Gamma-ray Burst 251017A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:41:02 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.386d {+22h 21m 33s} (J2000),
                 335.709d {+22h 22m 50s} (current),
                 334.760d {+22h 19m 02s} (1950)
GRB_DEC:          +7.051d {+07d 03' 02"} (J2000),
                  +7.181d {+07d 10' 53"} (current),
                  +6.798d {+06d 47' 53"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       2728 [cnts]    Image_Peak=190 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   146     E_range: 25-100 keV
BKG_INTEN:       15473 [cnts]
BKG_TIME:        31227.48 SOD {08:40:27.48} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20965 TJD;   290 DOY;   25/10/17
GRB_TIME:        31244.63 SOD {08:40:44.63} UT
GRB_PHI:          -0.87 [deg]
GRB_THETA:        21.09 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     15.71 [sigma]
IMAGE_SIGNIF:    9.52 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +2  +0  +0  +0 +68  +0 
SUN_POSTN:       202.44d {+13h 29m 45s}   -9.39d {-09d 23' 39"}
SUN_DIST:        133.74 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.74d {+10h 38m 58s}   +9.56d {+09d 33' 26"}
MOON_DIST:       162.79 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      339.89, 16.08 [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 = 169.41,20.14 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:43:08 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.3999d {+22h 21m 35.9s} (J2000),
                 335.7230d {+22h 22m 53.5s} (current),
                 334.7736d {+22h 19m 05.6s} (1950)
GRB_DEC:          +7.0391d {+07d 02' 20.7"} (J2000),
                  +7.1698d {+07d 10' 11.3"} (current),
                  +6.7866d {+06d 47' 11.7"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       71 [cnts]
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31354.16 SOD {08:42:34.16} UT,   109.5 [sec] since BAT Trigger Time
CENTROID_X:      336.24,  raw= 336  [pixels]
CENTROID_Y:      318.27,  raw= 318  [pixels]
ROLL:            263.71 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   46.14
GRB_POS_XRT_Z:   58.09
IMAGE_URL:       sw01404904000msxps_rw.img
SUN_POSTN:       202.44d {+13h 29m 46s}   -9.40d {-09d 23' 41"}
SUN_DIST:        133.75 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.76d {+10h 39m 02s}   +9.55d {+09d 32' 56"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.74,-40.18 [deg] galactic lon,lat of the burst
ECL_COORDS:      339.90, 16.07 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:43:11 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.3999d {+22h 21m 35.9s} (J2000),
                 335.7230d {+22h 22m 53.5s} (current),
                 334.7736d {+22h 19m 05.6s} (1950)
GRB_DEC:          +7.0391d {+07d 02' 20.7"} (J2000),
                  +7.1698d {+07d 10' 11.3"} (current),
                  +6.7866d {+06d 47' 11.7"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       71 [cnts]
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31354.16 SOD {08:42:34.16} UT,   109.5 [sec] since BAT Trigger Time
CENTROID_X:      336.24,  raw= 336  [pixels]
CENTROID_Y:      318.27,  raw= 318  [pixels]
ROLL:            263.71 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   46.14
GRB_POS_XRT_Z:   58.09
IMAGE_URL:       sw01404904000msxps_rw.img
SUN_POSTN:       202.44d {+13h 29m 46s}   -9.40d {-09d 23' 41"}
SUN_DIST:        133.75 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.76d {+10h 39m 02s}   +9.55d {+09d 32' 55"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.74,-40.18 [deg] galactic lon,lat of the burst
ECL_COORDS:      339.90, 16.07 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:42:57 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.3999d {+22h 21m 35.97s} (J2000),
                 335.7230d {+22h 22m 53.51s} (current),
                 334.7736d {+22h 19m 05.66s} (1950)
GRB_DEC:          +7.0391d {+07d 02' 20.7"} (J2000),
                  +7.1698d {+07d 10' 11.3"} (current),
                  +6.7866d {+06d 47' 11.7"} (1950)
GRB_ERROR:       5.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       2.03e-09 [erg/cm2/sec]
GRB_SIGNIF:      8.42 [sigma]
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31354.16 SOD {08:42:34.16} UT,   109.5 [sec] since BAT Trigger Time
TAM[0-3]:        327.64 237.18 261.53 243.80
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       202.44d {+13h 29m 46s}   -9.39d {-09d 23' 41"}
SUN_DIST:        133.75 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.76d {+10h 39m 02s}   +9.55d {+09d 32' 59"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.74,-40.18 [deg] galactic lon,lat of the burst
ECL_COORDS:      339.90, 16.07 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.06 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:44:54 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.386d {+22h 21m 33s} (J2000),
                 335.709d {+22h 22m 50s} (current),
                 334.760d {+22h 19m 02s} (1950)
GRB_DEC:          +7.051d {+07d 03' 02"} (J2000),
                  +7.181d {+07d 10' 53"} (current),
                  +6.798d {+06d 47' 53"} (1950)
GRB_DATE:        20965 TJD;   290 DOY;   25/10/17
GRB_TIME:        31244.63 SOD {08:40:44.63} UT
TRIGGER_INDEX:   146
GRB_PHI:          -0.87 [deg]
GRB_THETA:        21.09 [deg]
DELTA_TIME:      44.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     15.71 [sigma]
IMAGE_SIGNIF:    9.52 [sigma]
LC_URL:          sw01404904000msb.lc
SUN_POSTN:       202.44d {+13h 29m 46s}   -9.40d {-09d 23' 43"}
SUN_DIST:        133.73 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.77d {+10h 39m 05s}   +9.54d {+09d 32' 31"}
MOON_DIST:       162.79 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      339.89, 16.08 [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 = 169.41,20.14 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:45:49 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.382d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 03' 01"} (J2000)
POINT_ROLL:      263.712d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31364.75 SOD {08:42:44.75} UT,   120.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.188
N_STARS:         148
X_OFFSET:        331 [pixels]
Y_OFFSET:        533 [pixels]
X_MAX:           1290 [pixels]
Y_MAX:           1492 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01404904000msufc0120.fits
SUN_POSTN:       202.44d {+13h 29m 46s}   -9.40d {-09d 23' 43"}
SUN_DIST:        133.73 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.78d {+10h 39m 07s}   +9.54d {+09d 32' 17"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.16 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:45:56 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.382d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 03' 01"} (J2000)
POINT_ROLL:      263.712d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31364.75 SOD {08:42:44.75} UT,   120.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.188
N_STARS:         148
X_OFFSET:        331 [pixels]
Y_OFFSET:        533 [pixels]
X_MAX:           1290 [pixels]
Y_MAX:           1492 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01404904000msufc0120.fits
SUN_POSTN:       202.44d {+13h 29m 46s}   -9.40d {-09d 23' 44"}
SUN_DIST:        133.73 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.78d {+10h 39m 07s}   +9.54d {+09d 32' 16"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.16 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 08:48:12 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.382d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 03' 01"} (J2000)
ROLL:            263.712d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31364.75 SOD {08:42:44.75} UT,   120.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     782383401
X_OFFSET:        651 [pixels]
Y_OFFSET:        853 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       811
Y_GRB_POS:       1013
BINNING_INDEX:   1
IM_URL:          sw01404904000msuni0157.fits
SUN_POSTN:       202.44d {+13h 29m 47s}   -9.40d {-09d 23' 46"}
SUN_DIST:        133.73 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.80d {+10h 39m 12s}   +9.53d {+09d 31' 43"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.16 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 08:48:19 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.382d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 03' 01"} (J2000)
ROLL:            263.712d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31364.75 SOD {08:42:44.75} UT,   120.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     782383401
X_OFFSET:        651 [pixels]
Y_OFFSET:        853 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       811
Y_GRB_POS:       1013
BINNING_INDEX:   1
IM_URL:          sw01404904000msuni0157.fits
SUN_POSTN:       202.44d {+13h 29m 47s}   -9.40d {-09d 23' 46"}
SUN_DIST:        133.73 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.80d {+10h 39m 12s}   +9.53d {+09d 31' 42"}
MOON_DIST:       162.80 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.16 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 08:49:57 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.4009d {+22h 21m 36.21s} (J2000),
                 335.7240d {+22h 22m 53.75s} (current),
                 334.7746d {+22h 19m 05.90s} (1950)
GRB_DEC:          +7.0399d {+07d 02' 23.6"} (J2000),
                  +7.1706d {+07d 10' 14.2"} (current),
                  +6.7874d {+06d 47' 14.6"} (1950)
GRB_ERROR:       0.8 [arcsec radius, statistical only]
GRB_MAG:         20.42 +/- 0.20 [mag]
FILTER:          10, White
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31361.00 SOD {08:42:41.00} UT,   116.4 [sec] since BAT Trigger Time
SUN_POSTN:       202.44d {+13h 29m 47s}   -9.40d {-09d 23' 47"}
SUN_DIST:        133.74 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.81d {+10h 39m 15s}   +9.52d {+09d 31' 18"}
MOON_DIST:       162.82 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.74,-40.18 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      339.90, 16.07 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT UVOT Position Notice.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The UVOT position is 4.7 arcsec from the XRT position.  
COMMENTS:        Result based on Genie data.  
COMMENTS:        Notice generated automatically.

GCN Circular #42322
R. Gupta (NASA GSFC), R. Brivio (INAF-OAB), S. Dichiara (PSU), R. A. J. Eyles-Ferris (U Leicester), A. Mei (INAF-OAB), K. L. Page (U Leicester), C. Salvaggio (INAF-OAB) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team:
At 08:40:44 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251017A (trigger=1404904). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 335.386, +7.051 which is
```
   RA(J2000) = 22h 21m 33s
   Dec(J2000) = +07d 03' 02"
```
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 25 sec. The peak count rate was ~2136 counts/sec (15-350 keV), at ~6 sec after the trigger.
The XRT began observing the field at 08:42:34.1 UT, 109.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 335.40109, 7.04043 which is equivalent to:
```
   RA(J2000)  = 22h 21m 36.26s
   Dec(J2000) = +07d 02' 25.5"
```
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This location is 65 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (8.90 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 6.7 (+3.92/-3.27) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 2.03e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 120 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at
```
  RA(J2000)  =	22:21:36.24 = 335.40098
  DEC(J2000) = +07:02:23.6  =	7.03990
```
with a 90%-confidence error radius of about 0.77 arc sec. This position is 4.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 20.42 with a 1-sigma error of about 0.21. No correction has been made for the expected extinction corresponding to E(B-V) of 0.108.
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:     Fri 17 Oct 25 08:55:08 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
POINT_ROLL:      263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31576.74 SOD {08:46:16.74} UT,   332.1 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.630
N_STARS:         40
X_OFFSET:        331 [pixels]
Y_OFFSET:        533 [pixels]
X_MAX:           1290 [pixels]
Y_MAX:           1492 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01404904000msufc0332.fits
SUN_POSTN:       202.45d {+13h 29m 48s}   -9.40d {-09d 23' 52"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.85d {+10h 39m 25s}   +9.50d {+09d 30' 04"}
MOON_DIST:       162.81 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:55:18 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
POINT_ROLL:      263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31576.74 SOD {08:46:16.74} UT,   332.1 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.630
N_STARS:         40
X_OFFSET:        331 [pixels]
Y_OFFSET:        533 [pixels]
X_MAX:           1290 [pixels]
Y_MAX:           1492 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01404904000msufc0332.fits
SUN_POSTN:       202.45d {+13h 29m 48s}   -9.40d {-09d 23' 52"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.85d {+10h 39m 25s}   +9.50d {+09d 30' 01"}
MOON_DIST:       162.82 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 08:56:24 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
ROLL:            263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31576.74 SOD {08:46:16.74} UT,   332.1 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     782383613
X_OFFSET:        651 [pixels]
Y_OFFSET:        853 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       811
Y_GRB_POS:       1013
BINNING_INDEX:   1
IM_URL:          sw01404904000msuni0369.fits
SUN_POSTN:       202.45d {+13h 29m 48s}   -9.40d {-09d 23' 53"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.86d {+10h 39m 27s}   +9.50d {+09d 29' 45"}
MOON_DIST:       162.82 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 08:55:39 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1404904,   Seg_Num: 0
GRB_RA:          335.4016d {+22h 21m 36.38s} (J2000),
                 335.7247d {+22h 22m 53.92s} (current),
                 334.7753d {+22h 19m 06.07s} (1950)
GRB_DEC:          +7.0400d {+07d 02' 24.0"} (J2000),
                  +7.1707d {+07d 10' 14.6"} (current),
                  +6.7875d {+06d 47' 14.9"} (1950)
GRB_ERROR:       2.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31437.00 SOD {08:43:57.00} UT,   192.4 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       202.45d {+13h 29m 48s}   -9.40d {-09d 23' 52"}
SUN_DIST:        133.74 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.86d {+10h 39m 26s}   +9.50d {+09d 29' 56"}
MOON_DIST:       162.83 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.74,-40.19 [deg] galactic lon,lat of the burst
ECL_COORDS:      339.90, 16.07 [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:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.11% < P(seren) < 0.58%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 08:56:16 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
ROLL:            263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  31576.74 SOD {08:46:16.74} UT,   332.1 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     782383613
X_OFFSET:        651 [pixels]
Y_OFFSET:        853 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       811
Y_GRB_POS:       1013
BINNING_INDEX:   1
IM_URL:          sw01404904000msuni0369.fits
SUN_POSTN:       202.45d {+13h 29m 48s}   -9.40d {-09d 23' 53"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.86d {+10h 39m 27s}   +9.50d {+09d 29' 47"}
MOON_DIST:       162.82 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 09:02:14 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
POINT_ROLL:      263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  32105.98 SOD {08:55:05.98} UT,   861.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.107
N_STARS:         190
X_OFFSET:        91 [pixels]
Y_OFFSET:        293 [pixels]
X_MAX:           1530 [pixels]
Y_MAX:           1732 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01404904000msufc0861.fits
SUN_POSTN:       202.45d {+13h 29m 49s}   -9.40d {-09d 23' 58"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.91d {+10h 39m 38s}   +9.47d {+09d 28' 22"}
MOON_DIST:       162.83 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 09:02:27 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
POINT_ROLL:      263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  32105.98 SOD {08:55:05.98} UT,   861.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.107
N_STARS:         190
X_OFFSET:        91 [pixels]
Y_OFFSET:        293 [pixels]
X_MAX:           1530 [pixels]
Y_MAX:           1732 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01404904000msufc0861.fits
SUN_POSTN:       202.45d {+13h 29m 49s}   -9.40d {-09d 23' 59"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.91d {+10h 39m 38s}   +9.47d {+09d 28' 19"}
MOON_DIST:       162.83 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [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:     Fri 17 Oct 25 09:03:48 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
ROLL:            263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  32105.98 SOD {08:55:05.98} UT,   861.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     782384142
X_OFFSET:        650 [pixels]
Y_OFFSET:        852 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       810
Y_GRB_POS:       1012
BINNING_INDEX:   1
IM_URL:          sw01404904000msuni0898.fits
SUN_POSTN:       202.45d {+13h 29m 49s}   -9.40d {-09d 24' 00"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.92d {+10h 39m 41s}   +9.47d {+09d 27' 59"}
MOON_DIST:       162.83 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 09:03:55 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1404904,   Seg_Num: 0
POINT_RA:        335.383d {+22h 21m 32s} (J2000)
POINT_DEC:        +7.050d {+07d 02' 59"} (J2000)
ROLL:            263.711d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  32105.98 SOD {08:55:05.98} UT,   861.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     782384142
X_OFFSET:        650 [pixels]
Y_OFFSET:        852 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       810
Y_GRB_POS:       1012
BINNING_INDEX:   1
IM_URL:          sw01404904000msuni0898.fits
SUN_POSTN:       202.45d {+13h 29m 49s}   -9.40d {-09d 24' 00"}
SUN_DIST:        133.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      159.92d {+10h 39m 41s}   +9.47d {+09d 27' 57"}
MOON_DIST:       162.83 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       70.73,-40.17 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      339.88, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #42323
I. Perez-Garcia, E. J. Fernandez-Garcia, G. Garcia-Segura, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar, A. Castellon (Univ. de Malaga), Y.-D. Hu (INAF-OAB, Brera), S. Jeong (ADD, Daejeon) and D. Hiriart and W. H. Lee (UNAM), on behalf of a larger collaboration, report:
Following the detection of GRB 251017A by SWIFT/BAT trigger=1404904, the BOOTES-5/JG robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically responded to this event starting on 2025-10-17 08:41:17 UT (23 sec after detection). Series of 1 and 10 second images in clear filter were gathered and we detect an optical source consistent with the one reported by Gupta et al. (GCN 42322). Using GaiaDR3 Gmag as reference we report our photometry analysis:
```
| UT  mid exposure    | mag   | error | filter | exposure time (sec) |
| ------------------- | ----- | ----- | ------ | ------------------- |
| 2025-10-17 08:41:17 | >16.5 | ---   | clear  | 1                   |
| 2025-10-17 08:43:41 | 16.92 | 0.2   | clear  | 1                   |
| 2025-10-17 08:47:57 | 17.51 | 0.08  | clear  | 10                  |
| 2025-10-17 08:53:54 | 17.86 | 0.12  | clear  | 10                  |
```
Further analysis of the additional images is ongoing.
We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for their excellent support.
GCN Circular #42325
Sarah Antier (IJCLAB), Dalya Akl (NYUAD), Enrique Moreno Méndez (UNAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Ny Avo Rakotondrainibe (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the Swift GRB 251017A (Page et al., GCN Circ. 42322) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-17 08:41 to 09:15 UTC (from 1 min to 35 min after the trigger) and obtained 35 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.
We detected the optical counterpart reported by Page et al., GCN Circ. 4232, at the SVOM/UVOT, with preliminary magnitudes of our first images:
```
r = 19.90 +/- 0.17
z = 17.94 +/- 0.09
```
We note that the r-z color is ~2 mag. Concurrent observations were taken by BOOTES (I. Perez-Garcia et al., 42323).
Further observations in g/r/i/z/y are planned.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular #42326
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team.
Using 1230 s of XRT Photon Counting mode data and 2 UVOT images for GRB 251017A, 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 = 335.40133, +7.04008 which is equivalent to:
```
RA (J2000): 22h 21m 36.32s
Dec (J2000): +07d 02' 24.3"
```
with an uncertainty of 2.1 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 #42329
M. Sasada, A. Ochi, R. Kato, Y. Kubo, H. Hagio, H. Seki, S. Joshima, I. Takahashi, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration:
We observed the field of GRB 251017A detected by Swift/BAT (Gupta et al. GCN 42322) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno.
The observation started at 2025-10-17 08:41:53 UT (69 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We detected a point source in the Ic-band image at a position of the reported optical candidate (Gupta et al. GCN 42322; Perez-Garcia et al. GCN 42323; Antier et al. GCN 42325). Here we report the magnitude of the source as follows.
```
T0+[sec] | MID-UT | T-EXP[sec] | magnitude
------------------------------------------------------------------------------------------------
9256 | 2025-10-17 11:15:00 | 11520 | Ic=19.7+/-0.2
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time
```
We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire).
GCN Circular #42330
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 Swift GRB 251017A ( R. Gupta et al., GCN 42322) errorbox 26422 sec after notice time and 26441 sec after trigger time at 2025-10-17 16:01:26 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 43 deg. The sun altitude is -18.3 deg.
The galactic latitude b = -40 deg., longitude l = 72 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3016699
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   26532 |   MASTER-Kislovodsk |   C |   180 | 12.8 |        
   26532 |   MASTER-Kislovodsk |   C |   180 | 17.9 |        
   26731 |   MASTER-Kislovodsk |   C |   180 | 13.4 |        
   26732 |   MASTER-Kislovodsk |   C |   180 | 17.9 |        
   26931 |   MASTER-Kislovodsk |   C |   180 | 13.0 |        
   26932 |   MASTER-Kislovodsk |   C |   180 | 17.9 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #42331
S.Y. Fu (HUST), L.B. He, X. Liu, J. An, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), A.D. Zhu, L. Lei, H.Z. Wu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of Swift GRB 251017A (Gupta et al., GCN 42322) using the 100C telescope of the JinShan project, located at Altay, Xinjiang, China. Observations started at 2025-10-17 12:50:19.42 UT, i.e., 4.16 hours after the trigger, and a series of 300s frames in r and z bands were obtained.
The previously reported optical afterglow (Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Sasada et al., GCN 42329) was clearly detected in our images with r-band magnitude r = 21.17 +- 0.06, calibrated with nearby Pan-STARRS1 DR2 catalog and without the Galactic extinction correction.
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.
GCN Circular #42335
R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251017A, which was also detected by Swift/BAT (GCN 42322).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-17 08:40:42.816 with a duration of 8.2 s and a total significance of about 11.9 sigma. The light curve comprises two primary peaks.
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12.
```
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
```
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular #42336
Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 251017A (Gupta et al., GCN 42322; Goad et al., GCN 42326; Woolf et al., GCN 42335) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began at 2025-10-17T09:01:23 UTC in the J band (~21 minutes after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We detect a clear source at the optical counterpart location (Gupta et al., GCN 42322; Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331), with magnitude J ~ 18.7 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular #42339
C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), E. Le Floc'h (CEA/Irfu), S. Basa (Pytheas/OHP/LAM), B. Schneider (LAM), report on behalf of the MISTRAL GRB collaboration:
We carried out observations of the GRB 251017A (Gupta et al., GCN 42322; Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Woolf et al., GCN 42335; Mo et al., GCN 42336) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 3 exposures of 3min and 2 exposures of 10min in the i-band at a mid time of 2025-10-17 19:52:19UT, corresponding to T-T0 = 11.19 hr.
The afterglow is detected and we measured the following preliminary magnitude:
i’ = 21.39+/-0.32 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025).
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-longhi and the SOPHIE observers H. Bouy
GCN Circular #42341
L. P. Xin, H. L. Li, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team:
SVOM/VT performed a Target of Opportunity observation of GRB 251017A detected by Swift/BAT (Gupta et al., GCN 42322) and Glowbug (Woolf et al., GCN 42335;), starting at 2025-10-17T09:17:19 UTC, 37 min after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical counterpart (Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Mo et al., GCN 42336, Adami et al. GCN 42339) is detected in both channels.
```
Mid-time | exposure time (s) | band |    Magnitude (AB) 
---------|-------------------|------|----------------- 
3.96 h   |     27*70         | VT_B |    22.57+/-0.14 
3.96 h   |     27*70         | VT_R |    20.30+/-0.05 
```
Given the red color from the VT data, it is likely a medium/high redshift burst with a redshift > 4.
Our photometry was 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 Centre 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 #42347
M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Capalbi (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 5.3 ks of XRT data for GRB 251017A, from 96 s to 39.9 ks after the trigger. The data comprise 75 s in Windowed Timing (WT) mode (the first 11 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+4.7 ks) can be modelled with a power-law decay with a decay index of alpha=1.1 (+0.4, -0.3).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.67 (+/-0.15). The best-fitting absorption column is 1.4 (+/-0.5) x 10^21 cm^-2, consistent with the Galactic value of 8.9 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.09 (+0.22, -0.21) and a best-fitting absorption column of 1.9 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.9 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 8.9 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index:	     2.09 (+0.22, -0.21)
```
If the light curve continues to decay with a power-law decay index of 1.1, the count rate at T+24 hours will be 7.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x 10^-13 (3.5 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/01404904.
This circular is an official product of the Swift-XRT team.
GCN Circular #42348
Camila Angulo (UNAM), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Sarah Antier (IJCLAB), Dalya Akl (NYUAD), Enrique Moreno Méndez (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
COLIBRÍ performed follow-up observations of the Swift Swift GRB 251017A (Gupta et al., GCN Circ. 42322) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-18 02:20 to 03:20 UTC (from 17.65 h to 18.65 h after the trigger) and obtained 60 minutes of exposure in the g/r/i/z/y 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.
After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.092 mag (Schlafly & Finkbeiner 2011) and fitting a power-law model to the grizy-bands using the SMC extinction curve, we derive a photometric redshift of z = 4.34+0.15-0.42 (1-sigma c.l.).
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 #42350
L. Izzo (INAF/OACn & DARK/NBI), A. Saccardi (CEA/Irfu), M. Garnichey (LUX-Paris Obs.), M. Ferro (INAF-OABr), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF-IAPS), G. Corcoran (UCD), report on behalf of the Stargate collaboration:
We observed the optical afterglow (Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Mo et al., GCN 42336; Adami et al., GCN 42339; Xin et al., GCN 42341) of GRB 251017A (Gupta et al., GCN 42322; Woolf et al., GCN 42335), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. The mid time of our observation was 2025 Oct 18 01:14:28 UT (16.56 hr after the GRB trigger), and consisted of 8 exposures of 700 s each.
We extracted a 1D spectrum centered on the afterglow emission, using an aperture radius of 0.6 arcsec. In the reduced spectrum, which covers the wavelength range 4750 - 9330 AA, we detect a clear continuum and a trough due to Lya absorption visible at ~6470 AA. From the identification of several absorption features as due to Si II, Si II*, O I, O I*, CII, C II*, Si IV, C IV, Fe II, Al II, we infer a common redshift of z=4.327 for the GRB.
We note that our spectroscopic redshift measurement is consistent with the photometric redshift value provided by Angulo et al. (GCN 42348).
We acknowledge expert support from the observing staff in Paranal, in particular Robert de Rosa, Miguel Lopez, Thallis Pessi and Julien Drevon. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN Circular #42355
S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251017A 98 s after the BAT trigger (Gupta et al., GCN Circ. 42322).
A source consistent with the enhanced XRT position (Goad et al., GCN Circ. 42326) is detected in the initial UVOT exposures.
Preliminary detections and 3-sigma upper limits 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              121          270          147        20.09 +/- 0.22
v                   98         1234          109        >18.8
b                  588         5138           83        >19.6
u                  333         5126          501        >20.3
w1                 712         4921          255        >18.5
w2                 811         1384           58        >20.4
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.108 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #42366
T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team):
Using the data set from T-60 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251017A (trigger #1404904) (Gupta, et al., GCN Circ. 42322). The BAT ground-calculated position is RA, Dec = 335.404, 7.048 deg which is
```
   RA(J2000)  =  22h 21m 37.0s 
   Dec(J2000) = +07d 02' 54.4" 
```
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 93%.
The mask-weighted BAT light curve shows main emission followed by weaker emission. T90 (15-350 keV) is 116.90 +- 61.91 sec (estimated error including systematics).
The time-averaged spectrum from T-5.48 to T+125.08 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.40 +- 0.20. The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+6.41 sec in the 15-150 keV band is 1.3 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1404904
GCN Circular #42368
Dalya Akl (NYUAD), Margarita Pereyra (UNAM), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the Swift GRB 251017A (Gupta et al., GCN Circ. 42322) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-19 01:57 to 05:53 UTC (from 41.48 to 45.22 hours after the trigger) and obtained 96 minutes of simultaneous exposure in the i and z filters.
The data were 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.
Compared to our observations on the previous night (Angulo et al., GCN Circ. 42348), we find the optical counterpart has faded by only
Delta i = 0.06 +/- 0.04
We see similar behaviour in z. These results suggest that we may be observing a late plateau.
Further observations are planned and encouraged.
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 #42370
Thierry Midavaine on behalf of the RAPAS network reports (#5) : Pascal André, David Fardin, Patrick Martinez [1], Christian Pantacchini [2], Jean-Marie Lopez, Cyril Cavadore [3], Lisa Maris [4] observed the field of Gamma-Ray Burst GRB 251017A (R. Gupta et al. GCN 42322, I. Perez-Garcia GCN 42323) using : [1] ADAGIO N 820mm telescope f=3.1m at Belesta Observatory (IAU A05) equipped with a Moravian C3 CMOS camera, [2] N308 mm telescope f=1.1m equipped with a Moravian g3 KAI11000 CCD camera, [3] Société Astronomique de Montpellier N 500mm telescope f=2.2m at Observatoire des Pises (IAU 122) equipped with an ASI6200MMPro CMOS camera, [4] SC 280mm f=1.8m equipped with an ATIK4000 CCD camera. [1][2][3][4] are equipped with RAPAS filters meeting the Gaia G, Gbp, Grp photometric bands. The FITS files are reduced with the Gaia photometric catalog in respective G, Gbp and Grp bands.
The afterglow is detected at
```
RA(J2000) = 22h 21m 36.22s ; Dec(J2000) = +07° 02’ 23.6” ; ± 0.5’’ in G  and Grp bands [1]
RA(J2000) = 22h 21m 36.956s; Dec(J2000) = +07° 02’ 21.90” in G band [3]
```
At this RA Dec location the GRB is above the respective upper limit magnitude Gbp for [1], G for [2] and [4], Gbp and Grp for [3]
```
MJD (mid)     Gaia band   exp(s)   mag.(Gaia)  upperlim RAPAS station
60965.81618   G           1200     22.5 ± 0.3           [3]
60965.82986   G           4500                  20.24   [4]                       
60965.83819   G           3600     22.0 ± 0.3           [1]
60965.83819   Gbp          600                  21      [1]
60965.83819   Grp          600	  >20.00                [1]
60965.89722   G                                         [2]
```
Acknowledgements : RAPAS ( https://gemini.obspm.fr/20220101-rapas/ ) is a ProAm collaboration created by T. Midavaine (SAF), W. Thuillot (LTE, Obs. de Paris-PSL) and M. Dennefeld (IAP/CNRS and Sorbonne Univ.) and funded by the Paris Observatory under API ProAm of the Scientific Council. It aims at homogenizing observing procedures and filters, and is delivering to a network of french amateur observatories a set of 3 filters which have been chosen to meet the Gaia G, Gbp and Grp spectral bands. This network produces data on astrophysical alerts delivered by various Alert systems (Gaia Alerts, Atlas, ZTF, etc…) and collected by Astro-COLIBRI ( https://astro-colibri.science ). This network is similarly progressing towards an homogeneous spectroscopic equipment to deliver SED.
GCN Circular #42477
A. Volnova (IKI), A.N. Tarasenkov (INASAN), A. Pozanenko (IKI), N. Pankov (HSE) report on behalf of IKI GRB-FuN:
We observed the field of the Swift GRB 251017A (Gupta et al., GCN 42322) with RC500 telescope of the INASAN-Kislovodsk observatory. We took several 120-seconds frames in the R-band starting Oct. 17, 2025, 15:09:15 (UT). In the stacked image the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370) is clearly detected. Preliminary photometry is the following:
```
Date        UT start  t-T0       Exp.     Filter  OT     Err.  UL
                     (mid,days)  (n*s)                        (3sigma)
2025-10-17  15:09:15  0.34348    100*120  R       21.45  0.16  22.0
```
The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction.
GCN Circular #42479
A. Volnova (IKI), E. Klunko (ISTP), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI), N. Pankov (HSE, IKI), report on behalf of IKI-GRB-FuN:
We observed the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370; Volnova et al., 42477) of the Swift GRB 251017A (Gupta et al., GCN 42322) in the R-filter with 1.5-meter AZT-33IK telescope of Sayan Solar Observatory (Mondy) on Oct. 17,18,23, 2025, and in the Rb filter with 1-meter Zeiss-1000 telescope of the Koshka Observatory (INASAN) on Oct. 20, 2025. Preliminary photometry and observation details are the following:
```
Date        UT start  t-T0       Exp.    Filter  OT     Err.  UL      Site/Instrum
                     (mid,days)  (n*s)                       (3sigma)
2025-10-17  11:25:01  0.14333    20*120  R       20.41  0.07  21.8    Mondy/AZT-33IK
2025-10-17  12:49:15  0.19065    26*120  R       20.88  0.07  22.3    Mondy/AZT-33IK
2025-10-18  11:40:09  1.14891    35*120  R       21.79  0.13  22.5    Mondy/AZT-33IK
2025-10-20  16:36:07  3.37307    40*180  R       n/d    n/d   21.1    Koshka/Zeiss-1000
2025-10-23  13:18:38  6.22425    45*120  R       n/d    n/d   22.5    Mondy/AZT-33IK
```
The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction.

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