Gamma-ray Burst 250904A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:37:30 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1347179,   Seg_Num: 0
GRB_RA:           84.358d {+05h 37m 26s} (J2000),
                  84.696d {+05h 38m 47s} (current),
                  83.700d {+05h 34m 48s} (1950)
GRB_DEC:          +3.584d {+03d 35' 04"} (J2000),
                  +3.598d {+03d 35' 53"} (current),
                  +3.556d {+03d 33' 20"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       3248 [cnts]    Image_Peak=195 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   146     E_range: 25-100 keV
BKG_INTEN:       17392 [cnts]
BKG_TIME:        63411.73 SOD {17:36:51.73} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20922 TJD;   247 DOY;   25/09/04
GRB_TIME:        63423.05 SOD {17:37:03.05} UT
GRB_PHI:          -6.64 [deg]
GRB_THETA:        13.62 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     20.42 [sigma]
IMAGE_SIGNIF:    8.77 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +2  -1  +0  +0 -18  +0 
SUN_POSTN:       163.81d {+10h 55m 14s}   +6.89d {+06d 53' 31"}
SUN_DIST:         78.77 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.04d {+20h 28m 11s}  -22.93d {-22d 55' 44"}
MOON_DIST:       134.73 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       84.02,-19.74 [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 = 220.86,-19.68 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:38:31 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.357d {+05h 37m 26s} (J2000)
POINT_DEC:        +3.581d {+03d 34' 50"} (J2000)
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63505.44 SOD {17:38:25.44} UT,   82.4 [sec] since BAT Trigger Time
COUNTS:          17    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        2    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:41:34 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1347179,   Seg_Num: 0
GRB_RA:           84.358d {+05h 37m 26s} (J2000),
                  84.696d {+05h 38m 47s} (current),
                  83.700d {+05h 34m 48s} (1950)
GRB_DEC:          +3.584d {+03d 35' 04"} (J2000),
                  +3.598d {+03d 35' 53"} (current),
                  +3.556d {+03d 33' 20"} (1950)
GRB_DATE:        20922 TJD;   247 DOY;   25/09/04
GRB_TIME:        63423.05 SOD {17:37:03.05} UT
TRIGGER_INDEX:   146
GRB_PHI:          -6.64 [deg]
GRB_THETA:        13.62 [deg]
DELTA_TIME:      -11.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     20.42 [sigma]
IMAGE_SIGNIF:    8.77 [sigma]
LC_URL:          sw01347179000msb.lc
SUN_POSTN:       163.81d {+10h 55m 14s}   +6.89d {+06d 53' 28"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.08d {+20h 28m 20s}  -22.92d {-22d 55' 04"}
MOON_DIST:       134.70 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       84.02,-19.74 [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 = 220.86,-19.68 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:42:16 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.357d {+05h 37m 26s} (J2000)
POINT_DEC:        +3.580d {+03d 34' 50"} (J2000)
POINT_ROLL:      83.669d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63508.74 SOD {17:38:28.74} UT,   85.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.835
N_STARS:         190
X_OFFSET:        482 [pixels]
Y_OFFSET:        537 [pixels]
X_MAX:           1441 [pixels]
Y_MAX:           1496 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    11
SL_URL:          sw01347179000msufc0085.fits
SUN_POSTN:       163.81d {+10h 55m 14s}   +6.89d {+06d 53' 27"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.09d {+20h 28m 22s}  -22.92d {-22d 54' 57"}
MOON_DIST:       134.69 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.02,-19.74 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:42:29 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.357d {+05h 37m 26s} (J2000)
POINT_DEC:        +3.580d {+03d 34' 50"} (J2000)
POINT_ROLL:      83.669d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63508.74 SOD {17:38:28.74} UT,   85.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.835
N_STARS:         190
X_OFFSET:        482 [pixels]
Y_OFFSET:        537 [pixels]
X_MAX:           1441 [pixels]
Y_MAX:           1496 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    11
SL_URL:          sw01347179000msufc0085.fits
SUN_POSTN:       163.81d {+10h 55m 14s}   +6.89d {+06d 53' 27"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.09d {+20h 28m 22s}  -22.92d {-22d 54' 54"}
MOON_DIST:       134.69 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.02,-19.74 [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:     Thu 04 Sep 25 17:43:45 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.357d {+05h 37m 26s} (J2000)
POINT_DEC:        +3.580d {+03d 34' 50"} (J2000)
ROLL:            83.669d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63508.74 SOD {17:38:28.74} UT,   85.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     778700345
X_OFFSET:        801 [pixels]
Y_OFFSET:        856 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       961
Y_GRB_POS:       1016
BINNING_INDEX:   1
IM_URL:          sw01347179000msuni0122.fits
SUN_POSTN:       163.81d {+10h 55m 15s}   +6.89d {+06d 53' 26"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.10d {+20h 28m 25s}  -22.91d {-22d 54' 42"}
MOON_DIST:       134.68 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.02,-19.74 [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:     Thu 04 Sep 25 17:43:58 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.357d {+05h 37m 26s} (J2000)
POINT_DEC:        +3.580d {+03d 34' 50"} (J2000)
ROLL:            83.669d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63508.74 SOD {17:38:28.74} UT,   85.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     778700345
X_OFFSET:        801 [pixels]
Y_OFFSET:        856 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       961
Y_GRB_POS:       1016
BINNING_INDEX:   1
IM_URL:          sw01347179000msuni0122.fits
SUN_POSTN:       163.81d {+10h 55m 15s}   +6.89d {+06d 53' 25"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.11d {+20h 28m 25s}  -22.91d {-22d 54' 40"}
MOON_DIST:       134.68 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.02,-19.74 [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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:42:20 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1347179,   Seg_Num: 0
GRB_RA:           84.3800d {+05h 37m 31.19s} (J2000),
                  84.7179d {+05h 38m 52.30s} (current),
                  83.7222d {+05h 34m 53.32s} (1950)
GRB_DEC:          +3.5850d {+03d 35' 05.9"} (J2000),
                  +3.5986d {+03d 35' 54.8"} (current),
                  +3.5561d {+03d 33' 22.1"} (1950)
GRB_ERROR:       3.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63518.00 SOD {17:38:38.00} UT,   94.9 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       163.81d {+10h 55m 14s}   +6.89d {+06d 53' 27"}
SUN_DIST:         78.75 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.09d {+20h 28m 22s}  -22.92d {-22d 54' 56"}
MOON_DIST:       134.71 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.01,-14.66 [deg] galactic lon,lat of the burst
ECL_COORDS:       84.04,-19.74 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
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 http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN Circular #41704
C. Salvaggio (INAF-OAB), R. Brivio (INAF-OAB), S. Dichiara (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team:
At 17:37:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250904A (trigger=1347179). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 84.358, +3.584 which is
```
   RA(J2000) = 05h 37m 26s
   Dec(J2000) = +03d 35' 04"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single complex peak structure with a duration of about 50 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~8 sec after the trigger.
The XRT began observing the field at 17:38:25.4 UT, 82.4 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 84.38001, 3.58520 which is equivalent to:
```
   RA(J2000)  = 05h 37m 31.20s
   Dec(J2000) = +03d 35' 06.7"
```
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 79 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 3.34 x 10^21 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 85 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.292.
Burst Advocate for this burst is C. Salvaggio (chiara.salvaggio AT inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:49:52 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.356d {+05h 37m 25s} (J2000)
POINT_DEC:        +3.583d {+03d 34' 57"} (J2000)
POINT_ROLL:      83.668d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63721.55 SOD {17:42:01.55} UT,   298.5 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.158
N_STARS:         161
X_OFFSET:        242 [pixels]
Y_OFFSET:        297 [pixels]
X_MAX:           1681 [pixels]
Y_MAX:           1736 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01347179000msufc0298.fits
SUN_POSTN:       163.81d {+10h 55m 16s}   +6.89d {+06d 53' 20"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.16d {+20h 28m 39s}  -22.89d {-22d 53' 41"}
MOON_DIST:       134.64 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.01,-19.74 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:50:10 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.356d {+05h 37m 25s} (J2000)
POINT_DEC:        +3.583d {+03d 34' 57"} (J2000)
POINT_ROLL:      83.668d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63721.55 SOD {17:42:01.55} UT,   298.5 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.158
N_STARS:         161
X_OFFSET:        242 [pixels]
Y_OFFSET:        297 [pixels]
X_MAX:           1681 [pixels]
Y_MAX:           1736 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01347179000msufc0298.fits
SUN_POSTN:       163.82d {+10h 55m 16s}   +6.89d {+06d 53' 20"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.16d {+20h 28m 40s}  -22.89d {-22d 53' 38"}
MOON_DIST:       134.63 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.01,-19.74 [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:     Thu 04 Sep 25 17:51:17 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.356d {+05h 37m 25s} (J2000)
POINT_DEC:        +3.583d {+03d 34' 57"} (J2000)
ROLL:            83.668d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63721.55 SOD {17:42:01.55} UT,   298.5 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     778700557
X_OFFSET:        801 [pixels]
Y_OFFSET:        856 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       961
Y_GRB_POS:       1016
BINNING_INDEX:   1
IM_URL:          sw01347179000msuni0335.fits
SUN_POSTN:       163.82d {+10h 55m 16s}   +6.89d {+06d 53' 19"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.18d {+20h 28m 42s}  -22.89d {-22d 53' 26"}
MOON_DIST:       134.63 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.01,-19.74 [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:     Thu 04 Sep 25 17:51:30 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1347179,   Seg_Num: 0
POINT_RA:         84.356d {+05h 37m 25s} (J2000)
POINT_DEC:        +3.583d {+03d 34' 57"} (J2000)
ROLL:            83.668d
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63721.55 SOD {17:42:01.55} UT,   298.5 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     778700557
X_OFFSET:        801 [pixels]
Y_OFFSET:        856 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       961
Y_GRB_POS:       1016
BINNING_INDEX:   1
IM_URL:          sw01347179000msuni0335.fits
SUN_POSTN:       163.82d {+10h 55m 16s}   +6.89d {+06d 53' 18"}
SUN_DIST:         78.78 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.18d {+20h 28m 43s}  -22.89d {-22d 53' 24"}
MOON_DIST:       134.62 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.00,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       84.01,-19.74 [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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 04 Sep 25 17:50:20 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1347179,   Seg_Num: 0
GRB_RA:           84.3801d {+05h 37m 31.22s} (J2000),
                  84.7180d {+05h 38m 52.32s} (current),
                  83.7223d {+05h 34m 53.35s} (1950)
GRB_DEC:          +3.5846d {+03d 35' 04.5"} (J2000),
                  +3.5982d {+03d 35' 53.4"} (current),
                  +3.5557d {+03d 33' 20.6"} (1950)
GRB_ERROR:       2.2 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20922 TJD;   247 DOY;   25/09/04
IMG_START_TIME:  63518.00 SOD {17:38:38.00} UT,   94.9 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       163.82d {+10h 55m 16s}   +6.89d {+06d 53' 19"}
SUN_DIST:         78.76 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      307.17d {+20h 28m 40s}  -22.89d {-22d 53' 36"}
MOON_DIST:       134.66 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      201.01,-14.66 [deg] galactic lon,lat of the burst
ECL_COORDS:       84.04,-19.74 [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 http://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 0.58% < P(seren) < 1.1%.

GCN Circular #41706
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Using 343 s of promptly downlinked XRT event data for GRB 250904A, we find an enhanced XRT position of the afterglow: RA, Dec: 84.38029, 3.58466 which is equivalent to:
```
   RA (J2000)  = 05 37 31.27
   Dec (J2000) = +03 35 04.8
```
with an uncertainty of 2.2 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1347179.
Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.
GCN Circular #41709
S.Y. Fu (HUST), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of GRB 250904A (Salvaggio et al., GCN 41704), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 17:49:41.450 UTC on 2025-09-04, i.e., ~ 12.6 min after the Swift/BAT trigger and a series of frames in the R band were obtained.
An uncatalogued source is detected in our stacked image within the enhanced Swift/XRT error circle (Evans et al., GCN 41706) with magnitude of R = 20.1 +/- 0.2 (AB) at 18.97 min post-trigger, calibrated with Pan-STARRS1 DR2 catalog converted using Lupton (2005) equations and not corrected for Galactic extinction.
GCN Circular #41711
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team.
Using 343 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250904A, 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 = 84.38044, +3.58445 which is equivalent to:
```
RA (J2000): 05h 37m 31.31s
Dec (J2000): +03d 35' 04.0"
```
with an uncertainty of 2.5 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position can be viewed at http://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 #41712
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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB 250904A ( C. Salvaggio et al., GCN 41704) errorbox 19454 sec after notice time and 19494 sec after trigger time at 2025-09-04 23:01:57 UT, with upper limit up to 15.5 mag. The observations began at zenith distance = 81 deg. The sun altitude is -35.9 deg.
The galactic latitude b = -14 deg., longitude l = 201 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2984839
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   19585 |      MASTER-Tavrida |   C |   180 | 15.5 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #41719
J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.0 ks of XRT data for GRB 250904A, from 66 s to 45.6 ks after the trigger. The data comprise 9 s in Windowed Timing (WT) mode (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=0.85 (+0.05, -0.04).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.05 (+0.27, -0.25). The best-fitting absorption column is 4.4 (+1.4, -1.0) x 10^21 cm^-2, consistent with the Galactic value of 3.3 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (6.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     4.4 (+1.4, -1.0) x 10^21 cm^-2
Galactic foreground: 3.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.05 (+0.27, -0.25)
```
If the light curve continues to decay with a power-law decay index of 0.85, the count rate at T+24 hours will be 7.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x 10^-13 (4.5 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01347179.
This circular is an official product of the Swift-XRT team.

GCN Circular #41721
S. R. Oates (Lancaster Uni.) and C. Salvaggio (INAF-OAB) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250904A 86 s after the BAT trigger (Salvaggio et al., GCN Circ. 41704). A source consistent with the XRT position (Goad et al., GCN Circ. 41711) is detected in white and marginally in u.
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/3sigUL
white (FC)          86           235            147             20.23+\-0.36
u   (FC)            298           441             141            19.14+\-0.41 (2.7 sigma)
white              4990      10603           1097             20.60+\-0.16
v                   5401         5601             197             >19.5
b                   4786         6421             393             >20.4
u                   6016         6215             197             >19.6
uvw1             5811         6011             197             >19.5
uvm2             5606        5806             197             >19.4
uvw2             5196       10942             524             >20.2

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.284 in the direction of the burst (Schlegel et al. 1998).

GCN Circular #41723
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of GRB250904A (Salvaggio et al., GCN 41704) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x120s exposures in the SDSS i’ filter starting at 2025-09-05 05:47:54 UT, approximately 12.2 hours after the trigger.
We do not detect the reported optical counterpart (Fu et al., GCN 41709; Oates et al., GCN 41721) or any new source near the XRT position (Evans et al., GCN 41706; Goad et al., GCN 41711). The 3-sigma limiting magnitude on the stacked images is i > 22.4 mag.
GCN Circular #41730
D. M. Palmer (LANL), 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), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250904 A (trigger #1347179) (Salvaggio, et al., GCN Circ. 41704). The BAT ground-calculated position is RA, Dec = 84.377, 3.575 deg which is
```
   RA(J2000)  =  05h 37m 30.5s 
   Dec(J2000) = +03d 34' 29.9" 
```
with an uncertainty of 1.0 arcmin (radius, sys+stat, 90% containment). The partial coding was 100%.
The BAT light curve showed a complex structure with a duration of about 50 sec. T90 (15-350 keV) is 37.11 +- 13.89 sec (estimated error including systematics).
The time-averaged spectrum from T-19.68 to T+54.44 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.40 +- 0.11. The fluence in the 15-150 keV band is 1.7 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+5.11 sec in the 15-150 keV band is 1.1 +- 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/1347179

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Jochen Greiner, last update: 05-Sep-2025 [Disclaimer]