Gamma-ray Burst 110818A

(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 18 Aug 11 20:38:51 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     500914,   Seg_Num: 0
GRB_RA:          317.384d {+21h 09m 32s} (J2000),
                 317.622d {+21h 10m 29s} (current),
                 316.352d {+21h 05m 24s} (1950)
GRB_DEC:         -63.970d {-63d 58' 10"} (J2000),
                 -63.922d {-63d 55' 18"} (current),
                 -64.173d {-64d 10' 21"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       56986 [cnts]    Image_Peak=1067 [image_cnts]
TRIGGER_DUR:     12.160 [sec] 
TRIGGER_INDEX:   478     E_range: 25-100 keV
BKG_INTEN:       266606 [cnts]
BKG_TIME:        74176.72 SOD {20:36:16.72} UT
BKG_DUR:         64 [sec]
GRB_DATE:        15791 TJD;   230 DOY;   11/08/18
GRB_TIME:        74269.20 SOD {20:37:49.20} UT
GRB_PHI:         154.17 [deg]
GRB_THETA:        41.77 [deg]
SOLN_STATUS:     0x2003
RATE_SIGNIF:     16.03 [sigma]
IMAGE_SIGNIF:    14.23 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +2  +3  +0  +0 +62  +0 
SUN_POSTN:       147.82d {+09h 51m 17s}  +13.00d {+13d 00' 03"}
SUN_DIST:        128.58 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       18.85d {+01h 15m 25s}  +12.62d {+12d 37' 12"}
MOON_DIST:        89.42 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.71,-39.13 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      297.14,-44.93 [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:        There is a bright star (mag=5.76) 6.94 arcmin from this position.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 346.75,19.32 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:38:10 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     335392676
GRB_RA:          140.367d {+09h 21m 28s} (J2000),
                 140.378d {+09h 21m 31s} (current),
                 140.314d {+09h 21m 15s} (1950)
GRB_DEC:         -73.283d {-73d 16' 59"} (J2000),
                 -73.333d {-73d 19' 58"} (current),
                 -73.069d {-73d 04' 07"} (1950)
GRB_ERROR:       28.42 [deg radius, statistical plus systematic]
GRB_INTEN:       73 [cnts/sec]
DATA_SIGNIF:     4.90 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        15791 TJD;   230 DOY;   11/08/18
GRB_TIME:        74274.22 SOD {20:37:54.22} UT
GRB_PHI:         209.00 [deg]
GRB_THETA:       135.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.27
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   2%  Distant Particles
DETECTORS:       0,0,0, 0,0,0, 0,0,1, 0,0,1, 0,0,
SUN_POSTN:       147.82d {+09h 51m 17s}  +13.00d {+13d 00' 04"}
SUN_DIST:         86.47 [deg]   Sun_angle= 0.5 [hr] (West of Sun)
MOON_POSTN:       18.85d {+01h 15m 24s}  +12.62d {+12d 37' 05"}
MOON_DIST:       110.83 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      289.18,-16.31 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      223.83,-72.12 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 82.42,-17.68 [deg].

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:42:32 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      56
TRIGGER_NUM:     335392676
GRB_RA:          194.460d {+12h 57m 50s} (J2000),
                 194.797d {+12h 59m 11s} (current),
                 193.085d {+12h 52m 20s} (1950)
GRB_DEC:         -84.990d {-84d 59' 23"} (J2000),
                 -85.053d {-85d 03' 09"} (current),
                 -84.720d {-84d 43' 09"} (1950)
GRB_ERROR:       15.36 [deg radius, statistical only]
DATA_SIGNIF:     5.30 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        15791 TJD;   230 DOY;   11/08/18
GRB_TIME:        74274.22 SOD {20:37:54.22} UT
GRB_PHI:         197.00 [deg]
GRB_THETA:       124.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       147.82d {+09h 51m 17s}  +13.00d {+13d 00' 00"}
SUN_DIST:         99.60 [deg]   Sun_angle= -3.1 [hr] (East of Sun)
MOON_POSTN:       18.88d {+01h 15m 32s}  +12.63d {+12d 37' 48"}
MOON_DIST:       107.56 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      303.08,-22.12 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.52,-64.86 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:43:20 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      65
TRIGGER_NUM:     335392676
GRB_RA:          315.870d {+21h 03m 29s} (J2000),
                 316.097d {+21h 04m 23s} (current),
                 314.889d {+20h 59m 33s} (1950)
GRB_DEC:         -60.040d {-60d 02' 23"} (J2000),
                 -59.993d {-59d 59' 35"} (current),
                 -60.238d {-60d 14' 16"} (1950)
GRB_ERROR:       10.86 [deg radius, statistical only]
DATA_SIGNIF:     8.70 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        15791 TJD;   230 DOY;   11/08/18
GRB_TIME:        74274.22 SOD {20:37:54.22} UT
GRB_PHI:         188.00 [deg]
GRB_THETA:        93.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       147.82d {+09h 51m 17s}  +13.00d {+12d 59' 60"}
SUN_DIST:        132.21 [deg]   Sun_angle= -11.2 [hr] (East of Sun)
MOON_POSTN:       18.89d {+01h 15m 34s}  +12.63d {+12d 37' 56"}
MOON_DIST:        88.07 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      335.85,-39.58 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      298.37,-41.04 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:43:24 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      83
TRIGGER_NUM:     335392676
GRB_RA:          339.180d {+22h 36m 43s} (J2000),
                 339.363d {+22h 37m 27s} (current),
                 338.391d {+22h 33m 34s} (1950)
GRB_DEC:         -55.770d {-55d 46' 11"} (J2000),
                 -55.709d {-55d 42' 33"} (current),
                 -56.030d {-56d 01' 45"} (1950)
GRB_ERROR:       10.34 [deg radius, statistical only]
DATA_SIGNIF:     8.00 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        15791 TJD;   230 DOY;   11/08/18
GRB_TIME:        74274.22 SOD {20:37:54.22} UT
GRB_PHI:         199.00 [deg]
GRB_THETA:        86.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       147.82d {+09h 51m 17s}  +13.00d {+12d 59' 60"}
SUN_DIST:        136.36 [deg]   Sun_angle= 11.2 [hr] (West of Sun)
MOON_POSTN:       18.89d {+01h 15m 34s}  +12.63d {+12d 37' 57"}
MOON_DIST:        75.92 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      333.78,-52.52 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      315.74,-42.77 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:41:32 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     500914,   Seg_Num: 0
GRB_RA:          317.384d {+21h 09m 32s} (J2000),
                 317.622d {+21h 10m 29s} (current),
                 316.352d {+21h 05m 24s} (1950)
GRB_DEC:         -63.970d {-63d 58' 10"} (J2000),
                 -63.922d {-63d 55' 18"} (current),
                 -64.173d {-64d 10' 21"} (1950)
GRB_DATE:        15791 TJD;   230 DOY;   11/08/18
GRB_TIME:        74269.20 SOD {20:37:49.20} UT
TRIGGER_INDEX:   478
GRB_PHI:         154.17 [deg]
GRB_THETA:        41.77 [deg]
DELTA_TIME:      32.00 [sec]
TRIGGER_DUR:     12.160 [sec] 
SOLN_STATUS:     0x2003
RATE_SIGNIF:     16.03 [sigma]
IMAGE_SIGNIF:    14.23 [sigma]
LC_URL:          sw00500914000msb.lc
SUN_POSTN:       147.82d {+09h 51m 17s}  +13.00d {+13d 00' 01"}
SUN_DIST:        128.58 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       18.88d {+01h 15m 30s}  +12.63d {+12d 37' 38"}
MOON_DIST:        89.43 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.71,-39.13 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      297.14,-44.93 [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:        There is a bright star (mag=5.76) 6.94 arcmin from this position.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 346.75,19.32 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:44:17 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     500914,   Seg_Num: 0
POINT_RA:        317.380d {+21h 09m 31s} (J2000)
POINT_DEC:       -63.982d {-63d 58' 53"} (J2000)
IMG_START_DATE:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  74649.65 SOD {20:44:09.65} UT,   380.4 [sec] since BAT Trigger Time
COUNTS:          12    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 18 Aug 11 20:49:04 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     500914,   Seg_Num: 0
GRB_RA:          317.3412d {+21h 09m 21.88s} (J2000),
                 317.5798d {+21h 10m 19.14s} (current),
                 316.3087d {+21h 05m 14.08s} (1950)
GRB_DEC:         -63.9810d {-63d 58' 51.6"} (J2000),
                 -63.9333d {-63d 55' 59.8"} (current),
                 -64.1840d {-64d 11' 02.5"} (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:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  74716.00 SOD {20:45:16.00} UT,   446.8 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       147.83d {+09h 51m 18s}  +13.00d {+12d 59' 55"}
SUN_DIST:        128.56 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       18.94d {+01h 15m 44s}  +12.65d {+12d 38' 53"}
MOON_DIST:        89.49 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.71,-39.11 [deg] galactic lon,lat of the burst
ECL_COORDS:      297.11,-44.93 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        There is a bright star (mag=5.76) 6.22 arcmin from the XRT position.  
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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:56:27 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     500914,   Seg_Num: 0
POINT_RA:        317.375d {+21h 09m 30s} (J2000)
POINT_DEC:       -63.980d {-63d 58' 48"} (J2000)
POINT_ROLL:      193.034d
IMG_START_DATE:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  75125.31 SOD {20:52:05.31} UT,   856.1 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.400
N_STARS:         190
X_OFFSET:        158 [pixels]
Y_OFFSET:        347 [pixels]
X_MAX:           1597 [pixels]
Y_MAX:           1786 [pixels]
DET_THRESH:      6
PHOTO_THRESH:    2
SL_URL:          sw00500914000msufc0856.fits
SUN_POSTN:       147.83d {+09h 51m 19s}  +13.00d {+12d 59' 49"}
SUN_DIST:        128.57 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       18.99d {+01h 15m 59s}  +12.67d {+12d 40' 06"}
MOON_DIST:        89.52 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.70,-39.12 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      297.13,-44.94 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.  
COMMENTS:        There is a bright star (mag=5.76) 6.94 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:56:56 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     500914,   Seg_Num: 0
POINT_RA:        317.375d {+21h 09m 30s} (J2000)
POINT_DEC:       -63.980d {-63d 58' 48"} (J2000)
POINT_ROLL:      193.034d
IMG_START_DATE:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  75125.31 SOD {20:52:05.31} UT,   856.1 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.400
N_STARS:         190
X_OFFSET:        158 [pixels]
Y_OFFSET:        347 [pixels]
X_MAX:           1597 [pixels]
Y_MAX:           1786 [pixels]
DET_THRESH:      6
PHOTO_THRESH:    2
SL_URL:          sw00500914000msufc0856.fits
SUN_POSTN:       147.83d {+09h 51m 20s}  +13.00d {+12d 59' 49"}
SUN_DIST:        128.56 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       19.00d {+01h 15m 59s}  +12.67d {+12d 40' 10"}
MOON_DIST:        89.52 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.70,-39.12 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      297.13,-44.94 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.  
COMMENTS:        There is a bright star (mag=5.76) 6.94 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:57:13 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     500914,   Seg_Num: 0
GRB_RA:          317.3381d {+21h 09m 21.14s} (J2000),
                 317.5767d {+21h 10m 18.40s} (current),
                 316.3056d {+21h 05m 13.33s} (1950)
GRB_DEC:         -63.9814d {-63d 58' 53.0"} (J2000),
                 -63.9337d {-63d 56' 01.3"} (current),
                 -64.1844d {-64d 11' 03.9"} (1950)
GRB_ERROR:       2.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  74716.00 SOD {20:45:16.00} UT,   446.8 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       147.83d {+09h 51m 20s}  +13.00d {+12d 59' 48"}
SUN_DIST:        128.56 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       19.00d {+01h 16m 00s}  +12.67d {+12d 40' 13"}
MOON_DIST:        89.54 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.71,-39.11 [deg] galactic lon,lat of the burst
ECL_COORDS:      297.11,-44.93 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        There is a bright star (mag=5.76) 6.16 arcmin from the XRT position.  
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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:57:53 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     500914,   Seg_Num: 0
POINT_RA:        317.375d {+21h 09m 30s} (J2000)
POINT_DEC:       -63.980d {-63d 58' 48"} (J2000)
ROLL:            193.034d
IMG_START_DATE:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  75125.31 SOD {20:52:05.31} UT,   856.1 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     335393532
X_OFFSET:        717 [pixels]
Y_OFFSET:        906 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       877
Y_GRB_POS:       1066
BINNING_INDEX:   1
IM_URL:          sw00500914000msuni0864.fits
SUN_POSTN:       147.83d {+09h 51m 20s}  +13.00d {+12d 59' 48"}
SUN_DIST:        128.56 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       19.01d {+01h 16m 01s}  +12.67d {+12d 40' 20"}
MOON_DIST:        89.53 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.70,-39.12 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      297.13,-44.94 [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).  
COMMENTS:        There is a bright star (mag=5.76) 6.94 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Aug 11 20:58:13 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     500914,   Seg_Num: 0
POINT_RA:        317.375d {+21h 09m 30s} (J2000)
POINT_DEC:       -63.980d {-63d 58' 48"} (J2000)
ROLL:            193.034d
IMG_START_DATE:  15791 TJD;   230 DOY;   11/08/18
IMG_START_TIME:  75125.31 SOD {20:52:05.31} UT,   856.1 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     335393532
X_OFFSET:        717 [pixels]
Y_OFFSET:        906 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       877
Y_GRB_POS:       1066
BINNING_INDEX:   1
IM_URL:          sw00500914000msuni0864.fits
SUN_POSTN:       147.83d {+09h 51m 20s}  +13.00d {+12d 59' 48"}
SUN_DIST:        128.56 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       19.01d {+01h 16m 02s}  +12.67d {+12d 40' 23"}
MOON_DIST:        89.53 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:      330.70,-39.12 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      297.13,-44.94 [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.  
COMMENTS:        There is a bright star (mag=5.76) 6.94 arcmin from the BAT position.

GCN Circular #12279
C. B. Markwardt (NASA/GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), T. A. Pritchard (PSU), A. Rowlinson (U Leicester), T. Sakamoto (NASA/UMBC), C. J. Saxton (UCL-MSSL), M. H. Siegel (PSU) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team:
At 20:37:49 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110818A (trigger=500914). Because of an Earth-limb observing constraint, the slew to the burst was delayed by ~4 min. The BAT on-board calculated location is RA, Dec 317.384, -63.970 which is
```
   RA(J2000)  =  21h 09m 32s
   Dec(J2000) = -63d 58' 10"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows several peaks with a total duration of about 60 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~7 sec after the trigger.
The XRT began observing the field at 20:44:09.7 UT, 380.4 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 317.3382, -63.9814 which is equivalent to:
```
   RA(J2000)  = 21h 09m 21.17s
   Dec(J2000) = -63d 58' 53.1"
```
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 83 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 in excess of the Galactic value (2.62 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2 (+1.14/-1.05) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the U filter starting 856 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 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04.
Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt 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 Circular #12281
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (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 110818A (trigger #500914) (Markwardt, et al., GCN Circ. 12279). The BAT ground-calculated position is RA, Dec = 317.373, -63.981 deg which is
```
    RA(J2000)  =  21h 09m 29.6s
    Dec(J2000) = -63d 58' 52.7"
```
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 29%.
The mask-weighted light curve consists of a single broad peak, with several sharper peaks superimposed. T90 (15-350 keV) is 103 +- 18 sec (estimated error including systematics).
The time-averaged spectrum from T-14.2 to T+117.4 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.58 +- 0.11. The fluence in the 15-150 keV band is 4.0 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+27.3 sec in the 15-150 keV band is 1.6 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/500914/BA/
GCN Circular #12283
A. Rowlinson (U. Leicester) and C. B. Markwardt (NASA/GSFC) report on behalf of the Swift-XRT team:
We have analysed 7.8 ks of XRT data for GRB 110818A (Markwardt et al. GCN Circ. 12279), from 384 s to 18.3 ks after the BAT trigger. The data comprise 61 s in Windowed Timing (WT) mode 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 = 317.3378, -63.9813 which is equivalent to:
```
RA (J2000): 21 09 21.07
Dec(J2000): -63 58 52.7
```
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=5.8 (+0.6, -0.7). At T+461 s the decay flattens to an alpha of 1.57 (+0.14, -0.11) before breaking again at T+2167 s to a final decay with index alpha=0.95 (+0.10, -0.14).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.97 (+0.12, -0.11). The best-fitting absorption column is 7.8 (+2.7, -2.4) x 10^20 cm^-2, in excess of the Galactic value of 2.6 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     7.8 (+2.7, -2.4) x 10^20 cm^-2
Galactic foreground: 2.6 x 10^20 cm^-2
Excess significance: 5.3 sigma
Photon index:	     1.97 (+0.12, -0.11)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00500914.
This circular is an official product of the Swift-XRT team.
GCN Circular #12284
P. D'Avanzo (INAF/Brera), M. Sparre, D. Watson, J. P. U. Fynbo, D. Malesani, B. Milvang-Jensen (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), V. D'Elia (INAF/Rome), and N. R. Tanvir (U. Leicester), report on behalf of the X-shooter GTO GRB collaboration:
We observed the field of GRB 110818A (Markwardt et al. GCN 12279) with the ESO VLT equipped with X-shooter. Observations started on 2011-08-19 at 02:47 UT (6.15 hr after the GRB).
The acquisition image shows an optical afterglow candidate inside the XRT error circle (Markwardt et al. GCN 12279) at the following coordinates (J2000):
```
RA = 21:09:21.04
Dec = -63:58:52.3
```
with an uncertainty of about 0.5". The object has a magnitude R ~ 22.3, calibrated assuming R = 19.2 for the USNO-B1 star 0260-0726657 (RA, Dec = 21:09:23.14, -63:58:33.0).
A total spectroscopic exposure of 4x1200 s was obtained, covering the spectral range from 300 to 2500 nm.
We report a redshift of z = 3.36 based on detection of absorption features from Si II, C IV, Al II, Ca H, Ca K and Mg I. Emission from the [O III] doublet is also observed.
We would like to thank the staff at the VLT, in particular, Alain Smette, Patricia Guajardo and Dimitri Gadotti for carrying out the observations.
GCN Circular #12285
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 4176 s of XRT Photon Counting mode data and 5 UVOT images for GRB 110818A, 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 = 317.33705, -63.98105 which is equivalent to:
```
RA (J2000): 21h 09m 20.89s
Dec (J2000): -63d 58' 51.8"
```
with an uncertainty of 1.4 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 #12286
T. A. Pritchard (PSU) and C. B. Markwardt (NASA/GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 110818A 379 s after the BAT trigger (Markwardt et al., GCN Circ. 12279). No optical afterglow consistent with the Enhanced Swift-XRT position (GCN Circ. 12285) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

v                  379        14423         1513         >20.8
b                  477        18642         2455         >22.2
u                  452         8009          813         >20.4
w1                 428         7804          646         >20.9
m2                7399         7599          197         >20.9
w2                6989        13752         1082         >21.2
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #12287
S. Xiong (UAH) reports on behalf of the Fermi GBM Team:
"At 20:37:54.221 UT on 18 August 2011, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 110818A (trigger 335392676 / 110818860 ), which was also detected by the Swift (Markwardt et al. 2011, GCN 12279). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 96 degrees. This burst was also independently detected by INTEGRAL SPI-ACS.
The GBM light curve consists of multiple peaks with a duration (T90) of about 75 s (50-300 keV). The time-averaged spectrum from T0-16.4 s to T0+57.3 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.33 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 256.3 +/- 55.3 keV.
The event fluence (10-1000 keV) in this time interval is (8.2 +/- 0.6)E-6 erg/cm^2. The 64 ms peak photon flux measured starting from T0+22.66 s in the 10-1000 keV band is 5.0 +/- 1.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."

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Jochen Greiner, last update: 20-Aug-2011 [Disclaimer]