Gamma-ray Burst 151027A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 03:58:42 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     661775,   Seg_Num: 0
GRB_RA:          272.491d {+18h 09m 58s} (J2000),
                 272.533d {+18h 10m 08s} (current),
                 272.361d {+18h 09m 27s} (1950)
GRB_DEC:         +61.381d {+61d 22' 51"} (J2000),
                 +61.385d {+61d 23' 05"} (current),
                 +61.369d {+61d 22' 08"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       2699 [cnts]    Image_Peak=136 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   127     E_range: 50-350 keV
BKG_INTEN:       23807 [cnts]
BKG_TIME:        14288.67 SOD {03:58:08.67} UT
BKG_DUR:         8 [sec]
GRB_DATE:        17322 TJD;   300 DOY;   15/10/27
GRB_TIME:        14304.15 SOD {03:58:24.15} UT
GRB_PHI:           1.16 [deg]
GRB_THETA:        51.77 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     29.15 [sigma]
IMAGE_SIGNIF:    9.26 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +3  +0  +0  +0  -3  +0 
SUN_POSTN:       211.18d {+14h 04m 44s}  -12.65d {-12d 39' 03"}
SUN_DIST:         88.18 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.44d {+01h 49m 46s}   +8.67d {+08d 39' 55"}
MOON_DIST:        93.85 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.51, 28.49 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      283.05, 84.71 [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 = 136.64,-16.52 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(0.0<100sec) coincident with the FERMI_GBM event (trignum=467611108).

red DSS finding chart ps-file

GCN NOTICE

 
TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Tue 27 Oct 15 03:59:31 UT
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    7283,   Sub_Num: 0
GRB_INTEN:      9.83 [sigma]   
GRB_TIME:       14302.13 SOD {03:58:22.13} UT
GRB_DATE:       17322 TJD;   300 DOY;   15/10/27 
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.
COMMENTS:       Time_Scale=2.0000 and Time_Error=1.0000. 
COMMENTS:
COMMENTS:       NOTE: This SPIACS event is temporally(2.0<100sec) coincident
+with the FERMI_GBM event (trignum=467611108).
COMMENTS:
COMMENTS:       The SPIACS lightcurve can be found at:
COMMENTS:       ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2015-10/2015-10-27T03-58-21.9621-29609-56208-0.lc

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Oct 15 03:59:20 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      56
TRIGGER_NUM:     467611108
GRB_RA:          271.620d {+18h 06m 29s} (J2000),
                 271.657d {+18h 06m 38s} (current),
                 271.503d {+18h 06m 01s} (1950)
GRB_DEC:         +62.010d {+62d 00' 36"} (J2000),
                 +62.013d {+62d 00' 45"} (current),
                 +62.002d {+62d 00' 09"} (1950)
GRB_ERROR:       1.14 [deg radius, statistical only]
DATA_SIGNIF:     39.10 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        17322 TJD;   300 DOY;   15/10/27
GRB_TIME:        14304.03 SOD {03:58:24.03} UT
GRB_PHI:         334.00 [deg]
GRB_THETA:         9.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4153 (Gnd S/W Version number)
SUN_POSTN:       211.18d {+14h 04m 44s}  -12.65d {-12d 39' 04"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.0 [hr] (East of Sun)
MOON_POSTN:       27.45d {+01h 49m 48s}   +8.67d {+08d 40' 01"}
MOON_DIST:        93.94 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       91.19, 28.95 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      279.51, 85.40 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn151027166/quicklook/glg_lc_medres34_bn151027166.gif
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=661775).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Oct 15 03:58:50 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     467611108
GRB_RA:          281.017d {+18h 44m 04s} (J2000),
                 281.070d {+18h 44m 17s} (current),
                 280.849d {+18h 43m 24s} (1950)
GRB_DEC:         +59.967d {+59d 58' 00"} (J2000),
                 +59.984d {+59d 59' 01"} (current),
                 +59.914d {+59d 54' 50"} (1950)
GRB_ERROR:       4.73 [deg radius, statistical plus systematic]
GRB_INTEN:       662 [cnts/sec]
DATA_SIGNIF:     29.20 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        17322 TJD;   300 DOY;   15/10/27
GRB_TIME:        14304.03 SOD {03:58:24.03} UT
GRB_PHI:           0.00 [deg]
GRB_THETA:         5.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.90
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   2%  Cyg X-1
DETECTORS:       1,0,0, 1,0,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       211.18d {+14h 04m 44s}  -12.65d {-12d 39' 03"}
SUN_DIST:         91.25 [deg]   Sun_angle= -4.7 [hr] (East of Sun)
MOON_POSTN:       27.44d {+01h 49m 47s}   +8.67d {+08d 39' 56"}
MOON_DIST:        90.51 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       89.69, 24.15 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      311.96, 81.78 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn151027166/quicklook/glg_lc_medres34_bn151027166.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 163.07,17.28 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=661775).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:00:26 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     661775,   Seg_Num: 0
GRB_RA:          272.4886d {+18h 09m 57.26s} (J2000),
                 272.5302d {+18h 10m 07.25s} (current),
                 272.3571d {+18h 09m 25.70s} (1950)
GRB_DEC:         +61.3515d {+61d 21' 05.4"} (J2000),
                 +61.3554d {+61d 21' 19.2"} (current),
                 +61.3397d {+61d 20' 23.0"} (1950)
GRB_ERROR:       4.8 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       7.08e-09 [erg/cm2/sec]
GRB_SIGNIF:      13.34 [sigma]
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14391.15 SOD {03:59:51.15} UT,   87.0 [sec] since BAT Trigger Time
TAM[0-3]:        327.66 237.21 261.60 243.37
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       211.19d {+14h 04m 44s}  -12.65d {-12d 39' 05"}
SUN_DIST:         88.16 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.46d {+01h 49m 51s}   +8.67d {+08d 40' 13"}
MOON_DIST:        93.87 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.48, 28.49 [deg] galactic lon,lat of the burst
ECL_COORDS:      282.97, 84.68 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.76 arcmin from the BAT position.  
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:00:42 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     661775,   Seg_Num: 0
GRB_RA:          272.4886d {+18h 09m 57.2s} (J2000),
                 272.5302d {+18h 10m 07.2s} (current),
                 272.3571d {+18h 09m 25.7s} (1950)
GRB_DEC:         +61.3515d {+61d 21' 05.4"} (J2000),
                 +61.3554d {+61d 21' 19.2"} (current),
                 +61.3397d {+61d 20' 23.0"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       178 [cnts]
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14391.15 SOD {03:59:51.15} UT,   87.0 [sec] since BAT Trigger Time
CENTROID_X:      316.34,  raw= 316  [pixels]
CENTROID_Y:      344.28,  raw= 344  [pixels]
ROLL:            238.91 [deg]
GAIN:            4
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   109.57
GRB_POS_XRT_Z:   26.03
IMAGE_URL:       sw00661775000msxps_rw.img
SUN_POSTN:       211.19d {+14h 04m 44s}  -12.65d {-12d 39' 05"}
SUN_DIST:         88.16 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.46d {+01h 49m 51s}   +8.67d {+08d 40' 16"}
MOON_DIST:        93.87 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.48, 28.49 [deg] galactic lon,lat of the burst
ECL_COORDS:      282.97, 84.68 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.  
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:00:48 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     661775,   Seg_Num: 0
GRB_RA:          272.4886d {+18h 09m 57.2s} (J2000),
                 272.5302d {+18h 10m 07.2s} (current),
                 272.3571d {+18h 09m 25.7s} (1950)
GRB_DEC:         +61.3515d {+61d 21' 05.4"} (J2000),
                 +61.3554d {+61d 21' 19.2"} (current),
                 +61.3397d {+61d 20' 23.0"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       178 [cnts]
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14391.15 SOD {03:59:51.15} UT,   87.0 [sec] since BAT Trigger Time
CENTROID_X:      316.34,  raw= 316  [pixels]
CENTROID_Y:      344.28,  raw= 344  [pixels]
ROLL:            238.91 [deg]
GAIN:            4
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   109.57
GRB_POS_XRT_Z:   26.03
IMAGE_URL:       sw00661775000msxps_rw.img
SUN_POSTN:       211.19d {+14h 04m 45s}  -12.65d {-12d 39' 05"}
SUN_DIST:         88.16 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.46d {+01h 49m 51s}   +8.67d {+08d 40' 17"}
MOON_DIST:        93.87 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.48, 28.49 [deg] galactic lon,lat of the burst
ECL_COORDS:      282.97, 84.68 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.  
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:02:03 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     661775,   Seg_Num: 0
GRB_RA:          272.491d {+18h 09m 58s} (J2000),
                 272.533d {+18h 10m 08s} (current),
                 272.361d {+18h 09m 27s} (1950)
GRB_DEC:         +61.381d {+61d 22' 51"} (J2000),
                 +61.385d {+61d 23' 05"} (current),
                 +61.369d {+61d 22' 08"} (1950)
GRB_DATE:        17322 TJD;   300 DOY;   15/10/27
GRB_TIME:        14304.15 SOD {03:58:24.15} UT
TRIGGER_INDEX:   127
GRB_PHI:           1.16 [deg]
GRB_THETA:        51.77 [deg]
DELTA_TIME:      52.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     29.15 [sigma]
IMAGE_SIGNIF:    9.26 [sigma]
LC_URL:          sw00661775000msb.lc
SUN_POSTN:       211.19d {+14h 04m 45s}  -12.65d {-12d 39' 06"}
SUN_DIST:         88.18 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.48d {+01h 49m 55s}   +8.67d {+08d 40' 30"}
MOON_DIST:        93.86 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.51, 28.49 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      283.05, 84.71 [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 = 136.64,-16.52 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:05:26 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.442d {+18h 09m 46s} (J2000)
POINT_DEC:       +61.374d {+61d 22' 28"} (J2000)
POINT_ROLL:      238.907d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14399.67 SOD {03:59:59.67} UT,   95.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        7.523
N_STARS:         41
X_OFFSET:        312 [pixels]
Y_OFFSET:        608 [pixels]
X_MAX:           1271 [pixels]
Y_MAX:           1567 [pixels]
DET_THRESH:      24
PHOTO_THRESH:    15
SL_URL:          sw00661775000msufc0095.fits
SUN_POSTN:       211.19d {+14h 04m 45s}  -12.65d {-12d 39' 09"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.51d {+01h 50m 03s}   +8.68d {+08d 41' 06"}
MOON_DIST:        93.89 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.51, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.78, 84.71 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:05:55 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.442d {+18h 09m 46s} (J2000)
POINT_DEC:       +61.374d {+61d 22' 28"} (J2000)
POINT_ROLL:      238.907d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14399.67 SOD {03:59:59.67} UT,   95.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        7.523
N_STARS:         41
X_OFFSET:        312 [pixels]
Y_OFFSET:        608 [pixels]
X_MAX:           1271 [pixels]
Y_MAX:           1567 [pixels]
DET_THRESH:      24
PHOTO_THRESH:    15
SL_URL:          sw00661775000msufc0095.fits
SUN_POSTN:       211.19d {+14h 04m 45s}  -12.65d {-12d 39' 09"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.52d {+01h 50m 04s}   +8.69d {+08d 41' 11"}
MOON_DIST:        93.89 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.51, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.78, 84.71 [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:     Tue 27 Oct 15 04:07:04 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.442d {+18h 09m 46s} (J2000)
POINT_DEC:       +61.374d {+61d 22' 28"} (J2000)
ROLL:            238.907d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14399.67 SOD {03:59:59.67} UT,   95.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     467611215
X_OFFSET:        649 [pixels]
Y_OFFSET:        721 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       809
Y_GRB_POS:       881
BINNING_INDEX:   1
IM_URL:          sw00661775000msuni0111.fits
SUN_POSTN:       211.19d {+14h 04m 46s}  -12.65d {-12d 39' 10"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.53d {+01h 50m 07s}   +8.69d {+08d 41' 23"}
MOON_DIST:        93.89 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.51, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.78, 84.71 [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:     Tue 27 Oct 15 04:07:26 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.442d {+18h 09m 46s} (J2000)
POINT_DEC:       +61.374d {+61d 22' 28"} (J2000)
ROLL:            238.907d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14399.67 SOD {03:59:59.67} UT,   95.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     467611215
X_OFFSET:        649 [pixels]
Y_OFFSET:        721 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       809
Y_GRB_POS:       881
BINNING_INDEX:   1
IM_URL:          sw00661775000msuni0111.fits
SUN_POSTN:       211.19d {+14h 04m 46s}  -12.65d {-12d 39' 11"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.53d {+01h 50m 08s}   +8.69d {+08d 41' 27"}
MOON_DIST:        93.89 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.51, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.78, 84.71 [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:     Tue 27 Oct 15 04:12:04 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
POINT_ROLL:      238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14612.99 SOD {04:03:32.99} UT,   308.8 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        2.780
N_STARS:         31
X_OFFSET:        329 [pixels]
Y_OFFSET:        401 [pixels]
X_MAX:           1288 [pixels]
Y_MAX:           1360 [pixels]
DET_THRESH:      14
PHOTO_THRESH:    7
SL_URL:          sw00661775000msufc0308.fits
SUN_POSTN:       211.19d {+14h 04m 46s}  -12.65d {-12d 39' 15"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.58d {+01h 50m 19s}   +8.70d {+08d 42' 16"}
MOON_DIST:        93.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:12:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
POINT_ROLL:      238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14612.99 SOD {04:03:32.99} UT,   308.8 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        2.780
N_STARS:         31
X_OFFSET:        329 [pixels]
Y_OFFSET:        401 [pixels]
X_MAX:           1288 [pixels]
Y_MAX:           1360 [pixels]
DET_THRESH:      14
PHOTO_THRESH:    7
SL_URL:          sw00661775000msufc0308.fits
SUN_POSTN:       211.19d {+14h 04m 46s}  -12.65d {-12d 39' 15"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.58d {+01h 50m 20s}   +8.71d {+08d 42' 19"}
MOON_DIST:        93.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [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:     Tue 27 Oct 15 04:13:31 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
ROLL:            238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14612.99 SOD {04:03:32.99} UT,   308.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     467611428
X_OFFSET:        649 [pixels]
Y_OFFSET:        721 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       809
Y_GRB_POS:       881
BINNING_INDEX:   1
IM_URL:          sw00661775000msuni0324.fits
SUN_POSTN:       211.19d {+14h 04m 47s}  -12.65d {-12d 39' 16"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.59d {+01h 50m 22s}   +8.71d {+08d 42' 31"}
MOON_DIST:        93.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [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:     Tue 27 Oct 15 04:13:55 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
ROLL:            238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  14612.99 SOD {04:03:32.99} UT,   308.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     467611428
X_OFFSET:        649 [pixels]
Y_OFFSET:        721 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       809
Y_GRB_POS:       881
BINNING_INDEX:   1
IM_URL:          sw00661775000msuni0324.fits
SUN_POSTN:       211.19d {+14h 04m 47s}  -12.65d {-12d 39' 16"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.60d {+01h 50m 23s}   +8.71d {+08d 42' 35"}
MOON_DIST:        93.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [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:     Tue 27 Oct 15 04:15:38 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
POINT_ROLL:      238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  15162.83 SOD {04:12:42.83} UT,   858.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.233
N_STARS:         155
X_OFFSET:        89 [pixels]
Y_OFFSET:        161 [pixels]
X_MAX:           1528 [pixels]
Y_MAX:           1600 [pixels]
DET_THRESH:      15
PHOTO_THRESH:    8
SL_URL:          sw00661775000msufc0858.fits
SUN_POSTN:       211.20d {+14h 04m 47s}  -12.66d {-12d 39' 18"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.62d {+01h 50m 28s}   +8.71d {+08d 42' 53"}
MOON_DIST:        93.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 27 Oct 15 04:15:58 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
POINT_ROLL:      238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  15162.83 SOD {04:12:42.83} UT,   858.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.233
N_STARS:         155
X_OFFSET:        89 [pixels]
Y_OFFSET:        161 [pixels]
X_MAX:           1528 [pixels]
Y_MAX:           1600 [pixels]
DET_THRESH:      15
PHOTO_THRESH:    8
SL_URL:          sw00661775000msufc0858.fits
SUN_POSTN:       211.20d {+14h 04m 47s}  -12.66d {-12d 39' 18"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.62d {+01h 50m 28s}   +8.72d {+08d 42' 57"}
MOON_DIST:        93.90 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [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:     Tue 27 Oct 15 04:17:00 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
ROLL:            238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  15162.83 SOD {04:12:42.83} UT,   858.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     467611978
X_OFFSET:        648 [pixels]
Y_OFFSET:        720 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       808
Y_GRB_POS:       880
BINNING_INDEX:   1
IM_URL:          sw00661775000msuni0874.fits
SUN_POSTN:       211.20d {+14h 04m 47s}  -12.66d {-12d 39' 19"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.63d {+01h 50m 31s}   +8.72d {+08d 43' 08"}
MOON_DIST:        93.91 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [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:     Tue 27 Oct 15 04:17:11 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     661775,   Seg_Num: 0
POINT_RA:        272.445d {+18h 09m 47s} (J2000)
POINT_DEC:       +61.372d {+61d 22' 19"} (J2000)
ROLL:            238.910d
IMG_START_DATE:  17322 TJD;   300 DOY;   15/10/27
IMG_START_TIME:  15162.83 SOD {04:12:42.83} UT,   858.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     467611978
X_OFFSET:        648 [pixels]
Y_OFFSET:        720 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       808
Y_GRB_POS:       880
BINNING_INDEX:   1
IM_URL:          sw00661775000msuni0874.fits
SUN_POSTN:       211.20d {+14h 04m 47s}  -12.66d {-12d 39' 19"}
SUN_DIST:         88.15 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:       27.63d {+01h 50m 31s}   +8.72d {+08d 43' 10"}
MOON_DIST:        93.91 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:       90.50, 28.51 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      282.79, 84.70 [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 #18478
A. Maselli (INAF-IASFPA), A. D'Ai (INAF-IASFPA), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (LANL) report on behalf of the Swift Team:
At 03:58:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151027A (trigger=661775). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 272.491, +61.381 which is
```
   RA(J2000) = 18h 09m 58s
   Dec(J2000) = +61d 22' 51"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex peaked structure lasting at least 150 seconds. The peak count rate was ~6000 counts/sec (15-350 keV), at ~110 sec after the trigger.
The XRT began observing the field at 03:59:51.1 UT, 87.0 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 272.4886, 61.3515 which is equivalent to:
```
   RA(J2000)  = +18h 09m 57.26s
   Dec(J2000) = +61d 21' 05.4"
```
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 106 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy.
UVOT took a finding chart exposure of 150 seconds with the White filter starting 95 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at
```
RA(J2000) =	18:09:56.68 = 272.48615
DEC(J2000) = +61:21:13.4 = 61.35373
```
with a 90%-confidence error radius of about 0.61 arc sec. This position is 9.06 arc sec. from the center of the XRT error circle. The estimated magnitude is 14.46 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05.
Burst Advocate for this burst is A. Maselli (maselli AT ifc.inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular #18479
WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to Swift GRB 151027A (Maselli et al., GCN 18478) immediately after receiving the trigger. Observations were performed with an automatic sequence in the clear (roughly R), V, and I filters, and the exposure time was 20 s per image. Inside the XRT error circle we detected an un-cataloged varying source with coordinates of :
```
RA =  18:09:56.70 (J2000)
DEC= +61:21:13.01 (J2000)
```
The object location is consistent with the position reported from UVOT (Maselli et al., GCN 18478). The object has clear band mag of ~13.0 at the moment.
Follow-up observations are encouraged.
GCN Circular #18480
L. Elenin (KIAM), E. Mazaeva (IKI), A. Volnova (IKI), I. Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We observed the field of the Swift GRB 151027A (Maselli et al., GCN 18478) with 0.4-m telescope of ISON-NM observatory in robotic mode starting on Oct., 27 (UT) 03:59:43 i.e. 79 seconds after burst trigger. We obtained 50 unfiltered images of 30 s exposure. We clearly detect the optical counterpart of GRB 151027A (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) in coordinates (J2000) 18 09 56.69 +61 21 13.2. In the first image we estimated brightness of the optical counterpart as ~14m.
GCN Circular #18481
D. A. Perley (DARK/NBI) and S. B. Cenko (NASA/GSFC) report:
The Palomar 60-inch robotic telescope responded automatically to the alert for GRB 151027A (Maselli et al., GCN151027A) and began a sequence of i, r, and z-band imaging at 04:00:49 UT, 145 seconds after the BAT trigger. We identify a very bright afterglow consistent with the UVOT and KAIT (Zheng et al., GCN18479) positions in all filters.
The preliminary afterglow light curve shows a slow rise to a peak at about ~5 minutes after the GRB trigger, then slowly fades by about 1 magnitude between then and approximately 30 minutes after the trigger. Over the next 20 minutes it then rapidly rebrightens by about 0.7 magnitude. Little or no fading is seen after that point (through to at least 90 minutes after the trigger.)
Continued monitoring is encouraged, and should remain possible even from small telescopes for quite some time. High-resolution spectroscopy is also strongly encouraged.
GCN Circular #18482
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team.
Using 1445 s of XRT Photon Counting mode data and 3 UVOT images for GRB 151027A, 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 = 272.48695, +61.35344 which is equivalent to:
```
RA (J2000): 18h 09m 56.87s
Dec (J2000): +61d 21' 12.4"
```
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 #18483
S. Campana (INAF-OAB) report on behalf of the Swift Team:
Swift BAT triggered on the early activity of GRB 151027A (Maselli et al. 2015, GCN 18478). Swift XRT started observing 87 s after the trigger observing the main event. By using the Swift/XRT spectrum repository at http://www.swift.ac.uk/xrt_spectra/ (see Evans et al. 2009, MNRAS, 397, 1177) we selected a time interval with an almost constant hardness ratio, starting at 150 s after the burst onset and lasting 281 s. We then fit the Window Timing (WT) spectrum with XSPEC using the model tbabs*ztbabs*pow. We assume a Galactic column density of 3.75x10^20 cm^-2 (Willingale et al. 2013, MNRAS, 431, 394) and we allow for a 30% uncertainty in the fit. We fit the spectrum using C-statistics (C-stat=593.74 with 637 d.o.f.). In the intrinsic column density vs. redshift plane there is just one deep minimum hinting for a redshift z=0.38+/-0.17 (90% confidence level) and an intrinsic column density N_H(z)=(3.6+/-0.7)x10^21 cm^-2. The X-ray spectrum is soft with Gamma=2.6, (assuming a cut-off power law spectrum the allowed redshift range expands to 0.27-1.38).
The contour plot is available at http://www.brera.inaf.it/utenti/campana/151027.gif
GCN Circular #18485
D. Xu (NAOC/CAS), C.-M. Zhang, C. Cao, S.-M. Hu (SDU) report:
We observed the field of GRB 151027A (Maselli et al., GCN 18478) using the 1m telescope located at Weihai, Shandong, China. Observations started at 09:44 UT on 2015-07-27, i.e., 5.77 hr after the burst. We obtained 5x300s R-band and 5x150s I-band frames.
The afterglow (e.g., Maselli et al., GCN 18478; Zheng & Filippenko, GCN 18479; Elenin et al., GCN 18480; Perley & Cenko, GCN 18481) is clearly detected in each image, and it has decayed to m(R) = 16.0 +/- 0.1 mag for the first R-band exposure, calibrated with the nearby USNO B1 stars (with R2 magnitudes).
GCN Circular #18487
D. A. Perley (DARK/NBI), L. Hillenbrand (Caltech), and J. X. Prochaska (UCO/Lick) report:
We obtained a 900s spectrum of the optical afterglow of GRB 151027A (Maselli et al., GCN 18478) with Keck/HIRES starting at UT 06:54 on 2015-10-27. In the preliminary reduction, we identify a series of strong absorption lines including the MgII doublet at z=0.81. Associated MgI, FeII, and (likely) FeII* are also present, indicating that this is the redshift of the GRB. Analysis is ongoing.
GCN Circular #18490
K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester) and A. Maselli report on behalf of the Swift-XRT team:
We have analysed 6.0 ks of XRT data for GRB 151027A (Maselli et al. GCN Circ. 18478), from 80 s to 18.9 ks after the BAT trigger. The data comprise 1.6 ks in Windowed Timing (WT) mode (the first 5 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 Goad et al. (GCN Circ. 18482).
The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=4.1 (+1.1, -1.0). At T+208 s the decay flattens to an alpha of 1.46 (+0.10, -0.14). The light curve breaks again at T+537 s to a decay with alpha=0.04 (+0.06, -0.09), and again at T+2494 s s to alpha=1.11 (+0.15, -0.26), before a final break at T+11.6 ks s after which the decay index is 2.01 (+0.26, -0.25).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.851 (+0.024, -0.023). The best-fitting absorption column is 1.96 (+0.18, -0.17) x 10^21 cm^-2, at a redshift of 0.81, in addition to the Galactic value of 3.8 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.99 (+/-0.08) and a best-fitting absorption column of 3.3 (+/-0.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Galactic foreground: 3.8 x 10^20 cm^-2
Intrinsic column:    3.3 (+/-0.6) x 10^21 cm^-2 at z=0.81
Photon index:	     1.99 (+/-0.08)
```
If the light curve continues to decay with a power-law decay index of 2.01, the count rate at T+24 hours will be 0.035 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x 10^-12 (1.7 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/00661775.
This circular is an official product of the Swift-XRT team.
GCN Circular #18491
Y. Yano, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, S. Kurita, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 151027A (A. Maselli et al., GCN Circular #18478) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.
The observation started on 2015-10-27 09:13:52 UT ( 5.25 h after the burst). We detected the previously reported optical afterglow of GRB 151027A (WeiKang Zheng et al., GCN Circular #18479) in the g',Rc and Ic band.
The measured magnitudes are listed below.
```
T0+[sec] MID-UT  T-EXP[sec]       g'                   Rc                 Ic
------------------------------------------------------------------------------------------------------------------
 18928     09:34:24      2220     16.72+/-0.06 15.62+/-0.05 16.00+/-0.04
------------------------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst 
T-EXP: Total Exposure time 
```
We used GSC2.3 catalog for flux calibration.
GCN Circular #18492
Kilian Toelge, Hoi-Fung Yu (both MPE), and Charles A. Meegan (USRA) report on behalf of the Fermi GBM Team:
"At 03:58:24.03 UT on 27 Oct 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 151027A (trigger 467611108 / 151027166), which was also detected by the Swift (Maselli et al. 2015, GCN 18478) The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 10 degrees.
This burst was also independently detected by INTEGRAL SPI-ACS.
The GBM light curve consists of three pulses with a duration (T90) of about 124 s (50-300 keV). The time-averaged spectrum from T0-2.048 s to T0+133.120 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.41 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 340 +/- 63 keV.
The event fluence (10-1000 keV) in this time interval is (1.94 +/- 0.09)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.3840 s in the 10-1000 keV band is 11.37 +/- 0.34 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #18493
J. Zhang, J. Mao and J. Bai (YNAO) report:
We observed the field of GRB 151027A (Maselli et al., GCN 18478) with the 2.4-meter optical telescope at Gao-Mei-Gu of Yunnan Observatories. Observations began at 11:34:08 UT, Oct 27, 2015, about 7.5 hr after the trigger. We obtained a low S/N spectrum. The feature of absorption line identified as MgII by Perley et al. (GCN 18487) is clearly shown, and redshift is 0.81. However, we noticed that some possible absorption lines might be identified as OVI and NaID, indicating a redshift of 0.33. We cannot have confirmation due to the low S/N of the spectrum. We also performed multi-band photometry and we obtained R~16.9 mag. Further analysis is ongoing.
GCN Circular #18495
J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis, of Los Alamos National Laboratory report:
The RAPTOR network of robotic optical telescopes made follow-up observations of Swift trigger 661775 (Maselli et al., GCN 18478). Our narrow-field instruments in Los Alamos, NM USA, began imaging at 03:58:48.01 UT (23.86 s after the BAT trigger time). From the first frame we detected a bright optical counterpart at the location reported by UVOT. Starting with a magnitude of R~13.7 the RAPTOR telescopes measured a complex, fading lightcurve with seveal re-brightening intervals.
GCN Circular #18496
D. M. Palmer (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), A. Maselli (INAF-IASFPA), 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 the recent telemetry downlink, we report further analysis of BAT GRB 151027A (trigger #661775) (Maselli et al., GCN Circ. 18478). The BAT ground-calculated position is RA, Dec = 272.498, 61.361 deg which is
```
  RA(J2000)  =  18h 09m 59.6s
  Dec(J2000) = +61d 21' 39.6"
```
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 18%.
The mask-weighted light curve shows a complex structure with roughly two main pulses. The first pulse starts at ~T0, peaks at ~T+1 s, and ends at ~T+5 s. The second pulse starts at ~T+90 s, peaks at ~T+110 s, and ends at ~T+170 s. T90 (15-350 keV) is 129.69 +- 5.55 sec (estimated error including systematics).
The time-averaged spectrum from T-0.74 to T+164.70 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.05. The fluence in the 15-150 keV band is 7.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.20 sec in the 15-150 keV band is 6.8 +- 0.6 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/661775/BA/
GCN Circular #18502
B. G. Balzer (PSU), M. H. Siegel (PSU) and A. Maselli (INAF-IASFPA) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 151027A 96 s after the BAT trigger (Maselli et al., GCN Circ. 18478). We confirm the source initially reported by Maselli et al. (GCN Circ. 18478) and since observed by numerous ground-based observatories (Zheng and Filippenko, GCN Circ. 18479; Elenin et al., GCN Circ. 18480; Perley and Cenko, GCN Circ. 18481; Xu et al., GCN Circ. 18485; Yano et al., GCN Circ. 18491; Wren et al., GCN Circ. 18495). We report a position of:
```
  RA(J2000)  = +18h 09m 57.26s
  Dec(J2000) = +61d 21' 05.4"
```
The light curve shows complex behavior, with marginal evidence of brightening after the initial finding chart, then fading with a decay slope of 0.6-0.8 over the first orbit. The second orbit magnitudes are consistent with no fading from those measured at the end of the first orbit while the third orbit shows significant fading.
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
```
Filter       T_start(s)  T_stop(s)  Exp(s)        Mag

white (fc)       95        245        147     14.52+-0.02
white           589        609         19     14.44+-0.04
white           762        782         19     14.71+-0.04
white           858       1008        147     14.81+-0.02
white          1161       1354         38     15.07+-0.04
white          1510       1529         19     15.23+-0.04
white          6449       6649        197     15.28+-0.01
white         23966      24662        677     17.14+-0.01
v               639       1579        116     15.12+-0.04
b               564       1505         97     15.37+-0.03
u               308       1479        323     14.00+-0.03
w1              688       1455         77     14.71+-0.05
m2              663       1598         88     14.98+-0.06
w2              615       1555        116     15.12+-0.05
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #18503
Veli-Pekka Hentunen, Markku Nissinen and Tuomo Salmi (Taurus Hill Observatory, Varkaus, Finland) report:
We have detected GRB 151027A optical afterglow at Taurus Hill Observatory (A95) using Meade 16" ACF 0.40-m/8.0 telescope and SBIG ST-8XME CCD. The observations were started at 2015-10-27 17:11:39 (UT). Eight photometric R filter and eight photometric V filter images with 300 sec exposure time were taken.
The afterglow was detected at the following position RA 18:09:56.72 and DEC +61:21:13.2.
The following magnitudes were obtained from the observations using NOMAD1 1512-0243178 (R=13.200 and V=13.670) as a comparison star:
```
Tmid(h)+T0    Filter      Exp. time         Mag          Mag. Err.
13.393              R          4x300s              17.06      0.12
13.747              V          4x300s              17.56      0.25
14.103              R          4x300s              17.06      0.09
14.457              V          4x300s              17.49      0.10
```
GCN Circular #18508
T. Laskar (NRAO / UC Berkeley), K. Alexander, and E. Berger (Harvard) report on behalf of a larger collaboration:
"We observed GRB 151027A (Maselli et al.; GCN 18478) at multiple frequencies with the VLA beginning on 2015 October 27.95 UT (0.78 days after the burst). At a mean frequency of 21.8 GHz, we detect a bright radio source with a preliminary flux density of ~ 1.7 mJy at
```
RA = 18:09:56.691 +/- 0.001
Dec = 61:21:13.03 +/- 0.02
```
consistent with the enhanced Swift/XRT position (Goad et al.; GCN 18482) and the optical position (Maselli et al.; GCN 18478, Zheng et al.; GCN 18479, Hentunen et al.; GCN 18503). Follow-up observations are planned. We thank the VLA staff for rapidly scheduling these observations."
GCN Circular #18510
S. Dichiara (U. Ferrara, ICRANet), D. Kopac (U. Ljubljana), C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of a larger collaboration report:
The 1-m LCOGT McDonald observatory began observing Swift GRB 151027A (Maselli et al. GCN 18478) on October 28, 01:29:27 UT (0.90 days after the burst trigger) with SDSS R and I filters. We clearly detect the optical afterglow (Maselli et al.; Zheng & Filippenko GCN 18479; Elenin et al. GCN 18480; Perley & Cenko GCN 18481; Xu et al. GCN 18485) with the following magnitudes:
```
Mid Time      Exposure       Filter       Magnitude
(days)           (s)
-------------------------------------------------------
0.90            5x120         R           16.87 +- 0.04
0.91            6x120         I           17.26 +- 0.05
-------------------------------------------------------
```
Calibration is done against nearby USNOB-1 star RA(J2000)=18:09:53.742, DEC(J2000)=+61:20:57.27, assuming R2=17.21 mag and I=17.17 mag. We note the presence of another USNOB-1 object at RA(J2000)=18:09:56.489, DEC(J2000)=+61:21:10.64, lying at 3.1 arcsec from the GRB afterglow.
GCN Circular #18513
J. Zhang, J. Mao and J. Bai (YNAO) report:
We observed the field of GRB 151027A (Maselli et al., GCN 18478) with the 2.4-meter optical telescope at Gao-Mei-Gu of Yunnan Observatories. Observations began at 11:32:30 UT, Oct. 28, 2015, about 31.5 hr after the trigger. We clearly detected the afterglow of GRB 151027A. The magnitude was estimated as R=18.9 +/- 0.1 mag.
GCN Circular #18515
L. P. Xin, X. F. Wang, J. Y. Wei, Y. L. Qiu, J. S. Deng, J. Wang, X. H. Han and C. Wu on behalf of EAFON report:
We observed GRB 151027A (Maselli et al., GCN 18478) with Xinglong 0.8-m TNT telescope at 2015-10-27 and 2015-10-28.
The optical afterglow (Maselli et al., GCN 18478; Zheng & Filippenko GCN 18479; Elenin et al., GCN 18480; Perley & Cenko GCN 18481; Xu et al, 18485; Zhang et al., GCN 18513) was clearly detected in our multi-band images. The brightness of the optical afterglow is decayed for about 2.5 mag in R-band during our observations as shown in follows:
```
==============================
Date             Time(UT)       filter  mag   merr            
2015-10-27  11:21:59          R       16.2    0.1
2015-10-28  11:04:00          R       18.7    0.1
==============================
```
Calibrated by the USNO B1.0 R2 mag
More observations are encouraged.
The message may be cited.
GCN Circular #18516
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 long-duration GRB 151027A (Swift-BAT trigger #661775: Maselli et al., GCN Circ. 18478, Palmer et al., GCN Circ. 18496; Fermi GBM detection: Toelge et al., GCN Circ. 18492) triggered Konus-Wind at T0=14304.154 s UT (03:58:24.154).
The burst light curve consists of at least three pulses with a total duration of ~120 s. The emission is seen up to ~5 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB151027_T14304/
As observed by Konus-Wind, the burst had a fluence of 1.42(-0.21,+0.37)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.432 s, of 2.22(-0.61,+0.62)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst (measured from T0 to T0+131.328 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.44(-0.21,+0.24) and Ep = 173(-46,+135) keV (chi2 = 78/77 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.0 (chi2 = 77/76 dof)
The spectrum near the maximum count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 2 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.96(-0.28,+0.32) and Ep = 91(-11,+14) keV (chi2 = 56/61 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 56/60 dof)
Assuming the redshift z=0.81 (Perley et al., GCN Circ. 18487) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, and Omega_Lambda = 0.73, we estimate the following rest-frame parameters: the isotropic energy release E_iso is ~2.4x10^52 erg, the peak luminosity L_iso is ~7x10^51 erg/s, and the rest-frame peak energy of the time-integrated spectrum, Ep,i, is ~310 keV.
All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
GCN Circular #18518
E. Sonbas (Adiyaman Univ.), T. Guver (Istanbul Univ.), E. Gogus (Sabanci Univ.), O. Erece, M. Kocak, S. Eryilmaz, H. Kirbiyik (TUG) report on behalf of a larger collaboration
We observed the field of Swift GRB 151027A (Maselli et al., GCN#18478) with the 1.0 meter T100 telescope (Bakirlitepe, TUBITAK National Observatory, Turkey), starting October, 27, 18:32:21 UT (~ 14.5 hours after the trigger). Observations were carried out in the R filter. The afterglow is detected in the R band images with an exposure time of 150 s.
Using USNO-B1 star USNO-B1 1513-0237223 (R.A.=272.49, Dec=+61.37) in the field, the magnitudes of the OT were estimated as follows;
t-t0 (hr) exp.(s) filt mag err (+/-)
14.56 150 R 16.8 0.06
14.61 150 R 17.2 0.08
Analysis of further observations with the same filter is ongoing.
We thank to TUBITAK National Observatory for a partial support in using T100 telescope with project number 10CT100-95 and technical support.
GCN Circular #18519
Z. Cano (U. Iceland), D. Malesani (DARK/NBI), Jussi Harmanen (NOT & U. Turku), Thomas Reynolds (NOT & U. Turku.), Pere Blay Serrano (IAC/NOT) and P. Jakobsson (U. Iceland) report on behalf of a larger collaboration:
We observed the field of Swift GRB 151027A (Maselli et al., GCN Circ. 18478) with the Nordic Optical Telescope equipped with the StanCam (optical) and NOTCam (NIR) imagers, in filters BVRI and JHK, respectively. Observations started at 20:53 UT on 27 October 2015. The OT (Maselli et al.) is detected all filters.
A summary of our observations follows:
```
Filter       t-t0 (hr)      Mag +- Merr
-----------------------------------------
B            17.94          21.4 +- 0.2
R            18.17          20.6 +- 0.1
I            18.28          19.2 +- 0.1
J            16.92          18.2 +- 0.1
H            17.38          18.3 +- 0.1
K            17.60          17.2 +- 0.2
```
The optical filters are calibrated to USNO-B1 and the NIR filters to 2MASS, where a single star that appeared in both catalogs was used for the zeropoint calculation. These magnitudes are not corrected for foreground extinction.
When these extinguished magnitudes are converted to monochromatic fluxes (using the zeropoints from Fukugita et al. 1995; Hewett et al. 2006), a single power-law with an exponent of -1.25 provides an acceptable fit to the optical-to-NIR spectral energy distribution.
GCN Circular #18521
A. Moskvitin (SAO RAS, Russia), report on behalf of the larger GRB follow-up team:
The field of the GRB 151027A (Maselli et al., GCNC #18478) was observed with the Zeiss-1000, 1 meter telescope of SAO RAS on the October, 28. The observations started 36.3 hours after the trigger. Two series of 300 sec. images in Rc band: 6 frames (16:13:57--16:56:20 UT) and 3 frames (17:32:15--17:50:33 UT) were obtained under the tolerable weather conditions.
The OT is clearly detected in the stacked frames:
```
#  T_mid-T0,h   exp,s      R_mag
1  36.612       6 x 300    18.7 +/- 0.1
2  37.717       3 x 300    18.9 +/- 0.1
```
The photometry is based on nearby USNO-B1 stars proposed by A. Pozanenko (IKI RAS). The observations were provided with the help of the SAO RAS staff: V. Komarov, O. Spiridonova and R. Uklein.
GCN Circular #18525
T. Masumitsu, H. Negoro, (Nihon U.), N. Kawai (Tokyo Tech), T. Sakamoto (AGU), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, R. Imatani (Osaka U.), M. Nakajima, K. Tanaka (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM) report on behalf of the MAXI team:
MAXI/GSC performed scanning observations at the region of GRB 151027A (Maselli et al. GCN 18478) for 48 sec each at the centroid time 03:38:56, 1168 s before the Swift trigger, and 05:11:32, 4388 s after the Swift trigger. No positive 4-10 keV flux was obtained at the former scan transit with the 3 sigma upper limit of 0.037 photons/cm2/s (~ 31 mCrab). At the latter scan transit, the 4-10 keV flux was 0.0166 +/- 0.0175 photons/cm2/s (~ 14 +/- 15 mCrab). The detection is not significant, but the flux is consistent with the interpolation from the Swift/XRT light curve (V. D'Elica et al. #18509).
GCN Circular #18533
Yu. Protsyuk (RI NAO), O. Kovalchuk (RI NAO) report:=20
We observed the field of the Swift GRB 151027A (Maselli et al.=20 GCN 18478) with 0.5-m telescope Mobitel KT-50 of Nikolaev observatory= with Alta-U9000 CCD-camera with R filter in robotic mode=20 from Oct., 28 (UTC) 20:34:16 till 20:59:59.=20
We obtained 19 unfiltered images of 60 s exposure and calculated=20 coordinates and magnitudes of all detected objects in UCAC4 system.=20 We don't detect any optical counterpart of GRB 151027A (Maselli et al= GCN 18478; Zheng and Filippenko, GCN 18479) in coordinates near (J2000) 18 09 56 +61 21 12 up to ~17.2- 17.5 m .=20 After that we filtered all images and detected optical=20 counterpart=A0in 6 images=A0in coordinates (J2000)=20 18 09 56.680 (SD=3D0.s081) +61 21 12.08 (SD=3D0."63)=20 with brightness near 18.3m (SD=3D0.3m)=20
GCN Circular #18537
S. B. Cenko (NASA-GSFC) and D. A. Perley (DARK/NBI) report on behalf of a= larger collaboration:
We have continued to image the optical afterglow of GRB151027A (Maselli et al., GCN 18478) with the robotic Palomar 60-inch telescope (see Perley et al., GCN 18481). We report the following r'-band photometry, calibrated with respect to nearby point sources from the APASS survey:
```
t_mid                                time since burst (d)          Magnitude

2015-10-29T02:14:14      1.93                                   19.63 +/- 0.04
2015-10-30T02:02:28      2.92                                   20.48 +/- 0.08
```
This implies a relatively steep power-law decay index of ~ 1.9 at these times.
Continued observations are planned.

GCN Circular #18539
P. Wiggins reports:
Observed GRB 151027A with a .35-meter optical telescope at my home observatory, IAU 718, on 2015 October 27 from 0433 to 0732 UTC using a clear filter and obtained the following:

GRB Countpart: 18h 09m 56.71s  +61d 21m 12.78s
Reference One: 18h 10m 05.68s  +61d 23m 14.97s
Reference Two: 18h 09m 51.53s  +61d 22m 48.87s

Julian Date       Date          Ref. C    Ref. K    Var. V    C-K       Differential 
Mid Exposure   yyyy-mm-dd.ddddd Raw Mag.  Raw Mag.  Raw Mag.  Differ.   Mag.        
-------------- ---------------- --------- --------- --------- --------- ------------
2457322.689715 2015 10 27.18972    -2.937    -3.111    -1.085     0.174       15.051
2457322.692866 2015 10 27.19287    -2.433    -2.622    -1.355     0.190       14.278
2457322.700101 2015 10 27.20010    -2.732    -2.925    -1.433     0.192       14.499
2457322.703174 2015 10 27.20317    -2.921    -3.112    -1.605     0.191       14.516
2457322.724392 2015 10 27.22439    -2.909    -3.088    -1.391     0.180       14.718
2457322.758285 2015 10 27.25829    -2.949    -3.142    -1.151     0.193       14.998
2457322.786495 2015 10 27.28649    -2.906    -3.085    -0.916     0.180       15.189
2457322.801286 2015 10 27.30129    -2.901    -3.108    -0.722     0.207       15.379
2457322.814370 2015 10 27.31437    -2.879    -3.079    -0.406     0.201       15.673

GCN Circular #18552
Z. Cano (U. Iceland) reports on behalf of a larger collaboration:
Upon further investigation, it was discovered that the magnitudes given in GCN Circ. 18519 are incorrect. The presented photometry was not for the optical and NIR afterglow of GRB 151027A, but rather the fainter object that is 3.1 arcsec SW of the afterglow (Dichiara et al. GCN Circ. 18510).
A revised summary of the NOT observations follows:
```
Filter       t-t0 (hr)      Mag +- Merr
-----------------------------------------
B            17.94          18.2 +- 0.1
R            18.17          17.9 +- 0.1
I            18.28          17.4 +- 0.1
J            16.92          16.4 +- 0.1
H            17.38          15.5 +- 0.1
K            17.60          15.1 +- 0.1
```
The optical filters are calibrated to USNO-B1 and the NIR filters to 2MASS, where a single star that appears in both catalogs was used for the zeropoint calculation. These magnitudes are not corrected for foreground extinction.
When these extinguished magnitudes are converted to monochromatic fluxes (using the zeropoints from Fukugita et al. 1995; Hewett et al. 2006), a single power-law with an exponent of -0.8 provides a good fit to the optical-to-NIR spectral energy distribution.
My apologies for the confusion.
GCN Circular #18555
R. Ruffini, Y. Aimuratov, U. Barres, R. Belvedere, C.L. Bianco, M. Enderli, M. Kovacevic, R. Moradi, M. Muccino, A. Penacchioni, G.B. Pisani, J.A. Rueda, Y. Wang report:
From its overlapping [1] with GRB 090618, the prototype of binary-driven hypernovae (BdHNe), we can assert that this GRB belongs to the class of long GRBs originating in a binary system composed of a carbon-oxygen core and a companion neutron star (Rueda & Ruffini, 2012; Fryer et al. 2014).
At the redshift of z=0.81 (Perley et al, GCN 18487) the isotropic energy is Eiso ~ 4x10^(52) erg and the rest-frame spectral peak energy is Ep,i ~ 615 keV (Toelge et al., GCN 18492). A SN should appear after 13-15 days in rest-frame, namely between November 19th and November 23rd.
The exceptional feature of GRB 151027A is that, even if it belongs to the BdHN class, there is no high energy emission associated as of today although it was in the Fermi-LAT field of view (Toelge et al., GCN 18492). If confirmed this can be of support to probe the angular distribution of the high energy emission. Additional data in all wavelengths are requested for this most peculiar source.
[1] http://www.icranet.org/documents/GRB151027A.pdf
GCN Circular #18558
V. Kozlov (IC AMER, NASU), M. Andreev (Terskol Branch of INASAN), E. Mazaeva (IKI), A. Sergeev (Terskol Branch of INASAN), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We observed the field of GRB 151027A (Maselli et al., GCN 18478) with Zeiss-600 telescope of Mt. Terskol observatory in R-filter starting on Oct. 28 (UT) 21:23:11. We obtained several images in R-filter. The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in a combined image. The photometry of the combined image is following
```
Date             UT start    t-T0          Filter Exp.      OT      Err
                                      (mid, days)          (s)

2015-10-28 21:23:11 1.7431      R      25*120 19.56  0.12
```
The photometry is based on nearby USNO-B1.0 stars
```
USNO-B.1_id R2
1513-0237223 16.66
1513-0237170 15.58
1513-0237251 16.81
1513-0237270 16.78
```
GCN Circular #18559
E. Mazaeva (IKI), A. Volnova (IKI), E. Klunko (ISTP), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We observed the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-33IK telescope of Sayan observatory (Mondy) on several epochs. We obtained images in R-filter on Oct., 27-- Nov., 1 . The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in each epoch. Coordinates of the afterglow are (J2000) 18 09 56.66 +61 21 13.0 with uncertainties of 0.3 arcsec in each coordinate. We also detected the USNO-B1.0 source mentioned in GCN 18510 (Dichiara et al.) in a position (J2000) 18 09 56.44 +61 21 10.8 with uncertainties of 0.3 arcsec in each coordinate.
Preliminary photometry of the afterglow on October-29 -- November, 1 is following
```
Date                UT start   t-T0        Filter   Exp.       OT       Err.
                                        (mid, days)        (s)

2015-10-29   13:18:41  2.4082   R         55*60   19.84  0.05
2015-10-30   12:11:18  3.3736   R         78*60   20.32  0.06
2015-10-31   12:47:18  4.3958   R         41*120 21.25  0.07
2015-11-01   12:28:18  5.3694   R        19*120  21.50  0.12
```
The photometry is based on nearby USNO-B1.0 stars
```
USNO-B.1_id R2
1513-0237223 16.66
1513-0237170 15.58
1513-0237251 16.81
1513-0237270 16.78
```
Late time photometry could be influenced by the nearby USNO-B1.0 source.
The overall light curve of our observations as well as photometry reported in GCNs 18480, 18521,18558 can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_lc.png
GCN Circular #18567
Arto Oksanen (Hankasalmi Obs., Hankasalmi, Finland) reports the following observations of GRB 151027A (Maselli et al. 2015, GCN Circular #18478; Zheng et al. 2015, GCN Circular #18479, and many subsequent Circulars) to the AAVSO High Energy Network:
A. Oksanen observed the location of GRB 151027A using the Hankasalmi Observatory 0.4-m Richey-Chretien telescope using an SBIG STL-1001E camera. Time-series images were obtained with both Rc and clear filters, with fifty 60-second frames obtained in each filter. Clear filtered images were obtained between 16:27:07 UT and 22:01:23 UT on 2015 October 27, and Rc-filtered images were obtained between 18:59:58 and 21:45.04 UT. Photometry was performed using an ensemble of comparison stars with APASS photometry available from AAVSO VSP (www.aavso.org/vsp). The afterglow is detected in both Rc- and clear-filtered observations, with evidence of fading between the start and end of the observing run.
Photometry of co-added groups of images yields the following:
Clear filter:
```
t-t0(d)     m(CR)     err(CR)
0.5235      16.872    0.030
0.5334      16.816    0.030
0.6531      17.160    0.044
0.6644      17.322    0.047
0.7468      17.575    0.065
```
Rc filter:
```
t-t0(d)     m(R)     err(R)
0.6365      17.257    0.058
0.6848      17.544    0.074
0.7353      17.580    0.118
```
These magnitudes of GRB 151027A are consistent with other magnitudes obtained at similar epochs of this burst (e.g. Hentunen et al. GCN Circular #18503; Sonbas et al. #18518).
GCN Circular #18575
E. Mazaeva (IKI), E. Klunko (ISTP), A. Volnova (IKI), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We continue observations (GCN 18559) of the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-33IK telescope of Sayan observatory (Mondy). We obtained images in R-filter on Nov., 4, 5, 7-9. In a combined image obtained on Nov. 7 we clearly detect a galaxy which coincide with the object 1513-0237216 of USNO-B1.0 catalog. The object was also mentioned in GCN 18510 (Dichiara et al.) and GCN 18559 (Mazaeva et al.)
The finding chart can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_20151107_AZT33IK_host.png
The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is not well detected. The afterglow might overlap with North-East wing of the galaxy. The galaxy could be suggested as a host galaxy of GRB 151027A.
Preliminary photometry of the galaxy is R= 20.60+/-0.04 at November, 7.
The photometry is based on nearby USNO-B1.0 stars referenced in GCN 18559.
GCN Circular #18608
Poonam Chandra (NCRA-TIFR) and A. J. Nayana (NCRA-TIFR) reports:
We carried out Giant Metrewave Radio Telescope (GMRT) observations of GRB 151027A (GCN Circ. 18478) at 1390 MHz band on 2015 Nov 15.19 UT. We detect the radio afterglow of the GRB in the Swift error circle (GCN Circ. 18482). The 1390 MHz band flux density of the afterglow is 312+/-64 uJy. Map rms is 37 uJy.
Further observations are planned. We thank GMRT staff for making these observations possible.
GCN Circular #18609
We observed the field of GRB 151027A (Maselli et al., GCN 18478) using the 2m Himalayan Chandra Telescope of Indian Astronmical Observatory, Hanle, India. The GRB field was observed in Bessells R band, during 14:56 UT to 16:20 UT on 2015-10-27. We obtained 20 frames, each of 150 seconds exposure time. The optical afterglow of GRB 151027A (e.g., Maselli et al., GCN 18478; Zheng & Filippenko, GCN 18479; Elenin et al., GCN 18480; Perley & Cenko, GCN 18481) is clearly detected in each image. The measured magnitudes, calibrated using nearby USNO B1.0 (R2 magnitudes) stars are listed below.
```
---------------------------------------------------------------------
Time (UT start)        Filter       Mag    error
14:56                R          16.60   0.06
15:36                R          16.67   0.07
16:20                R          16.86   0.08
-----------------------------------------------------------------------
```
This message may be cited.
D.K. Sahu and G.C. Anupama (Indian Institute of Astrophysics, Bengaluru)
GCN Circular #18616
A. S. Moskvitin (SAO RAS), I. V. Sokolov (Terskol Branch of INASAN) report on behalf of larger GRB follow-up team.
We observed the field of GRB 151027A twice: with 2-m Zeiss-2000 + FLI CCD (Mt. Terskol) and 1-m Zeiss-1000 + EEV 42-40 CCD (SAO RAS) on November 6 and 12 respectively (T-T0 = 10.5 and 16.5 days).
We have obtained 10x300 and 24x300 sec. frames in R band. We do not detect the GRB OT (Maselli et al., GCNC #18478) down to the limiting magnitude R_lim = 22.8 in both stacked images. As the standard stars we used USNO-B1 objects from GCNCs #18521, 18558 and 18559.
We should note that nearby USNO-B1 source reported by S. Dichiara et al. (GCNC #18510) and E. Mazaeva et al. (GCNC #18559) is clearly detected in our images.
GCN Circular #18620
Poonam Chandra (NCRA-TIFR) and A. J. Nayana (NCRA-TIFR) reports:
We carried out Giant Metrewave Radio Telescope (GMRT) observations of GRB 151027A (GCN Circ. 18478) at 610 MHz band on 2015 Nov 19.19 UT. We detect the radio afterglow of the GRB in the Swift error circle (GCN Circ. 18482). The 610 MHz band flux density of the afterglow is 522+/-94 uJy. Map rms is 56 uJy.
Further observations are planned. We thank GMRT staff for making these observations possible.
GCN Circular #18635
A. Pozanenko (IKI), E. Mazaeva (IKI), A. Volnova (IKI), O. Burhonov (UBAI) report on behalf of larger GRB follow-up collaboration:
We observed the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-22 telescope of Maidanak observatory equipped with SNUCAM in R filter. We obtained several images in R-filter on Oct., 30, Nov., 6 and Nov., 9 under mean FWHM of about 0.9". The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in each epoch. The afterglow is well separated from nearby source (Dichiara et al.GCN 18510; Mazaeva et al., GCN 18559).
Preliminary photometry of the afterglow is following
```
Date         UT start   t-T0    Filter   Exp.     OT      Err.
                        (mid, days)        (s)

2015-11-06   15:04:07  10.474   R        10*300   23.30   0.24
2015-11-09   14:06:04  13.443   R        10*300   23.33   0.20
```
The photometry is based on nearby USNO-B1.0 stars
```
USNO-B.1_id  R2
1513-0237223 16.66
1513-0237251 16.81
1513-0237270 16.78
```
A preliminary light curve of the afterglow can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_lc.png
At this time it is unclear what is a reason of flattening of the light curve at 11-13 days. It might be SN signature or it is continuing bumps of the light curve previously seen at least on ~ 1.3 days and ~3 days.
1604.08204 from 29 Apr 16
F. Nappo et al.: The 999th Swift Gamma-Ray Burst: some like it thermal
We present a multiwavelength study of GRB 151027A. This is the 999th GRB detected by the Swift satellite and it has a densely sampled emission in the X-ray and optical band and has been observed and detected in the radio up to 140 days after the prompt. The multiwavelength light curve from 500 s to 140 days can be modelled through a standard forward shock afterglow but requires an additional component to reproduce the early X-ray and optical emission. We present TNG and LBT optical observations performed 19.6, 33.9 and 92.3 days after the trigger which show a bump with respect to a standard afterglow flux decay and are possibly interpreted as due to the underlying SN and host galaxy (of 0.4 uJy in the R band). Radio observations, performed with SRT, Medicina, EVN and VLBA between day 4 and 140, suggest that the burst exploded in an environment characterised by a density profile scaling with the distance from the source (wind profile). A remarkable feature of the prompt emission is the presence of a bright flare 100 s after the trigger, lasting 70 seconds in the soft X-ray band, which was simultaneously detected from the optical band up to the MeV energy range. By combining Swift-BAT/XRT and Fermi-GBM data, the broadband (0.3-1000 keV) time resolved spectral analysis of the flare reveals the coexistence of a non-thermal (power law) and thermal blackbody components. The BB component contributes up to 35% of the luminosity in the 0.3-1000 keV band. The gamma-ray emission observed in Swift-BAT and Fermi-GBM anticipates and lasts less than the soft X-ray emission as observed by Swift-XRT, arguing against a Comptonization origin. The BB component could either be produced by an outflow becoming transparent or by the collision of a fast shell with a slow, heavy and optically thick fireball ejected during the quiescent time interval between the initial and later flares of the burst.

Back to JG's homepage

Jochen Greiner, last update: 29-Apr-2016 [Disclaimer]