Gamma-ray Burst 150831A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:34:36 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     653838,   Seg_Num: 0
GRB_RA:          221.023d {+14h 44m 05s} (J2000),
                 221.251d {+14h 45m 00s} (current),
                 220.295d {+14h 41m 11s} (1950)
GRB_DEC:         -25.649d {-25d 38' 57"} (J2000),
                 -25.715d {-25d 42' 54"} (current),
                 -25.438d {-25d 26' 17"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       3027 [cnts]    Image_Peak=282 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   483     E_range: 50-350 keV
BKG_INTEN:       16908 [cnts]
BKG_TIME:        38040.93 SOD {10:34:00.93} UT
BKG_DUR:         8 [sec]
GRB_DATE:        17265 TJD;   243 DOY;   15/08/31
GRB_TIME:        38052.89 SOD {10:34:12.89} UT
GRB_PHI:         -59.47 [deg]
GRB_THETA:        31.20 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     56.48 [sigma]
IMAGE_SIGNIF:    14.35 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +3  +3  +0  +0 -36  +0 
SUN_POSTN:       159.40d {+10h 37m 35s}   +8.67d {+08d 40' 24"}
SUN_DIST:         69.22 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.90d {+00h 03m 36s}   +0.50d {+00d 30' 18"}
MOON_DIST:       133.66 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.58, 30.66 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      226.43, -9.31 [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 = 93.75,-6.25 [deg].

red DSS finding chart ps-file

GCN NOTICE

 
TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Mon 31 Aug 15 10:34:25 UT
NOTICE_TYPE:    INTEGRAL Weak  
TRIGGER_NUM:    7228,   Sub_Num: 0
GRB_RA:         220.9816d {+14h 43m 56s} (J2000),
                221.2098d {+14h 44m 50s} (current),
                220.2544d {+14h 41m 01s} (1950)
GRB_DEC:        -25.6493d {-25d 38' 56"} (J2000),
                -25.7150d {-25d 42' 53"} (current),
                -25.4379d {-25d 26' 16"} (1950)
GRB_ERROR:      3.43 [arcmin, radius, statistical only]
GRB_INTEN:      7.34 [sigma]   
GRB_TIME:       38060.78 SOD {10:34:20.78} UT
GRB_DATE:       17265 TJD;   243 DOY;   15/08/31
SC_RA:          233.31 [deg] (J2000)
SC_DEC:         -33.86 [deg] (J2000)
SUN_POSTN:      159.40d {+10h 37m 35s}   +8.67d {+08d 40' 24"}
SUN_DIST:        69.19 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       0.90d {+00h 03m 35s}   +0.50d {+00d 30' 15"}
MOON_DIST:      133.69 [deg]   
GAL_COORDS:     332.54, 30.68 [deg] galactic lon,lat of the burst  
ECL_COORDS:     226.40, -9.32 [deg] ecliptic lon,lat of the burst
COMMENTS:       INTEGRAL GRB Coordinates -- this is the weak/subthreshold trigger notice.
COMMENTS:       This notice may or may not be followed by a Wakeup/Refined/Offline notice.
COMMENTS:       Time_Scale=0.3199 and Time_Error=8.0000.
COMMENTS:       Possibly real GRB event (WEAK detection)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:36:10 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     653838,   Seg_Num: 0
GRB_RA:          221.0257d {+14h 44m 06.16s} (J2000),
                 221.2540d {+14h 45m 00.95s} (current),
                 220.2985d {+14h 41m 11.64s} (1950)
GRB_DEC:         -25.6361d {-25d 38' 09.9"} (J2000),
                 -25.7018d {-25d 42' 06.3"} (current),
                 -25.4249d {-25d 25' 29.6"} (1950)
GRB_ERROR:       5.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       8.91e-10 [erg/cm2/sec]
GRB_SIGNIF:      6.00 [sigma]
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38136.33 SOD {10:35:36.33} UT,   83.4 [sec] since BAT Trigger Time
TAM[0-3]:        327.69 237.22 261.53 243.34
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       159.40d {+10h 37m 35s}   +8.67d {+08d 40' 22"}
SUN_DIST:         69.22 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.91d {+00h 03m 40s}   +0.51d {+00d 30' 36"}
MOON_DIST:       133.68 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.67 [deg] galactic lon,lat of the burst
ECL_COORDS:      226.43, -9.30 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 0.82 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:36:28 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     653838,   Seg_Num: 0
GRB_RA:          221.0257d {+14h 44m 06.1s} (J2000),
                 221.2540d {+14h 45m 00.9s} (current),
                 220.2985d {+14h 41m 11.6s} (1950)
GRB_DEC:         -25.6361d {-25d 38' 09.9"} (J2000),
                 -25.7018d {-25d 42' 06.3"} (current),
                 -25.4249d {-25d 25' 29.6"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       36 [cnts]
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38136.33 SOD {10:35:36.33} UT,   83.4 [sec] since BAT Trigger Time
CENTROID_X:      266.89,  raw= 267  [pixels]
CENTROID_Y:      269.57,  raw= 270  [pixels]
ROLL:            291.31 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -66.54
GRB_POS_XRT_Z:   -90.53
IMAGE_URL:       sw00653838000msxps_rw.img
SUN_POSTN:       159.40d {+10h 37m 35s}   +8.67d {+08d 40' 22"}
SUN_DIST:         69.22 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.92d {+00h 03m 40s}   +0.51d {+00d 30' 40"}
MOON_DIST:       133.68 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.67 [deg] galactic lon,lat of the burst
ECL_COORDS:      226.43, -9.30 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:36:19 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     653838,   Seg_Num: 0
GRB_RA:          221.0257d {+14h 44m 06.1s} (J2000),
                 221.2540d {+14h 45m 00.9s} (current),
                 220.2985d {+14h 41m 11.6s} (1950)
GRB_DEC:         -25.6361d {-25d 38' 09.9"} (J2000),
                 -25.7018d {-25d 42' 06.3"} (current),
                 -25.4249d {-25d 25' 29.6"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       36 [cnts]
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38136.33 SOD {10:35:36.33} UT,   83.4 [sec] since BAT Trigger Time
CENTROID_X:      266.89,  raw= 267  [pixels]
CENTROID_Y:      269.57,  raw= 270  [pixels]
ROLL:            291.31 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -66.54
GRB_POS_XRT_Z:   -90.53
IMAGE_URL:       sw00653838000msxps_rw.img
SUN_POSTN:       159.40d {+10h 37m 35s}   +8.67d {+08d 40' 22"}
SUN_DIST:         69.22 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.92d {+00h 03m 40s}   +0.51d {+00d 30' 38"}
MOON_DIST:       133.68 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.67 [deg] galactic lon,lat of the burst
ECL_COORDS:      226.43, -9.30 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:38:14 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     653838,   Seg_Num: 0
GRB_RA:          221.023d {+14h 44m 05s} (J2000),
                 221.251d {+14h 45m 00s} (current),
                 220.295d {+14h 41m 11s} (1950)
GRB_DEC:         -25.649d {-25d 38' 57"} (J2000),
                 -25.715d {-25d 42' 54"} (current),
                 -25.438d {-25d 26' 17"} (1950)
GRB_DATE:        17265 TJD;   243 DOY;   15/08/31
GRB_TIME:        38052.89 SOD {10:34:12.89} UT
TRIGGER_INDEX:   483
GRB_PHI:         -59.47 [deg]
GRB_THETA:        31.20 [deg]
DELTA_TIME:      -75.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     56.48 [sigma]
IMAGE_SIGNIF:    14.35 [sigma]
LC_URL:          sw00653838000msb.lc
SUN_POSTN:       159.40d {+10h 37m 36s}   +8.67d {+08d 40' 20"}
SUN_DIST:         69.22 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.94d {+00h 03m 44s}   +0.52d {+00d 31' 01"}
MOON_DIST:       133.70 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.58, 30.66 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      226.43, -9.31 [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 = 93.75,-6.25 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:39:39 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.044d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.662d {-25d 39' 43"} (J2000)
POINT_ROLL:      291.307d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38141.25 SOD {10:35:41.25} UT,   88.4 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.407
N_STARS:         66
X_OFFSET:        664 [pixels]
Y_OFFSET:        512 [pixels]
X_MAX:           1623 [pixels]
Y_MAX:           1471 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw00653838000msufc0088.fits
SUN_POSTN:       159.40d {+10h 37m 36s}   +8.67d {+08d 40' 19"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.95d {+00h 03m 48s}   +0.52d {+00d 31' 18"}
MOON_DIST:       133.69 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:39:57 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.044d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.662d {-25d 39' 43"} (J2000)
POINT_ROLL:      291.307d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38141.25 SOD {10:35:41.25} UT,   88.4 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.407
N_STARS:         66
X_OFFSET:        664 [pixels]
Y_OFFSET:        512 [pixels]
X_MAX:           1623 [pixels]
Y_MAX:           1471 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw00653838000msufc0088.fits
SUN_POSTN:       159.40d {+10h 37m 36s}   +8.67d {+08d 40' 19"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.95d {+00h 03m 49s}   +0.52d {+00d 31' 21"}
MOON_DIST:       133.69 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:41:40 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.044d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.662d {-25d 39' 43"} (J2000)
ROLL:            291.307d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38141.25 SOD {10:35:41.25} UT,   88.4 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     462710156
X_OFFSET:        1044 [pixels]
Y_OFFSET:        904 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1204
Y_GRB_POS:       1064
BINNING_INDEX:   1
IM_URL:          sw00653838000msuni0104.fits
SUN_POSTN:       159.40d {+10h 37m 36s}   +8.67d {+08d 40' 17"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.97d {+00h 03m 53s}   +0.53d {+00d 31' 42"}
MOON_DIST:       133.71 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:41:44 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.044d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.662d {-25d 39' 43"} (J2000)
ROLL:            291.307d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38141.25 SOD {10:35:41.25} UT,   88.4 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     462710156
X_OFFSET:        1044 [pixels]
Y_OFFSET:        904 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1204
Y_GRB_POS:       1064
BINNING_INDEX:   1
IM_URL:          sw00653838000msuni0104.fits
SUN_POSTN:       159.40d {+10h 37m 36s}   +8.67d {+08d 40' 17"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        0.97d {+00h 03m 53s}   +0.53d {+00d 31' 43"}
MOON_DIST:       133.71 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:47:44 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
POINT_ROLL:      291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38353.34 SOD {10:39:13.34} UT,   300.4 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.312
N_STARS:         38
X_OFFSET:        724 [pixels]
Y_OFFSET:        584 [pixels]
X_MAX:           1683 [pixels]
Y_MAX:           1543 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw00653838000msufc0300.fits
SUN_POSTN:       159.40d {+10h 37m 37s}   +8.67d {+08d 40' 12"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.03d {+00h 04m 07s}   +0.55d {+00d 32' 54"}
MOON_DIST:       133.77 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:48:23 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     653838,   Seg_Num: 0
GRB_RA:          221.0244d {+14h 44m 05.85s} (J2000),
                 221.2527d {+14h 45m 00.63s} (current),
                 220.2972d {+14h 41m 11.33s} (1950)
GRB_DEC:         -25.6356d {-25d 38' 08.1"} (J2000),
                 -25.7013d {-25d 42' 04.5"} (current),
                 -25.4244d {-25d 25' 27.8"} (1950)
GRB_ERROR:       2.6 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38254.00 SOD {10:37:34.00} UT,   201.1 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       159.40d {+10h 37m 37s}   +8.67d {+08d 40' 11"}
SUN_DIST:         69.21 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.04d {+00h 04m 09s}   +0.55d {+00d 33' 02"}
MOON_DIST:       133.80 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.67 [deg] galactic lon,lat of the burst
ECL_COORDS:      226.43, -9.30 [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:     Mon 31 Aug 15 10:48:18 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
POINT_ROLL:      291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38353.34 SOD {10:39:13.34} UT,   300.4 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.312
N_STARS:         38
X_OFFSET:        724 [pixels]
Y_OFFSET:        584 [pixels]
X_MAX:           1683 [pixels]
Y_MAX:           1543 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw00653838000msufc0300.fits
SUN_POSTN:       159.40d {+10h 37m 37s}   +8.67d {+08d 40' 11"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.04d {+00h 04m 09s}   +0.55d {+00d 33' 01"}
MOON_DIST:       133.77 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:49:22 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
ROLL:            291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38353.34 SOD {10:39:13.34} UT,   300.4 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     462710368
X_OFFSET:        1044 [pixels]
Y_OFFSET:        904 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1204
Y_GRB_POS:       1064
BINNING_INDEX:   1
IM_URL:          sw00653838000msuni0316.fits
SUN_POSTN:       159.41d {+10h 37m 37s}   +8.67d {+08d 40' 10"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.05d {+00h 04m 11s}   +0.55d {+00d 33' 13"}
MOON_DIST:       133.78 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:49:29 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
ROLL:            291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38353.34 SOD {10:39:13.34} UT,   300.4 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     462710368
X_OFFSET:        1044 [pixels]
Y_OFFSET:        904 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1204
Y_GRB_POS:       1064
BINNING_INDEX:   1
IM_URL:          sw00653838000msuni0316.fits
SUN_POSTN:       159.41d {+10h 37m 37s}   +8.67d {+08d 40' 10"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.05d {+00h 04m 11s}   +0.55d {+00d 33' 15"}
MOON_DIST:       133.78 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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 #18209
A. Y. Lien (GSFC/UMBC), D. N. Burrows (PSU) and J. A. Kennea (PSU) report on behalf of the Swift Team:
At 10:34:12 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150831A (trigger=653838). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 221.023, -25.649 which is
```
   RA(J2000) = 14h 44m 05s
   Dec(J2000) = -25d 38' 57"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a short pulse with a duration of about 1.2 sec. The peak count rate was ~10000 counts/sec (15-350 keV), at ~ 0.1 sec after the trigger.
The XRT began observing the field at 10:35:36.3 UT, 83.4 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 221.0245, -25.6356 which is equivalent to:
```
   RA(J2000)  = 14h 44m 05.87s
   Dec(J2000) = -25d 38' 08.2"
```
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This location is 48 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 http://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 1.14 x 10^21 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 8.91e-10 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 88 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 0.11.
Burst Advocate for this burst is A. Y. Lien (amy.y.lien 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/too.html.)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:55:11 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
POINT_ROLL:      291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38931.35 SOD {10:48:51.35} UT,   878.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.690
N_STARS:         186
X_OFFSET:        484 [pixels]
Y_OFFSET:        344 [pixels]
X_MAX:           1923 [pixels]
Y_MAX:           1783 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw00653838000msufc0878.fits
SUN_POSTN:       159.41d {+10h 37m 38s}   +8.67d {+08d 40' 05"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.10d {+00h 04m 25s}   +0.57d {+00d 34' 23"}
MOON_DIST:       133.84 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 31 Aug 15 10:55:28 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
POINT_ROLL:      291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38931.35 SOD {10:48:51.35} UT,   878.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.690
N_STARS:         186
X_OFFSET:        484 [pixels]
Y_OFFSET:        344 [pixels]
X_MAX:           1923 [pixels]
Y_MAX:           1783 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw00653838000msufc0878.fits
SUN_POSTN:       159.41d {+10h 37m 38s}   +8.67d {+08d 40' 05"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.11d {+00h 04m 26s}   +0.57d {+00d 34' 26"}
MOON_DIST:       133.84 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:57:12 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
ROLL:            291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38931.35 SOD {10:48:51.35} UT,   878.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     462710946
X_OFFSET:        1043 [pixels]
Y_OFFSET:        903 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1203
Y_GRB_POS:       1063
BINNING_INDEX:   1
IM_URL:          sw00653838000msuni0894.fits
SUN_POSTN:       159.41d {+10h 37m 38s}   +8.67d {+08d 40' 03"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.12d {+00h 04m 30s}   +0.58d {+00d 34' 47"}
MOON_DIST:       133.86 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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:     Mon 31 Aug 15 10:57:33 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     653838,   Seg_Num: 0
POINT_RA:        221.047d {+14h 44m 11s} (J2000)
POINT_DEC:       -25.665d {-25d 39' 53"} (J2000)
ROLL:            291.305d
IMG_START_DATE:  17265 TJD;   243 DOY;   15/08/31
IMG_START_TIME:  38931.35 SOD {10:48:51.35} UT,   878.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     462710946
X_OFFSET:        1043 [pixels]
Y_OFFSET:        903 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1203
Y_GRB_POS:       1063
BINNING_INDEX:   1
IM_URL:          sw00653838000msuni0894.fits
SUN_POSTN:       159.41d {+10h 37m 39s}   +8.67d {+08d 40' 03"}
SUN_DIST:         69.24 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:        1.13d {+00h 04m 31s}   +0.58d {+00d 34' 51"}
MOON_DIST:       133.86 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      332.59, 30.63 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      226.46, -9.32 [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 #18210
S.Mereghetti (IASF-Milano), D.Gotz (CEA, Saclay), C.Ferrigno, E.Bozzo, L.Ducci (ISDC, Versoix), and J.Borkowski (CAMK, Torun) on behalf of the IBAS Localization Team report:
GRB 150831A (Lien et al. GCN 18209) has been detected by IBAS in the IBIS/ISGRI data with a significance slightly below the threshold for automatic alert delivery (IBAS Weak Alert n.7228 was distributed at 10:34:24 UT).
The burst consists of a single peak with duration of 2 s and starting at 10:34:12 UT.
The IBIS/ISGRI refined coordinates (J2000) are:
```
R.A.= 221.0207 deg
DEC.= -25.6474 deg
```
with an uncertainty of 3 arcmin (90% c.l.).
The burst had a fluence of about 3x10e-7 erg/cm2 in the the 20-200 keV energy range.
A plot of the light curve will be posted at http://ibas.iasf-milano.inaf.it/IBAS_Results.html
GCN Circular #18211
L. Elenin (KIAM), A. Volnova (IKI), E. Mazaeva (IKI), I. Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We observed the field of Swift and INTEGRAL short GRB 150309A (Lien et al., GCN 18209; Mereghetti et al., GCN 18210) with with 0.4-m f/2.4 telescope of ISON-SSO (Siding Spring Observatory) starting on Aug. 31 (UT) 10:44:10 (i.e. 10 minutes after burst trigger). We obtained 30 unfiltered images of 30 s exposure. We do not detect any optical source within XRT error circle (Lien et al., GCN 18209). Preliminary photometry of the filed is following
```
Date       UT start   t-T0     Filter   Exp.   UL (3 sigma)
                       (mid, days)       (s)

2015-08-31 10:44:10   0.01299  none    30*30   18.8
```
Photometry is based on nearby USNO-B1.0 stars (R2)
GCN Circular #18212
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 1089 s of XRT Photon Counting mode data and 2 UVOT images for GRB 150831A, 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 = 221.02422, -25.63499 which is equivalent to:
```
RA (J2000): 14h 44m 5.81s
Dec (J2000): -25d 38' 06.0"
```
with an uncertainty of 1.7 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 #18214
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), J. Norris (BSU), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), (i.e. the Swift-BAT team):
Using the data set from T-240 to T+938 sec from the recent telemetry downlink, we report further analysis of BAT GRB 150831A (trigger #653838) (Lien, et al., GCN Circ. 18209). The BAT ground-calculated position is RA, Dec = 221.034, -25.619 deg which is
```
  RA(J2000)  =  14h 44m 08.1s
  Dec(J2000) = -25d 37' 08.4"
```
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 52%.
The mask-weighted light curve shows a short pulse that starts and peaks at ~ T0, and ends at ~ T+1.4 s. T90 (15-350 keV) is 1.15 +- 0.23 sec (estimated error including systematics).
The time-averaged spectrum from T-0.03 to T+1.40 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 0.81 +- 0.16. The fluence in the 15-150 keV band is 3.8 +- 0.3 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.0 sec in the 15-150 keV band is 3.4 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The lag analysis using 8-ms binned light curve gives a spectral lag of -2 ms +- 5 ms for the 100-350 keV and 25-50 keV band, and 13 ms +- 20 ms for the 50-100 keV and 15-25 keV band. These values are consistent with short GRBs.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/653838/BA/
GCN Circular #18216
A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (ASDC) and A.Y. Lien report on behalf of the Swift-XRT team:
We have analysed 8.6 ks of XRT data for GRB 150831A (Lien et al. GCN Circ. 18209), from 72 s to 22.5 ks after the BAT trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 18212).
The light curve can be modelled with a power-law decay with a decay index of alpha=2.52 (+0.21, -0.22).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.25 (+0.17, -0.12). The best-fitting absorption column is 1.27 (+0.89, -0.13) x 10^21 cm^-2, consistent with the Galactic value of 1.1 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 5.0 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
```
Total column:	     1.27 (+0.89, -0.13) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.25 (+0.17, -0.12)
```
If the light curve continues to decay with a power-law decay index of 2.52, the count rate at T+24 hours will be 2.1 x 10^-7 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-17 (1.2 x 10^-17) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00653838.
This circular is an official product of the Swift-XRT team.
GCN Circular #18218
M. H. Siegel (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150831A 88 s after the BAT trigger (Lien et al., GCN Circ. 18209). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 18212) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            88          238          147         >20.5
u_FC               300          550          246         >19.9
white               88         6622          746         >21.2
v                  631        17885         1356         >19.8
b                  557         6417          452         >20.4
u                  300        12784         1326         >21.0
w1                 680        12112         1153         >21.3
m2                 655        18529         1750         >21.3
w2                 607        16972         1357         >21.1
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #18219
F. Knust (MPE Garching), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 150831A (Swift trigger 653838; Lien et al., GCN #18209) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 23:21UT on 2015-08-31, 13hrs after the GRB trigger. They were performed at an average seeing of 2.4" and at an average airmass of 1.5.
We do not detect a source within the Swift-XRT error circle reported by Osborne et al. (GCN #18212) down to
```
g'> 24.9 mag, 
r'> 24.5 mag, 
i'> 23.8 mag, 
z'> 23.8 mag, 
J> 21.4 mag, 
H> 20.9 mag, and 
K> 18.6 mag. 
```
The given limits are derived based on calibrating the images against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.1 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular #18226
S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, report:
The short-duration GRB 150831A (Swift trigger 648437: Lien, et al., GCN Circ. 18209; Ukwatta, et al., GCN Circ. 18214; INTEGRAL detection: Mereghetti et al., GCN Circ. 18210) triggered Konus-Wind at T0=38049.519 s UT (10:34:09.519).
The burst light curve shows a short pulse with a total duration of ~1 s.
As observed by Konus-Wind, the burst had a fluence of (2.4 +/- 0.4)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.082 s, of (9.1 +/- 2.5)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
Since the most intense part of the burst was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data.
Modeling the 3-channel time-integrated spectrum (from T0-0.108 s to T0+0.912 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -0.5 +/- 0.3, and Ep = 564 +/- 122 keV.
The K-W light curve of this burst is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB150831_T38049/
All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary.
GCN Circular #18235
W. Fong (U. Arizona) and B. A. Zauderer (Harvard) report:
"We observed the field of the short-duration GRB 150831A (Lien et al., GCN 18209) with the Karl G. Jansky Very Large Array (VLA) beginning on 2015 Aug 31.934 UT (11.9 hr post-burst) at a mean frequency of 9.8 GHz. In 1 hour of observations, we do not detect any radio source within or around the enhanced XRT position (Osborne et al., GCN 18212) to a 3-sigma limit of 25 microJy. Furthermore, we obtained a second set of observations beginning on 2015 Sep 2.954 UT (2.5 days post-burst) at a mean frequency of 9.8 GHz and do not detect any radio source in or around the XRT position to a 3-sigma limit of 21 microJy.
We therefore place 3-sigma limits of 25 microJy and 21 microJy on the radio afterglow of GRB 150831A at 11.9 hr and 2.5 days after the burst, respectively.
We thank the VLA staff for quickly executing these observations."
Redshift z= 1.180 +- 0.001 from host galaxy emission ([OIII])
W.-F. Fong et al. 2022, ApJ 940, 56

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Jochen Greiner, last update: 17-Jan-2023 [Disclaimer]