Gamma-ray Burst 150120A

(All information courtesy of the instrument teams.)

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 02:58:01 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     627137,   Seg_Num: 0
GRB_RA:           10.308d {+00h 41m 14s} (J2000),
                  10.511d {+00h 42m 03s} (current),
                   9.635d {+00h 38m 32s} (1950)
GRB_DEC:         +33.981d {+33d 58' 52"} (J2000),
                 +34.064d {+34d 03' 49"} (current),
                 +33.707d {+33d 42' 25"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       1374 [cnts]    Image_Peak=95 [image_cnts]
TRIGGER_DUR:     0.256 [sec] 
TRIGGER_INDEX:   123     E_range: 25-100 keV
BKG_INTEN:       27676 [cnts]
BKG_TIME:        10650.92 SOD {02:57:30.92} UT
BKG_DUR:         8 [sec]
GRB_DATE:        17042 TJD;    20 DOY;   15/01/20
GRB_TIME:        10666.41 SOD {02:57:46.41} UT
GRB_PHI:         -143.68 [deg]
GRB_THETA:        29.65 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     16.15 [sigma]
IMAGE_SIGNIF:    7.25 [sigma]
MERIT_PARAMS:     +1  +0  +0  -2  +2  -3  +0  +0  -9  +0 
SUN_POSTN:       301.89d {+20h 07m 33s}  -20.21d {-20d 12' 28"}
SUN_DIST:         84.84 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.72d {+19h 38m 52s}  -16.52d {-16d 31' 02"}
MOON_DIST:        87.96 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.52,-28.84 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       23.72, 26.99 [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 = 212.34,-15.08 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=443415470).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 20 Jan 15 02:58:16 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     443415470
GRB_RA:           32.400d {+02h 09m 36s} (J2000),
                  32.624d {+02h 10m 30s} (current),
                  31.657d {+02h 06m 38s} (1950)
GRB_DEC:         +34.817d {+34d 49' 00"} (J2000),
                 +34.887d {+34d 53' 15"} (current),
                 +34.581d {+34d 34' 50"} (1950)
GRB_ERROR:       28.50 [deg radius, statistical plus systematic]
GRB_INTEN:       174 [cnts/sec]
DATA_SIGNIF:     5.40 [sigma]
INTEG_TIME:      0.512 [sec]
GRB_DATE:        17042 TJD;    20 DOY;   15/01/20
GRB_TIME:        10667.00 SOD {02:57:47.00} UT
GRB_PHI:         332.00 [deg]
GRB_THETA:       115.00 [deg]
DATA_TIME_SCALE: 0.5120 [sec]
HARD_RATIO:      1.08
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       0,0,0, 0,1,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       301.89d {+20h 07m 33s}  -20.21d {-20d 12' 28"}
SUN_DIST:        101.98 [deg]   Sun_angle= -6.0 [hr] (East of Sun)
MOON_POSTN:      294.72d {+19h 38m 53s}  -16.52d {-16d 31' 00"}
MOON_DIST:       105.71 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      140.62,-25.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       42.30, 20.42 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150120123/quicklook/glg_lc_medres34_bn150120123.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 115.75,22.10 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=627137).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 20 Jan 15 02:58:27 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     443415470
GRB_RA:           25.830d {+01h 43m 19s} (J2000),
                  26.046d {+01h 44m 11s} (current),
                  25.114d {+01h 40m 27s} (1950)
GRB_DEC:         +32.380d {+32d 22' 48"} (J2000),
                 +32.455d {+32d 27' 19"} (current),
                 +32.129d {+32d 07' 43"} (1950)
GRB_ERROR:       20.88 [deg radius, statistical only]
DATA_SIGNIF:     5.20 [sigma]
DATA_INTERVAL:   0.512 [sec]
GRB_DATE:        17042 TJD;    20 DOY;   15/01/20
GRB_TIME:        10667.00 SOD {02:57:47.00} UT
GRB_PHI:         332.00 [deg]
GRB_THETA:       109.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4153 (Gnd S/W Version number)
SUN_POSTN:       301.89d {+20h 07m 33s}  -20.21d {-20d 12' 28"}
SUN_DIST:         96.02 [deg]   Sun_angle= -5.6 [hr] (East of Sun)
MOON_POSTN:      294.72d {+19h 38m 53s}  -16.52d {-16d 31' 00"}
MOON_DIST:        99.86 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      135.48,-29.22 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       35.92, 20.18 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150120123/quicklook/glg_lc_medres34_bn150120123.gif
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=627137).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 02:59:14 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.326d {+00h 41m 18s} (J2000)
POINT_DEC:       +33.986d {+33d 59' 09"} (J2000)
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10742.65 SOD {02:59:02.65} UT,   76.2 [sec] since BAT Trigger Time
COUNTS:          5    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        2    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:01:36 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     627137,   Seg_Num: 0
GRB_RA:           10.308d {+00h 41m 14s} (J2000),
                  10.511d {+00h 42m 03s} (current),
                   9.635d {+00h 38m 32s} (1950)
GRB_DEC:         +33.981d {+33d 58' 52"} (J2000),
                 +34.064d {+34d 03' 49"} (current),
                 +33.707d {+33d 42' 25"} (1950)
GRB_DATE:        17042 TJD;    20 DOY;   15/01/20
GRB_TIME:        10666.41 SOD {02:57:46.41} UT
TRIGGER_INDEX:   123
GRB_PHI:         -143.68 [deg]
GRB_THETA:        29.65 [deg]
DELTA_TIME:      52.00 [sec]
TRIGGER_DUR:     0.256 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     16.15 [sigma]
IMAGE_SIGNIF:    7.25 [sigma]
LC_URL:          sw00627137000msb.lc
SUN_POSTN:       301.89d {+20h 07m 33s}  -20.21d {-20d 12' 26"}
SUN_DIST:         84.84 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.75d {+19h 39m 01s}  -16.51d {-16d 30' 41"}
MOON_DIST:        87.92 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.52,-28.84 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       23.72, 26.99 [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 = 212.34,-15.08 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:02:11 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.326d {+00h 41m 18s} (J2000)
POINT_DEC:       +33.986d {+33d 59' 09"} (J2000)
POINT_ROLL:      241.227d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10749.17 SOD {02:59:09.17} UT,   82.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.816
N_STARS:         42
X_OFFSET:        591 [pixels]
Y_OFFSET:        498 [pixels]
X_MAX:           1550 [pixels]
Y_MAX:           1457 [pixels]
DET_THRESH:      14
PHOTO_THRESH:    7
SL_URL:          sw00627137000msufc0082.fits
SUN_POSTN:       301.89d {+20h 07m 33s}  -20.21d {-20d 12' 26"}
SUN_DIST:         84.86 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.76d {+19h 39m 03s}  -16.51d {-16d 30' 38"}
MOON_DIST:        87.93 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.53,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.98 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:02:38 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.326d {+00h 41m 18s} (J2000)
POINT_DEC:       +33.986d {+33d 59' 09"} (J2000)
POINT_ROLL:      241.227d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10749.17 SOD {02:59:09.17} UT,   82.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.816
N_STARS:         42
X_OFFSET:        591 [pixels]
Y_OFFSET:        498 [pixels]
X_MAX:           1550 [pixels]
Y_MAX:           1457 [pixels]
DET_THRESH:      14
PHOTO_THRESH:    7
SL_URL:          sw00627137000msufc0082.fits
SUN_POSTN:       301.89d {+20h 07m 33s}  -20.21d {-20d 12' 25"}
SUN_DIST:         84.86 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.77d {+19h 39m 04s}  -16.51d {-16d 30' 36"}
MOON_DIST:        87.93 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.53,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.98 [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 20 Jan 15 03:03:40 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     627137,   Seg_Num: 0
GRB_RA:           10.3188d {+00h 41m 16.51s} (J2000),
                  10.5219d {+00h 42m 05.25s} (current),
                   9.6459d {+00h 38m 35.01s} (1950)
GRB_DEC:         +33.9947d {+33d 59' 40.9"} (J2000),
                 +34.0771d {+34d 04' 37.6"} (current),
                 +33.7205d {+33d 43' 13.8"} (1950)
GRB_ERROR:       3.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10753.00 SOD {02:59:13.00} UT,   86.6 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       301.89d {+20h 07m 34s}  -20.21d {-20d 12' 25"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.78d {+19h 39m 06s}  -16.51d {-16d 30' 30"}
MOON_DIST:        87.92 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.53,-28.83 [deg] galactic lon,lat of the burst
ECL_COORDS:       23.74, 26.99 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:03:48 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.326d {+00h 41m 18s} (J2000)
POINT_DEC:       +33.986d {+33d 59' 09"} (J2000)
ROLL:            241.227d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10749.17 SOD {02:59:09.17} UT,   82.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     443415562
X_OFFSET:        910 [pixels]
Y_OFFSET:        817 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1070
Y_GRB_POS:       977
BINNING_INDEX:   1
IM_URL:          sw00627137000msuni0096.fits
SUN_POSTN:       301.89d {+20h 07m 34s}  -20.21d {-20d 12' 25"}
SUN_DIST:         84.86 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.78d {+19h 39m 07s}  -16.51d {-16d 30' 29"}
MOON_DIST:        87.92 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.53,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.98 [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 20 Jan 15 03:04:05 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.326d {+00h 41m 18s} (J2000)
POINT_DEC:       +33.986d {+33d 59' 09"} (J2000)
ROLL:            241.227d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10749.17 SOD {02:59:09.17} UT,   82.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     443415562
X_OFFSET:        910 [pixels]
Y_OFFSET:        817 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1070
Y_GRB_POS:       977
BINNING_INDEX:   1
IM_URL:          sw00627137000msuni0096.fits
SUN_POSTN:       301.89d {+20h 07m 34s}  -20.21d {-20d 12' 25"}
SUN_DIST:         84.86 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.78d {+19h 39m 07s}  -16.51d {-16d 30' 27"}
MOON_DIST:        87.92 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.53,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.98 [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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:10:41 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.327d {+00h 41m 19s} (J2000)
POINT_DEC:       +33.989d {+33d 59' 21"} (J2000)
ROLL:            241.229d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10961.17 SOD {03:02:41.17} UT,   294.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     443415774
X_OFFSET:        910 [pixels]
Y_OFFSET:        817 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1070
Y_GRB_POS:       977
BINNING_INDEX:   1
IM_URL:          sw00627137000msuni0308.fits
SUN_POSTN:       301.90d {+20h 07m 35s}  -20.21d {-20d 12' 21"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.85d {+19h 39m 24s}  -16.50d {-16d 29' 50"}
MOON_DIST:        87.86 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.54,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.99 [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 20 Jan 15 03:10:59 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.327d {+00h 41m 19s} (J2000)
POINT_DEC:       +33.989d {+33d 59' 21"} (J2000)
ROLL:            241.229d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10961.17 SOD {03:02:41.17} UT,   294.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     443415774
X_OFFSET:        910 [pixels]
Y_OFFSET:        817 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1070
Y_GRB_POS:       977
BINNING_INDEX:   1
IM_URL:          sw00627137000msuni0308.fits
SUN_POSTN:       301.90d {+20h 07m 35s}  -20.21d {-20d 12' 21"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.85d {+19h 39m 25s}  -16.50d {-16d 29' 49"}
MOON_DIST:        87.86 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.54,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.99 [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:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_image.fits.gz file does not exist; skipping the attachment.

GCN Circular #17310
V. D'Elia (ASDC), D. N. Burrows (PSU), M. M. Chester (PSU), N. Gehrels (NASA/GSFC), L. Izzo (URoma/ICRA), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team:
At 02:57:46 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150120A (trigger=627137). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 10.308, +33.981 which is
```
   RA(J2000) = 00h 41m 14s
   Dec(J2000) = +33d 58' 52"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single symmetric peak structure with a duration of about 1.5 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~0.5 sec after the trigger.
The XRT began observing the field at 02:59:02.6 UT, 76.2 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 10.31883, 33.99480 which is equivalent to:
```
   RA(J2000)  = 00h 41m 16.52s
   Dec(J2000) = +33d 59' 41.3"
```
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 59 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 (7.86 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 6 (+5.52/-4.12) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 82 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.10.
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:     Tue 20 Jan 15 03:14:08 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.327d {+00h 41m 19s} (J2000)
POINT_DEC:       +33.989d {+33d 59' 21"} (J2000)
POINT_ROLL:      241.229d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  11538.88 SOD {03:12:18.88} UT,   872.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.350
N_STARS:         78
X_OFFSET:        351 [pixels]
Y_OFFSET:        258 [pixels]
X_MAX:           1790 [pixels]
Y_MAX:           1697 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw00627137000msufc0872.fits
SUN_POSTN:       301.90d {+20h 07m 35s}  -20.21d {-20d 12' 19"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.89d {+19h 39m 33s}  -16.49d {-16d 29' 31"}
MOON_DIST:        87.83 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.54,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.99 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:14:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.327d {+00h 41m 19s} (J2000)
POINT_DEC:       +33.989d {+33d 59' 21"} (J2000)
POINT_ROLL:      241.229d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  11538.88 SOD {03:12:18.88} UT,   872.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.350
N_STARS:         78
X_OFFSET:        351 [pixels]
Y_OFFSET:        258 [pixels]
X_MAX:           1790 [pixels]
Y_MAX:           1697 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw00627137000msufc0872.fits
SUN_POSTN:       301.90d {+20h 07m 35s}  -20.21d {-20d 12' 19"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.89d {+19h 39m 33s}  -16.49d {-16d 29' 30"}
MOON_DIST:        87.83 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.54,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.99 [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 20 Jan 15 03:15:20 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.327d {+00h 41m 19s} (J2000)
POINT_DEC:       +33.989d {+33d 59' 21"} (J2000)
ROLL:            241.229d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  11538.88 SOD {03:12:18.88} UT,   872.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     443416351
X_OFFSET:        910 [pixels]
Y_OFFSET:        817 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1070
Y_GRB_POS:       977
BINNING_INDEX:   1
IM_URL:          sw00627137000msuni0886.fits
SUN_POSTN:       301.90d {+20h 07m 36s}  -20.21d {-20d 12' 19"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.90d {+19h 39m 36s}  -16.49d {-16d 29' 24"}
MOON_DIST:        87.82 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.54,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.99 [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 20 Jan 15 03:15:29 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     627137,   Seg_Num: 0
POINT_RA:         10.327d {+00h 41m 19s} (J2000)
POINT_DEC:       +33.989d {+33d 59' 21"} (J2000)
ROLL:            241.229d
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  11538.88 SOD {03:12:18.88} UT,   872.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     443416351
X_OFFSET:        910 [pixels]
Y_OFFSET:        817 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1070
Y_GRB_POS:       977
BINNING_INDEX:   1
IM_URL:          sw00627137000msuni0886.fits
SUN_POSTN:       301.90d {+20h 07m 36s}  -20.21d {-20d 12' 18"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.90d {+19h 39m 36s}  -16.49d {-16d 29' 23"}
MOON_DIST:        87.82 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.54,-28.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       23.74, 26.99 [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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 20 Jan 15 03:15:06 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     627137,   Seg_Num: 0
GRB_RA:           10.3186d {+00h 41m 16.46s} (J2000),
                  10.5217d {+00h 42m 05.20s} (current),
                   9.6457d {+00h 38m 34.96s} (1950)
GRB_DEC:         +33.9943d {+33d 59' 39.4"} (J2000),
                 +34.0767d {+34d 04' 36.1"} (current),
                 +33.7201d {+33d 43' 12.3"} (1950)
GRB_ERROR:       2.2 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  17042 TJD;    20 DOY;   15/01/20
IMG_START_TIME:  10753.00 SOD {02:59:13.00} UT,   86.6 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       301.90d {+20h 07m 36s}  -20.21d {-20d 12' 19"}
SUN_DIST:         84.85 [deg]   Sun_angle= -4.6 [hr] (East of Sun)
MOON_POSTN:      294.90d {+19h 39m 35s}  -16.49d {-16d 29' 25"}
MOON_DIST:        87.81 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      120.53,-28.83 [deg] galactic lon,lat of the burst
ECL_COORDS:       23.74, 26.99 [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 Circular #17311
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Using promptly downlinked XRT event data for GRB 150120A, we find an enhanced XRT position of the afterglow: RA, Dec: 10.3187, 33.9944 which is equivalent to:
```
   RA (J2000)  = 00 41 16.49
   Dec (J2000) = +33 59 39.7
```
with an uncertainty of 2.2 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/627137.
Position enhancement is is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.
GCN Circular #17312
D. A. Perley (Caltech) and S. B. Cenko (NASA/GSFC) report:
The Palomar 60-inch robotic telescope began automatic follow-up of the location of possibly-short GRB 150120A (D'Elia et al. GCN 17310) starting at 2015-01-30 03:00:33 UT, approximately 2.7 minutes after the GRB trigger. A sequence of rotating r, i, and z 60-second exposures was acquired, followed by five 180-second exposures in each of r and i bands, under good conditions.
No sources are clearly detected inside the enhanced XRT error circle (Evans et al., GCN 17311), either in either individual exposures or in stacks of all 60-second exposures taken in each filter (approximate UT center time 15 minutes post-trigger, limiting magnitudes r>22.5, i>22.4, z>20.9). We detect two faint sources slightly outside the error circle in the stacked frames:
```
  Source A:  RA=00:41:16.55, dec=+33:59:42.87
  Source B:  RA=00:41:16.76, dec=+33:59:42.11
```
Both sources appear to be marginally detected in SDSS pre-imaging and we do not yet have evidence of fading behavior. Further observations and analysis are ongoing.
GCN Circular #17313
W. Fong (U. Arizona), R. Chornock (Ohio U.) and D. Fox (PSU) report:
"We observed the location of the possibly short GRB 150120A (D'Elia et al., GCN 17310) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini-North 8-m telescope starting on 2015 Jan 20.206 UT (2.0 hr after the BAT trigger). We obtained 1800-sec in each of the riz-bands in 0.5" seeing. Within the enhanced XRT position (Evans, GCN 17311), we do not detect any optical sources in our images. Tied to SDSS, we calculate a 3-sigma limit of r>26.3 AB mag.
We clearly detect two sources on the outskirts of the XRT position (Sources A and B from P60 observations; Perley et al., GCN 17312), both of which appear extended in our images. We do not find any evidence for variability of these sources over the duration of our observations.
We thank Gemini observers and staff Sabrina Pakzad, Katherine Roth, Joe Burchett, and Rongmon Bordoloi for the quick scheduling and execution of these observations."
GCN Circular #17317
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 465 s of XRT Photon Counting mode data and 1 UVOT images for GRB 150120A, 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 = 10.31893, +33.99485 which is equivalent to:
```
RA (J2000): 00h 41m 16.54s
Dec (J2000): +33d 59' 41.5"
```
with an uncertainty of 1.8 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 #17319
A. von Kienlin (MPE) and E. Burns (UAH) report on behalf of the Fermi GBM Team:
"At 02:57:47.00 UT on 20 January 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150120A (trigger 443415470/150120123), which was also detected by the Swift/BAT & XRT (D'Elia et al. 2015, GCN 17310). The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 98 degrees.
The GBM light curve shows a single pulse with a duration (T90) of about 2 s (50-300 keV). The time-averaged spectrum from T0-1.024 s to T0+0.512 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -1.43 (+0.28/-0.24) and the cutoff energy, parameterized as Epeak, is 130 (+150/-50) keV
The event fluence (10-1000 keV) in this time interval is (3.4 +/- 0.8)E-07 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0-0.64 s in the 10-1000 keV band is 3.1 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #17323
M. M. Chester (PSU) and V. D'Elia (ASDC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150120A 83 s after the BAT trigger (D'Elia et al., GCN Circ. 17310). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 17317) 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) exposures and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            83          233          147         >20.6
u_FC               295          545          246         >20.1
white               83         5674          461         >21.0
v                  624         6085          432         >19.5
b                  550        10198          449         >21.0
u                  295         6700          658         >20.6
w1                 674         6495          432         >20.5
m2                 649         6290          432         >21.1
w2                 600         5880          432         >20.5
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.10 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #17329
A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), V. D'Elia (ASDC), N. Gehrels (GSFC), J. Norris (BSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 150120A (trigger #627137) (D'Elia, et al., GCN Circ. 17310). The BAT ground-calculated position is RA, Dec = 10.330, 33.980 deg which is
```
   RA(J2000)  =  00h 41m 19.1s
   Dec(J2000) = +33d 58' 48.6"
```
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 71%.
The mask-weighted light curve shows a single short spike that starts at ~ T-0.4 s, peaks at ~ T+0.4 s, and ends at ~ T+1.0 s. T90 (15-350 keV) is 1.20 +- 0.16 sec (estimated error including systematics).
The time-averaged spectrum from T-0.40 to T+0.95 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.81 +- 0.18. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.06 sec in the 15-150 keV band is 1.8 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The burst spectrum appears to be at the softer end of short bursts, which have an average spectral index of 1.2 when fitting with a simple power-law model (Sakamoto et al. 2011). However, the fast fading shown in the X-ray light curve (http://www.swift.ac.uk/xrt_curves/00627137/) suggests that this is indeed a short burst. The lag analysis of this burst does not show a constraining result due to the low intensity.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/627137/BA/
GCN Circular #17332
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 150120A (D'Elia et al., GCN 17310) starting at 02:59:24 UT, 98 s after the burst. 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. We do not detect any new source in our images within the enhanced XRT error circle (Evans et al., GCN 17317). The typical limiting magnitude of our single clear image is about 18.5 calibrated to USNO B1.0.
GCN Circular #17334
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), V. Mangano (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU) and V. D'Elia report on behalf of the Swift-XRT team:
We have analysed 5.9 ks of XRT data for GRB 150120A (D'Elia et al. GCN Circ. 17310), from 86 s to 16.2 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 17311).
The light curve can be modelled with a power-law decay with a decay index of alpha=~4.6.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+/-0.5). The best-fitting absorption column is 6.5 (+4.8, -3.3) x 10^21 cm^-2, in excess of the Galactic value of 7.9 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.4 x 10^-11 (7.4 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     6.5 (+4.8, -3.3) x 10^21 cm^-2
Galactic foreground: 7.9 x 10^20 cm^-2
Excess significance: 2.8 sigma
Photon index:	     2.0 (+/-0.5)
```
If the light curve continues to decay with a power-law decay index of ~4.6, the count rate at T+24 hours will be 1.2 x 10^-13 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.4 x 10^-24 (9.0 x 10^-24) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00627137.
This circular is an official product of the Swift-XRT team.
GCN Circular #17341
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 150120A (D'Elia et al., GCN 17310) with 0.4-m telescope of ISON-NM observatory in robotic mode starting on Jan., 20 (UT) 02:58:58, i.e. 72 seconds after burst trigger. We obtained 60 unfiltered images of 30 s exposure. We do not detect any source within enhanced XRT error circle (Evans et al., GCN 17317):
```
Date      UT start   t-T0         Exp.    Filter  UL (3sigma)
                      (mid.,days)    (s)
2015-01-20 02:58:58  0.00227      5*30    Clear   19.0
2015-01-20 02:58:58  0.01950     60*30    Clear   20.2
```
The photometry is based on nearby SDSS DR9 stars
```
SDSS9_id                R_Lupton
J004136.43+340051.9     15.61
J004135.94+335950.0     14.56
J004101.23+335851.1     15.84
```
GCN Circular #17350
G. E. Anderson, R. P. Fender, T. D. Staley (University of Oxford), A. J. van der Horst (George Washington University), A. Rowlinson (CASS)
We observed the position of the possibly-short burst GRB 150120A (D=92Elia et al., GCN 17310) at 15 GHz with the Arcminute Microkelvin Imager (AMI-LA) starting on 2015 Jan 21.690 to 21.856 UT, corresponding to 1.6 days post-burst. On this date we possibly detected a ~4 sigma radio source with flux 0.17 +/- 0.04 mJy at the position
```
RA(J200): 0:41:16.72
Dec(J2000): 33:59:55.4
```
with a positional uncertainty of ~10 arcseconds. This is ~14 arcseconds from the best XRT position quoted by Evan et al., GCN 17317.
An earlier and later observation was conducted on 2015 Jan 20.475 to 20.559 UT and 2015 Jan 22.666 to 22.832 UT, corresponding to 0.4 and 2.5 days post-burst, yielding 3 sigma flux upper limits of 0.19 mJy and 0.10 mJy, respectively.
Further AMI monitoring is planned. We thank the AMI staff for scheduling these observations.
GCN Circular #17358
R. Chornock (Ohio University) and W. Fong (University of Arizona) report:
We re-imaged the field of the possibly-short GRB 150120A (D'Elia et al., GCN 17310) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini-North 8-m telescope starting on 2015 Jan 22.284 UT (2.16 days post-burst and 49.8 hr after our first Gemini observations; Fong et al., GCN 17313). We obtained a total of 2160s of observations in r-band in 1.0" seeing at an airmass of 1.6. Image subtraction using the ISIS package reveals no residuals in or around the enhanced XRT position (Evans et al., GCN 17317). Based on the 3-sigma limit of the second epoch, which is not deep as our first epoch due to poorer conditions, we place a limit of r(AB)>25.0 mag on the optical afterglow of GRB 150120A at 2.0 hr post-burst.
We note that the enhanced XRT position (Evans et al., GCN 17317) shifted relative to the prompt enhanced XRT position (Evans, GCN 17311) and now encompasses Source A of Perley & Cenko (GCN 17312), while Source B is now just outside the XRT error circle. We placed a spectroscopic slit across both Sources A and B and obtained a pair of 900s GMOS spectra on 2014 Jan. 27 with the R400 grating (range 4900-9200 Angs). Both galaxies exhibit nebular emission lines (H-beta, [O III]) at the same common redshift of z=0.460.
We thank the staff at Gemini for their assistance scheduling and performing these observations.
GCN Circular #17361
W. Fong (U. Arizona) reports:
"We observed the field of the possibly-short GRB 150120A (D'Elia et al., GCN 17310) with the Karl G. Jansky Very Large Array (VLA) beginning on 2015 Jan 21.027 UT (21.7 hr post-burst) at a mean frequency of 9.8 GHz. In 70 min of observations, we do not detect any radio source within or around the enhanced XRT position (Evans et al., GCN 17317). In addition, we do not detect any radio source within or near the position of the possible AMI source at 15 GHz (Anderson et al., GCN 17350). We therefore place a 3-sigma limit of ~30 microJy on the 9.8 GHz radio afterglow of GRB 150120A at 21.7 hr after the burst.
We thank the VLA staff for quickly executing these observations."
Redshift z= 0.4604 +- 0.0004 from host galaxy emission (Hbeta, [OII])
W.-F. Fong et al. 2022, ApJ 940, 56

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