Gamma-ray Burst 251018A

(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 18 Oct 25 03:12:22 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1405083,   Seg_Num: 0
GRB_RA:          282.071d {+18h 48m 17s} (J2000),
                 282.507d {+18h 50m 02s} (current),
                 281.224d {+18h 44m 54s} (1950)
GRB_DEC:         -37.028d {-37d 01' 41"} (J2000),
                 -36.998d {-36d 59' 51"} (current),
                 -37.085d {-37d 05' 04"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       3459 [cnts]    Image_Peak=181 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   146     E_range: 25-100 keV
BKG_INTEN:       19293 [cnts]
BKG_TIME:        11507.47 SOD {03:11:47.47} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20966 TJD;   291 DOY;   25/10/18
GRB_TIME:        11522.38 SOD {03:12:02.38} UT
GRB_PHI:         128.29 [deg]
GRB_THETA:        10.74 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     18.65 [sigma]
IMAGE_SIGNIF:    8.46 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +2  -1  +0  +1 -25  +0 
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 30"}
SUN_DIST:         75.72 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.34d {+11h 13m 21s}   +5.07d {+05d 03' 55"}
MOON_DIST:       112.26 [deg]
MOON_ILLUM:      11 [%]
GAL_COORDS:      358.81,-15.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      279.91,-14.00 [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 = 226.91,20.25 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(2.0<100sec) coincident with the FERMI_GBM event (trignum=782449925).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:12:04 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     782449925
GRB_RA:          295.133d {+19h 40m 32s} (J2000),
                 295.558d {+19h 42m 14s} (current),
                 294.308d {+19h 37m 14s} (1950)
GRB_DEC:         -36.117d {-36d 07' 00"} (J2000),
                 -36.055d {-36d 03' 18"} (current),
                 -36.233d {-36d 13' 58"} (1950)
GRB_ERROR:       19.32 [deg radius, statistical plus systematic]
GRB_INTEN:       116 [cnts/sec]
DATA_SIGNIF:     5.40 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20966 TJD;   291 DOY;   25/10/18
GRB_TIME:        11520.63 SOD {03:12:00.63} UT
GRB_PHI:         274.00 [deg]
GRB_THETA:        40.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      -0.07
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   3%  SGR_1806n20
DETECTORS:       0,0,0, 1,0,0, 0,1,0, 0,0,0, 0,0,
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 30"}
SUN_DIST:         86.24 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      168.34d {+11h 13m 21s}   +5.07d {+05d 03' 60"}
MOON_DIST:       122.62 [deg]
MOON_ILLUM:      11 [%]
GAL_COORDS:        3.45,-24.94 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      290.75,-14.47 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_lc_medres34_bn251018133.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 263.02,-24.95 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:12:12 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     782449925
GRB_RA:          291.233d {+19h 24m 56s} (J2000),
                 291.684d {+19h 26m 44s} (current),
                 290.358d {+19h 21m 26s} (1950)
GRB_DEC:         -41.983d {-41d 58' 59"} (J2000),
                 -41.931d {-41d 55' 50"} (current),
                 -42.082d {-42d 04' 55"} (1950)
GRB_ERROR:       12.27 [deg radius, statistical plus systematic]
GRB_INTEN:       113 [cnts/sec]
DATA_SIGNIF:     10.80 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20966 TJD;   291 DOY;   25/10/18
GRB_TIME:        11520.63 SOD {03:12:00.63} UT
GRB_PHI:         281.00 [deg]
GRB_THETA:        35.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.44
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 1,0,0, 0,1,0, 0,0,0, 0,0,
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 30"}
SUN_DIST:         82.46 [deg]   Sun_angle= -5.9 [hr] (East of Sun)
MOON_POSTN:      168.34d {+11h 13m 21s}   +5.07d {+05d 03' 58"}
MOON_DIST:       117.80 [deg]
MOON_ILLUM:      11 [%]
GAL_COORDS:      356.34,-23.66 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      286.62,-19.76 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_lc_medres34_bn251018133.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 263.02,-24.95 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:12:19 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     782449925
GRB_RA:          290.660d {+19h 22m 38s} (J2000),
                 291.071d {+19h 24m 17s} (current),
                 289.863d {+19h 19m 27s} (1950)
GRB_DEC:         -30.840d {-30d 50' 23"} (J2000),
                 -30.789d {-30d 47' 19"} (current),
                 -30.936d {-30d 56' 10"} (1950)
GRB_ERROR:       3.54 [deg radius, statistical only]
DATA_SIGNIF:     11.20 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20966 TJD;   291 DOY;   25/10/18
GRB_TIME:        11520.63 SOD {03:12:00.63} UT
GRB_PHI:         278.00 [deg]
GRB_THETA:        46.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 30"}
SUN_DIST:         83.29 [deg]   Sun_angle= -5.9 [hr] (East of Sun)
MOON_POSTN:      168.34d {+11h 13m 21s}   +5.07d {+05d 03' 56"}
MOON_DIST:       120.52 [deg]
MOON_ILLUM:      11 [%]
GAL_COORDS:        7.58,-19.72 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      287.84, -8.67 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_lc_medres34_bn251018133.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_782449925.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:     Sat 18 Oct 25 03:18:16 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     782449925
GRB_RA:          294.670d {+19h 38m 41s} (J2000),
                 295.111d {+19h 40m 27s} (current),
                 293.813d {+19h 35m 15s} (1950)
GRB_DEC:         -40.350d {-40d 21' 00"} (J2000),
                 -40.290d {-40d 17' 21"} (current),
                 -40.464d {-40d 27' 51"} (1950)
GRB_ERROR:       6.81 [deg radius, statistical only]
GRB_DATE:        20966 TJD;   291 DOY;   25/10/18
GRB_TIME:        11520.63 SOD {03:12:00.63} UT
GRB_PHI:         276.00 [deg]
GRB_THETA:        36.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       203.17d {+13h 32m 40s}   -9.68d {-09d 40' 35"}
SUN_DIST:         85.23 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:      168.38d {+11h 13m 32s}   +5.04d {+05d 02' 29"}
MOON_DIST:       120.74 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.83,-25.73 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      289.61,-18.58 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_lc_medres34_bn251018133.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_locplot_all_bn251018133.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.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(2.0<100sec) coincident with the SWIFT_BAT event (trignum=1405083).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:13:55 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1405083,   Seg_Num: 0
GRB_RA:          282.0433d {+18h 48m 10.3s} (J2000),
                 282.4796d {+18h 49m 55.1s} (current),
                 281.1969d {+18h 44m 47.2s} (1950)
GRB_DEC:         -37.0265d {-37d 01' 35.3"} (J2000),
                 -36.9960d {-36d 59' 45.6"} (current),
                 -37.0826d {-37d 04' 57.2"} (1950)
GRB_ERROR:       6.1 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       24 [cnts]
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11596.77 SOD {03:13:16.77} UT,   74.4 [sec] since BAT Trigger Time
CENTROID_X:      280.64,  raw= 281  [pixels]
CENTROID_Y:      292.63,  raw= 293  [pixels]
ROLL:            268.82 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -14.30
GRB_POS_XRT_Z:   -72.96
IMAGE_URL:       sw01405083000msxps_rw.img
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 32"}
SUN_DIST:         75.69 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.35d {+11h 13m 24s}   +5.06d {+05d 03' 33"}
MOON_DIST:       112.23 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.34 [deg] galactic lon,lat of the burst
ECL_COORDS:      279.89,-14.00 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:13:43 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1405083,   Seg_Num: 0
GRB_RA:          282.0433d {+18h 48m 10.39s} (J2000),
                 282.4796d {+18h 49m 55.10s} (current),
                 281.1969d {+18h 44m 47.25s} (1950)
GRB_DEC:         -37.0265d {-37d 01' 35.3"} (J2000),
                 -36.9960d {-36d 59' 45.6"} (current),
                 -37.0826d {-37d 04' 57.2"} (1950)
GRB_ERROR:       6.3 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       5.19e-10 [erg/cm2/sec]
GRB_SIGNIF:      4.89 [sigma]
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11596.77 SOD {03:13:16.77} UT,   74.4 [sec] since BAT Trigger Time
TAM[0-3]:        327.63 237.12 261.54 243.68
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 31"}
SUN_DIST:         75.69 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.35d {+11h 13m 24s}   +5.06d {+05d 03' 35"}
MOON_DIST:       112.23 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.34 [deg] galactic lon,lat of the burst
ECL_COORDS:      279.89,-14.00 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.32 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:16:24 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1405083,   Seg_Num: 0
GRB_RA:          282.071d {+18h 48m 17s} (J2000),
                 282.507d {+18h 50m 02s} (current),
                 281.224d {+18h 44m 54s} (1950)
GRB_DEC:         -37.028d {-37d 01' 41"} (J2000),
                 -36.998d {-36d 59' 51"} (current),
                 -37.085d {-37d 05' 04"} (1950)
GRB_DATE:        20966 TJD;   291 DOY;   25/10/18
GRB_TIME:        11522.38 SOD {03:12:02.38} UT
TRIGGER_INDEX:   146
GRB_PHI:         128.29 [deg]
GRB_THETA:        10.74 [deg]
DELTA_TIME:      -50.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     18.65 [sigma]
IMAGE_SIGNIF:    8.46 [sigma]
LC_URL:          sw01405083000msb.lc
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 34"}
SUN_DIST:         75.71 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.37d {+11h 13m 29s}   +5.05d {+05d 02' 56"}
MOON_DIST:       112.23 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.81,-15.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      279.91,-14.00 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
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 = 226.91,20.25 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:13:53 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1405083,   Seg_Num: 0
GRB_RA:          282.0433d {+18h 48m 10.3s} (J2000),
                 282.4796d {+18h 49m 55.1s} (current),
                 281.1969d {+18h 44m 47.2s} (1950)
GRB_DEC:         -37.0265d {-37d 01' 35.3"} (J2000),
                 -36.9960d {-36d 59' 45.6"} (current),
                 -37.0826d {-37d 04' 57.2"} (1950)
GRB_ERROR:       6.1 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       24 [cnts]
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11596.77 SOD {03:13:16.77} UT,   74.4 [sec] since BAT Trigger Time
CENTROID_X:      280.64,  raw= 281  [pixels]
CENTROID_Y:      292.63,  raw= 293  [pixels]
ROLL:            268.82 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -14.30
GRB_POS_XRT_Z:   -72.96
IMAGE_URL:       sw01405083000msxps_rw.img
SUN_POSTN:       203.16d {+13h 32m 39s}   -9.68d {-09d 40' 32"}
SUN_DIST:         75.69 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.35d {+11h 13m 24s}   +5.06d {+05d 03' 33"}
MOON_DIST:       112.23 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.34 [deg] galactic lon,lat of the burst
ECL_COORDS:      279.89,-14.00 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN Circular #42342
The Fermi GBM team reports the detection of a likely LONG GRB
At 03:12:00 UT on 18 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251018A (trigger 782449925.633958 / 251018133).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 294.7, Dec = -40.3 (J2000 degrees, equivalent to J2000 19h 38m, -40d 17'), with a statistical uncertainty of 6.8 degrees.
The angle from the Fermi LAT boresight is 36.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_skymap_all_bn251018133.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/bn251018133/quicklook/glg_healpix_all_bn251018133.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/quicklook/glg_lc_medres34_bn251018133.gif

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:20:13 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1405083,   Seg_Num: 0
POINT_RA:        282.067d {+18h 48m 16s} (J2000)
POINT_DEC:       -37.030d {-37d 01' 46"} (J2000)
ROLL:            268.824d
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11606.07 SOD {03:13:26.07} UT,   83.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     782450042
X_OFFSET:        932 [pixels]
Y_OFFSET:        832 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1092
Y_GRB_POS:       992
BINNING_INDEX:   1
IM_URL:          sw01405083000msuni0120.fits
SUN_POSTN:       203.17d {+13h 32m 40s}   -9.68d {-09d 40' 37"}
SUN_DIST:         75.71 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.40d {+11h 13m 36s}   +5.03d {+05d 01' 60"}
MOON_DIST:       112.19 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      279.90,-14.00 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:20:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1405083,   Seg_Num: 0
POINT_RA:        282.067d {+18h 48m 16s} (J2000)
POINT_DEC:       -37.030d {-37d 01' 46"} (J2000)
ROLL:            268.824d
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11606.07 SOD {03:13:26.07} UT,   83.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     782450042
X_OFFSET:        932 [pixels]
Y_OFFSET:        832 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1092
Y_GRB_POS:       992
BINNING_INDEX:   1
IM_URL:          sw01405083000msuni0120.fits
SUN_POSTN:       203.17d {+13h 32m 40s}   -9.68d {-09d 40' 37"}
SUN_DIST:         75.71 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.40d {+11h 13m 36s}   +5.03d {+05d 01' 58"}
MOON_DIST:       112.19 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      279.90,-14.00 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:25:50 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1405083,   Seg_Num: 0
POINT_RA:        282.067d {+18h 48m 16s} (J2000)
POINT_DEC:       -37.030d {-37d 01' 47"} (J2000)
POINT_ROLL:      268.824d
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11818.33 SOD {03:16:58.33} UT,   296.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.260
N_STARS:         190
X_OFFSET:        612 [pixels]
Y_OFFSET:        512 [pixels]
X_MAX:           1571 [pixels]
Y_MAX:           1471 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01405083000msufc0295.fits
SUN_POSTN:       203.17d {+13h 32m 41s}   -9.68d {-09d 40' 42"}
SUN_DIST:         75.71 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.44d {+11h 13m 46s}   +5.01d {+05d 00' 37"}
MOON_DIST:       112.15 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      279.90,-14.00 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN Circular #42343
R. Gupta (NASA GSFC), R. Brivio (INAF-OAB), S. Dichiara (PSU), M. Ferro (INAF-OAB), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 03:12:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251018A (trigger=1405083). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 282.071, -37.028 which is
```
   RA(J2000) = 18h 48m 17s
   Dec(J2000) = -37d 01' 41"
```
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 60 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 03:13:16.7 UT, 74.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 282.0433, -37.0265 which is equivalent to:
```
   RA(J2000)  = 18h 48m 10.39s
   Dec(J2000) = -37d 01' 35.4"
```
with an uncertainty of 6.3 arcseconds (radius, 90% containment). This location is 79 arcseconds from the BAT onboard position, within the BAT error circle. The initial flux in the 2.5 s image was 5.19e-10 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 83 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at
```
  RA(J2000)  =	18:48:10.04 = 282.04183
  DEC(J2000) = -37:01:42.2  = -37.02840
```
with a 90%-confidence error radius of about 0.62 arc sec. This position is 8.0 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.96 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.100.
Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com). 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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:26:06 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1405083,   Seg_Num: 0
POINT_RA:        282.067d {+18h 48m 16s} (J2000)
POINT_DEC:       -37.030d {-37d 01' 47"} (J2000)
POINT_ROLL:      268.824d
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11818.33 SOD {03:16:58.33} UT,   296.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.260
N_STARS:         190
X_OFFSET:        612 [pixels]
Y_OFFSET:        512 [pixels]
X_MAX:           1571 [pixels]
Y_MAX:           1471 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01405083000msufc0295.fits
SUN_POSTN:       203.17d {+13h 32m 41s}   -9.68d {-09d 40' 43"}
SUN_DIST:         75.71 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.44d {+11h 13m 46s}   +5.01d {+05d 00' 34"}
MOON_DIST:       112.14 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      279.90,-14.00 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:27:23 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1405083,   Seg_Num: 0
POINT_RA:        282.067d {+18h 48m 16s} (J2000)
POINT_DEC:       -37.030d {-37d 01' 47"} (J2000)
ROLL:            268.824d
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11818.33 SOD {03:16:58.33} UT,   296.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     782450254
X_OFFSET:        932 [pixels]
Y_OFFSET:        832 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1092
Y_GRB_POS:       992
BINNING_INDEX:   1
IM_URL:          sw01405083000msuni0332.fits
SUN_POSTN:       203.17d {+13h 32m 41s}   -9.68d {-09d 40' 44"}
SUN_DIST:         75.70 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.45d {+11h 13m 49s}   +5.00d {+05d 00' 15"}
MOON_DIST:       112.13 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      279.90,-14.00 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:27:14 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1405083,   Seg_Num: 0
POINT_RA:        282.067d {+18h 48m 16s} (J2000)
POINT_DEC:       -37.030d {-37d 01' 47"} (J2000)
ROLL:            268.824d
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11818.33 SOD {03:16:58.33} UT,   296.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     782450254
X_OFFSET:        932 [pixels]
Y_OFFSET:        832 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1092
Y_GRB_POS:       992
BINNING_INDEX:   1
IM_URL:          sw01405083000msuni0332.fits
SUN_POSTN:       203.17d {+13h 32m 41s}   -9.68d {-09d 40' 44"}
SUN_DIST:         75.71 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.45d {+11h 13m 48s}   +5.00d {+05d 00' 17"}
MOON_DIST:       112.13 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      279.90,-14.00 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN Circular #42344
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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 251018A ( R. Gupta et al., GCN 42343) errorbox 105 sec after notice time and 141 sec after trigger time at 2025-10-18 03:14:24 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 68 deg. The sun altitude is -46.5 deg.
The galactic latitude b = -16 deg., longitude l = 359 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3017251
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

     147 |         MASTER-OAFA |   C |    10 | 17.8 |        
     168 |         MASTER-OAFA |   C |    20 | 18.3 |        
     194 |         MASTER-OAFA |   C |    20 | 18.2 |        
     225 |         MASTER-OAFA |   C |    30 | 18.4 |        
     263 |         MASTER-OAFA |   C |    30 | 18.4 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 18 Oct 25 03:40:02 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1405083,   Seg_Num: 0
GRB_RA:          282.0454d {+18h 48m 10.89s} (J2000),
                 282.4817d {+18h 49m 55.61s} (current),
                 281.1990d {+18h 44m 47.75s} (1950)
GRB_DEC:         -37.0277d {-37d 01' 39.7"} (J2000),
                 -36.9972d {-36d 59' 49.9"} (current),
                 -37.0838d {-37d 05' 01.6"} (1950)
GRB_ERROR:       5.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20966 TJD;   291 DOY;   25/10/18
IMG_START_TIME:  11866.00 SOD {03:17:46.00} UT,   343.6 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       203.18d {+13h 32m 43s}   -9.68d {-09d 40' 55"}
SUN_DIST:         75.68 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      168.55d {+11h 14m 12s}   +4.95d {+04d 57' 09"}
MOON_DIST:       112.01 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      358.80,-15.34 [deg] galactic lon,lat of the burst
ECL_COORDS:      279.89,-14.00 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See https://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 1.1% < P(seren) < 2.8%.

GCN Circular #42345
S.Y. Fu (HUST), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), Z.P. Zhu, L.B. He, X. Liu, J. An, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of GRB 251018A (Gupta et al., GCN 423243) using the 0.7-m telescope of the Thai Robotic Telescope (TRT) network, located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 2025-10-17 03:14:29.2 UT, i. e., 147 s after the trigger, and a series frames in the Sloan r filter were obtained.
An uncatalogued and varying optical transient (OT) is clearly detected at the Swift-UVOT position (Gupta et al., GCN 42343), with r = 17.96 +/-0.03 (AB) at ~ 865 s post-burst, calibrated with nearby SKYMAPPER-DR2 catalog and without the Galactic extinction correction. We thus confirm that the OT is indeed the optical afterglow of the burst.
GCN Circular #42346
V. Lipunov, I.Panchenko, A.Kuznetsov, G.Antipov, P.Balanutsa, E.Gorbovskoy, K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, Yu. Tselik, M.Shilova, A.Chasovnikov, V.Topolev, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, P.Rudominskaya (Lomonosov MSU, SAI, Moscow), 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.Sosnovskij (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 MASTER Global Robotic Net [1-4] started Fermi (GCN 42342) and Swift GRB 251018A (Gupta et al. GCN 42343, Trigger time 2025-10-18 03:12:02UT) 105s after notice time (141s after trigger time) at 2025-10-18 03:14:24 UT (Lipunov et al. GCN 42344, cover map and OT https://master.sai.msu.ru/site/master2/observ.php?id=3017251
There is MASTER OT J184810.01-370141.6,detected since first image (03:14:24) with m_OT=16.5 at 2025-10-18 03:16:46 (unfiltered, automatically calculated) This OT was discovered by Swift-UVOT (Gupta et al. GCN 42343) and observed by TRT (S.Y.Fu et al. GCN 42345) at the same time.
Observation and reduction 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 #42353
N.P.M. Kuin (MSSL-UCL) and R. Gupta (NASA GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251018A 84 s after the BAT trigger (Gupta et al., GCN Circ. 42343). A source consistent with the XRT position is detected in the initial UVOT exposures.
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white               84          128           44         17.98 +/- 0.08
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.101 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #42361
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 2660 s of XRT Photon Counting mode data and 4 UVOT images for GRB 251018A, 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 = 282.04220, -37.02921 which is equivalent to:
```
RA (J2000): 18h 48m 10.13s
Dec (J2000): -37d 01' 45.2"
```
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 #42362
E. Ambrosi (INAF-IASFPA) , J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.5 ks of XRT data for GRB 251018A, from 63 s to 50.2 ks after the trigger. The data comprise 259 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 a power-law decay with a decay index of alpha=1.122 (+0.031, -0.029).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.68 (+0.15, -0.14). The best-fitting absorption column is 1.4 (+0.6, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 9.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.81 (+0.25, -0.23) and a best-fitting absorption column of 2.1 (+1.1, -0.9) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (5.2 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     2.1 (+1.1, -0.9) x 10^21 cm^-2
Galactic foreground: 9.4 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index:	     1.81 (+0.25, -0.23)
```
If the light curve continues to decay with a power-law decay index of 1.122, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x 10^-13 (3.3 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/01405083.
This circular is an official product of the Swift-XRT team.
GCN Circular #42363
Y.-D. Hu (GXU), I. Perez-Garcia, A. J. Castro-Tirado, E. J. Fernandez-Garcia, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, and S. Guziy (IAA-CSIC), I. M. Carrasco (SMA), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar (Univ. of Malaga), S. Jeong (ADD, Daejeon), G. Garcia-Segura and D. Hiriart (IA-UNAM, Ensenada), W. H. Lee (UNAM, Mexico DF), D.-R. Xiong (YNAO), B.-B. Zhang (NJU), and A. Maury (Space Obs., San Pedro de Atacama) on behalf of a larger collaboration, report:
Following the detection of GRB251018A by Swift (Gupta et al., GCN 42343) and Fermi (Fermi GBM team, GCN 42342), the 0.6m BOOTES-5/JGU robotic telescope at San Pedro Martir Observatory (Mexico) automatically responded to this high-energy event starting on Oct 18, 03:12:45 UT (i.e., 43 sec after detection). Series of images in clear filter were gathered and we detect an optical source. Using USNO B-1.0 as a reference, we measure an initial magnitude of 16.78 +/- 0.16 in the first 1 x 5 s stacked image.
Meanwhile, the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) also automatically observed the GRB location starting on Oct. 18, 03:13:22 UT (i.e. 80 s after trigger). The afterglow is also detected with 16.04 +/- 0.11. These detections are consistent with the one reported by MASTER (Lipunov et al., GCN 42346), TRT (Fu et al., GCN 42345), and UVOT (Kuin et al., GCN 42353). Further analysis of the additional images is ongoing.
We would like to thank the staff at San Pedro Martir Observatory and San Pedro de Atacama Space Observatory for their excellent support.
GCN Circular #42364
B. Hristov (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 03:12:00.63 UT on 18 October 2025 , the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 251018A (trigger 782449925 / 251018133), which was also detected by the Swift/XRT (R. Gupta et al. 2025, GCN 42343) The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 42 degrees.
The GBM light curve consists of multiple peaks, with a duration (T90) of about 27.1 s (50-300 keV). The time-averaged spectrum from T0-6.1 s to T0+21.5 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.91 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 715 +/- 162 keV.
The event fluence (10-1000 keV) in this time interval is (6.8 +/- 0.3)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3 s in the 10-1000 keV band 0.95 +/- 0.04 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 #42769
Anurag Talele (University of Potsdam),
Martin Jelinek, Alzbeta Malenakova, Jan Strobl (ASU CAS Ondrejov, CZ),
Filip Novotny (ASU Ondrejov + Masaryk University),
Martin Masek, Petr Janecek, Sergey Karpov, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ)
report:
The 30 cm robotic telescope at the FRAM-Auger in Malargue (Argentina) reacted robotically to the Swift/BAT alert of GRB251018A (trigger 1405083, Gupta et. al. GCN42343) issued at 03:12:02 UT.
FRAM obtained its first unfiltered exposure 42 seconds after the trigger, at 03:12:44 UT, followed by a sequence of 20s and 60s exposures.
An optical transient is detected at the UVOT position. It appears at R(Vega) roughly 15.5 mag at T0 + 78s and fades to roughly 18.0 mag by the end of our 28 minutes observing run consistent with detections by Lipunov et. al. GCN42346, Hu et. al. GCN42363 and Kuin et. al. GCN42353.

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Jochen Greiner, last update: 19-Nov-2025 [Disclaimer]