Gamma-ray Burst 250809A

(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 09 Aug 25 16:54:29 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1340954,   Seg_Num: 0
GRB_RA:          233.015d {+15h 32m 04s} (J2000),
                 233.497d {+15h 33m 59s} (current),
                 232.079d {+15h 28m 19s} (1950)
GRB_DEC:         -53.289d {-53d 17' 18"} (J2000),
                 -53.374d {-53d 22' 25"} (current),
                 -53.119d {-53d 07' 08"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       39566 [cnts]    Image_Peak=725 [image_cnts]
TRIGGER_DUR:     16.384 [sec] 
TRIGGER_INDEX:   479     E_range: 25-100 keV
BKG_INTEN:       142064 [cnts]
BKG_TIME:        60699.88 SOD {16:51:39.88} UT
BKG_DUR:         64 [sec]
GRB_DATE:        20896 TJD;   221 DOY;   25/08/09
GRB_TIME:        60799.53 SOD {16:53:19.53} UT
GRB_PHI:         -78.73 [deg]
GRB_THETA:        10.19 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.84 [sigma]
IMAGE_SIGNIF:    9.22 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +2  +0  +0  +1 +24  +0 
SUN_POSTN:       139.80d {+09h 19m 13s}  +15.63d {+15d 37' 50"}
SUN_DIST:        104.67 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.24d {+21h 40m 59s}  -16.43d {-16d 26' 00"}
MOON_DIST:        77.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      244.59,-33.06 [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 = 48.96,-18.84 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 16:55:59 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1340954,   Seg_Num: 0
GRB_RA:          233.0032d {+15h 32m 00.7s} (J2000),
                 233.4847d {+15h 33m 56.3s} (current),
                 232.0672d {+15h 28m 16.1s} (1950)
GRB_DEC:         -53.2946d {-53d 17' 40.5"} (J2000),
                 -53.3799d {-53d 22' 47.6"} (current),
                 -53.1252d {-53d 07' 30.8"} (1950)
GRB_ERROR:       6.1 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       23 [cnts]
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60925.08 SOD {16:55:25.08} UT,   125.6 [sec] since BAT Trigger Time
CENTROID_X:      295.85,  raw= 296  [pixels]
CENTROID_Y:      312.12,  raw= 312  [pixels]
ROLL:            276.99 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   31.64
GRB_POS_XRT_Z:   -37.11
IMAGE_URL:       sw01340954000msxps_rw.img
SUN_POSTN:       139.80d {+09h 19m 13s}  +15.63d {+15d 37' 49"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.26d {+21h 41m 02s}  -16.43d {-16d 25' 39"}
MOON_DIST:        77.92 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.62,  2.35 [deg] galactic lon,lat of the burst
ECL_COORDS:      244.58,-33.07 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 16:56:02 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1340954,   Seg_Num: 0
GRB_RA:          233.0032d {+15h 32m 00.7s} (J2000),
                 233.4847d {+15h 33m 56.3s} (current),
                 232.0672d {+15h 28m 16.1s} (1950)
GRB_DEC:         -53.2946d {-53d 17' 40.5"} (J2000),
                 -53.3799d {-53d 22' 47.6"} (current),
                 -53.1252d {-53d 07' 30.8"} (1950)
GRB_ERROR:       6.1 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       23 [cnts]
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60925.08 SOD {16:55:25.08} UT,   125.6 [sec] since BAT Trigger Time
CENTROID_X:      295.85,  raw= 296  [pixels]
CENTROID_Y:      312.12,  raw= 312  [pixels]
ROLL:            276.99 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   31.64
GRB_POS_XRT_Z:   -37.11
IMAGE_URL:       sw01340954000msxps_rw.img
SUN_POSTN:       139.80d {+09h 19m 13s}  +15.63d {+15d 37' 49"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.26d {+21h 41m 02s}  -16.43d {-16d 25' 38"}
MOON_DIST:        77.92 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.62,  2.35 [deg] galactic lon,lat of the burst
ECL_COORDS:      244.58,-33.07 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 16:55:49 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1340954,   Seg_Num: 0
GRB_RA:          233.0032d {+15h 32m 00.76s} (J2000),
                 233.4847d {+15h 33m 56.33s} (current),
                 232.0672d {+15h 28m 16.12s} (1950)
GRB_DEC:         -53.2946d {-53d 17' 40.5"} (J2000),
                 -53.3799d {-53d 22' 47.6"} (current),
                 -53.1252d {-53d 07' 30.8"} (1950)
GRB_ERROR:       6.3 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       5.16e-10 [erg/cm2/sec]
GRB_SIGNIF:      4.79 [sigma]
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60925.08 SOD {16:55:25.08} UT,   125.6 [sec] since BAT Trigger Time
TAM[0-3]:        327.65 237.19 261.61 243.82
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       139.80d {+09h 19m 13s}  +15.63d {+15d 37' 49"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.26d {+21h 41m 02s}  -16.43d {-16d 25' 41"}
MOON_DIST:        77.92 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.62,  2.35 [deg] galactic lon,lat of the burst
ECL_COORDS:      244.58,-33.07 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 0.56 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 16:58:12 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1340954,   Seg_Num: 0
GRB_RA:          233.015d {+15h 32m 04s} (J2000),
                 233.497d {+15h 33m 59s} (current),
                 232.079d {+15h 28m 19s} (1950)
GRB_DEC:         -53.289d {-53d 17' 18"} (J2000),
                 -53.374d {-53d 22' 25"} (current),
                 -53.119d {-53d 07' 08"} (1950)
GRB_DATE:        20896 TJD;   221 DOY;   25/08/09
GRB_TIME:        60799.53 SOD {16:53:19.53} UT
TRIGGER_INDEX:   479
GRB_PHI:         -78.73 [deg]
GRB_THETA:        10.19 [deg]
DELTA_TIME:      -43.00 [sec]
TRIGGER_DUR:     16.384 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.84 [sigma]
IMAGE_SIGNIF:    9.22 [sigma]
LC_URL:          sw01340954000msb.lc
SUN_POSTN:       139.80d {+09h 19m 13s}  +15.63d {+15d 37' 48"}
SUN_DIST:        104.67 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.28d {+21h 41m 07s}  -16.42d {-16d 25' 08"}
MOON_DIST:        77.93 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      244.59,-33.06 [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 = 48.96,-18.84 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 17:00:05 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.022d {+15h 32m 05s} (J2000)
POINT_DEC:       -53.287d {-53d 17' 12"} (J2000)
POINT_ROLL:      276.989d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60927.68 SOD {16:55:27.68} UT,   128.2 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.897
N_STARS:         190
X_OFFSET:        264 [pixels]
Y_OFFSET:        288 [pixels]
X_MAX:           1703 [pixels]
Y_MAX:           1727 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    4
SL_URL:          sw01340954000msufc0128.fits
SUN_POSTN:       139.81d {+09h 19m 13s}  +15.63d {+15d 37' 46"}
SUN_DIST:        104.67 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.30d {+21h 41m 11s}  -16.41d {-16d 24' 43"}
MOON_DIST:        77.94 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 17:00:23 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.022d {+15h 32m 05s} (J2000)
POINT_DEC:       -53.287d {-53d 17' 12"} (J2000)
POINT_ROLL:      276.989d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60927.68 SOD {16:55:27.68} UT,   128.2 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.897
N_STARS:         190
X_OFFSET:        264 [pixels]
Y_OFFSET:        288 [pixels]
X_MAX:           1703 [pixels]
Y_MAX:           1727 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    4
SL_URL:          sw01340954000msufc0128.fits
SUN_POSTN:       139.81d {+09h 19m 13s}  +15.63d {+15d 37' 46"}
SUN_DIST:        104.67 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.30d {+21h 41m 11s}  -16.41d {-16d 24' 39"}
MOON_DIST:        77.95 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [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 09 Aug 25 17:01:42 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.022d {+15h 32m 05s} (J2000)
POINT_DEC:       -53.287d {-53d 17' 12"} (J2000)
ROLL:            276.989d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60927.68 SOD {16:55:27.68} UT,   128.2 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     776451363
X_OFFSET:        838 [pixels]
Y_OFFSET:        782 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       998
Y_GRB_POS:       942
BINNING_INDEX:   1
IM_URL:          sw01340954000msuni0165.fits
SUN_POSTN:       139.81d {+09h 19m 14s}  +15.63d {+15d 37' 45"}
SUN_DIST:        104.67 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.31d {+21h 41m 14s}  -16.41d {-16d 24' 21"}
MOON_DIST:        77.96 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [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 09 Aug 25 17:01:51 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.022d {+15h 32m 05s} (J2000)
POINT_DEC:       -53.287d {-53d 17' 12"} (J2000)
ROLL:            276.989d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60927.68 SOD {16:55:27.68} UT,   128.2 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     776451363
X_OFFSET:        838 [pixels]
Y_OFFSET:        782 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       998
Y_GRB_POS:       942
BINNING_INDEX:   1
IM_URL:          sw01340954000msuni0165.fits
SUN_POSTN:       139.81d {+09h 19m 14s}  +15.63d {+15d 37' 45"}
SUN_DIST:        104.67 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.31d {+21h 41m 15s}  -16.41d {-16d 24' 19"}
MOON_DIST:        77.96 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [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 Circular #41303
T. M. Parsotan (GSFC), R. Brivio (INAF-OAB), J. J. DeLaunay (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team:
At 16:53:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250809A (trigger=1340954). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.015, -53.289 which is
```
   RA(J2000) = 15h 32m 04s
   Dec(J2000) = -53d 17' 18"
```
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 40 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~11 sec after the trigger.
The XRT began observing the field at 16:55:25.0 UT, 125.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 233.00282, -53.29640 which is equivalent to: RA(J2000) = 15h 32m 00.68s Dec(J2000) = -53d 17' 47.0" with an uncertainty of 4.3 arcseconds (radius, 90% containment). This location is 37 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 consistent with the Galactic value of 8.04 x 10^21 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 5.16e-10 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 250 seconds with the U filter starting 128 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain, extinction expected.
Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov). 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 09 Aug 25 17:12:58 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.024d {+15h 32m 06s} (J2000)
POINT_DEC:       -53.288d {-53d 17' 15"} (J2000)
POINT_ROLL:      276.987d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  61662.76 SOD {17:07:42.76} UT,   863.2 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.562
N_STARS:         190
X_OFFSET:        278 [pixels]
Y_OFFSET:        222 [pixels]
X_MAX:           1717 [pixels]
Y_MAX:           1661 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01340954000msufc0863.fits
SUN_POSTN:       139.81d {+09h 19m 15s}  +15.63d {+15d 37' 37"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.41d {+21h 41m 39s}  -16.36d {-16d 21' 46"}
MOON_DIST:        78.05 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 17:13:19 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.024d {+15h 32m 06s} (J2000)
POINT_DEC:       -53.288d {-53d 17' 15"} (J2000)
POINT_ROLL:      276.987d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  61662.76 SOD {17:07:42.76} UT,   863.2 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.562
N_STARS:         190
X_OFFSET:        278 [pixels]
Y_OFFSET:        222 [pixels]
X_MAX:           1717 [pixels]
Y_MAX:           1661 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01340954000msufc0863.fits
SUN_POSTN:       139.81d {+09h 19m 16s}  +15.63d {+15d 37' 37"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.41d {+21h 41m 39s}  -16.36d {-16d 21' 42"}
MOON_DIST:        78.05 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [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 09 Aug 25 17:14:11 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.024d {+15h 32m 06s} (J2000)
POINT_DEC:       -53.288d {-53d 17' 15"} (J2000)
ROLL:            276.987d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  61662.76 SOD {17:07:42.76} UT,   863.2 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     776452098
X_OFFSET:        837 [pixels]
Y_OFFSET:        781 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       997
Y_GRB_POS:       941
BINNING_INDEX:   1
IM_URL:          sw01340954000msuni0900.fits
SUN_POSTN:       139.82d {+09h 19m 16s}  +15.63d {+15d 37' 36"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.42d {+21h 41m 41s}  -16.36d {-16d 21' 30"}
MOON_DIST:        78.06 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [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:     Sat 09 Aug 25 17:13:40 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1340954,   Seg_Num: 0
GRB_RA:          233.0004d {+15h 32m 00.09s} (J2000),
                 233.4819d {+15h 33m 55.66s} (current),
                 232.0644d {+15h 28m 15.45s} (1950)
GRB_DEC:         -53.2963d {-53d 17' 46.6"} (J2000),
                 -53.3816d {-53d 22' 53.7"} (current),
                 -53.1269d {-53d 07' 36.9"} (1950)
GRB_ERROR:       3.0 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  60943.00 SOD {16:55:43.00} UT,   143.5 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       139.81d {+09h 19m 16s}  +15.63d {+15d 37' 36"}
SUN_DIST:        104.65 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.42d {+21h 41m 40s}  -16.36d {-16d 21' 37"}
MOON_DIST:        78.07 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.61,  2.35 [deg] galactic lon,lat of the burst
ECL_COORDS:      244.58,-33.07 [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 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 0.11% < P(seren) < 0.58%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 09 Aug 25 17:14:25 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1340954,   Seg_Num: 0
POINT_RA:        233.024d {+15h 32m 06s} (J2000)
POINT_DEC:       -53.288d {-53d 17' 15"} (J2000)
ROLL:            276.987d
IMG_START_DATE:  20896 TJD;   221 DOY;   25/08/09
IMG_START_TIME:  61662.76 SOD {17:07:42.76} UT,   863.2 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     776452098
X_OFFSET:        837 [pixels]
Y_OFFSET:        781 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       997
Y_GRB_POS:       941
BINNING_INDEX:   1
IM_URL:          sw01340954000msuni0900.fits
SUN_POSTN:       139.82d {+09h 19m 16s}  +15.63d {+15d 37' 36"}
SUN_DIST:        104.66 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      325.42d {+21h 41m 42s}  -16.36d {-16d 21' 26"}
MOON_DIST:        78.06 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      325.63,  2.35 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      244.59,-33.06 [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 #41304
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Using 923 s of promptly downlinked XRT event data for GRB 250809A, we find an enhanced XRT position of the afterglow: RA, Dec: 233.00043, -53.29626 which is equivalent to:
```
   RA (J2000)  = 15 32 00.10
   Dec (J2000) = -53 17 46.5
```
with an uncertainty of 3.0 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1340954.
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 #41310
R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:
We observed the Swift GRB 250809A field (Parsotan et al., GCN 41303) with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on August 9, from 23:10 to 23:42 UT (corresponding to 6.28 to 6.85 hours after the GRB trigger time) with the Bessel R and I filters.
We performed a series of 3x300s exposures in I-band and R-band. We do not detect an uncatalogued source within the Prompt Swift XRT error region (Evans et al., GCN 41304) in either band.
The following 3-sigma upper limits are calculated using the USNO-B1.0 catalog as reference:
```
R > 20.6
I > 20.3
```
These magnitudes are not corrected for galactic extinction.
GCN Circular #41313
J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), M.A. Williams (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 6.7 ks of XRT data for GRB 250809A, from 113 s to 51.4 ks after the trigger. The data comprise 910 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 233.00043, -53.29626 which is equivalent to:
```
RA (J2000): 01h 00m 00.00s
Dec(J2000): -53d 00' 00.0"
```
with an uncertainty of 3.0 arcsec (radius, 90% confidence).
The light curve can be modelled with an initial rise, with a power-law index of alpha=-1.5 (NaN, NaN), followed by a break at T+281 s to an alpha of 8.0 (NaN, NaN).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.41 (+/-0.13). The best-fitting absorption column is 2.05 (+0.18, -0.17) x 10^22 cm^-2, in excess of the Galactic value of 8.0 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 4.9 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
```
Total column:	     2.05 (+0.18, -0.17) x 10^22 cm^-2
Galactic foreground: 8.0 x 10^21 cm^-2
Excess significance: 11.9 sigma
Photon index:	     2.41 (+/-0.13)
```
If the light curve continues to decay with a power-law decay index of 2.96, the count rate at T+24 hours will be 3.7 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x 10^-18 (6.1 x 10^-18) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01340954.
This circular is an official product of the Swift-XRT team.
GCN Circular #41314
K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team:
GCN Circ. 41313 provided an incomplete automatic modelling of the XRT light-curve of GRB 250809A. The first snapshot of data is dominated by a large flare, peaking at 240 s after the BAT trigger. The underlying decay can be modelled as a power-law with alpha = 3.0 +/- 0.2.
If the light curve continues to decay with a power-law decay index of 3.0, the count rate at T+24 hours will be 2.3 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.3 x 10^-20 (1.5 x 10^-19) erg cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular #41316
N.P.M. Kuin (UCL/MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250809A 128 s after the BAT trigger (Parsotan et al., GCN Circ. 41303). A source consistent with the XRT position ( Evans et al. GCN Circ. 41304 ) 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

v                  435          755           58         17.62 +/- 0.21
b                  384         1038           97         18.86 +/- 0.19
u                  128         1013          452         19.57 +/- 0.21
w1                 484          805           58        >18.4
m2                 459          780           58        >20.1
w2                 410         1064           78        >18.8
```
The earliest exposures were fainter; these detections are near the peak of the light curve.
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.919 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #41321
D. Sadaula (GSFC/UMBC), 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), T. Parsotan (GSFC), T. Sakamoto (AGU) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250809A (trigger #1340954) (Parsotan, et al., GCN Circ. 41303). The BAT ground-calculated position is RA, Dec = 233.034, -53.314 deg which is
```
   RA(J2000)  =  15h 32m 08.2s 
   Dec(J2000) = -53d 18' 50.6" 
```
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%.
The BAT light curve showed a complex structure with a duration of about 32 sec. T90 (15-350 keV) is 17.79 +- 2.77 sec (estimated error including systematics).
The time-averaged spectrum from T+1.01 to T+20.94 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.83 +- 0.20. The fluence in the 15-150 keV band is 3.9 +- 0.5 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+11.58 sec in the 15-150 keV band is 0.6 +- 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/1340954

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Jochen Greiner, last update: 12-Aug-2025 [Disclaimer]