Gamma-ray Burst 150817A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:05:28 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.643d {+16h 38m 34s} (J2000),
                 249.861d {+16h 39m 27s} (current),
                 248.947d {+16h 35m 47s} (1950)
GRB_DEC:         -12.066d {-12d 03' 55"} (J2000),
                 -12.096d {-12d 05' 44"} (current),
                 -11.967d {-11d 58' 01"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       1518 [cnts]    Image_Peak=159 [image_cnts]
TRIGGER_DUR:     0.256 [sec] 
TRIGGER_INDEX:   123     E_range: 25-100 keV
BKG_INTEN:       24187 [cnts]
BKG_TIME:        7496.99 SOD {02:04:56.99} UT
BKG_DUR:         8 [sec]
GRB_DATE:        17251 TJD;   229 DOY;   15/08/17
GRB_TIME:        7513.38 SOD {02:05:13.38} UT
GRB_PHI:         -103.01 [deg]
GRB_THETA:        21.67 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     26.26 [sigma]
IMAGE_SIGNIF:    10.83 [sigma]
MERIT_PARAMS:     +1  +0  +0  -2  +2  +0  +0  +0 +26  +0 
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 32"}
SUN_DIST:        105.88 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.43d {+11h 25m 44s}   +2.76d {+02d 45' 49"}
MOON_DIST:        79.29 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.42 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      249.80,  9.96 [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 = 301.39,6.11 [deg]. 
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(5.0<100sec) coincident with the FERMI_GBM event (trignum=461469912).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:05:35 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     461469912
GRB_RA:          253.833d {+16h 55m 20s} (J2000),
                 254.049d {+16h 56m 12s} (current),
                 253.144d {+16h 52m 34s} (1950)
GRB_DEC:         -10.483d {-10d 28' 59"} (J2000),
                 -10.507d {-10d 30' 26"} (current),
                 -10.404d {-10d 24' 14"} (1950)
GRB_ERROR:       22.47 [deg radius, statistical plus systematic]
GRB_INTEN:       91 [cnts/sec]
DATA_SIGNIF:     5.30 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        17251 TJD;   229 DOY;   15/08/17
GRB_TIME:        7508.40 SOD {02:05:08.40} UT
GRB_PHI:          86.00 [deg]
GRB_THETA:       110.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      1.50
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      63%  Distant Particles
2nd_MOST_LIKELY:  24%  GRB
DETECTORS:       0,0,1, 0,0,0, 0,0,0, 0,1,0, 0,0,
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 32"}
SUN_DIST:        109.62 [deg]   Sun_angle= -7.2 [hr] (East of Sun)
MOON_POSTN:      171.43d {+11h 25m 44s}   +2.76d {+02d 45' 48"}
MOON_DIST:        83.25 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        9.12, 19.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      253.74, 12.05 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150817087/quicklook/glg_lc_medres34_bn150817087.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 146.82,-25.25 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(5.0<100sec) coincident with the SWIFT_BAT event (trignum=652334).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:05:45 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     461469912
GRB_RA:          250.250d {+16h 41m 00s} (J2000),
                 250.460d {+16h 41m 50s} (current),
                 249.580d {+16h 38m 19s} (1950)
GRB_DEC:          -6.517d {-06d 31' 00"} (J2000),
                  -6.546d {-06d 32' 44"} (current),
                  -6.421d {-06d 25' 15"} (1950)
GRB_ERROR:       12.35 [deg radius, statistical plus systematic]
GRB_INTEN:       222 [cnts/sec]
DATA_SIGNIF:     9.20 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        17251 TJD;   229 DOY;   15/08/17
GRB_TIME:        7508.40 SOD {02:05:08.40} UT
GRB_PHI:          89.00 [deg]
GRB_THETA:       105.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      1.25
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      53%  Distant Particles
2nd_MOST_LIKELY:  44%  GRB
DETECTORS:       0,0,1, 0,0,0, 0,0,0, 0,1,0, 0,0,
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 31"}
SUN_DIST:        105.34 [deg]   Sun_angle= -7.0 [hr] (East of Sun)
MOON_POSTN:      171.44d {+11h 25m 45s}   +2.76d {+02d 45' 47"}
MOON_DIST:        79.43 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:       10.52, 25.14 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      249.61, 15.54 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150817087/quicklook/glg_lc_medres34_bn150817087.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 146.82,-25.25 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(5.0<100sec) coincident with the SWIFT_BAT event (trignum=652334).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:05:57 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      69
TRIGGER_NUM:     461469912
GRB_RA:          247.083d {+16h 28m 20s} (J2000),
                 247.287d {+16h 29m 09s} (current),
                 246.432d {+16h 25m 44s} (1950)
GRB_DEC:          -2.417d {-02d 25' 00"} (J2000),
                  -2.450d {-02d 27' 01"} (current),
                  -2.307d {-02d 18' 24"} (1950)
GRB_ERROR:       9.68 [deg radius, statistical plus systematic]
GRB_INTEN:       938 [cnts/sec]
DATA_SIGNIF:     13.30 [sigma]
INTEG_TIME:      0.128 [sec]
GRB_DATE:        17251 TJD;   229 DOY;   15/08/17
GRB_TIME:        7508.40 SOD {02:05:08.40} UT
GRB_PHI:          93.00 [deg]
GRB_THETA:       100.00 [deg]
DATA_TIME_SCALE: 0.1280 [sec]
HARD_RATIO:      0.53
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      59%  Distant Particles
2nd_MOST_LIKELY:  39%  GRB
DETECTORS:       0,0,1, 0,0,0, 0,0,0, 0,1,0, 0,0,
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 31"}
SUN_DIST:        101.35 [deg]   Sun_angle= -6.7 [hr] (East of Sun)
MOON_POSTN:      171.44d {+11h 25m 45s}   +2.76d {+02d 45' 45"}
MOON_DIST:        76.00 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:       12.38, 30.04 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      245.69, 19.11 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150817087/quicklook/glg_lc_medres34_bn150817087.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 146.82,-25.25 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(5.0<100sec) coincident with the SWIFT_BAT event (trignum=652334).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:05:59 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      73
TRIGGER_NUM:     461469912
GRB_RA:          252.033d {+16h 48m 08s} (J2000),
                 252.239d {+16h 48m 57s} (current),
                 251.376d {+16h 45m 30s} (1950)
GRB_DEC:          -3.750d {-03d 45' 00"} (J2000),
                  -3.777d {-03d 46' 35"} (current),
                  -3.663d {-03d 39' 44"} (1950)
GRB_ERROR:       4.90 [deg radius, statistical plus systematic]
GRB_INTEN:       1062 [cnts/sec]
DATA_SIGNIF:     44.40 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        17251 TJD;   229 DOY;   15/08/17
GRB_TIME:        7508.40 SOD {02:05:08.40} UT
GRB_PHI:          94.00 [deg]
GRB_THETA:       105.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.58
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      74%  Distant Particles
2nd_MOST_LIKELY:  24%  GRB
DETECTORS:       0,0,1, 0,0,0, 0,0,0, 0,1,0, 0,0,
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 31"}
SUN_DIST:        106.47 [deg]   Sun_angle= -7.1 [hr] (East of Sun)
MOON_POSTN:      171.44d {+11h 25m 45s}   +2.76d {+02d 45' 44"}
MOON_DIST:        81.02 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:       14.15, 25.17 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      251.06, 18.52 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150817087/quicklook/glg_lc_medres34_bn150817087.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 146.82,-25.25 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(5.0<100sec) coincident with the SWIFT_BAT event (trignum=652334).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:06:59 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.6328d {+16h 38m 31.87s} (J2000),
                 249.8504d {+16h 39m 24.10s} (current),
                 248.9369d {+16h 35m 44.85s} (1950)
GRB_DEC:         -12.0527d {-12d 03' 09.7"} (J2000),
                 -12.0828d {-12d 04' 58.1"} (current),
                 -11.9542d {-11d 57' 15.1"} (1950)
GRB_ERROR:       5.4 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.27e-09 [erg/cm2/sec]
GRB_SIGNIF:      6.92 [sigma]
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  7578.28 SOD {02:06:18.28} UT,   64.9 [sec] since BAT Trigger Time
TAM[0-3]:        327.68 237.19 261.65 243.74
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 30"}
SUN_DIST:        105.87 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.45d {+11h 25m 47s}   +2.76d {+02d 45' 35"}
MOON_DIST:        79.27 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.44 [deg] galactic lon,lat of the burst
ECL_COORDS:      249.78,  9.97 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 0.99 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:07:21 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.6328d {+16h 38m 31.8s} (J2000),
                 249.8504d {+16h 39m 24.1s} (current),
                 248.9369d {+16h 35m 44.8s} (1950)
GRB_DEC:         -12.0527d {-12d 03' 09.7"} (J2000),
                 -12.0828d {-12d 04' 58.1"} (current),
                 -11.9542d {-11d 57' 15.1"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       48 [cnts]
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  7578.28 SOD {02:06:18.28} UT,   64.9 [sec] since BAT Trigger Time
CENTROID_X:      242.79,  raw= 243  [pixels]
CENTROID_Y:      287.30,  raw= 287  [pixels]
ROLL:            280.87 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -24.74
GRB_POS_XRT_Z:   -147.34
IMAGE_URL:       sw00652334000msxps_rw.img
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 30"}
SUN_DIST:        105.87 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.45d {+11h 25m 48s}   +2.76d {+02d 45' 32"}
MOON_DIST:        79.26 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.44 [deg] galactic lon,lat of the burst
ECL_COORDS:      249.78,  9.97 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:07:10 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.6328d {+16h 38m 31.8s} (J2000),
                 249.8504d {+16h 39m 24.1s} (current),
                 248.9369d {+16h 35m 44.8s} (1950)
GRB_DEC:         -12.0527d {-12d 03' 09.7"} (J2000),
                 -12.0828d {-12d 04' 58.1"} (current),
                 -11.9542d {-11d 57' 15.1"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       48 [cnts]
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  7578.28 SOD {02:06:18.28} UT,   64.9 [sec] since BAT Trigger Time
CENTROID_X:      242.79,  raw= 243  [pixels]
CENTROID_Y:      287.30,  raw= 287  [pixels]
ROLL:            280.87 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -24.74
GRB_POS_XRT_Z:   -147.34
IMAGE_URL:       sw00652334000msxps_rw.img
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 30"}
SUN_DIST:        105.87 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.45d {+11h 25m 47s}   +2.76d {+02d 45' 33"}
MOON_DIST:        79.27 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.44 [deg] galactic lon,lat of the burst
ECL_COORDS:      249.78,  9.97 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:09:00 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.643d {+16h 38m 34s} (J2000),
                 249.861d {+16h 39m 27s} (current),
                 248.947d {+16h 35m 47s} (1950)
GRB_DEC:         -12.066d {-12d 03' 55"} (J2000),
                 -12.096d {-12d 05' 44"} (current),
                 -11.967d {-11d 58' 01"} (1950)
GRB_DATE:        17251 TJD;   229 DOY;   15/08/17
GRB_TIME:        7513.38 SOD {02:05:13.38} UT
TRIGGER_INDEX:   123
GRB_PHI:         -103.01 [deg]
GRB_THETA:        21.67 [deg]
DELTA_TIME:      -37.00 [sec]
TRIGGER_DUR:     0.256 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     26.26 [sigma]
IMAGE_SIGNIF:    10.83 [sigma]
LC_URL:          sw00652334000msb.lc
SUN_POSTN:       146.20d {+09h 44m 48s}  +13.56d {+13d 33' 29"}
SUN_DIST:        105.88 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.46d {+11h 25m 51s}   +2.75d {+02d 45' 17"}
MOON_DIST:        79.26 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.42 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      249.80,  9.96 [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 = 301.39,6.11 [deg].

GCN Circular #18143
V. D'Elia (ASDC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), L. Izzo (URoma/ICRA), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team:
At 02:05:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150817A (trigger=652334). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 249.643, -12.066 which is
```
   RA(J2000) = 16h 38m 34s
   Dec(J2000) = -12d 03' 55"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of at least 50 sec. The peak count rate was ~17000 counts/sec (15-350 keV), at ~11 sec after the trigger.
The XRT began observing the field at 02:06:18.2 UT, 64.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 249.63352, -12.05336 which is equivalent to:
```
   RA(J2000)  = 16h 38m 32.04s
   Dec(J2000) = -12d 03' 12.1"
```
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 56 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. We cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (2.71 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 4.5 (+3.63/-3.05) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 1.27e-09 erg cm^-2 s^-1 (0.2-10 keV).
There will be no prompt UVOT data available for this burst.
Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 02:21:44 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.6335d {+16h 38m 32.03s} (J2000),
                 249.8511d {+16h 39m 24.27s} (current),
                 248.9376d {+16h 35m 45.02s} (1950)
GRB_DEC:         -12.0533d {-12d 03' 11.8"} (J2000),
                 -12.0834d {-12d 05' 00.3"} (current),
                 -11.9548d {-11d 57' 17.3"} (1950)
GRB_ERROR:       3.8 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  7619.00 SOD {02:06:59.00} UT,   105.6 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       146.21d {+09h 44m 50s}  +13.56d {+13d 33' 19"}
SUN_DIST:        105.86 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.56d {+11h 26m 15s}   +2.72d {+02d 43' 19"}
MOON_DIST:        79.15 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.44 [deg] galactic lon,lat of the burst
ECL_COORDS:      249.78,  9.97 [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:        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:     Mon 17 Aug 15 03:15:58 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     652334,   Seg_Num: 0
POINT_RA:        249.657d {+16h 38m 38s} (J2000)
POINT_DEC:       -12.057d {-12d 03' 25"} (J2000)
POINT_ROLL:      280.895d
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  11468.09 SOD {03:11:08.09} UT,   3954.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        6.956
N_STARS:         50
X_OFFSET:        610 [pixels]
Y_OFFSET:        468 [pixels]
X_MAX:           1569 [pixels]
Y_MAX:           1427 [pixels]
DET_THRESH:      23
PHOTO_THRESH:    14
SL_URL:          sw00652334000msufc3954.fits
SUN_POSTN:       146.24d {+09h 44m 59s}  +13.54d {+13d 32' 36"}
SUN_DIST:        105.85 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.99d {+11h 27m 57s}   +2.58d {+02d 34' 58"}
MOON_DIST:        78.72 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.21, 22.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      249.81,  9.97 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 03:16:24 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     652334,   Seg_Num: 0
POINT_RA:        249.657d {+16h 38m 38s} (J2000)
POINT_DEC:       -12.057d {-12d 03' 25"} (J2000)
POINT_ROLL:      280.895d
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  11468.09 SOD {03:11:08.09} UT,   3954.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        6.956
N_STARS:         50
X_OFFSET:        610 [pixels]
Y_OFFSET:        468 [pixels]
X_MAX:           1569 [pixels]
Y_MAX:           1427 [pixels]
DET_THRESH:      23
PHOTO_THRESH:    14
SL_URL:          sw00652334000msufc3954.fits
SUN_POSTN:       146.25d {+09h 44m 59s}  +13.54d {+13d 32' 35"}
SUN_DIST:        105.85 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.99d {+11h 27m 58s}   +2.58d {+02d 34' 54"}
MOON_DIST:        78.72 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.21, 22.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      249.81,  9.97 [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 17 Aug 15 03:16:29 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     652334,   Seg_Num: 0
GRB_RA:          249.6330d {+16h 38m 31.92s} (J2000),
                 249.8506d {+16h 39m 24.15s} (current),
                 248.9371d {+16h 35m 44.90s} (1950)
GRB_DEC:         -12.0530d {-12d 03' 10.8"} (J2000),
                 -12.0831d {-12d 04' 59.2"} (current),
                 -11.9545d {-11d 57' 16.2"} (1950)
GRB_ERROR:       2.4 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  7619.00 SOD {02:06:59.00} UT,   105.6 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       146.25d {+09h 44m 59s}  +13.54d {+13d 32' 35"}
SUN_DIST:        105.82 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      171.99d {+11h 27m 58s}   +2.58d {+02d 34' 53"}
MOON_DIST:        78.70 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.19, 22.44 [deg] galactic lon,lat of the burst
ECL_COORDS:      249.78,  9.97 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 17 Aug 15 03:17:41 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     652334,   Seg_Num: 0
POINT_RA:        249.657d {+16h 38m 38s} (J2000)
POINT_DEC:       -12.057d {-12d 03' 25"} (J2000)
ROLL:            280.895d
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  11468.09 SOD {03:11:08.09} UT,   3954.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     461473883
X_OFFSET:        929 [pixels]
Y_OFFSET:        787 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1089
Y_GRB_POS:       947
BINNING_INDEX:   1
IM_URL:          sw00652334000msuni3970.fits
SUN_POSTN:       146.25d {+09h 44m 59s}  +13.54d {+13d 32' 34"}
SUN_DIST:        105.85 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      172.00d {+11h 28m 00s}   +2.58d {+02d 34' 42"}
MOON_DIST:        78.71 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.21, 22.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      249.81,  9.97 [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 17 Aug 15 03:17:51 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     652334,   Seg_Num: 0
POINT_RA:        249.657d {+16h 38m 38s} (J2000)
POINT_DEC:       -12.057d {-12d 03' 25"} (J2000)
ROLL:            280.895d
IMG_START_DATE:  17251 TJD;   229 DOY;   15/08/17
IMG_START_TIME:  11468.09 SOD {03:11:08.09} UT,   3954.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     461473883
X_OFFSET:        929 [pixels]
Y_OFFSET:        787 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1089
Y_GRB_POS:       947
BINNING_INDEX:   1
IM_URL:          sw00652334000msuni3970.fits
SUN_POSTN:       146.25d {+09h 44m 59s}  +13.54d {+13d 32' 34"}
SUN_DIST:        105.84 [deg]   Sun_angle= -6.9 [hr] (East of Sun)
MOON_POSTN:      172.00d {+11h 28m 01s}   +2.58d {+02d 34' 40"}
MOON_DIST:        78.71 [deg]
MOON_ILLUM:      6 [%]
GAL_COORDS:        5.21, 22.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      249.81,  9.97 [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 #18144
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:
We observed the field of GRB 150817A (V. D'Elia, et al., GCN 18143) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from 2015/08 17.14 to 2015/08 17.16 UTC (1.29 to 1.70 hours after the BAT trigger), obtaining a total of 0.36 hours exposure in the r, i, and z bands.
We find an uncatalogued source within the Swift-XRT error circle at RA, Dec =3D 16:38:31.98, -12:3:11.5 (J2000, +/-0.5"). In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections and upper limit (3-sigma):
```
   r =3D 21.50 +/- 0.20
   i =3D 21.26 +/- 0.10
   z > 17.83
```
These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
Further observations are planned.
We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
GCN Circular #18145
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), Willia= m H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier Proch= aska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora T= roja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A= . de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Car= los Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC)= , John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:
We continue to observe the field of GRB 150817A (V. D'Elia, et al., GCN 1= 8143) with the Reionization and Transients Infrared Camera (RATIR; www.ra= tir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3= mico Nacional on Sierra San Pedro M=E1rtir from 2015/08 17.14 to 2015/08 = 17.25 UTC (1.29 to 3.93 hours after the BAT trigger), obtaining a total o= f 2.13 hours exposure in the r, i, and z bands.
We note that the source reported in Butler et al. (GCN 18144) appears to = have remained constant in flux over the time period quoted above, while a= n uncatalogued source just west of the XRT error circle has faded strongl= y as t^(-0.8+/-0.1). This second source is located at RA, Dec =3D 16:38:= 31.51, -12:03:9.6 (J2000, +/-0.5").
In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections and upper limit (3-sigma):
```
   r =3D 22.06 +/- 0.09
   i =3D 21.49 +/- 0.07
   z > 20.33
```
These magnitudes, corresponding to the midpoint of our observation, are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
GCN Circular #18146
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 1629 s of XRT Photon Counting mode data and 4 UVOT images for GRB 150817A, 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 = 249.63108, -12.05293 which is equivalent to:
```
RA (J2000): 16h 38m 31.46s
Dec (J2000): -12d 03' 10.5"
```
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 #18147
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester), P. D'Avanzo (INAF-OAB), A. D'ai (INAF-IASFPA), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU) and V. D'Elia report on behalf of the Swift-XRT team:
We have analysed 11 ks of XRT data for GRB 150817A (D'Elia et al. GCN Circ. 18143), from 56 s to 29.2 ks after the BAT trigger. The data comprise 32 s in Windowed Timing (WT) mode (the first 7 s were 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. 18146).
The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=3.6 (+/-0.4). At T+104 s the decay flattens to an alpha of 0.57 (+0.06, -1.00) before breaking again at T+4285 s to a final decay with index alpha=1.07 (+/-0.07).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.77 (+/-0.11). The best-fitting absorption column is 4.5 (+0.7, -0.6) x 10^21 cm^-2, in excess of the Galactic value of 2.7 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 4.5 x 10^-11 (6.4 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     4.5 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 2.7 x 10^21 cm^-2
Excess significance: 4.6 sigma
Photon index:	     1.77 (+/-0.11)
```
If the light curve continues to decay with a power-law decay index of 1.07, the count rate at T+24 hours will be 0.021 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.7 x 10^-13 (1.4 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00652334.
This circular is an official product of the Swift-XRT team.
GCN Circular #18148
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), V. D'Elia (ASDC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 150817A (trigger #652334) (D'Elia, et al., GCN Circ. 18143). The BAT ground-calculated position is RA, Dec = 249.635, -12.050 deg, which is
```
   RA(J2000)  =  16h 38m 32.3s 
   Dec(J2000) = -12d 03' 01.7" 
```
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 71%.
The mask-weighted light curve shows multiple strong peaks starting at ~T-20, with the brightest peak at ~T+12 sec and ending at ~T+70 sec. T90 (15-350 keV) is 38.8 +- 2.1 sec (estimated error including systematics).
The time-averaged spectrum from T-16.76 to T+53.28 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.78 +- 0.04. The fluence in the 15-150 keV band is 5.9 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+11.22 sec in the 15-150 keV band is 9.6 +- 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/652334/BA/
GCN Circular #18149
H.-F. Yu (MPE) and P. Jenke (UAH) report on behalf of the Fermi GBM Team:
"At 02:05:08.40 UT on 17 August 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150817A (trigger 461469912 / 150817087), which was also detected by the Swift/BAT (D'Elia et al. 2015, GCN 18143). The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 102 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 36 s (50-300 keV). The time-averaged spectrum from T0-10.240 s to T0+45.057 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.34 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 109.0 +/- 8.8 keV.
The event fluence (10-1000 keV) in this time interval is (1.15 +/- 0.05)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+16.256 s in the 10-1000 keV band is 15.7 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #18150
F. E. Marshall (NASA/GSFC) and V. D'Elia (ASDC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150817A 3955 s after the BAT trigger (D'Elia et al., GCN Circ. 18143). No optical afterglow consistent with the enhanced X-ray position (Osborne et al. GCN Circ. 18146) or the optical position (Butler et al. GCN Circ. 18145) 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          3955         4104          147         >20.5
white             3955        12079          930         >21.4
v                 4111        28678         1278         >20.9
b                 4932        17880         1723         >21.7
u                 4727        23627         2613         >21.7
w1                4522        22957         2144         >21.0
w2               26865        27765          886         >20.5
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.48 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #18153
S. B. Cenko (NASA/GSFC) and D. A. Perley (DARK) report on behalf of a larger collaboration:
We observed the location of GRB150817A (D=92Elia et al., GCN 18143) with the robotic Palomar 60 inch telescope (P60). Observations began at 3:35 UT on 2015 Aug 17 (~ 90 min after the Swift trigger time). We detect a faint source at the location of the (second) candidate optical afterglow from RATIR (Butler et al., GCN 18145). Using nearby point sources from the APASS survey, we measure an i-band magnitude of 21.42 +/- 0.11 in a stacked frame at a median epoch of dt =3D 125 min after the Swift trigger.
GCN Circular #18156
Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), Willia= m=20 H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier=20 Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC),=20 Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC)= ,=20 Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UN= AM),=20 Carlos Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GS= FC),=20 John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:
We observed the field of GRB 150817A (D'Elia, et al., GCN 18143) with the= =20 Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the= =20 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional = on=20 Sierra San Pedro M=E1rtir from 2015/08 18.16 to 2015/08 18.27 UTC (25.78 = to=20 28.42 hours after the BAT trigger), obtaining a total of 1.77 hours=20 exposure in the r, i, and z bands.
The first source reported by Butler et al. (GCN 18144) has not faded sinc= e=20 our first epoch of observations.
The second source, reported by Butler et al. (GCN 18145), has continued t= o=20 fade and is now only marginally detected. In comparison with the USNO-B1=20 and 2MASS catalogs, we obtain the following marginal detections and upper limit (3-sigma):
```
   r	=3D 23.8 =B1 0.4
   i	=3D 23.8 =B1 0.3
   z	> 20.2
```
These magnitudes are in the AB system and are not corrected for Galactic=20 extinction in the direction of the GRB.
We note that the second source is consistent with the enhanced Swift-XRT=20 error circle (Osborne et al. GCN 18146). This coincidence and the clear=20 fading suggest that it is the afterglow of the GRB.
We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
GCN Circular #18158
S. Dichiara, C. Guidorzi (U. Ferrara), C.G. Mundell (U. Bath), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of a large collaboration report:
The 1-m telescopes in Cerro Tololo (Chile) and McDonald (Texas) began observing Swift GRB 150817A (V. D'Elia, et al., GCN 18143). on August 17 at 03:16:31 UT, i.e. ~70 minutes since the BAT trigger, with the r' and i' filters. Further observations with the i' filter were performed using the 2-m Faulkes Telescope North ~400 min after the trigger.
Within the enhanced XRT error circle (Osborne et al. GCN Circ. 18146) we find no optical counterpart to the following limiting magnitude:
```
Mid time from  Total Exp   Filter    Magnitude
trigger (min)   (s)
-------------------------------------------------
75.9         120x9       r'        > 19.6
86.3         120x8       i'        > 18.5
107.6        120x5       r'        > 19.7
119.2        120x5       i'        > 19.1
408.1        120x5       i'        > 20.7
-------------------------------------------------
```
Our results are consistent with the previous observations reported by Butler et al. (GCN Circ. 18144) and Cenko et al. (GCN Circ. 18153).
Magnitudes are calibrated against nearby USNO-B1 stars (R2 and I).
GCN Circular #18160
E. Mazaeva (IKI), R. Inasaridze (AAO), V. Ayvazian (AAO), I. Molotov=20 (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up=20 collaboration:
We observed the field of the Swift GRB 150817A (D=E2=80=99Elia et al., GC= N=20 18143) with AS-32 (0.7m) telescope of Abastumani Observatory starting on=20 Aug. 17 (UT) 17:00:31. Within the enhanced XRT error circle (Osborne et=20 al., GCN 18146) we do not detect the optical afterglow (Butler et al.,=20 GCN 18145; Cenko et al., GCN 18153). In particular the magnitude of the=20 first object (Butler et al., GCN 18144) is 21.6 +/- 0.2. Upper limit of=20 the object is following
```
Date       UT start    t-T0     Filter  Exp.     UL(3 sigam)
                        (mid, days)      (s)

2015-08-17 17:00:31    0.64432  None    24*120   22.4
```
The photometry is based on nearby USNO-B1.0 stars
```
USNO-B.1_id  R2
0779-0405699 16.12
0779-0405721 16.40
0779-0405742 16.47
0779-0405723 16.94
0779-0405664 17.60
```

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Jochen Greiner, last update: 18-Aug-2015 [Disclaimer]