Gamma-ray Burst 170921A

(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:     Thu 21 Sep 17 14:29:35 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     773509,   Seg_Num: 0
GRB_RA:           26.849d {+01h 47m 24s} (J2000),
                  27.103d {+01h 48m 25s} (current),
                  26.135d {+01h 44m 32s} (1950)
GRB_DEC:         +30.874d {+30d 52' 27"} (J2000),
                 +30.962d {+30d 57' 44"} (current),
                 +30.625d {+30d 37' 30"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       10937 [cnts]    Image_Peak=392 [image_cnts]
TRIGGER_DUR:     4.096 [sec] 
TRIGGER_INDEX:   298     E_range: 25-100 keV
BKG_INTEN:       88213 [cnts]
BKG_TIME:        52068.27 SOD {14:27:48.27} UT
BKG_DUR:         40 [sec]
GRB_DATE:        18017 TJD;   264 DOY;   17/09/21
GRB_TIME:        52128.50 SOD {14:28:48.50} UT
GRB_PHI:          86.42 [deg]
GRB_THETA:        14.00 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     16.88 [sigma]
IMAGE_SIGNIF:    10.20 [sigma]
MERIT_PARAMS:     +1  +0  +0  +2  +2  +0  +0  +0 +75  +0 
SUN_POSTN:       178.90d {+11h 55m 35s}   +0.48d {+00d 28' 42"}
SUN_DIST:        138.71 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.83d {+13h 03m 20s}   -2.30d {-02d 18' 04"}
MOON_DIST:       149.42 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.86,-30.48 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       36.17, 18.46 [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 = 149.16,-2.60 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:30:31 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.866d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.872d {+30d 52' 21"} (J2000)
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52225.81 SOD {14:30:25.81} UT,   97.3 [sec] since BAT Trigger Time
COUNTS:          12    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        1    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:32:51 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     773509,   Seg_Num: 0
GRB_RA:           26.849d {+01h 47m 24s} (J2000),
                  27.103d {+01h 48m 25s} (current),
                  26.135d {+01h 44m 32s} (1950)
GRB_DEC:         +30.874d {+30d 52' 27"} (J2000),
                 +30.962d {+30d 57' 44"} (current),
                 +30.625d {+30d 37' 30"} (1950)
GRB_DATE:        18017 TJD;   264 DOY;   17/09/21
GRB_TIME:        52128.50 SOD {14:28:48.50} UT
TRIGGER_INDEX:   298
GRB_PHI:          86.42 [deg]
GRB_THETA:        14.00 [deg]
DELTA_TIME:      57.00 [sec]
TRIGGER_DUR:     4.096 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     16.88 [sigma]
IMAGE_SIGNIF:    10.20 [sigma]
LC_URL:          sw00773509000msb.lc
SUN_POSTN:       178.90d {+11h 55m 36s}   +0.48d {+00d 28' 39"}
SUN_DIST:        138.71 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.86d {+13h 03m 26s}   -2.31d {-02d 18' 39"}
MOON_DIST:       149.44 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.86,-30.48 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       36.17, 18.46 [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 = 149.16,-2.60 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:33:31 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.866d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.872d {+30d 52' 20"} (J2000)
POINT_ROLL:      45.505d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52229.07 SOD {14:30:29.07} UT,   100.6 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.989
N_STARS:         34
X_OFFSET:        373 [pixels]
Y_OFFSET:        527 [pixels]
X_MAX:           1332 [pixels]
Y_MAX:           1486 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw00773509000msufc0100.fits
SUN_POSTN:       178.90d {+11h 55m 36s}   +0.48d {+00d 28' 38"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.87d {+13h 03m 28s}   -2.31d {-02d 18' 47"}
MOON_DIST:       149.44 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:33:45 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.866d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.872d {+30d 52' 20"} (J2000)
POINT_ROLL:      45.505d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52229.07 SOD {14:30:29.07} UT,   100.6 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.989
N_STARS:         34
X_OFFSET:        373 [pixels]
Y_OFFSET:        527 [pixels]
X_MAX:           1332 [pixels]
Y_MAX:           1486 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw00773509000msufc0100.fits
SUN_POSTN:       178.90d {+11h 55m 36s}   +0.48d {+00d 28' 38"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.87d {+13h 03m 28s}   -2.31d {-02d 18' 49"}
MOON_DIST:       149.44 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:34:37 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     773509,   Seg_Num: 0
GRB_RA:           26.8485d {+01h 47m 23.64s} (J2000),
                  27.1024d {+01h 48m 24.57s} (current),
                  26.1340d {+01h 44m 32.16s} (1950)
GRB_DEC:         +30.9063d {+30d 54' 22.6"} (J2000),
                 +30.9942d {+30d 59' 39.2"} (current),
                 +30.6571d {+30d 39' 25.6"} (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:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52247.00 SOD {14:30:47.00} UT,   118.5 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       178.90d {+11h 55m 36s}   +0.48d {+00d 28' 37"}
SUN_DIST:        138.69 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.87d {+13h 03m 30s}   -2.32d {-02d 18' 59"}
MOON_DIST:       149.42 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.85,-30.45 [deg] galactic lon,lat of the burst
ECL_COORDS:       36.18, 18.49 [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:     Thu 21 Sep 17 14:34:59 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.866d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.872d {+30d 52' 20"} (J2000)
ROLL:            45.505d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52229.07 SOD {14:30:29.07} UT,   100.6 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     527697048
X_OFFSET:        692 [pixels]
Y_OFFSET:        846 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       852
Y_GRB_POS:       1006
BINNING_INDEX:   1
IM_URL:          sw00773509000msuni0120.fits
SUN_POSTN:       178.90d {+11h 55m 36s}   +0.48d {+00d 28' 37"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.88d {+13h 03m 31s}   -2.32d {-02d 19' 03"}
MOON_DIST:       149.45 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:35:12 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.866d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.872d {+30d 52' 20"} (J2000)
ROLL:            45.505d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52229.07 SOD {14:30:29.07} UT,   100.6 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     527697048
X_OFFSET:        692 [pixels]
Y_OFFSET:        846 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       852
Y_GRB_POS:       1006
BINNING_INDEX:   1
IM_URL:          sw00773509000msuni0120.fits
SUN_POSTN:       178.90d {+11h 55m 36s}   +0.48d {+00d 28' 36"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.88d {+13h 03m 31s}   -2.32d {-02d 19' 05"}
MOON_DIST:       149.45 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:41:28 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.874d {+30d 52' 27"} (J2000)
POINT_ROLL:      45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52387.24 SOD {14:33:07.24} UT,   258.7 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.569
N_STARS:         98
X_OFFSET:        133 [pixels]
Y_OFFSET:        287 [pixels]
X_MAX:           1572 [pixels]
Y_MAX:           1726 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw00773509000msufc0258.fits
SUN_POSTN:       178.90d {+11h 55m 37s}   +0.48d {+00d 28' 30"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.93d {+13h 03m 44s}   -2.34d {-02d 20' 13"}
MOON_DIST:       149.48 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:41:52 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     773509,   Seg_Num: 0
GRB_RA:           26.8484d {+01h 47m 23.61s} (J2000),
                  27.1023d {+01h 48m 24.55s} (current),
                  26.1339d {+01h 44m 32.13s} (1950)
GRB_DEC:         +30.9069d {+30d 54' 24.8"} (J2000),
                 +30.9948d {+30d 59' 41.3"} (current),
                 +30.6577d {+30d 39' 27.8"} (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:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52247.00 SOD {14:30:47.00} UT,   118.5 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       178.90d {+11h 55m 37s}   +0.47d {+00d 28' 30"}
SUN_DIST:        138.69 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.94d {+13h 03m 45s}   -2.34d {-02d 20' 17"}
MOON_DIST:       149.46 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.85,-30.45 [deg] galactic lon,lat of the burst
ECL_COORDS:       36.18, 18.49 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:41:43 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.874d {+30d 52' 27"} (J2000)
POINT_ROLL:      45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52387.24 SOD {14:33:07.24} UT,   258.7 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.569
N_STARS:         98
X_OFFSET:        133 [pixels]
Y_OFFSET:        287 [pixels]
X_MAX:           1572 [pixels]
Y_MAX:           1726 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw00773509000msufc0258.fits
SUN_POSTN:       178.90d {+11h 55m 37s}   +0.48d {+00d 28' 30"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.93d {+13h 03m 44s}   -2.34d {-02d 20' 15"}
MOON_DIST:       149.49 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:42:33 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.874d {+30d 52' 27"} (J2000)
ROLL:            45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52387.24 SOD {14:33:07.24} UT,   258.7 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     527697206
X_OFFSET:        692 [pixels]
Y_OFFSET:        846 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       852
Y_GRB_POS:       1006
BINNING_INDEX:   1
IM_URL:          sw00773509000msuni0278.fits
SUN_POSTN:       178.90d {+11h 55m 37s}   +0.47d {+00d 28' 29"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.94d {+13h 03m 46s}   -2.34d {-02d 20' 24"}
MOON_DIST:       149.49 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:42:40 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.874d {+30d 52' 27"} (J2000)
ROLL:            45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52387.24 SOD {14:33:07.24} UT,   258.7 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     527697206
X_OFFSET:        692 [pixels]
Y_OFFSET:        846 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       852
Y_GRB_POS:       1006
BINNING_INDEX:   1
IM_URL:          sw00773509000msuni0278.fits
SUN_POSTN:       178.90d {+11h 55m 37s}   +0.47d {+00d 28' 29"}
SUN_DIST:        138.70 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      195.94d {+13h 03m 46s}   -2.34d {-02d 20' 26"}
MOON_DIST:       149.49 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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 #21901
A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), P. A. Evans (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), B. Sbarufatti (PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team:
At 14:28:48 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 170921A (trigger=773509). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 26.849, +30.874 which is
```
   RA(J2000) = 01h 47m 24s
   Dec(J2000) = +30d 52' 27"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 20 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger.
The XRT began observing the field at 14:30:25.8 UT, 97.3 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 26.8484, 30.9069 which is equivalent to:
```
   RA(J2000)  = 01h 47m 23.63s
   Dec(J2000) = +30d 54' 24.8"
```
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 118 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (5.49 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.4 (+0.67/-0.55) x 10^22 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 100 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 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 0.05.
Burst Advocate for this burst is A. D'Ai (antonino.dai 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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:49:22 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.875d {+30d 52' 28"} (J2000)
POINT_ROLL:      45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52990.36 SOD {14:43:10.36} UT,   861.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.823
N_STARS:         190
X_OFFSET:        133 [pixels]
Y_OFFSET:        287 [pixels]
X_MAX:           1572 [pixels]
Y_MAX:           1726 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw00773509000msufc0861.fits
SUN_POSTN:       178.91d {+11h 55m 38s}   +0.47d {+00d 28' 23"}
SUN_DIST:        138.71 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      196.00d {+13h 04m 00s}   -2.36d {-02d 21' 38"}
MOON_DIST:       149.53 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Sep 17 14:49:37 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.875d {+30d 52' 28"} (J2000)
POINT_ROLL:      45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52990.36 SOD {14:43:10.36} UT,   861.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.823
N_STARS:         190
X_OFFSET:        133 [pixels]
Y_OFFSET:        287 [pixels]
X_MAX:           1572 [pixels]
Y_MAX:           1726 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw00773509000msufc0861.fits
SUN_POSTN:       178.91d {+11h 55m 38s}   +0.47d {+00d 28' 22"}
SUN_DIST:        138.71 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      196.00d {+13h 04m 00s}   -2.36d {-02d 21' 41"}
MOON_DIST:       149.53 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:50:45 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.875d {+30d 52' 28"} (J2000)
ROLL:            45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52990.36 SOD {14:43:10.36} UT,   861.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     527697810
X_OFFSET:        692 [pixels]
Y_OFFSET:        846 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       852
Y_GRB_POS:       1006
BINNING_INDEX:   1
IM_URL:          sw00773509000msuni0881.fits
SUN_POSTN:       178.91d {+11h 55m 38s}   +0.47d {+00d 28' 21"}
SUN_DIST:        138.71 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      196.01d {+13h 04m 03s}   -2.36d {-02d 21' 53"}
MOON_DIST:       149.54 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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:     Thu 21 Sep 17 14:50:55 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     773509,   Seg_Num: 0
POINT_RA:         26.867d {+01h 47m 28s} (J2000)
POINT_DEC:       +30.875d {+30d 52' 28"} (J2000)
ROLL:            45.503d
IMG_START_DATE:  18017 TJD;   264 DOY;   17/09/21
IMG_START_TIME:  52990.36 SOD {14:43:10.36} UT,   861.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     527697810
X_OFFSET:        692 [pixels]
Y_OFFSET:        846 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       852
Y_GRB_POS:       1006
BINNING_INDEX:   1
IM_URL:          sw00773509000msuni0881.fits
SUN_POSTN:       178.91d {+11h 55m 38s}   +0.47d {+00d 28' 21"}
SUN_DIST:        138.71 [deg]   Sun_angle= 10.1 [hr] (West of Sun)
MOON_POSTN:      196.01d {+13h 04m 03s}   -2.37d {-02d 21' 55"}
MOON_DIST:       149.54 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.88,-30.48 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       36.18, 18.45 [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 #21903
Klotz A., Atteia J.L. (CNRS-OMP-IRAP), Boer, M., Laugier, R. (CNRS-ARTEMIS), Gendre B. (UVI - Etelman Obs.) report:
We imaged the field of GRB 170921A detected by SWIFT (trigger 773509) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France.
The observations started 3.86h after the GRB trigger. The elevation of the field increased from 12 degrees above horizon and weather conditions were good.
We co-added a series of exposures. No OT is detected with a limiting magnitude of:
t0+3.86h to t0+4.23h : Rlim = 19.5
Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction.
GCN Circular #21904
B. Sbarufatti (INAF-OAB/PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V. D'Elia (ASDC), A. Melandri (INAF-OAB), D.N. Burrows (PSU), A. Tohuvavohu (PSU) and A. D'Ai report on behalf of the Swift-XRT team:
We have analysed 6.5 ks of XRT data for GRB 170921A (D'Ai et al. GCN Circ. 21901), from 82 s to 16.5 ks after the BAT trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 26.8487, 30.9067 which is equivalent to:
```
RA (J2000): 01 47 23.70
Dec(J2000): +30 54 24.3
```
with an uncertainty of 2.1 arcsec (radius, 90% confidence).
The light curve can be modelled with an initial power-law decay with an index of alpha=3.3 (+0.5, -0.4), followed by a break at T+238 s to an alpha of 0.85 (+0.10, -0.09).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.7 (+0.4, -0.3). The best-fitting absorption column is 1.00 (+0.27, -0.23) x 10^22 cm^-2, in excess of the Galactic value of 5.5 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 3.5 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.00 (+0.27, -0.23) x 10^22 cm^-2
Galactic foreground: 5.5 x 10^20 cm^-2
Excess significance: 6.7 sigma
Photon index:	     2.7 (+0.4, -0.3)
```
If the light curve continues to decay with a power-law decay index of 0.85, the count rate at T+24 hours will be 2.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.3 x 10^-14 (2.5 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00773509.
This circular is an official product of the Swift-XRT team.
GCN Circular #21905
D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Subaru, NAOJ), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of MITSuME collaboration:
We observed the field of GRB 170921A (D'Ai et al., GCNC 21901) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2017-09-21 14:39:14 UT (~10 min after the burst). We did not find any new point source within the XRT error circle (D'Ai et al., GCNC 21901) in all the three bands.
Three sigma upper limits of the OT are listed below. We used SDSS-DR8 catalog for flux calibration.
```
#T0+[day]  MID-UT    T-EXP[sec]   g'    Rc     Ic
-----------------------------------------------------
0.04269    15:30:16    5760.0   >20.1  >19.8  >18.8
-----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]
```
GCN Circular #21906
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 2671 s of XRT Photon Counting mode data and 5 UVOT images for GRB 170921A, 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 = 26.84906, +30.90673 which is equivalent to:
```
RA (J2000): 01h 47m 23.77s
Dec (J2000): +30d 54' 24.2"
```
with an uncertainty of 1.5 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 #21907
H.X. Feng (NAOC), Y.D. Hu (IAA-CSIC), D. Xu, Z.P. Zhu (NAOC), X. Zhang, T.Z. Yang, J.Z. Liu, A. Esamdin, L. Ma (XAO), Y. Qin (Geneva Obs.) report:
We observed the field of long GRB 170921A (D'Ai et al., GCN 21901) using the 1m telescope located at Nanshan, Xinjiang, China. We obtained 3*180s R-band frames, starting at 15:52:35.04 UT on 2017-09-21 (i.e., 1.39 hr after the BATtrigger).=A0 No optical source is detected at the XRT position (Beardmore et al., GCN 21906) in the stacked image, down to a limiting magnitude of m(R)~20.3,=A0calibrated with the USNO-B1 catalog.
GCN Circular #21909
D. Malesani (DARK/NBI), K. E. Heintz (Univ. Iceland and DARK/NBI), N. R. Tanvir (Univ. Leicester), D. A. Kann (IAA/CSIC), T. Pursimo (NOT), and S. Dyrbye (NOT) report on behalf of a larger collaboration:
We observed the field of GRB 170921A (D'Ai et al., GCN 21901) with the Nordic Optical Telescope equipped with the AlFOSC imager. Observations were carried out with the SDSS r' and z' filters, for a total exposure of 900 and 1800 s, respectively.
We did not detect any new object inside or in the proximity of the enhanced X-ray error circle (Beardmore et al., GCN 21906). At mean epochs 2017 Sep 21.941 and Sep 21.958 UT (8.1 and 8.5 hr after the GRB), we report 3-sigma limiting magnitudes r' > 24.3 and z' > 23.3, respectively (both AB, calibrated against the Pan-STARRS catalog).
Our non-detections are consistent with the reports by TAROT (Klotz et al., GCN 21903), MITSuME (Kuroda et al., GCN 21905), and Nanshan (Feng et al., GCN 21907).
GCN Circular #21910
C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), A. Cucchiara, D. Morris, and B. Gendre (U. Virgin Islands) on behalf of a large collaboration report:
We began observing Swift GRB 170921A (D'Ai et al. GCN 21901) on September 21, from 14:52 to 15:05 UT (from 24 to 37 minutes since the GRB trigger time) with the LCO 2-m telescope in Hawaii in the SDSS R and I filters. Within the enhanced Swift-XRT circle (Beardmore et al. GCN 21906) we do not detect any optical counterpart down to the following limits, in agreement with previous reports (Klotz et al. GCN 21903; Kuroda et al. GCN 21905; Feng et al. GCN 21907; Malesani et al. GCN 21909):
```
Mid Time Exposure Filter Magnitude (AB)  
(min)     (s)
-------------------------------------------------------
26.8       5x60   SDSS-R   > 20.7
34.0       3x60   SDSS-I   > 19.8
-------------------------------------------------------
```
as calibrated against nearby SDSS objects.
GCN Circular #21912
T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), A. D'Ai (INAF-IASFPA) H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), 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 170921A (trigger #773509) (D'Ai et al., GCN Circ. 21901). The BAT ground-calculated position is RA, Dec = 26.840, 30.880 deg which is
```
  RA(J2000)  =  01h 47m 21.6s
  Dec(J2000) = +30d 52' 47.1"
```
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 86%.
The mask-weighted light curve shows a single-peaked structure that starts at ~T-22 s, peaks at ~T+3 s, and ends at ~T+13 s. T90 (15-350 keV) is 28.9 +- 6.0 sec (estimated error including systematics).
The time-averaged spectrum from T-21.82 to T+13.00 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.76 +- 0.17. The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+2.74 sec in the 15-150 keV band is 0.8 +- 0.2 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/773509/BA/
GCN Circular #21913
GRB 170921A: Swift/UVOT Upper Limits
S. J. LaPorte (PSU) and A. D'Ai (INAF-IASFPA) report on behalf of the Swift/UVOT team: (Beardmore et al. GCN Circ. 21906) The Swift/UVOT began settled observations of the field of GRB 170921A 101 s after the BAT trigger (D'Ai et al., GCN Circ. 21901). No optical afterglow consistent with the XRT position
is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           101          251          147         >20.7
u_FC               259          509          246         >20.4
white              101         6816          766         >21.4
v                  590         7186          451         >19.9
b                  516         6611          471         >20.6
u                  259        12926         1346         >21.1
w1                 639        12273         1171         >20.6
m2                1412        11366         1102         >21.0
w2                 566        16512          687         >21.0
```
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 #21915
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1iga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:
We observed the field of GRB 170921A (D'Ai, et al., GCN 21901) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from 2017/09 22.18 to 2017/09 22.51 UTC (13.82 to 21.76 hours after the BAT trigger), obtaining a total of 5.29 hours exposure in the r and i bands and 2.22 hours exposure in the Z, Y, J, and H bands.
For a source within the Swift-XRT error circle (Beardmore, et al., GCN 21906), in comparison with the SDSS DR9 and 2MASS catalogs, we obtain the following weak detections and upper limits (3-sigma):
```
  r = 24.45 +/- 0.34
  i = 24.38 +/- 0.34
  Z > 23.05
  Y > 22.83
  J > 22.47
  H > 22.19
```
These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
GCN Circular #21919
Y. F. Zhang, S. L. Xiong, J. Y. Liao, C. K. Li, X. B. Li, C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:
During the commissioning phase, at 2017-09-21T00:43:37.00 (T0), Insight-HXMT/HE detected GRB 170921A (trigger ID: HEB170921030) with a significance of 12 sigma in a routine search of the data, which is also detected by Fermi/GBM subthreshold trigger (trig time: 2017-09-21T00:43:37.18).
The Insight-HXMT light curve mainly consists of a single pulse with a duration (T90) of 1.2 s measured from T0-0.27 s. The 500-ms peak rate, measured from T0+0.06 s, is 1220.3 cnts/sec. The total counts from this burst is 1247.3 counts.
URL_LC: http://www.hxmt.org/images/GRB/HEB170921030_lc.jpg
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (record energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
The analysis results presented above are preliminary; final results will be published elsewhere.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org/index.php/enhome .
GCN Circular #21951
K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender (Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D. Titterington, S. H. Carey, J. Hickish, Y. C. Perrott, N. Razavi-Ghods, P. Scott (Cambridge), K. Grainge, A. Scaife (Manchester)
The AMI Large Array robotically triggered on the Swift alert for GRB 170921A (D'Ai et al., GCN 21901) as part of the 4pisky program, and subsequent follow up observations were obtained up to 10 days post-burst. Our observations at 15 GHz on 2017 Sep 21.89, Sep 27.04 and Sep 28.97 (UT) do not reveal any radio source at the XRT location (Beardmore et al., GCN 21906), with 3sigma upper limits of 186 uJy, 117 uJy and 159 uJy respectively.
We thank the AMI staff for scheduling these observations. The AMI-GRB database is a log of all GRB follow up observations with the AMI, and is available at http://4pisky.org/ami-grb/.

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Jochen Greiner, last update: 01-Oct-2017 [Disclaimer]