Gamma-ray Burst 150301A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 01 Mar 15 01:04:42 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     632995,   Seg_Num: 0
GRB_RA:          244.286d {+16h 17m 09s} (J2000),
                 244.567d {+16h 18m 16s} (current),
                 243.362d {+16h 13m 27s} (1950)
GRB_DEC:         -48.697d {-48d 41' 48"} (J2000),
                 -48.733d {-48d 44' 00"} (current),
                 -48.574d {-48d 34' 26"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       675 [cnts]    Image_Peak=131 [image_cnts]
TRIGGER_DUR:     0.032 [sec] 
TRIGGER_INDEX:   10318     E_range: 25-100 keV
BKG_INTEN:       28411 [cnts]
BKG_TIME:        3858.75 SOD {01:04:18.75} UT
BKG_DUR:         8 [sec]
GRB_DATE:        17082 TJD;    60 DOY;   15/03/01
GRB_TIME:        3868.35 SOD {01:04:28.35} UT
GRB_PHI:          21.77 [deg]
GRB_THETA:        16.07 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     43.52 [sigma]
IMAGE_SIGNIF:    13.43 [sigma]
MERIT_PARAMS:     +1  +0  +0  -5  +2  +2  +0  +1  -1  +0 
SUN_POSTN:       341.65d {+22h 46m 35s}   -7.77d {-07d 46' 21"}
SUN_DIST:         88.79 [deg]   Sun_angle= 6.5 [hr] (West of Sun)
MOON_POSTN:      109.35d {+07h 17m 24s}  +17.02d {+17d 01' 18"}
MOON_DIST:       131.89 [deg]
MOON_ILLUM:      81 [%]
GAL_COORDS:      334.01,  1.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      251.27,-26.92 [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 = 114.07,17.26 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(0.0<100sec) coincident with the FERMI_GBM event (trignum=446864671).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 01 Mar 15 01:04:54 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     446864671
GRB_RA:          171.433d {+11h 25m 44s} (J2000),
                 171.603d {+11h 26m 25s} (current),
                 170.875d {+11h 23m 30s} (1950)
GRB_DEC:         -62.633d {-62d 37' 59"} (J2000),
                 -62.717d {-62d 43' 00"} (current),
                 -62.358d {-62d 21' 29"} (1950)
GRB_ERROR:       12.28 [deg radius, statistical plus systematic]
GRB_INTEN:       2300 [cnts/sec]
DATA_SIGNIF:     11.40 [sigma]
INTEG_TIME:      0.032 [sec]
GRB_DATE:        17082 TJD;    60 DOY;   15/03/01
GRB_TIME:        3868.65 SOD {01:04:28.65} UT
GRB_PHI:         263.00 [deg]
GRB_THETA:       145.00 [deg]
DATA_TIME_SCALE: 0.0320 [sec]
HARD_RATIO:      0.00
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:     100%  Below horizon
2nd_MOST_LIKELY:   0%  n/a
DETECTORS:       0,0,0, 1,1,0, 0,0,1, 0,0,0, 0,0,
SUN_POSTN:       341.65d {+22h 46m 35s}   -7.77d {-07d 46' 21"}
SUN_DIST:        109.10 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
MOON_POSTN:      109.35d {+07h 17m 25s}  +17.02d {+17d 01' 18"}
MOON_DIST:        93.22 [deg]
MOON_ILLUM:      81 [%]
GAL_COORDS:      293.26, -1.38 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      212.58,-57.36 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2015/bn150301045/quicklook/glg_lc_medres34_bn150301045.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 146.12,5.00 [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=632995).

GCN NOTICE

 
TITLE:           GCN/SWIFT NOTICE 
NOTICE_DATE:     Sun 01 Mar 15 01:06:03 UT 
NOTICE_TYPE:     Swift-XRT Position 
TRIGGER_NUM:     632995,   Seg_Num: 0 
GRB_RA:          244.3047d {+16h 17m 13.12s} (J2000), 
                 244.5857d {+16h 18m 20.57s} (current), 
                 243.3802d {+16h 13m 31.25s} (1950) 
GRB_DEC:         -48.7131d {-48d 42' 47.1"} (J2000), 
                 -48.7495d {-48d 44' 58.2"} (current), 
                 -48.5904d {-48d 35' 25.3"} (1950) 
GRB_ERROR:       5.0 [arcsec radius, statistical plus systematic, 90% containment] 
GRB_INTEN:       3.11e-09 [erg/cm2/sec] 
GRB_SIGNIF:      9.11 [sigma] 
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01 
IMG_START_TIME:  3926.63 SOD {01:05:26.63} UT,   58.3 [sec] since BAT Trigger Time 
TAM[0-3]:        327.67 237.21 261.65 243.42 
AMPLIFIER:       2 
WAVEFORM:        134 
SUN_POSTN:       341.65d {+22h 46m 35s}   -7.77d {-07d 46' 20"} 
SUN_DIST:         88.77 [deg]   Sun_angle= 6.5 [hr] (West of Sun) 
MOON_POSTN:      109.36d {+07h 17m 27s}  +17.02d {+17d 01' 14"} 
MOON_DIST:       131.88 [deg] 
MOON_ILLUM:      81 [%] 
GAL_COORDS:      334.01,  1.34 [deg] galactic lon,lat of the burst 
ECL_COORDS:      251.28,-26.93 [deg] ecliptic lon,lat of the burst 
COMMENTS:        SWIFT-XRT Coordinates.   
COMMENTS:        The XRT position is 1.22 arcmin from the BAT position.

GCN NOTICE

 
TITLE:           GCN/SWIFT NOTICE 
NOTICE_DATE:     Sun 01 Mar 15 01:06:12 UT 
NOTICE_TYPE:     Swift-XRT Image 
TRIGGER_NUM:     632995,   Seg_Num: 0 
GRB_RA:          244.3047d {+16h 17m 13.1s} (J2000), 
                 244.5857d {+16h 18m 20.5s} (current), 
                 243.3802d {+16h 13m 31.2s} (1950) 
GRB_DEC:         -48.7131d {-48d 42' 47.1"} (J2000), 
                 -48.7495d {-48d 44' 58.2"} (current), 
                 -48.5904d {-48d 35' 25.3"} (1950) 
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic] 
GRB_INTEN:       83 [cnts] 
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01 
IMG_START_TIME:  3926.63 SOD {01:05:26.63} UT,   58.3 [sec] since BAT Trigger Time 
CENTROID_X:      322.66,  raw= 323  [pixels] 
CENTROID_Y:      286.49,  raw= 286  [pixels] 
ROLL:            100.59 [deg] 
GAIN:            1 
MODE:            3, Long Image mode 
WAVEFORM:        134 
EXPO_TIME:       2.50 [sec] 
GRB_POS_XRT_Y:   -26.64 
GRB_POS_XRT_Z:   40.93 
IMAGE_URL:       sw00632995000msxps_rw.img 
SUN_POSTN:       341.65d {+22h 46m 35s}   -7.77d {-07d 46' 20"} 
SUN_DIST:         88.78 [deg]   Sun_angle= 6.5 [hr] (West of Sun) 
MOON_POSTN:      109.36d {+07h 17m 28s}  +17.02d {+17d 01' 13"} 
MOON_DIST:       131.88 [deg] 
MOON_ILLUM:      81 [%] 
GAL_COORDS:      334.01,  1.34 [deg] galactic lon,lat of the burst 
ECL_COORDS:      251.28,-26.93 [deg] ecliptic lon,lat of the burst 
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

 
TITLE:           GCN/SWIFT NOTICE 
NOTICE_DATE:     Sun 01 Mar 15 01:06:20 UT 
NOTICE_TYPE:     Swift-XRT Processed Image 
TRIGGER_NUM:     632995,   Seg_Num: 0 
GRB_RA:          244.3047d {+16h 17m 13.1s} (J2000), 
                 244.5857d {+16h 18m 20.5s} (current), 
                 243.3802d {+16h 13m 31.2s} (1950) 
GRB_DEC:         -48.7131d {-48d 42' 47.1"} (J2000), 
                 -48.7495d {-48d 44' 58.2"} (current), 
                 -48.5904d {-48d 35' 25.3"} (1950) 
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic] 
GRB_INTEN:       83 [cnts] 
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01 
IMG_START_TIME:  3926.63 SOD {01:05:26.63} UT,   58.3 [sec] since BAT Trigger Time 
CENTROID_X:      322.66,  raw= 323  [pixels] 
CENTROID_Y:      286.49,  raw= 286  [pixels] 
ROLL:            100.59 [deg] 
GAIN:            1 
MODE:            3, Long Image mode 
WAVEFORM:        134 
EXPO_TIME:       2.50 [sec] 
GRB_POS_XRT_Y:   -26.64 
GRB_POS_XRT_Z:   40.93 
IMAGE_URL:       sw00632995000msxps_rw.img 
SUN_POSTN:       341.65d {+22h 46m 35s}   -7.77d {-07d 46' 20"} 
SUN_DIST:         88.78 [deg]   Sun_angle= 6.5 [hr] (West of Sun) 
MOON_POSTN:      109.37d {+07h 17m 28s}  +17.02d {+17d 01' 13"} 
MOON_DIST:       131.88 [deg] 
MOON_ILLUM:      81 [%] 
GAL_COORDS:      334.01,  1.34 [deg] galactic lon,lat of the burst 
ECL_COORDS:      251.28,-26.93 [deg] ecliptic lon,lat of the burst 
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

 
TITLE:           GCN/SWIFT NOTICE 
NOTICE_DATE:     Sun 01 Mar 15 01:08:04 UT 
NOTICE_TYPE:     Swift-BAT GRB Lightcurve 
TRIGGER_NUM:     632995,   Seg_Num: 0 
GRB_RA:          244.286d {+16h 17m 09s} (J2000), 
                 244.567d {+16h 18m 16s} (current), 
                 243.362d {+16h 13m 27s} (1950) 
GRB_DEC:         -48.697d {-48d 41' 48"} (J2000), 
                 -48.733d {-48d 44' 00"} (current), 
                 -48.574d {-48d 34' 26"} (1950) 
GRB_DATE:        17082 TJD;    60 DOY;   15/03/01 
GRB_TIME:        3868.63 SOD {01:04:28.63} UT 
TRIGGER_INDEX:   10318 
GRB_PHI:          21.77 [deg] 
GRB_THETA:        16.07 [deg] 
DELTA_TIME:      -27.00 [sec] 
TRIGGER_DUR:     0.032 [sec]  
SOLN_STATUS:     0x3 
RATE_SIGNIF:     43.52 [sigma] 
IMAGE_SIGNIF:    13.43 [sigma] 
LC_URL:          sw00632995000msb.lc 
SUN_POSTN:       341.65d {+22h 46m 35s}   -7.77d {-07d 46' 18"} 
SUN_DIST:         88.79 [deg]   Sun_angle= 6.5 [hr] (West of Sun) 
MOON_POSTN:      109.38d {+07h 17m 31s}  +17.02d {+17d 01' 06"} 
MOON_DIST:       131.87 [deg] 
MOON_ILLUM:      81 [%] 
GAL_COORDS:      334.01,  1.36 [deg] galactic lon,lat of the burst (or transient) 
ECL_COORDS:      251.27,-26.92 [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 = 114.07,17.26 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 01 Mar 15 01:09:41 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     632995,   Seg_Num: 0
POINT_RA:        244.324d {+16h 17m 18s} (J2000)
POINT_DEC:       -48.709d {-48d 42' 30"} (J2000)
POINT_ROLL:      100.588d
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01
IMG_START_TIME:  3933.95 SOD {01:05:33.95} UT,   65.6 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        5.576
N_STARS:         184
X_OFFSET:        288 [pixels]
Y_OFFSET:        624 [pixels]
X_MAX:           1247 [pixels]
Y_MAX:           1583 [pixels]
DET_THRESH:      20
PHOTO_THRESH:    12
SL_URL:          sw00632995000msufc0065.fits
SUN_POSTN:       341.65d {+22h 46m 36s}   -7.77d {-07d 46' 17"}
SUN_DIST:         88.77 [deg]   Sun_angle= 6.5 [hr] (West of Sun)
MOON_POSTN:      109.40d {+07h 17m 35s}  +17.02d {+17d 01' 01"}
MOON_DIST:       131.87 [deg]
MOON_ILLUM:      81 [%]
GAL_COORDS:      334.02,  1.33 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      251.30,-26.92 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 01 Mar 15 01:10:35 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     632995,   Seg_Num: 0
POINT_RA:        244.324d {+16h 17m 18s} (J2000)
POINT_DEC:       -48.709d {-48d 42' 30"} (J2000)
ROLL:            100.588d
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01
IMG_START_TIME:  3933.95 SOD {01:05:33.95} UT,   65.6 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     446864747
X_OFFSET:        752 [pixels]
Y_OFFSET:        974 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       912
Y_GRB_POS:       1134
BINNING_INDEX:   1
IM_URL:          sw00632995000msuni0079.fits
SUN_POSTN:       341.65d {+22h 46m 36s}   -7.77d {-07d 46' 16"}
SUN_DIST:         88.77 [deg]   Sun_angle= 6.5 [hr] (West of Sun)
MOON_POSTN:      109.40d {+07h 17m 37s}  +17.02d {+17d 00' 57"}
MOON_DIST:       131.87 [deg]
MOON_ILLUM:      81 [%]
GAL_COORDS:      334.02,  1.33 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      251.30,-26.92 [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:     Sun 01 Mar 15 01:10:02 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     632995,   Seg_Num: 0
POINT_RA:        244.324d {+16h 17m 18s} (J2000)
POINT_DEC:       -48.709d {-48d 42' 30"} (J2000)
POINT_ROLL:      100.588d
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01
IMG_START_TIME:  3933.95 SOD {01:05:33.95} UT,   65.6 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        5.576
N_STARS:         184
X_OFFSET:        288 [pixels]
Y_OFFSET:        624 [pixels]
X_MAX:           1247 [pixels]
Y_MAX:           1583 [pixels]
DET_THRESH:      20
PHOTO_THRESH:    12
SL_URL:          sw00632995000msufc0065.fits
SUN_POSTN:       341.65d {+22h 46m 36s}   -7.77d {-07d 46' 16"}
SUN_DIST:         88.77 [deg]   Sun_angle= 6.5 [hr] (West of Sun)
MOON_POSTN:      109.40d {+07h 17m 36s}  +17.02d {+17d 00' 59"}
MOON_DIST:       131.87 [deg]
MOON_ILLUM:      81 [%]
GAL_COORDS:      334.02,  1.33 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      251.30,-26.92 [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:     Sun 01 Mar 15 01:10:18 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     632995,   Seg_Num: 0
POINT_RA:        244.324d {+16h 17m 18s} (J2000)
POINT_DEC:       -48.709d {-48d 42' 30"} (J2000)
ROLL:            100.588d
IMG_START_DATE:  17082 TJD;    60 DOY;   15/03/01
IMG_START_TIME:  3933.95 SOD {01:05:33.95} UT,   65.6 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     446864747
X_OFFSET:        752 [pixels]
Y_OFFSET:        974 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       912
Y_GRB_POS:       1134
BINNING_INDEX:   1
IM_URL:          sw00632995000msuni0079.fits
SUN_POSTN:       341.65d {+22h 46m 36s}   -7.77d {-07d 46' 16"}
SUN_DIST:         88.77 [deg]   Sun_angle= 6.5 [hr] (West of Sun)
MOON_POSTN:      109.40d {+07h 17m 36s}  +17.02d {+17d 00' 58"}
MOON_DIST:       131.87 [deg]
MOON_ILLUM:      81 [%]
GAL_COORDS:      334.02,  1.33 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      251.30,-26.92 [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 Circular #17510
```
TITLE:   GCN CIRCULAR
NUMBER:  17510 
SUBJECT: GRB 150301A: Swift detection of a short burst or new SGR
DATE:    15/03/01 01:26:16 GMT 
FROM:    Scott Barthelmy at NASA/GSFC  
```
A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), M. De Pasquale (INAF-IASFPA), L. M. Z. Hagen (PSU), J. A. Kennea (PSU), C. B. Markwardt (NASA/GSFC), A. Maselli (INAF-IASFPA), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team:
At 01:04:28 UT, the Swift Burst Alert Telescope (BAT) triggered and located a source which could be a short GRB or a new SGR (trigger=632995). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 244.286, -48.697, which is
```
   RA(J2000)  =  16h 17m 09s
   Dec(J2000) = -48d 41' 48"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak structure with a duration of about 0.1 sec. The peak count rate was ~8500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 01:05:26.6 UT, 58.3 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 244.3047, -48.7131 which is equivalent to:
```
   RA(J2000)  = +16h 17m 13.13s
   Dec(J2000) = -48d 42' 47.2"
```
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This location is 73 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 113 seconds with the White filter starting 65 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 none of the XRT error circle. The coverage of the XRT error circle by the 8'x8' region for the list of sources generated on-board is uncertain because the large number of sources filled the available telemetry. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain extinction expected.
We note that this source is near the Galactic Plane and Bulge (lat = 1.36, lon = 334) and so this might be a previously-unknown Soft Gamma Repeater. The burst has significant emission above 100 keV, which is unusual, but not unprecedented, for an SGR. Further analysis of the full data set and continued observation is required to determine the nature of this source.
Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular #17511
Valerie Connaughton and Peter Jenke (UAH) and Adam Goldstein (NASA MSFC) report on behalf of the Fermi GBM Team:
"At 01:04:28.65 UT on 01 March 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150301A (trigger 446864671 / 150301045) which was also detected by the Swift/BAT (Lien et al. 2015, GCN 17510). The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 105 degrees.
The GBM light curve consists of a single peak about 50 ms in duration. The counts registered in the NaI detectors are strongly peaked in the 50 - 300 keV energy range typical for GRBs. From the quicklook data, the softness ratio for the event (20 - 100 keV / 100 - 500 keV) is 0.4 +/- 0.3, typical for fairly hard GRBs. By contrast, the corresponding softness ratios for recent triggers from SGR 1935+2154 and AXP 4U 0142+61 were 4.4 +/- 1.8, 3.4 +/- 1.0, and 2.2 +/- 0.4.
The time-averaged spectrum from T0-0.016 s to T0+0.032 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.53 +/- 0.35 and the cutoff energy, parameterized as Epeak, is 185 +/- 49 keV.
The event fluence (10-1000 keV) in this time interval is (1.2 +/- 0.2)E-07 erg/cm^2. The 16-msec peak photon flux measured starting from T0-0.016 s in the 10-1000 keV band is 29 +/- 4 ph/s/cm^2.
The spectral characteristics of this burst are more like a GRB than an SGR. We think it is therefore unlikely that this event is a burst from a new SGR and conclude that it is, instead, a short GRB.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #17513
M. Tanga, C. Delvaux, J. Greiner (all MPE Garching) and D. A. Kann (TLS Tautenburg) report on behalf of the GROND team:
We observed the field of GRB 150301A (Swift trigger 632995; Lien et al., GCN #17510) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).
Observations started at 06:02 UT on 01-03-2015, 4.97 hrs after the GRB trigger. They were performed at an average seeing of 1.4" and at an average airmass of 1.5.
We found two point sources within the 5.0" Swift-XRT error circle reported by Lien et al. (GCN #17510). The first source is at
```
RA (J2000.0) =3D 16 h 17 m 13.08 s
DEC (J2000.0) =3D -48d 42' 45.7"
```
The second source is at
```
RA (J2000.0) =3D 16 h 17 m 13.34 s
DEC (J2000.0) =3D -48d 42' 49.7"=A0
```
with an uncertainty of 0.3" in each coordinate for both sources.
Based on the first 50 min of total exposures in g'r'i'z' and 40 min in JHK, we estimate the following preliminary magnitudes (all in AB system):
For the first source:
```
g' > 24.4 mag,
r' > 24.5 mag,
i' = 22.0 +/- 0.1 mag,
z' = 21.0 +/- 0.3 mag,
J = 18.8 +/- 0.2 mag,
H = 18.3 +/- 0.2 mag, and
K > 18.3 mag.
```
For the second source:
```
g' > 24.4 mag,
r' > 24.5 mag,
i' = 23.1 +/- 0.1 mag,
z' = 22.2 +/- 0.1 mag,
J = 19.6 +/- 0.3 mag,
H = 19.1 +/- 0.4 mag, and
K > 18.3 mag.
```
Both objects appear to be constant over the duration of our observation. Therefore we suppose they are not related to the burst.
We note the field is crowded. We also notice the presence of a bright star (~14 mag) west of the Swift-XRT error circle covering around 10% of the encircled region.
Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=3D3.31 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
GCN Circular #17517
M. de Pasquale (INAF-IASFPA), A. Maselli (INAF-IASFPA), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), P.A. Evans (U. Leicester), A. Amaral-Rogers (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB) and A.Y. Lien report on behalf of the Swift-XRT team:
We have analysed 147 s of XRT data for GRB 150301A (Lien et al. GCN Circ. 17510), from 50 s to 43.7 ks after the BAT trigger. The data are entirely in Windowed Timing (WT) mode (the first 6 s were taken while Swift was slewing).
The light curve can be modelled with an initial power-law decay with an index of alpha=0.53 (+0.18, -0.59), followed by a break at T+112 s to an alpha of 2.6 (+0.6, -0.7).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.71 (+0.21, -0.20). The best-fitting absorption column is 5.6 (+/-0.7) x 10^22 cm^-2, in excess of the Galactic value of 1.3 x 10^22 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 9.1 x 10^-11 (2.0 x 10^-10) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
```
Total column:	     5.6 (+/-0.7) x 10^22 cm^-2
Galactic foreground: 1.3 x 10^22 cm^-2
Excess significance: 10.5 sigma
Photon index:	     1.71 (+0.21, -0.20)
```
If the light curve continues to decay with a power-law decay index of 2.6, the count rate at T+24 hours will be 9.7 x 10^-7 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.8 x 10^-17 (1.9 x 10^-16) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00632995.
This circular is an official product of the Swift-XRT team.
GCN Circular #17519
T. Sakamoto (AGU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-210 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 150301A (trigger #632995) (Lien, et al., GCN Circ. 17510). The BAT ground-calculated position is RA, Dec = 244.281, -48.732 deg which is
```
  RA(J2000)  =  16h 17m 07.5s
  Dec(J2000) = -48d 43' 56.2"
```
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%.
The mask-weighted light curve shows a single short FRED peak that starts at ~ T0 and ends at ~ T+0.5 s. T90 (15-350 keV) is 0.48 +- 0.14 sec (estimated error including systematics).
The time-averaged spectrum from T+0.00 to T+0.56 sec fit by a simple power-law model has a power law index of 1.44 +- 0.23 (chi squared 54.10 for 57 d.o.f.). The fluence in the 15-150 keV band is 7.4 +- 1.0 x 10^-8 erg/cm2. The 1-sec peak photon flux measured from T-0.22 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec.
A single blackbody fit to the time-averaged spectrum shows a blackbody temperature of 15.11 +- 2.92 keV (chi squared 74.66 for 57 d.o.f.). A thermal bremsstrahlung model fit shows the temperature of 199.36 keV (chi squared 55.72 for 57 d.o.f.).
Despite being near the Galactic Plane and Bulge (lat = 1.36, lon = 334), both the fast-decaying XRT light curve and Fermi/GBM observation (Connaughton et al., GCN Circ. 17511) suggests that this source is more likely to be a short GRB than a SGR. In addition, there are no other BAT detections of this source before or since this trigger.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/632995/BA/
GCN Circular #17521
L. M. Z. Hagen (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150301A 66 s after the BAT trigger (Lien et al., GCN Circ. 17510). No optical afterglow consistent with the XRT position (Lien et al. GCN Circ. 17510) or GROND candidates (Tanga et al. GCN Circ. 17513) 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 exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white               66         4931          306        >21.08
v                 5143         5343          196        >19.40
b                 4526        10879          750        >21.16
u                 4321         5926          362        >20.08
uvw1              5553         5752          196        >19.61
uvm2              5347         5547          196        >19.40
uvw2              4937         5137          196        >19.82
```
The magnitudes in the table are not corrected for the substantial Galactic extinction due to the reddening of E(B-V) = 3.84 in the direction of the burst (Schlegel et al. 1998). We note that the photometry is likely affected by a nearby bright foreground star.

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Jochen Greiner, last update: 02-Mar-2015 [Disclaimer]