Gamma-ray Burst 251006B = EP251006a

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 06 Oct 25 20:05:42 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      60
TRIGGER_NUM:     781473909
GRB_RA:           58.383d {+03h 53m 32s} (J2000),
                  58.700d {+03h 54m 48s} (current),
                  57.769d {+03h 51m 05s} (1950)
GRB_DEC:          -6.333d {-06d 19' 59"} (J2000),
                  -6.258d {-06d 15' 29"} (current),
                  -6.481d {-06d 28' 49"} (1950)
GRB_ERROR:       4.57 [deg radius, statistical plus systematic]
GRB_INTEN:       1816 [cnts/sec]
DATA_SIGNIF:     112.20 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        20954 TJD;   279 DOY;   25/10/06
GRB_TIME:        72304.04 SOD {20:05:04.04} UT
GRB_PHI:         138.00 [deg]
GRB_THETA:       115.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.39
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 0,1,1, 0,0,
SUN_POSTN:       192.72d {+12h 50m 53s}   -5.45d {-05d 27' 04"}
SUN_DIST:        132.63 [deg]   Sun_angle= 8.9 [hr] (West of Sun)
MOON_POSTN:        7.73d {+00h 30m 55s}   +5.34d {+05d 20' 13"}
MOON_DIST:        52.18 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      195.75,-42.07 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       54.58,-25.97 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 355.05,12.88 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 06 Oct 25 20:05:33 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      49
TRIGGER_NUM:     781473909
GRB_RA:           27.767d {+01h 51m 04s} (J2000),
                  28.035d {+01h 52m 08s} (current),
                  27.245d {+01h 48m 59s} (1950)
GRB_DEC:         -42.567d {-42d 34' 00"} (J2000),
                 -42.440d {-42d 26' 23"} (current),
                 -42.814d {-42d 48' 48"} (1950)
GRB_ERROR:       4.77 [deg radius, statistical plus systematic]
GRB_INTEN:       1283 [cnts/sec]
DATA_SIGNIF:     79.80 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20954 TJD;   279 DOY;   25/10/06
GRB_TIME:        72304.04 SOD {20:05:04.04} UT
GRB_PHI:         134.00 [deg]
GRB_THETA:        70.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.27
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      97%  GRB
2nd_MOST_LIKELY:   1%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 0,1,1, 0,0,
SUN_POSTN:       192.72d {+12h 50m 53s}   -5.45d {-05d 27' 03"}
SUN_DIST:        130.12 [deg]   Sun_angle= 11.0 [hr] (West of Sun)
MOON_POSTN:        7.73d {+00h 30m 55s}   +5.34d {+05d 20' 10"}
MOON_DIST:        51.22 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      268.61,-70.37 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:        4.01,-49.21 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 355.05,12.88 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 06 Oct 25 20:05:52 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      59
TRIGGER_NUM:     781473909
GRB_RA:           40.450d {+02h 41m 48s} (J2000),
                  40.776d {+02h 43m 06s} (current),
                  39.818d {+02h 39m 16s} (1950)
GRB_DEC:          -2.630d {-02d 37' 47"} (J2000),
                  -2.521d {-02d 31' 15"} (current),
                  -2.843d {-02d 50' 33"} (1950)
GRB_ERROR:       3.65 [deg radius, statistical only]
DATA_SIGNIF:     126.30 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        20954 TJD;   279 DOY;   25/10/06
GRB_TIME:        72304.04 SOD {20:05:04.04} UT
GRB_PHI:         155.00 [deg]
GRB_THETA:       106.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       192.72d {+12h 50m 53s}   -5.45d {-05d 27' 04"}
SUN_DIST:        150.86 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:        7.73d {+00h 30m 56s}   +5.34d {+05d 20' 16"}
MOON_DIST:        33.93 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      174.82,-53.99 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       37.17,-17.45 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_781473909.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
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:     Mon 06 Oct 25 20:06:19 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     781473909
GRB_RA:           46.390d {+03h 05m 34s} (J2000),
                  46.692d {+03h 06m 46s} (current),
                  45.803d {+03h 03m 13s} (1950)
GRB_DEC:         -14.910d {-14d 54' 35"} (J2000),
                 -14.811d {-14d 48' 40"} (current),
                 -15.103d {-15d 06' 10"} (1950)
GRB_ERROR:       3.00 [deg radius, statistical only]
DATA_SIGNIF:     57.80 [sigma]
DATA_INTERVAL:   3.072 [sec]
GRB_DATE:        20954 TJD;   279 DOY;   25/10/06
GRB_TIME:        72304.04 SOD {20:05:04.04} UT
GRB_PHI:         142.00 [deg]
GRB_THETA:       101.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       192.72d {+12h 50m 53s}   -5.45d {-05d 27' 04"}
SUN_DIST:        140.70 [deg]   Sun_angle= 9.7 [hr] (West of Sun)
MOON_POSTN:        7.74d {+00h 30m 57s}   +5.34d {+05d 20' 24"}
MOON_DIST:        43.55 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      198.41,-56.54 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       38.99,-30.96 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_781473909.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
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:     Mon 06 Oct 25 20:06:40 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     781473909
GRB_RA:           41.840d {+02h 47m 22s} (J2000),
                  42.164d {+02h 48m 39s} (current),
                  41.213d {+02h 44m 51s} (1950)
GRB_DEC:          -3.960d {-03d 57' 35"} (J2000),
                  -3.853d {-03d 51' 11"} (current),
                  -4.168d {-04d 10' 05"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
DATA_SIGNIF:     111.90 [sigma]
DATA_INTERVAL:   8.192 [sec]
GRB_DATE:        20954 TJD;   279 DOY;   25/10/06
GRB_TIME:        72304.04 SOD {20:05:04.04} UT
GRB_PHI:         153.00 [deg]
GRB_THETA:       106.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       192.72d {+12h 50m 53s}   -5.45d {-05d 27' 04"}
SUN_DIST:        149.16 [deg]   Sun_angle= 10.0 [hr] (West of Sun)
MOON_POSTN:        7.74d {+00h 30m 58s}   +5.34d {+05d 20' 30"}
MOON_DIST:        35.59 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      178.09,-53.92 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       38.11,-19.15 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_781473909.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
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:     Mon 06 Oct 25 20:14:24 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     781473909
GRB_RA:           40.460d {+02h 41m 50s} (J2000),
                  40.784d {+02h 43m 08s} (current),
                  39.832d {+02h 39m 20s} (1950)
GRB_DEC:          -3.990d {-03d 59' 23"} (J2000),
                  -3.881d {-03d 52' 51"} (current),
                  -4.203d {-04d 12' 09"} (1950)
GRB_ERROR:       1.20 [deg radius, statistical only]
GRB_DATE:        20954 TJD;   279 DOY;   25/10/06
GRB_TIME:        72304.04 SOD {20:05:04.04} UT
GRB_PHI:         154.00 [deg]
GRB_THETA:       105.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       192.73d {+12h 50m 54s}   -5.45d {-05d 27' 12"}
SUN_DIST:        150.46 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:        7.81d {+00h 31m 14s}   +5.38d {+05d 22' 44"}
MOON_DIST:        34.21 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      176.50,-54.94 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       36.72,-18.74 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_locplot_all_bn251006837.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:        Bright hard burst in the GBM.  
COMMENTS:        This is likely a Long GRB.

GCN Circular #42131
The Fermi GBM team reports the detection of a likely LONG GRB
At 20:05:04 UT on 6 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251006B (trigger 781473909.040226 / 251006837).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 40.5, Dec = -4.0 (J2000 degrees, equivalent to J2000 02h 42m, -4d 00'), with a statistical uncertainty of 1.2 degrees.
The angle from the Fermi LAT boresight is 105.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_skymap_all_bn251006837.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/bn251006837/quicklook/glg_healpix_all_bn251006837.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/quicklook/glg_lc_medres34_bn251006837.gif
GCN Circular #42132
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 781473909 at 20:05:04 on 06 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) = 41.9 deg
Decl.(2000.0) = -6.8 deg
```
The 1 sigma statistical error radius is 3.4 deg. We estimate an additional systematic error of 1 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB251006837/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251006837/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251006837/json

GCN Circular #42133
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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 251006B ( Fermi GBM team, GCN 42131) errorbox 532 sec after notice time and 575 sec after trigger time at 2025-10-06 20:14:39 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 63 deg. The sun altitude is -41.2 deg.
MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251006B errorbox 545 sec after notice time and 587 sec after trigger time at 2025-10-06 20:14:51 UT, with upper limit up to 14.9 mag. The observations began at zenith distance = 59 deg. The sun altitude is -51.1 deg.
MASTER-Tunka robotic telescope located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 251006B errorbox 563 sec after notice time and 606 sec after trigger time at 2025-10-06 20:15:10 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 58 deg. The sun altitude is -28.3 deg.
The galactic latitude b = -54 deg., longitude l = 177 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3008721
We obtain a following upper limits.

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

     605 | 2025-10-06 20:14:39 |         MASTER-SAAO | (02h 39m 49.30s , -04d 20m 36.1s) |   C |    60 | 17.6 |        
     665 | 2025-10-06 20:14:39 |         MASTER-SAAO | (02h 39m 49.30s , -04d 20m 36.1s) |   C |   180 | 18.4 |  Coadd 
     605 | 2025-10-06 20:14:39 |         MASTER-SAAO | (02h 37m 57.07s , -04d 05m 19.3s) |   C |    60 | 17.5 |        
     665 | 2025-10-06 20:14:39 |         MASTER-SAAO | (02h 37m 57.07s , -04d 05m 19.3s) |   C |   180 | 18.2 |  Coadd 
     648 | 2025-10-06 20:14:51 |   MASTER-Kislovodsk | (02h 39m 53.89s , -04d 03m 53.7s) |  P| |   120 | 13.3 |        
     648 | 2025-10-06 20:14:51 |   MASTER-Kislovodsk | (02h 39m 44.13s , -03d 40m 31.4s) |  P- |   120 | 14.9 |        
     609 | 2025-10-06 20:15:10 |        MASTER-Tunka | (02h 42m 02.24s , -03d 51m 31.9s) |   C |     5 | 16.2 |        
     614 | 2025-10-06 20:15:10 |        MASTER-Tunka | (02h 42m 02.24s , -03d 51m 31.9s) |   C |    15 | 16.7 |  Coadd 
     609 | 2025-10-06 20:15:10 |             MASTER- | (02h 41m 39.21s , -03d 46m 29.9s) |   C |     5 | 15.9 |        
     618 | 2025-10-06 20:15:18 |             MASTER- | (02h 41m 39.20s , -03d 46m 30.4s) |   C |     5 | 15.8 |        
     618 | 2025-10-06 20:15:18 |        MASTER-Tunka | (02h 42m 02.24s , -03d 51m 32.3s) |   C |     5 | 16.1 |        
     627 | 2025-10-06 20:15:27 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 32.7s) |   C |     5 | 16.1 |        
     627 | 2025-10-06 20:15:28 |             MASTER- | (02h 41m 39.22s , -03d 46m 30.9s) |   C |     5 | 15.9 |        
     639 | 2025-10-06 20:15:40 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 33.0s) |   C |     5 | 16.1 |        
     644 | 2025-10-06 20:15:40 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 32.9s) |   C |    15 | 16.6 |  Coadd 
     639 | 2025-10-06 20:15:40 |             MASTER- | (02h 41m 39.21s , -03d 46m 31.1s) |   C |     5 | 15.9 |        
     652 | 2025-10-06 20:15:52 |        MASTER-Tunka | (02h 42m 02.24s , -03d 51m 33.2s) |   C |     5 | 16.0 |        
     652 | 2025-10-06 20:15:52 |             MASTER- | (02h 41m 39.21s , -03d 46m 31.6s) |   C |     5 | 15.8 |        
     684 | 2025-10-06 20:15:58 |         MASTER-SAAO | (02h 39m 49.23s , -04d 20m 36.1s) |   C |    60 | 17.6 |        
     684 | 2025-10-06 20:15:58 |         MASTER-SAAO | (02h 37m 56.96s , -04d 05m 19.4s) |   C |    60 | 17.6 |        
     661 | 2025-10-06 20:16:01 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 33.4s) |   C |     5 | 16.0 |        
     661 | 2025-10-06 20:16:01 |             MASTER- | (02h 41m 39.22s , -03d 46m 31.7s) |   C |     5 | 15.9 |        
     669 | 2025-10-06 20:16:10 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 33.8s) |   C |     5 | 16.0 |        
     674 | 2025-10-06 20:16:10 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 33.8s) |   C |    15 | 16.6 |  Coadd 
     669 | 2025-10-06 20:16:10 |             MASTER- | (02h 41m 39.22s , -03d 46m 32.1s) |   C |     5 | 15.8 |        
     678 | 2025-10-06 20:16:18 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 34.2s) |   C |     5 | 16.1 |        
     678 | 2025-10-06 20:16:18 |             MASTER- | (02h 41m 39.22s , -03d 46m 32.5s) |   C |     5 | 15.8 |        
     686 | 2025-10-06 20:16:27 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 34.3s) |   C |     5 | 16.0 |        
     686 | 2025-10-06 20:16:27 |             MASTER- | (02h 41m 39.23s , -03d 46m 32.7s) |   C |     5 | 15.9 |        
     715 | 2025-10-06 20:16:55 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 35.5s) |   C |     5 | 16.1 |        
     720 | 2025-10-06 20:16:55 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 35.4s) |   C |    15 | 16.5 |  Coadd 
     715 | 2025-10-06 20:16:55 |             MASTER- | (02h 41m 39.23s , -03d 46m 33.7s) |   C |     5 | 15.9 |        
     723 | 2025-10-06 20:17:03 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 35.7s) |   C |     5 | 16.0 |        
     723 | 2025-10-06 20:17:03 |             MASTER- | (02h 41m 39.22s , -03d 46m 34.0s) |   C |     5 | 15.9 |        
     787 | 2025-10-06 20:17:11 |   MASTER-Kislovodsk | (02h 39m 44.20s , -03d 40m 29.1s) |  P- |   120 | 14.3 |        
     787 | 2025-10-06 20:17:11 |   MASTER-Kislovodsk | (02h 39m 55.26s , -04d 03m 41.8s) |  P| |   120 | 13.6 |        
     732 | 2025-10-06 20:17:12 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 35.8s) |   C |     5 | 16.1 |        
     732 | 2025-10-06 20:17:13 |             MASTER- | (02h 41m 39.22s , -03d 46m 34.3s) |   C |     5 | 15.9 |        
     763 | 2025-10-06 20:17:17 |         MASTER-SAAO | (02h 39m 49.17s , -04d 20m 36.1s) |   C |    60 | 17.6 |        
     763 | 2025-10-06 20:17:17 |         MASTER-SAAO | (02h 37m 56.87s , -04d 05m 19.6s) |   C |    60 | 17.4 |        
     740 | 2025-10-06 20:17:21 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 36.1s) |   C |     5 | 16.0 |        
     745 | 2025-10-06 20:17:21 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 36.1s) |   C |    15 | 16.6 |  Coadd 
     740 | 2025-10-06 20:17:21 |             MASTER- | (02h 41m 39.22s , -03d 46m 34.5s) |   C |     5 | 15.8 |        
     749 | 2025-10-06 20:17:29 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 36.3s) |   C |     5 | 16.1 |        
     749 | 2025-10-06 20:17:29 |             MASTER- | (02h 41m 39.21s , -03d 46m 34.8s) |   C |     5 | 15.8 |        
     757 | 2025-10-06 20:17:38 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 36.4s) |   C |     5 | 16.1 |        
     757 | 2025-10-06 20:17:38 |             MASTER- | (02h 41m 39.21s , -03d 46m 35.1s) |   C |     5 | 15.8 |        
     766 | 2025-10-06 20:17:46 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 36.9s) |   C |     5 | 16.0 |        
     771 | 2025-10-06 20:17:46 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 36.9s) |   C |    15 | 16.7 |  Coadd 
     766 | 2025-10-06 20:17:46 |             MASTER- | (02h 41m 39.21s , -03d 46m 35.4s) |   C |     5 | 15.8 |        
     774 | 2025-10-06 20:17:54 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 37.2s) |   C |     5 | 16.1 |        
     774 | 2025-10-06 20:17:54 |             MASTER- | (02h 41m 39.21s , -03d 46m 35.7s) |   C |     5 | 15.9 |        
     782 | 2025-10-06 20:18:03 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 37.2s) |   C |     5 | 16.1 |        
     782 | 2025-10-06 20:18:03 |             MASTER- | (02h 41m 39.21s , -03d 46m 36.0s) |   C |     5 | 15.9 |        
     814 | 2025-10-06 20:18:35 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 38.1s) |   C |     5 | 16.1 |        
     819 | 2025-10-06 20:18:35 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 38.2s) |   C |    15 | 16.7 |  Coadd 
     814 | 2025-10-06 20:18:35 |             MASTER- | (02h 41m 39.20s , -03d 46m 37.1s) |   C |     5 | 16.0 |        
     842 | 2025-10-06 20:18:36 |         MASTER-SAAO | (02h 39m 49.10s , -04d 20m 36.0s) |   C |    60 | 17.6 |        
     842 | 2025-10-06 20:18:36 |         MASTER-SAAO | (02h 37m 56.77s , -04d 05m 19.7s) |   C |    60 | 17.6 |        
     838 | 2025-10-06 20:18:59 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 38.9s) |   C |     5 | 16.0 |        
     838 | 2025-10-06 20:18:59 |             MASTER- | (02h 41m 39.22s , -03d 46m 38.0s) |   C |     5 | 15.9 |        
     847 | 2025-10-06 20:19:07 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 39.2s) |   C |     5 | 16.0 |        
     847 | 2025-10-06 20:19:07 |             MASTER- | (02h 41m 39.20s , -03d 46m 38.2s) |   C |     5 | 15.9 |        
     856 | 2025-10-06 20:19:17 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 39.5s) |   C |     5 | 16.1 |        
     861 | 2025-10-06 20:19:17 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 39.5s) |   C |    15 | 16.5 |  Coadd 
     856 | 2025-10-06 20:19:17 |             MASTER- | (02h 41m 39.22s , -03d 46m 38.6s) |   C |     5 | 15.9 |        
     865 | 2025-10-06 20:19:25 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 39.7s) |   C |     5 | 16.2 |        
     865 | 2025-10-06 20:19:25 |             MASTER- | (02h 41m 39.21s , -03d 46m 38.8s) |   C |     5 | 15.9 |        
     927 | 2025-10-06 20:19:31 |   MASTER-Kislovodsk | (02h 39m 55.35s , -04d 03m 40.8s) |  P| |   120 | 13.6 |        
     927 | 2025-10-06 20:19:31 |   MASTER-Kislovodsk | (02h 39m 44.35s , -03d 40m 26.8s) |  P- |   120 | 14.5 |        
     874 | 2025-10-06 20:19:34 |             MASTER- | (02h 41m 39.21s , -03d 46m 39.1s) |   C |     5 | 16.0 |        
     874 | 2025-10-06 20:19:34 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.0s) |   C |     5 | 16.2 |        
     883 | 2025-10-06 20:19:43 |             MASTER- | (02h 41m 39.21s , -03d 46m 39.1s) |   C |     5 | 16.0 |        
     883 | 2025-10-06 20:19:43 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.1s) |   C |     5 | 16.1 |        
     888 | 2025-10-06 20:19:43 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.1s) |   C |    15 | 16.7 |  Coadd 
     892 | 2025-10-06 20:19:52 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.3s) |   C |     5 | 16.1 |        
     892 | 2025-10-06 20:19:52 |             MASTER- | (02h 41m 39.21s , -03d 46m 39.4s) |   C |     5 | 16.0 |        
     900 | 2025-10-06 20:20:01 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.5s) |   C |     5 | 16.1 |        
     900 | 2025-10-06 20:20:01 |             MASTER- | (02h 41m 39.22s , -03d 46m 39.8s) |   C |     5 | 15.9 |        
     928 | 2025-10-06 20:20:29 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 41.5s) |   C |     5 | 16.2 |        
     933 | 2025-10-06 20:20:29 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 41.5s) |   C |    15 | 16.7 |  Coadd 
     928 | 2025-10-06 20:20:29 |             MASTER- | (02h 41m 39.20s , -03d 46m 40.5s) |   C |     5 | 15.9 |        
     936 | 2025-10-06 20:20:37 |        MASTER-Tunka | (02h 42m 02.24s , -03d 51m 41.8s) |   C |     5 | 16.2 |        
     937 | 2025-10-06 20:20:37 |             MASTER- | (02h 41m 39.20s , -03d 46m 40.8s) |   C |     5 | 15.9 |        
     946 | 2025-10-06 20:20:47 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 42.0s) |   C |     5 | 16.2 |        
     946 | 2025-10-06 20:20:47 |             MASTER- | (02h 41m 39.22s , -03d 46m 41.0s) |   C |     5 | 16.0 |        
     956 | 2025-10-06 20:20:57 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 42.3s) |   C |     5 | 16.1 |        
     961 | 2025-10-06 20:20:57 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 42.3s) |   C |    15 | 16.7 |  Coadd 
     956 | 2025-10-06 20:20:57 |             MASTER- | (02h 41m 39.21s , -03d 46m 41.3s) |   C |     5 | 16.0 |        
     965 | 2025-10-06 20:21:05 |             MASTER- | (02h 41m 39.22s , -03d 46m 41.6s) |   C |     5 | 16.0 |        
     965 | 2025-10-06 20:21:05 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 42.5s) |   C |     5 | 16.1 |        
     973 | 2025-10-06 20:21:14 |        MASTER-Tunka | (02h 42m 02.28s , -03d 51m 42.6s) |   C |     5 | 16.1 |        
     973 | 2025-10-06 20:21:14 |             MASTER- | (02h 41m 39.23s , -03d 46m 41.8s) |   C |     5 | 16.0 |        
     982 | 2025-10-06 20:21:22 |        MASTER-Tunka | (02h 42m 02.28s , -03d 51m 42.9s) |   C |     5 | 16.1 |        
     987 | 2025-10-06 20:21:22 |        MASTER-Tunka | (02h 42m 02.28s , -03d 51m 43.0s) |   C |    15 | 16.7 |  Coadd 
     982 | 2025-10-06 20:21:22 |             MASTER- | (02h 41m 39.23s , -03d 46m 41.9s) |   C |     5 | 16.0 |        
     990 | 2025-10-06 20:21:31 |             MASTER- | (02h 41m 39.23s , -03d 46m 42.3s) |   C |     5 | 15.9 |        
     990 | 2025-10-06 20:21:31 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 43.2s) |   C |     5 | 16.1 |        
     999 | 2025-10-06 20:21:40 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 43.6s) |   C |     5 | 16.1 |        
     999 | 2025-10-06 20:21:40 |             MASTER- | (02h 41m 39.23s , -03d 46m 42.6s) |   C |     5 | 15.9 |        
    1008 | 2025-10-06 20:21:48 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 43.8s) |   C |     5 | 16.1 |        
    1013 | 2025-10-06 20:21:48 |        MASTER-Tunka | (02h 42m 02.28s , -03d 51m 43.8s) |   C |    15 | 16.7 |  Coadd 
    1008 | 2025-10-06 20:21:48 |             MASTER- | (02h 41m 39.23s , -03d 46m 42.9s) |   C |     5 | 16.0 |        
    1067 | 2025-10-06 20:21:50 |   MASTER-Kislovodsk | (02h 39m 44.50s , -03d 40m 23.0s) |  P- |   120 | 14.3 |        
    1067 | 2025-10-06 20:21:51 |   MASTER-Kislovodsk | (02h 39m 55.40s , -04d 03m 37.6s) |  P| |   120 | 13.7 |        
    1016 | 2025-10-06 20:21:57 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.0s) |   C |     5 | 16.2 |        
    1016 | 2025-10-06 20:21:57 |             MASTER- | (02h 41m 39.22s , -03d 46m 43.0s) |   C |     5 | 16.0 |        
    1024 | 2025-10-06 20:22:05 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.3s) |   C |     5 | 16.1 |        
    1024 | 2025-10-06 20:22:05 |             MASTER- | (02h 41m 39.21s , -03d 46m 43.1s) |   C |     5 | 16.0 |        
    1033 | 2025-10-06 20:22:14 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.6s) |   C |     5 | 16.1 |        
    1038 | 2025-10-06 20:22:14 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 44.5s) |   C |    15 | 16.6 |  Coadd 
    1033 | 2025-10-06 20:22:14 |             MASTER- | (02h 41m 39.21s , -03d 46m 43.8s) |   C |     5 | 16.0 |        
    1042 | 2025-10-06 20:22:22 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.7s) |   C |     5 | 16.0 |        
    1042 | 2025-10-06 20:22:22 |             MASTER- | (02h 41m 39.20s , -03d 46m 43.9s) |   C |     5 | 16.0 |        
    1050 | 2025-10-06 20:22:31 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.9s) |   C |     5 | 16.1 |        
    1050 | 2025-10-06 20:22:31 |             MASTER- | (02h 41m 39.20s , -03d 46m 44.3s) |   C |     5 | 15.9 |        
    1059 | 2025-10-06 20:22:39 |             MASTER- | (02h 41m 39.20s , -03d 46m 44.5s) |   C |     5 | 16.0 |        
    1059 | 2025-10-06 20:22:39 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 45.1s) |   C |     5 | 16.1 |        
    1064 | 2025-10-06 20:22:39 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 45.2s) |   C |    15 | 16.6 |  Coadd 
    1067 | 2025-10-06 20:22:48 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 45.5s) |   C |     5 | 16.1 |        
    1068 | 2025-10-06 20:22:48 |             MASTER- | (02h 41m 39.19s , -03d 46m 44.8s) |   C |     5 | 15.9 |        
    1076 | 2025-10-06 20:22:57 |             MASTER- | (02h 41m 39.18s , -03d 46m 45.2s) |   C |     5 | 15.9 |        
    1076 | 2025-10-06 20:22:57 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 45.6s) |   C |     5 | 16.1 |        
    1085 | 2025-10-06 20:23:06 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 45.8s) |   C |     5 | 16.1 |        
    1090 | 2025-10-06 20:23:06 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 45.8s) |   C |    15 | 16.6 |  Coadd 
    1085 | 2025-10-06 20:23:06 |             MASTER- | (02h 41m 39.20s , -03d 46m 45.4s) |   C |     5 | 15.9 |        
    1094 | 2025-10-06 20:23:14 |             MASTER- | (02h 41m 39.19s , -03d 46m 45.8s) |   C |     5 | 15.9 |        
    1094 | 2025-10-06 20:23:14 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 46.2s) |   C |     5 | 16.0 |        
    1102 | 2025-10-06 20:23:23 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 46.5s) |   C |     5 | 16.1 |        
    1102 | 2025-10-06 20:23:23 |             MASTER- | (02h 41m 39.18s , -03d 46m 46.1s) |   C |     5 | 15.9 |        
    1111 | 2025-10-06 20:23:31 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 46.6s) |   C |     5 | 16.1 |        
    1116 | 2025-10-06 20:23:31 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 46.6s) |   C |    15 | 16.6 |  Coadd 
    1111 | 2025-10-06 20:23:31 |             MASTER- | (02h 41m 39.18s , -03d 46m 46.1s) |   C |     5 | 16.0 |        
    1119 | 2025-10-06 20:23:40 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 46.7s) |   C |     5 | 16.1 |        
    1120 | 2025-10-06 20:23:40 |             MASTER- | (02h 41m 39.19s , -03d 46m 46.4s) |   C |     5 | 15.9 |        
    1128 | 2025-10-06 20:23:48 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 46.9s) |   C |     5 | 16.1 |        
    1128 | 2025-10-06 20:23:48 |             MASTER- | (02h 41m 39.19s , -03d 46m 46.6s) |   C |     5 | 15.9 |        
    1136 | 2025-10-06 20:23:57 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.1s) |   C |     5 | 16.1 |        
    1141 | 2025-10-06 20:23:57 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.1s) |   C |    15 | 16.6 |  Coadd 
    1136 | 2025-10-06 20:23:57 |             MASTER- | (02h 41m 39.18s , -03d 46m 46.7s) |   C |     5 | 15.9 |        
    1145 | 2025-10-06 20:24:05 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 47.4s) |   C |     5 | 16.1 |        
    1145 | 2025-10-06 20:24:05 |             MASTER- | (02h 41m 39.18s , -03d 46m 46.9s) |   C |     5 | 16.0 |        
    1207 | 2025-10-06 20:24:10 |   MASTER-Kislovodsk | (02h 39m 44.60s , -03d 40m 18.3s) |  P- |   120 | 14.3 |        
    1207 | 2025-10-06 20:24:10 |   MASTER-Kislovodsk | (02h 39m 55.41s , -04d 03m 34.1s) |  P| |   120 | 13.7 |        
    1160 | 2025-10-06 20:24:20 |             MASTER- | (02h 41m 39.19s , -03d 46m 47.2s) |   C |     5 | 15.9 |        
    1160 | 2025-10-06 20:24:20 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.7s) |   C |     5 | 16.1 |        
    1168 | 2025-10-06 20:24:29 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.9s) |   C |     5 | 16.1 |        
    1168 | 2025-10-06 20:24:29 |             MASTER- | (02h 41m 39.19s , -03d 46m 47.4s) |   C |     5 | 15.9 |        
    1177 | 2025-10-06 20:24:37 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 48.1s) |   C |     5 | 16.1 |        
    1177 | 2025-10-06 20:24:37 |             MASTER- | (02h 41m 39.20s , -03d 46m 47.7s) |   C |     5 | 15.8 |        
    1185 | 2025-10-06 20:24:46 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 48.5s) |   C |     5 | 16.2 |        
    1185 | 2025-10-06 20:24:46 |             MASTER- | (02h 41m 39.19s , -03d 46m 48.0s) |   C |     5 | 15.9 |        
    1194 | 2025-10-06 20:24:54 |        MASTER-Tunka | (02h 42m 02.25s , -03d 51m 48.6s) |   C |     5 | 16.2 |        
    1194 | 2025-10-06 20:24:54 |             MASTER- | (02h 41m 39.20s , -03d 46m 48.2s) |   C |     5 | 15.9 |        
    1203 | 2025-10-06 20:25:03 |             MASTER- | (02h 41m 39.21s , -03d 46m 48.2s) |   C |     5 | 15.9 |        
    1203 | 2025-10-06 20:25:03 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 48.7s) |   C |     5 | 16.1 |        
    1214 | 2025-10-06 20:25:14 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 49.0s) |   C |     5 | 16.1 |        
    1214 | 2025-10-06 20:25:14 |             MASTER- | (02h 41m 39.20s , -03d 46m 48.7s) |   C |     5 | 16.0 |        
    1222 | 2025-10-06 20:25:23 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 49.3s) |   C |     5 | 16.2 |        
    1222 | 2025-10-06 20:25:23 |             MASTER- | (02h 41m 39.21s , -03d 46m 49.0s) |   C |     5 | 15.9 |        
    1231 | 2025-10-06 20:25:31 |        MASTER-Tunka | (02h 42m 02.27s , -03d 51m 49.8s) |   C |     5 | 16.1 |        
    1231 | 2025-10-06 20:25:31 |             MASTER- | (02h 41m 39.21s , -03d 46m 49.3s) |   C |     5 | 15.9 |        
    1270 | 2025-10-06 20:26:10 |        MASTER-Tunka | (02h 42m 02.26s , -03d 51m 50.6s) |   C |     5 | 16.1 |        
    1270 | 2025-10-06 20:26:10 |             MASTER- | (02h 41m 39.20s , -03d 46m 50.5s) |   C |     5 | 16.0 |        
    1347 | 2025-10-06 20:26:30 |   MASTER-Kislovodsk | (02h 39m 44.69s , -03d 40m 13.3s) |  P- |   120 | 14.3 |        
    1347 | 2025-10-06 20:26:30 |   MASTER-Kislovodsk | (02h 39m 55.49s , -04d 03m 29.7s) |  P| |   120 | 13.7 |        
    1487 | 2025-10-06 20:28:50 |   MASTER-Kislovodsk | (02h 39m 44.76s , -03d 40m 09.2s) |  P- |   120 | 14.3 |        
    1487 | 2025-10-06 20:28:50 |   MASTER-Kislovodsk | (02h 39m 55.53s , -04d 03m 26.9s) |  P| |   120 | 13.8 |        
    1626 | 2025-10-06 20:31:10 |   MASTER-Kislovodsk | (02h 39m 44.78s , -03d 40m 03.9s) |  P- |   120 | 14.3 |        
    1626 | 2025-10-06 20:31:10 |   MASTER-Kislovodsk | (02h 39m 55.58s , -04d 03m 23.2s) |  P| |   120 | 13.5 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN Circular #42137
Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient, designated EP251006a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at T0 = 2025-10-06T20:05:04 (UTC). The position of the source is R.A. = 40.505 deg, DEC = -5.989 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 251006B (GCN 42131, GCN 42132).
The analysis of the WXT data shows that the event lasted for about 100 seconds with a two-pulse main emission within T0 - T0 + 10 s followed by a much weaker tail. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.28 (-0.60/+0.64). The derived average unabsorbed 0.5-4 keV flux is 1.61 (-0.72/+0.50) x 10^-10 erg/s/cm^2. The peak flux is around 9.09 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.09 (-0.76/+0.84).
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular #42138
Jean-Grégoire Ducoin (CPPM), Diego López-Cámara (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (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):
We imaged the field of the Fermi GRB 251006B (Fermi GBM Team, GCN Circ. 42131, Preis et al., GCN Circ 42132, Yin et al., GCN Circ. 42137) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-07T06:00:50 to 06:19:48 UTC (from 9.93 to 10.25 hours after the trigger) and obtained 13 minutes of simultaneous exposure in the r and z filters.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the EP-WXT source position (Yin et al., GCN Circ. 42137) down to the following 5-sigma limit:
```
r > 21.0
z > 20.6
```
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 #42139
SVOM/GRM team: Yue Wang, Chen-Wei Wang, Wen-Jun Tan, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Feliu Lacreu (IAP), Olivier GODET (IRAP), Frédéric Piron (LUPM)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 251006B (SVOM trigger reference: sb25100602) at 2025-10-06T20:05:08.000 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42131).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two pulses with a T90 of 6.2 +0.2/-0.1 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251006B.png
In addition, the position of this burst, as determined by Fermi/GBM (RA = 40.5, Dec = -4.0, GCN #42131), is located at about 40.5 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view. But ECLAIRs was not collecting data at the time of this burst.
With this localization, the time-averaged spectrum from T0-5 to T0+5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.76 +0.03/-0.03 and the cutoff energy, parameterized as Epeak, is 433 +27/-24 keV. The event fluence (10-1000 keV) in this time interval is (2.02 +0.05/-0.05)E-05 erg/cm^2.
The localization of GRB 251006B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251006B_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/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang@ihep.ac.cn)
GCN Circular #42140
Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of GRB 251006B/EP251006a (GCN 42131, GCN 42137, GCN 42139) at 2025-10-07T06:50:56 (UTC), about 11 hours after the WXT detection, with an exposure time of 2.7 ks. The source was also followed by several optical telescopes (GCN 42133, GCN 42138). Two uncatalogued sources were detected within the WXT error circle. Preliminary analyses on these sources are automatically conducted, and the details are listed as follows.
Source 1: EPF_J024205.3-055701 RA (J2000): 40.5219 Dec (J2000): -5.9501 Flux: 3.25 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 9.45 x 10^-14 erg/s/cm^2 (1 sigma) Source 2: EPF_J024204.7-060206
```
RA (J2000): 40.5194
Dec (J2000): -6.0350
Flux: 3.52 x 10^-12 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 4.30 x 10^-13 erg/s/cm^2 (1 sigma)
```
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular #42141
L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. Q. Wang, K. Liu (GXU) report on behalf of the SVOM/VT team.
SVOM/VT conducted ToO follow-up observations of GRB 251006B / EP251006a (Fermi GBM Team, GCN 42131; Yin et al. GCN 42137; Wang et al., GCN 42139). The observation started on 2025-10-07T09:37:56 UT (i.e. 13.56 hour after Fermi trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
Within the error box of EP-FXT source 2 (Yin et al., GCN 42140), an uncatalogued source was detected, compared to the Legacy survey. The position is at R.A., Dec. = 40.518487, -6.034955 degrees, equivalent to:
```
R.A. (J2000) =  02:42:04.43
Dec. (J2000) =  -06:02:05.8
```
with an uncertainty of 0.5 arcsec.
The magnitudes of the candidate are given below:
```
  Mid_time        Band        Exposure Time       Magnitude (AB)
13.5672  hour     VT_B          41*70 sec         22.37+/-0.11 mag                      
13.5672  hour     VT_R          39*70 sec         22.12+/-0.12 mag 
```
Our photometry is in AB magnitude and not corrected for Galactic extinction.
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.
GCN Circular #42155
Chen-Wei Wang, Yue Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2025-10-06T20:05:04.350 (T0), Insight-HXMT/HE detected the burst GRB 251006B, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42131), EP (Yin et al., GCN#42137) and SVOM/GRM (Wang et al., GCN#42139).
The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 4.6 +1.1/-0.8 s. The 1s peak rate, measured from T0-0.1 s, is 3694 cnts/sec. The total counts from this burst is 5990 counts.
The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251006B.png
All measurements above are made with the CsI detectors 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.
GCN Circular #42166
Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a second follow-up observation of GRB 251006B/EP251006a (GCN 42131, GCN 42137, GCN 42139, GCN 42155) at 2025-10-07T18:08:41 (UTC), about 22 hours after the WXT detection, with an exposure time of 4.9 ks. The source was also followed by several optical telescopes (GCN 42133, GCN 42138, GCN 42141). Two uncatalogued sources were detected within the WXT error circle (GCN 42140), of which Source 2 has faded with an unabsorbed flux of 3.37 x 10^-13 erg/s/cm^2 (22 hours) from the first observation at about 3.52 x 10^-12 erg/s/cm^2 (11 hours) in 0.5-10 keV. The position of Source 2 is R.A. = 40.5195 deg, DEC = -6.0346 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the SVOM/VT optical candidate (GCN 42141), and is therefore likely the GRB afterglow.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular #42169
Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 20:05:04.04 UT on 06 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251006B (trigger 781473909/251006837), which was also detected by Einstein Probe (Yin et al. 2025, GCN 42137) and SVOM/GRM (Wang et al. 2025, GCN 42139). The Fermi GBM on-ground location is consistent with the EP position.
The angle from the Fermi LAT boresight is 104 degrees.
The GBM light curve consists of one bright emission with a weaker secondary peak with total duration (T90) of about 5.9 s (50-300 keV). The time-averaged spectrum from T0-2.0 to T0+7.2 s is best fit by a Band function with Epeak = 330 +/- 14 keV, alpha = -0.61 +/- 0.03, and beta = -2.4 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is (2.06 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.38 s in the 10-1000 keV band is 26.2 +/- 0.4 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 #42176
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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251006a ( EP Team et al., GCN 42137) errorbox 196 sec after trigger time at 2025-10-07 18:11:57 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 79 deg. The sun altitude is -37.7 deg.
MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the EP251006a errorbox 3541 sec after trigger time at 2025-10-07 19:07:42 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 75 deg. The sun altitude is -29.6 deg.
MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP251006a errorbox 40526 sec after trigger time at 2025-10-08 05:24:07 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 27 deg. The sun altitude is -50.3 deg.
The galactic latitude b = -56 deg., longitude l = 180 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3010044
We obtain a following upper limits.

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

     226 | 2025-10-07 18:11:57 |   MASTER-Kislovodsk | (02h 39m 56.00s , -06d 09m 59.8s) |   C |    60 | 14.6 |        
     226 | 2025-10-07 18:11:57 |   MASTER-Kislovodsk | (02h 39m 54.59s , -05d 47m 17.6s) |   C |    60 | 15.4 |        
     508 | 2025-10-07 18:16:38 |   MASTER-Kislovodsk | (02h 39m 49.79s , -05d 48m 02.3s) |   C |    60 | 15.5 |        
     508 | 2025-10-07 18:16:38 |   MASTER-Kislovodsk | (02h 39m 51.52s , -06d 10m 40.5s) |   C |    60 | 14.6 |        
     823 | 2025-10-07 18:21:54 |   MASTER-Kislovodsk | (02h 39m 48.84s , -05d 45m 43.0s) |   C |    60 | 15.5 |        
     883 | 2025-10-07 18:21:54 |   MASTER-Kislovodsk | (02h 39m 48.82s , -05d 45m 42.9s) |   C |   180 | 16.2 |  Coadd 
     823 | 2025-10-07 18:21:54 |   MASTER-Kislovodsk | (02h 39m 51.15s , -06d 08m 22.6s) |   C |    60 | 14.9 |        
     903 | 2025-10-07 18:23:14 |   MASTER-Kislovodsk | (02h 39m 51.14s , -06d 10m 23.8s) |   C |    60 | 14.9 |        
     903 | 2025-10-07 18:23:14 |   MASTER-Kislovodsk | (02h 39m 48.76s , -05d 47m 43.3s) |   C |    60 | 15.5 |        
    1250 | 2025-10-07 18:29:00 |   MASTER-Kislovodsk | (02h 39m 55.32s , -05d 47m 15.7s) |   C |    60 | 15.6 |        
    1250 | 2025-10-07 18:29:00 |   MASTER-Kislovodsk | (02h 39m 57.09s , -06d 10m 09.1s) |   C |    60 | 14.6 |        
    3572 | 2025-10-07 19:07:42 |         MASTER-SAAO | (02h 38m 20.93s , -06d 05m 34.6s) |   C |    60 | 17.0 |        
    3572 | 2025-10-07 19:07:42 |         MASTER-SAAO | (02h 40m 07.46s , -06d 21m 24.6s) |   C |    60 | 13.5 |        
   40556 | 2025-10-08 05:24:07 |         MASTER-OAFA | (02h 38m 04.24s , -06d 11m 37.8s) |   C |    60 | 18.6 |        
   40631 | 2025-10-08 05:25:22 |         MASTER-OAFA | (02h 38m 03.16s , -06d 10m 39.1s) |   C |    60 | 18.6 |        
   40868 | 2025-10-08 05:29:18 |         MASTER-OAFA | (02h 38m 02.78s , -06d 12m 42.4s) |   C |    60 | 18.7 |        
   40945 | 2025-10-08 05:30:36 |         MASTER-OAFA | (02h 46m 13.59s , -06d 12m 15.1s) |   C |    60 | 18.7 |        
   41021 | 2025-10-08 05:31:52 |         MASTER-OAFA | (02h 46m 09.43s , -06d 10m 39.7s) |   C |    60 | 18.6 |        
   41099 | 2025-10-08 05:33:10 |         MASTER-OAFA | (02h 46m 09.23s , -06d 12m 05.1s) |   C |    60 | 18.6 |        
   43486 | 2025-10-08 06:12:57 |         MASTER-OAFA | (02h 46m 25.97s , -05d 55m 21.1s) |   C |    60 | 18.7 |        
   43564 | 2025-10-08 06:14:15 |         MASTER-OAFA | (02h 46m 30.99s , -05d 55m 10.3s) |   C |    60 | 18.7 |        
   43638 | 2025-10-08 06:15:29 |         MASTER-OAFA | (02h 46m 28.25s , -05d 53m 31.6s) |   C |    60 | 18.7 |        
   86664 | 2025-10-08 18:12:34 |   MASTER-Kislovodsk | (02h 39m 48.87s , -05d 45m 56.5s) |   C |    60 | 15.5 |        
   86724 | 2025-10-08 18:12:34 |   MASTER-Kislovodsk | (02h 39m 48.87s , -05d 45m 56.4s) |   C |   180 | 16.0 |  Coadd 
   86664 | 2025-10-08 18:12:34 |   MASTER-Kislovodsk | (02h 39m 49.14s , -06d 09m 00.5s) |   C |    60 | 14.8 |        
   86744 | 2025-10-08 18:13:54 |   MASTER-Kislovodsk | (02h 39m 58.79s , -05d 49m 41.8s) |   C |    60 | 15.4 |        
   86744 | 2025-10-08 18:13:54 |   MASTER-Kislovodsk | (02h 39m 59.30s , -06d 12m 47.1s) |   C |    60 | 14.1 |        
   87245 | 2025-10-08 18:22:15 |   MASTER-Kislovodsk | (02h 39m 49.23s , -05d 46m 24.8s) |   C |    60 | 15.4 |        
   87245 | 2025-10-08 18:22:15 |   MASTER-Kislovodsk | (02h 39m 52.54s , -06d 09m 03.4s) |   C |    60 | 15.4 |        
   88594 | 2025-10-08 18:44:45 |   MASTER-Kislovodsk | (02h 39m 53.25s , -05d 46m 54.7s) |   C |    60 | 15.8 |        
   88654 | 2025-10-08 18:44:45 |   MASTER-Kislovodsk | (02h 39m 53.24s , -05d 46m 54.5s) |   C |   180 | 16.6 |  Coadd 
   88594 | 2025-10-08 18:44:45 |   MASTER-Kislovodsk | (02h 39m 57.09s , -06d 10m 00.7s) |   C |    60 | 16.3 |        
   88935 | 2025-10-08 18:50:26 |   MASTER-Kislovodsk | (02h 39m 52.51s , -05d 45m 44.1s) |   C |    60 | 16.0 |        
   88935 | 2025-10-08 18:50:26 |   MASTER-Kislovodsk | (02h 39m 58.82s , -06d 08m 32.2s) |   C |    60 | 16.4 |        
   89015 | 2025-10-08 18:51:46 |   MASTER-Kislovodsk | (02h 39m 58.46s , -05d 46m 41.6s) |   C |    60 | 16.0 |        
   89015 | 2025-10-08 18:51:46 |   MASTER-Kislovodsk | (02h 40m 04.85s , -06d 09m 31.8s) |   C |    60 | 16.3 |        
   89095 | 2025-10-08 18:53:06 |   MASTER-Kislovodsk | (02h 39m 48.54s , -05d 44m 54.1s) |   C |    60 | 15.9 |        
   89155 | 2025-10-08 18:53:06 |   MASTER-Kislovodsk | (02h 39m 48.54s , -05d 44m 54.2s) |   C |   180 | 16.6 |  Coadd 
   89095 | 2025-10-08 18:53:06 |   MASTER-Kislovodsk | (02h 39m 55.02s , -06d 07m 45.0s) |   C |    60 | 16.4 |        
   89175 | 2025-10-08 18:54:25 |   MASTER-Kislovodsk | (02h 39m 54.56s , -05d 46m 36.7s) |   C |    60 | 16.0 |        
   89175 | 2025-10-08 18:54:25 |   MASTER-Kislovodsk | (02h 40m 01.09s , -06d 09m 28.4s) |   C |    60 | 16.2 |        
   89255 | 2025-10-08 18:55:46 |   MASTER-Kislovodsk | (02h 39m 54.62s , -05d 44m 51.0s) |   C |    60 | 16.1 |        
   89255 | 2025-10-08 18:55:46 |   MASTER-Kislovodsk | (02h 40m 01.20s , -06d 07m 42.8s) |   C |    60 | 16.4 |        
   89335 | 2025-10-08 18:57:06 |   MASTER-Kislovodsk | (02h 40m 00.54s , -05d 48m 27.7s) |   C |    60 | 15.9 |        
   89335 | 2025-10-08 18:57:06 |   MASTER-Kislovodsk | (02h 40m 07.15s , -06d 11m 19.7s) |   C |    60 | 16.3 |        
   89937 | 2025-10-08 19:07:07 |   MASTER-Kislovodsk | (02h 39m 50.59s , -05d 42m 57.7s) |   C |    60 | 16.1 |        
   89937 | 2025-10-08 19:07:07 |   MASTER-Kislovodsk | (02h 39m 56.71s , -06d 06m 09.4s) |   C |    60 | 16.4 |        
   90017 | 2025-10-08 19:08:27 |   MASTER-Kislovodsk | (02h 39m 53.56s , -05d 47m 41.3s) |   C |    60 | 16.0 |        
   90017 | 2025-10-08 19:08:27 |   MASTER-Kislovodsk | (02h 39m 59.66s , -06d 10m 54.2s) |   C |    60 | 16.4 |        
  111807 | 2025-10-09 01:11:38 |         MASTER-SAAO | (02h 41m 40.45s , -06d 20m 51.9s) |   C |    60 | 18.2 |        
  111807 | 2025-10-09 01:11:38 |         MASTER-SAAO | (02h 39m 51.83s , -06d 05m 32.4s) |   C |    60 | 18.5 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

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Jochen Greiner, last update: 08-Oct-2025 [Disclaimer]