d {+15h 49m 43s} (current),
                 237.049d {+15h 48m 12s} (1950)
GRB_DEC:         +58.950d {+58d 57' 00"} (J2000),
                 +58.872d {+58d 52' 20"} (current),
                 +59.101d {+59d 06' 03"} (1950)
GRB_ERROR:       6.23 [deg radius, statistical plus systematic]
GRB_INTEN:       282 [cnts/sec]
DATA_SIGNIF:     26.10 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         281.00 [deg]
GRB_THETA:        45.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      1.17
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       0,0,0, 1,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       241.82d {+16h 07m 17s}  -20.91d {-20d 54' 39"}
SUN_DIST:         79.87 [deg]   Sun_angle= 0.3 [hr] (West of Sun)
MOON_POSTN:      308.50d {+20h 33m 59s}  -22.01d {-22d 00' 27"}
MOON_DIST:        99.51 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:       91.66, 45.92 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      191.65, 73.47 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 288.05,21.45 [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 25 Nov 25 20:24:33 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     785795030
GRB_RA:          237.400d {+15h 49m 36s} (J2000),
                 237.536d {+15h 50m 09s} (current),
                 237.139d {+15h 48m 33s} (1950)
GRB_DEC:         +58.250d {+58d 15' 00"} (J2000),
                 +58.172d {+58d 10' 21"} (current),
                 +58.401d {+58d 24' 02"} (1950)
GRB_ERROR:       4.81 [deg radius, statistical only]
DATA_SIGNIF:     20.90 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         282.00 [deg]
GRB_THETA:        45.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       241.82d {+16h 07m 17s}  -20.91d {-20d 54' 39"}
SUN_DIST:         79.16 [deg]   Sun_angle= 0.3 [hr] (West of Sun)
MOON_POSTN:      308.50d {+20h 34m 00s}  -22.01d {-22d 00' 26"}
MOON_DIST:        99.14 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:       90.72, 46.18 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      193.58, 73.04 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_785795030.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 25 Nov 25 20:25:08 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     785795030
GRB_RA:          226.750d {+15h 07m 00s} (J2000),
                 226.927d {+15h 07m 42s} (current),
                 226.409d {+15h 05m 38s} (1950)
GRB_DEC:         +55.900d {+55d 53' 60"} (J2000),
                 +55.801d {+55d 48' 05"} (current),
                 +56.091d {+56d 05' 29"} (1950)
GRB_ERROR:       4.06 [deg radius, statistical only]
DATA_SIGNIF:     19.90 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         283.00 [deg]
GRB_THETA:        51.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       241.82d {+16h 07m 17s}  -20.91d {-20d 54' 39"}
SUN_DIST:         77.75 [deg]   Sun_angle= 1.0 [hr] (West of Sun)
MOON_POSTN:      308.50d {+20h 34m 01s}  -22.01d {-22d 00' 20"}
MOON_DIST:       103.51 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:       92.15, 52.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      186.72, 67.24 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_785795030.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 25 Nov 25 20:25:19 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     785795030
GRB_RA:          227.680d {+15h 10m 43s} (J2000),
                 227.843d {+15h 11m 22s} (current),
                 227.365d {+15h 09m 28s} (1950)
GRB_DEC:         +57.700d {+57d 42' 00"} (J2000),
                 +57.603d {+57d 36' 11"} (current),
                 +57.888d {+57d 53' 17"} (1950)
GRB_ERROR:       2.32 [deg radius, statistical only]
DATA_SIGNIF:     29.10 [sigma]
DATA_INTERVAL:   6.144 [sec]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         281.00 [deg]
GRB_THETA:        50.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       241.82d {+16h 07m 17s}  -20.91d {-20d 54' 39"}
SUN_DIST:         79.38 [deg]   Sun_angle= 0.9 [hr] (West of Sun)
MOON_POSTN:      308.51d {+20h 34m 01s}  -22.01d {-22d 00' 19"}
MOON_DIST:       103.64 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:       94.01, 50.88 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      184.18, 68.86 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_785795030.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 25 Nov 25 20:25:44 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     785795030
GRB_RA:          226.050d {+15h 04m 12s} (J2000),
                 226.220d {+15h 04m 53s} (current),
                 225.723d {+15h 02m 54s} (1950)
GRB_DEC:         +57.400d {+57d 23' 60"} (J2000),
                 +57.300d {+57d 18' 00"} (current),
                 +57.594d {+57d 35' 38"} (1950)
GRB_ERROR:       2.07 [deg radius, statistical only]
DATA_SIGNIF:     27.20 [sigma]
DATA_INTERVAL:   8.192 [sec]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         281.00 [deg]
GRB_THETA:        51.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       241.82d {+16h 07m 17s}  -20.91d {-20d 54' 40"}
SUN_DIST:         79.30 [deg]   Sun_angle= 1.0 [hr] (West of Sun)
MOON_POSTN:      308.51d {+20h 34m 02s}  -22.00d {-22d 00' 14"}
MOON_DIST:       104.36 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:       94.47, 51.76 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      183.18, 68.01 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_785795030.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 25 Nov 25 20:33:08 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     785795030
GRB_RA:          237.490d {+15h 49m 58s} (J2000),
                 237.631d {+15h 50m 31s} (current),
                 237.219d {+15h 48m 53s} (1950)
GRB_DEC:         +57.550d {+57d 32' 60"} (J2000),
                 +57.473d {+57d 28' 22"} (current),
                 +57.700d {+57d 42' 01"} (1950)
GRB_ERROR:       3.08 [deg radius, statistical only]
GRB_DATE:        21004 TJD;   329 DOY;   25/11/25
GRB_TIME:        73425.88 SOD {20:23:45.88} UT
GRB_PHI:         283.00 [deg]
GRB_THETA:        45.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       241.83d {+16h 07m 18s}  -20.91d {-20d 54' 43"}
SUN_DIST:         78.46 [deg]   Sun_angle= 0.3 [hr] (West of Sun)
MOON_POSTN:      308.57d {+20h 34m 18s}  -21.98d {-21d 59' 02"}
MOON_DIST:        98.79 [deg]
MOON_ILLUM:      26 [%]
GAL_COORDS:       89.77, 46.44 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      195.41, 72.59 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_locplot_all_bn251125850.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 #42836
The Fermi GBM team reports the detection of a likely LONG GRB
At 20:23:45 UT on 25 Nov 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251125B (trigger 785795030.880336 / 251125850).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 237.5, Dec = 57.5 (J2000 degrees, equivalent to J2000 15h 50m, 57d 30'), with a statistical uncertainty of 3.1 degrees.
The angle from the Fermi LAT boresight is 45.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_skymap_all_bn251125850.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/bn251125850/quicklook/glg_healpix_all_bn251125850.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251125850/quicklook/glg_lc_medres34_bn251125850.gif

GCN Circular #42837
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 [1] located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 251125B ( Fermi GBM team, GCN 42836) errorbox 37 sec after notice time and 71 sec after trigger time at 2025-11-25 20:24:57 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 62 deg. The sun altitude is -39.2 deg.
MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251125B errorbox 40 sec after notice time and 74 sec after trigger time at 2025-11-25 20:25:00 UT, with upper limit up to 13.2 mag. The observations began at zenith distance = 79 deg. The sun altitude is -66.8 deg.
The galactic latitude b = 46 deg., longitude l = 89 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3051835
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      76 | 2025-11-25 20:24:57 |        MASTER-Tunka | (15h 49m 53.68s , +58d 02m 46.1s) |   C |    10 | 19.0 |        
      77 | 2025-11-25 20:24:57 |             MASTER- | (15h 50m 33.82s , +57d 56m 14.3s) |   C |    10 | 18.9 |        
      80 | 2025-11-25 20:25:00 |   MASTER-Kislovodsk | (15h 48m 55.38s , +57d 57m 14.7s) |   C |    10 | 12.3 |        
      81 | 2025-11-25 20:25:01 |   MASTER-Kislovodsk | (15h 41m 25.24s , +58d 17m 41.9s) |   C |    10 | 12.3 |        
     613 | 2025-11-25 20:33:29 |        MASTER-Tunka | (15h 50m 14.31s , +57d 20m 48.8s) |   C |    60 | 19.0 |        
     673 | 2025-11-25 20:33:29 |        MASTER-Tunka | (15h 50m 14.31s , +57d 20m 48.8s) |   C |   180 | 19.8 |  Coadd 
     613 | 2025-11-25 20:33:29 |             MASTER- | (15h 50m 55.15s , +57d 14m 04.0s) |   C |    60 | 18.9 |        
     649 | 2025-11-25 20:33:35 |   MASTER-Kislovodsk | (15h 49m 05.73s , +57d 13m 41.7s) |   C |   120 | 12.9 |        
     677 | 2025-11-25 20:34:32 |        MASTER-Tunka | (15h 50m 14.11s , +57d 20m 48.0s) |   C |    60 | 19.2 |        
     677 | 2025-11-25 20:34:32 |             MASTER- | (15h 50m 55.07s , +57d 14m 02.7s) |   C |    60 | 19.1 |        
     740 | 2025-11-25 20:35:36 |        MASTER-Tunka | (15h 50m 13.87s , +57d 20m 46.9s) |   C |    60 | 18.9 |        
     740 | 2025-11-25 20:35:36 |             MASTER- | (15h 50m 54.92s , +57d 14m 02.1s) |   C |    60 | 18.7 |        
     789 | 2025-11-25 20:35:54 |   MASTER-Kislovodsk | (15h 49m 06.58s , +57d 13m 30.8s) |   C |   120 | 13.2 |        
     803 | 2025-11-25 20:36:39 |        MASTER-Tunka | (15h 50m 13.66s , +57d 20m 45.9s) |   C |    60 | 19.5 |        
     804 | 2025-11-25 20:36:39 |             MASTER- | (15h 50m 54.78s , +57d 14m 01.8s) |   C |    60 | 19.3 |        
     928 | 2025-11-25 20:38:14 |   MASTER-Kislovodsk | (15h 49m 07.46s , +57d 13m 23.9s) |   C |   120 | 13.1 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html

GCN Circular #42838
O.A.Gress, N.M.Budnev (Irkutsk State University), V.M. Lipunov, A.Kuznetsov, I.Panchenko, E.Gorbovskoy, G.Antipov, P.Balanutsa, V.Senik, I.Panchenko, N. Tiurina, K.Zhirkov, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, Yu. Tselik(Lomonosov MSU, SAI, Moscow), R. Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D. Buckley (SAAO, South Africa), O.Ershova (Irkutsk State University), A. Sosnovskij (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain),
MASTER-Tunka robotic telescope (Global MASTER-Net [1-4], http://observ.pereplet.ru) started inspect (Lipunov et al. GCN 42837) of Fermi GRB 251125B ( GCN 42836) at MASTER-Tunka and MASTER-Kislovodsk.
MASTER auto-detection system discovered optical counterpart of this GRB
MASTER OT J155558.56+581224.1 with unfiltered m_OT=18.2 at 2025-11-25 20:34:32UT with typical for GRB light curve with decay. https://www.wis-tns.org/object/2025aevl
Real time updated cover map and discovered OT position is available here: https://master.sai.msu.ru/site/master2/observ.php?id=3051835
Observations and data analysis will be continued.
```
[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 #42840
Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Nathaniel R. Butler (ASU), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the MASTER OT J155558.56+581224.1 candidate afterglow (Gress et al., GCN Circ. 42838) of the Fermi GRB 251125B (Fermi GBM team., GCN Circ. 42836) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-11-26 01:36 to 02:39 UTC (median epoch 5.73 hours after the trigger) and obtained 48 minutes of simultaneous exposure in each of the r and z filters. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detect the optical candidate at preliminary magnitudes of:
```
r = 20.46 +/- 0.02
z = 20.17 +/- 0.05
```
The source has faded considerably since the observation of Gress et al. (GCN Circ 42838), which confirms that it is likely to be the afterglow of the GRB.
Further observations are planned.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular #42842
Jean-Grégoire Ducoin (CPPM), Noémie Globus (UNAM), N. A. Rakotondrainibe (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We reobserved the field of the MASTER OT J155558.56+581224.1 candidate afterglow (Gress et al., GCN Circ. 42838) of the Fermi GRB 251125B (Fermi GBM team., GCN Circ. 42836) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-11-26 11:44 to 13:00 UTC (from 15.34 to 16.60 hours after the trigger) and obtained 20 minutes of exposure in each of the g, r, and i filters and 60 minutes of simultaneous exposure in the z filter.
The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
Compared to our first epoch of observations (Globus et al., GCN Circ. 42840), the afterglow has continued to fade.
After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.013 mag (Schlafly & Finkbeiner 2011) and fitting a power-law with a no-dust extinction model to the griz-bands, we estimate a photometric redshift upper limit of z < 3. We therefore encourage follow-up observations.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular #42854
Yang-Zhao Ren, 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 251125B, at 2025-11-25T20:23:45.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #42836).
According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a pulse with a duration (T90) of 8.5 +2.0/-3.5 s.
The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251125B.png
The time-averaged spectrum from T0-0.8 s to T0+9.3 s is best fitted by a power law function. The power law index is -1.36 +0.06/-0.05. The event fluence (10-1000 keV) in this time interval is (2.86 +0.34/-0.31)E-06 erg/cm^2.
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).

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Jochen Greiner, last update: 27-Nov-2025 [Disclaimer]