Gamma-ray Burst 191221B

(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:     Sat 21 Dec 19 20:39:31 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     945521,   Seg_Num: 0
GRB_RA:          154.832d {+10h 19m 20s} (J2000),
                 155.051d {+10h 20m 12s} (current),
                 154.285d {+10h 17m 08s} (1950)
GRB_DEC:         -38.141d {-38d 08' 28"} (J2000),
                 -38.242d {-38d 14' 31"} (current),
                 -37.890d {-37d 53' 23"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       9285 [cnts]    Image_Peak=333 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   155     E_range: 50-350 keV
BKG_INTEN:       16713 [cnts]
BKG_TIME:        74335.87 SOD {20:38:55.87} UT
BKG_DUR:         8 [sec]
GRB_DATE:        18838 TJD;   355 DOY;   19/12/21
GRB_TIME:        74353.15 SOD {20:39:13.15} UT
GRB_PHI:         119.33 [deg]
GRB_THETA:        39.77 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     145.16 [sigma]
IMAGE_SIGNIF:    11.67 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +3  +1  +0  +0  +5  +0 
SUN_POSTN:       269.66d {+17h 58m 37s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.09 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.86d {+14h 15m 27s}   -8.57d {-08d 34' 26"}
MOON_DIST:        60.37 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.72, 15.65 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      175.09,-44.40 [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 = 102.82,-16.37 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:41:03 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     945521,   Seg_Num: 0
GRB_RA:          154.8286d {+10h 19m 18.86s} (J2000),
                 155.0474d {+10h 20m 11.37s} (current),
                 154.2816d {+10h 17m 07.59s} (1950)
GRB_DEC:         -38.1579d {-38d 09' 28.4"} (J2000),
                 -38.2586d {-38d 15' 31.0"} (current),
                 -37.9065d {-37d 54' 23.4"} (1950)
GRB_ERROR:       6.8 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       9.72e-09 [erg/cm2/sec]
GRB_SIGNIF:      4.69 [sigma]
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74439.35 SOD {20:40:39.35} UT,   86.2 [sec] since BAT Trigger Time
TAM[0-3]:        327.68 237.21 261.66 243.77
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.88d {+14h 15m 31s}   -8.58d {-08d 34' 46"}
MOON_DIST:        60.38 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.73, 15.63 [deg] galactic lon,lat of the burst
ECL_COORDS:      175.09,-44.42 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.00 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:41:15 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     945521,   Seg_Num: 0
GRB_RA:          154.8286d {+10h 19m 18.8s} (J2000),
                 155.0474d {+10h 20m 11.3s} (current),
                 154.2816d {+10h 17m 07.5s} (1950)
GRB_DEC:         -38.1579d {-38d 09' 28.4"} (J2000),
                 -38.2586d {-38d 15' 31.0"} (current),
                 -37.9065d {-37d 54' 23.4"} (1950)
GRB_ERROR:       6.5 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       22 [cnts]
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74439.35 SOD {20:40:39.35} UT,   86.2 [sec] since BAT Trigger Time
CENTROID_X:      322.09,  raw= 322  [pixels]
CENTROID_Y:      281.56,  raw= 282  [pixels]
ROLL:            123.46 [deg]
GAIN:            1
MODE:            2, Short Image mode
WAVEFORM:        134
EXPO_TIME:       0.10 [sec]
GRB_POS_XRT_Y:   -38.97
GRB_POS_XRT_Z:   34.65
IMAGE_URL:       sw00945521000msxps_rw.img
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.88d {+14h 15m 31s}   -8.58d {-08d 34' 48"}
MOON_DIST:        60.38 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.73, 15.63 [deg] galactic lon,lat of the burst
ECL_COORDS:      175.09,-44.42 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:41:18 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     945521,   Seg_Num: 0
GRB_RA:          154.8286d {+10h 19m 18.8s} (J2000),
                 155.0474d {+10h 20m 11.3s} (current),
                 154.2816d {+10h 17m 07.5s} (1950)
GRB_DEC:         -38.1579d {-38d 09' 28.4"} (J2000),
                 -38.2586d {-38d 15' 31.0"} (current),
                 -37.9065d {-37d 54' 23.4"} (1950)
GRB_ERROR:       6.5 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       22 [cnts]
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74439.35 SOD {20:40:39.35} UT,   86.2 [sec] since BAT Trigger Time
CENTROID_X:      322.09,  raw= 322  [pixels]
CENTROID_Y:      281.56,  raw= 282  [pixels]
ROLL:            123.46 [deg]
GAIN:            1
MODE:            2, Short Image mode
WAVEFORM:        134
EXPO_TIME:       0.10 [sec]
GRB_POS_XRT_Y:   -38.97
GRB_POS_XRT_Z:   34.65
IMAGE_URL:       sw00945521000msxps_rw.img
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.88d {+14h 15m 31s}   -8.58d {-08d 34' 49"}
MOON_DIST:        60.38 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.73, 15.63 [deg] galactic lon,lat of the burst
ECL_COORDS:      175.09,-44.42 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:43:07 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     945521,   Seg_Num: 0
GRB_RA:          154.832d {+10h 19m 20s} (J2000),
                 155.051d {+10h 20m 12s} (current),
                 154.285d {+10h 17m 08s} (1950)
GRB_DEC:         -38.141d {-38d 08' 28"} (J2000),
                 -38.242d {-38d 14' 31"} (current),
                 -37.890d {-37d 53' 23"} (1950)
GRB_DATE:        18838 TJD;   355 DOY;   19/12/21
GRB_TIME:        74353.15 SOD {20:39:13.15} UT
TRIGGER_INDEX:   155
GRB_PHI:         119.33 [deg]
GRB_THETA:        39.77 [deg]
DELTA_TIME:      32.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     145.16 [sigma]
IMAGE_SIGNIF:    11.67 [sigma]
LC_URL:          sw00945521000msb.lc
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.09 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.90d {+14h 15m 35s}   -8.59d {-08d 35' 13"}
MOON_DIST:        60.38 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.72, 15.65 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      175.09,-44.40 [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 = 102.82,-16.37 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:43:46 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.846d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.153d {-38d 09' 11"} (J2000)
POINT_ROLL:      123.457d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74444.77 SOD {20:40:44.77} UT,   91.6 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.801
N_STARS:         190
X_OFFSET:        344 [pixels]
Y_OFFSET:        584 [pixels]
X_MAX:           1303 [pixels]
Y_MAX:           1543 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw00945521000msufc0091.fits
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.90d {+14h 15m 37s}   -8.59d {-08d 35' 21"}
MOON_DIST:        60.38 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.74, 15.65 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:44:02 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.846d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.153d {-38d 09' 11"} (J2000)
POINT_ROLL:      123.457d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74444.77 SOD {20:40:44.77} UT,   91.6 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.801
N_STARS:         190
X_OFFSET:        344 [pixels]
Y_OFFSET:        584 [pixels]
X_MAX:           1303 [pixels]
Y_MAX:           1543 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw00945521000msufc0091.fits
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.91d {+14h 15m 37s}   -8.59d {-08d 35' 25"}
MOON_DIST:        60.38 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.74, 15.65 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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:     Sat 21 Dec 19 20:45:13 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.846d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.153d {-38d 09' 11"} (J2000)
ROLL:            123.457d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74444.77 SOD {20:40:44.77} UT,   91.6 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     598653668
X_OFFSET:        756 [pixels]
Y_OFFSET:        976 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       916
Y_GRB_POS:       1136
BINNING_INDEX:   1
IM_URL:          sw00945521000msuni0116.fits
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.92d {+14h 15m 40s}   -8.59d {-08d 35' 40"}
MOON_DIST:        60.39 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.74, 15.65 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:45:28 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.846d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.153d {-38d 09' 11"} (J2000)
ROLL:            123.457d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74444.77 SOD {20:40:44.77} UT,   91.6 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     598653668
X_OFFSET:        756 [pixels]
Y_OFFSET:        976 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       916
Y_GRB_POS:       1136
BINNING_INDEX:   1
IM_URL:          sw00945521000msuni0116.fits
SUN_POSTN:       269.66d {+17h 58m 38s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.92d {+14h 15m 41s}   -8.60d {-08d 35' 43"}
MOON_DIST:        60.39 [deg]
MOON_ILLUM:      22 [%]
GAL_COORDS:      272.74, 15.65 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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:     Sat 21 Dec 19 20:50:15 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
POINT_ROLL:      123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74657.13 SOD {20:44:17.13} UT,   304.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.620
N_STARS:         105
X_OFFSET:        436 [pixels]
Y_OFFSET:        656 [pixels]
X_MAX:           1395 [pixels]
Y_MAX:           1615 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw00945521000msufc0303.fits
SUN_POSTN:       269.66d {+17h 58m 39s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.96d {+14h 15m 51s}   -8.61d {-08d 36' 45"}
MOON_DIST:        60.41 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:50:36 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
POINT_ROLL:      123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74657.13 SOD {20:44:17.13} UT,   304.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.620
N_STARS:         105
X_OFFSET:        436 [pixels]
Y_OFFSET:        656 [pixels]
X_MAX:           1395 [pixels]
Y_MAX:           1615 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw00945521000msufc0303.fits
SUN_POSTN:       269.66d {+17h 58m 39s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.97d {+14h 15m 52s}   -8.61d {-08d 36' 50"}
MOON_DIST:        60.41 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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:     Sat 21 Dec 19 20:51:38 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
ROLL:            123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74657.13 SOD {20:44:17.13} UT,   304.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     598653881
X_OFFSET:        756 [pixels]
Y_OFFSET:        976 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       916
Y_GRB_POS:       1136
BINNING_INDEX:   1
IM_URL:          sw00945521000msuni0328.fits
SUN_POSTN:       269.66d {+17h 58m 39s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.98d {+14h 15m 54s}   -8.62d {-08d 37' 03"}
MOON_DIST:        60.42 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:51:55 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
ROLL:            123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74657.13 SOD {20:44:17.13} UT,   304.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     598653881
X_OFFSET:        756 [pixels]
Y_OFFSET:        976 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       916
Y_GRB_POS:       1136
BINNING_INDEX:   1
IM_URL:          sw00945521000msuni0328.fits
SUN_POSTN:       269.66d {+17h 58m 40s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.07 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.98d {+14h 15m 55s}   -8.62d {-08d 37' 07"}
MOON_DIST:        60.42 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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:     Sat 21 Dec 19 20:52:34 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     945521,   Seg_Num: 0
GRB_RA:          154.8301d {+10h 19m 19.22s} (J2000),
                 155.0489d {+10h 20m 11.74s} (current),
                 154.2831d {+10h 17m 07.95s} (1950)
GRB_DEC:         -38.1576d {-38d 09' 27.3"} (J2000),
                 -38.2583d {-38d 15' 29.9"} (current),
                 -37.9062d {-37d 54' 22.3"} (1950)
GRB_ERROR:       0.6 [arcsec radius, statistical only]
GRB_MAG:         11.73 +/- 0.14 [mag]
FILTER:          7, U
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  74654.00 SOD {20:44:14.00} UT,   300.9 [sec] since BAT Trigger Time
SUN_POSTN:       269.67d {+17h 58m 40s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.09 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      213.98d {+14h 15m 56s}   -8.62d {-08d 37' 16"}
MOON_DIST:        60.43 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.73, 15.64 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      175.10,-44.42 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT UVOT Position Notice.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The UVOT position is 4.3 arcsec from the XRT position.  
COMMENTS:        Result based on Genie data.  
COMMENTS:        Notice generated automatically.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:56:27 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
POINT_ROLL:      123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  75212.44 SOD {20:53:32.44} UT,   859.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.528
N_STARS:         190
X_OFFSET:        196 [pixels]
Y_OFFSET:        416 [pixels]
X_MAX:           1635 [pixels]
Y_MAX:           1855 [pixels]
DET_THRESH:      16
PHOTO_THRESH:    9
SL_URL:          sw00945521000msufc0859.fits
SUN_POSTN:       269.67d {+17h 58m 40s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      214.02d {+14h 16m 05s}   -8.64d {-08d 38' 06"}
MOON_DIST:        60.44 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 21 Dec 19 20:56:42 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
POINT_ROLL:      123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  75212.44 SOD {20:53:32.44} UT,   859.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.528
N_STARS:         190
X_OFFSET:        196 [pixels]
Y_OFFSET:        416 [pixels]
X_MAX:           1635 [pixels]
Y_MAX:           1855 [pixels]
DET_THRESH:      16
PHOTO_THRESH:    9
SL_URL:          sw00945521000msufc0859.fits
SUN_POSTN:       269.67d {+17h 58m 40s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      214.02d {+14h 16m 05s}   -8.64d {-08d 38' 09"}
MOON_DIST:        60.44 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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:     Sat 21 Dec 19 20:58:16 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
ROLL:            123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  75212.44 SOD {20:53:32.44} UT,   859.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     598654436
X_OFFSET:        755 [pixels]
Y_OFFSET:        975 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       915
Y_GRB_POS:       1135
BINNING_INDEX:   1
IM_URL:          sw00945521000msuni0884.fits
SUN_POSTN:       269.67d {+17h 58m 41s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      214.04d {+14h 16m 09s}   -8.64d {-08d 38' 30"}
MOON_DIST:        60.45 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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:     Sat 21 Dec 19 20:58:30 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     945521,   Seg_Num: 0
POINT_RA:        154.848d {+10h 19m 23s} (J2000)
POINT_DEC:       -38.156d {-38d 09' 22"} (J2000)
ROLL:            123.456d
IMG_START_DATE:  18838 TJD;   355 DOY;   19/12/21
IMG_START_TIME:  75212.44 SOD {20:53:32.44} UT,   859.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     598654436
X_OFFSET:        755 [pixels]
Y_OFFSET:        975 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       915
Y_GRB_POS:       1135
BINNING_INDEX:   1
IM_URL:          sw00945521000msuni0884.fits
SUN_POSTN:       269.67d {+17h 58m 41s}  -23.44d {-23d 26' 08"}
SUN_DIST:         93.08 [deg]   Sun_angle= 7.6 [hr] (West of Sun)
MOON_POSTN:      214.04d {+14h 16m 09s}   -8.64d {-08d 38' 33"}
MOON_DIST:        60.45 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      272.74, 15.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      175.11,-44.41 [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 #26534
S Laha (GSFC/UMBC/CRESST), S. D. Barthelmy (GSFC), J.D. Gropp (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and K. K. Simpson (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 20:39:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 191221B (trigger=945521). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 154.832, -38.141 which is
```
   RA(J2000) = 10h 19m 20s
   Dec(J2000) = -38d 08' 28"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 15 sec. The peak count rate was ~17000 counts/sec (15-350 keV), at ~5 sec after the trigger.
The XRT began observing the field at 20:40:39.3 UT, 86.2 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 154.8286, -38.1579 which is equivalent to:
```
   RA(J2000)  = 10h 19m 18.86s
   Dec(J2000) = -38d 09' 28.4"
```
with an uncertainty of 6.8 arcseconds (radius, 90% containment). This location is 61 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy.
UVOT took a finding chart exposure of 150 seconds with the White filter starting 91 seconds after the BAT trigger. A very bright afterglow candidate has been found at the XRT position in the initial data products. Because of coincidence loss we cannot calculate the magnitude accurately at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.08.
Burst Advocate for this burst is S Laha (sib.laha AT gmail.com). 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/)
GCN Circular #26536
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 191221B ( S Laha et al., GCN 26534) errorbox 1677 sec after notice time and 1700 sec after trigger time at 2019-12-21 21:07:33 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 69 deg. The sun altitude is -30.6 deg.
The galactic latitude b = 16 deg., longitude l = 273 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1234924
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

    1790 |         MASTER-SAAO |  P\ |   180 | 16.0 |        
    1991 |         MASTER-SAAO |  P\ |   180 | 16.7 |        
    2192 |         MASTER-SAAO |  P\ |   180 | 16.6 |        
    2394 |         MASTER-SAAO |  P\ |   180 | 17.0 |        
```
The observation and reduction will continue. The message may be cited.
GCN Circular #26537
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa,A.Kuznetsov,F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov(Lomonosov Moscow State University, SAI, Physics Department), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), R. Podesta, C.Lopez, F. Podesta, C.Francile(Observatorio Astronomico Felix Aguilar OAFA), H.Levato(Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), D. Buckley(South African Astronomical Observatory), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), V. Yurkov, A. Gabovich, Yu. Sergienko(Blagoveschensk Educational State University)
MASTER auto-detection system discovered OT in Swift GRB 191221B (Laha et al GCN 26534) error-box at coordinates
RA,Dec(2000)=10h 19m 19.24s , -38d 09m 28s.7
with quick decay with m_OT=14.4 at 2019-12-21 21:07:33 UT
The observation and reduction will be continued. The message may be cited.
GCN Circular #26538
N. P. M. Kuin (UCL-MSSL) reports on behalf of the Swift/UVOT team:
The Swift/UVOT obtained a 49s grism spectrum of GRB 191221B 242 s after the BAT trigger (Laha et al., GCN Circ. 26534). The spectrum shows a clear break at 2008 Angstrom, suggesting a redshift of z=1.19. At that redshift, the line of He II 1640A is well defined and N II 2143A is present, as well as possibly N V at 1243 A.
GCN Circular #26540
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 1950 s of XRT Photon Counting mode data and 3 UVOT images for GRB 191221B, 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 = 154.82992, -38.15759 which is equivalent to:
```
RA (J2000): 10h 19m 19.18s
Dec (J2000): -38d 09' 27.3"
```
with an uncertainty of 1.7 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #26549
F. Longo (UniTS and INFN Trieste), M. Pilia (INAF/OA-Cagliari), F. Verrecchia (SSDC, and INAF/OAR) , A. Ursi (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Argan, M. Cardillo, C. Casentini, Y. Evangelista, G. Piano (INAF/IAPS), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, F. Fuschino, N. Parmiggiani (INAF/OAS-Bologna), M. Marisaldi (INAF/OAS-Bologna, and Bergen University), A. Trois (INAF/OA-Cagliari), I. Donnarumma (ASI), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team:
The AGILE Mini-CALorimeter (MCAL) detected the long GRB191221B at T0 = 2019-12-21 20:39:11.42 (+/- 0.01 s) already detected by Swift (Laha et al., 2019; GCN #26534).
In the MCAL energy range (0.4-100 MeV), the burst lasted about ~15 s and released a total number of ~12000 counts over a background rate of 650 Hz.
The light curve shows several peaks and can be found at http://www.agilescienceapp.it/notices/GRB_065726_504045551.415264.png.
The AGILE-MCAL detector is a CsI detector with a 4 pi FoV, sensitive in the energy range 0.4-100 MeV. Additional analysis of AGILE data is in progress.
GCN Circular #26551
P. Gokuldass (UVI), D. Morris (UVI), N. Orange (OrangeWave Innovative Science, LLC), A. Cucchiara (College of Marin), R. Strausbaugh (UVI) report:
We observed the field of GRB191221B (Laha et al, GCN 26534) with the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of the Virgin Islands' Etelman Observatory on 12-22-2019 starting at 07:16:00 UT (T+10.6hrs). We performed a series of 50x10s exposures in R-band filter. The weather conditions were clear during the hours of observation and the zenith angle at the start of observations was 60 degrees and rising. We observed the enhanced Swift-XRT position with a 20'x20' field of view.
We clearly detect the uncatalogued source within the enhanced Swift-XRT error radius that was reported by Lipunov et al (GCN 26537). We measure the source with a magnitude:
R = 16.7 � 0.1
The magnitude is estimated from comparison to nearby USNO B1 stars and is not corrected for Galactic extinction. The VIRT is still in the commissioning phase.
Observations and data analysis are ongoing.
This work is supported by NASA-MUREP-MIRO grant NNX15AP95A and NSF-EiR grant 1901296. This message can be cited.
GCN Circular #26552
P. Gokuldass (UVI), D. Morris (UVI), N. Orange (OrangeWave Innovative Science, LLC), A. Cucchiara (College of Marin), R. Strausbaugh (UVI) report:
We observed the field of GRB191221B (Laha et al, GCN 26534) with the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of the Virgin Islands' Etelman Observatory on 12-22-2019 starting at 07:16:00 UT (T+10.6hrs). We performed a series of 50x10s exposures in R-band filter. The weather conditions were clear during the hours of observation and the zenith angle at the start of observations was 60 degrees and rising. We observed the enhanced Swift-XRT position with a 20'x20' field of view.
We clearly detect the uncatalogued source within the enhanced Swift-XRT error radius that was reported by Lipunov et al (GCN 26537). We measure the source with a magnitude:
R = 16.7 + / - 0.1
The magnitude is estimated from comparison to nearby USNO B1 stars and is not corrected for Galactic extinction. The VIRT is still in the commissioning phase.
Observations and data analysis are ongoing.
This work is supported by NASA-MUREP-MIRO grant NNX15AP95A and NSF-EiR grant 1901296. This message can be cited.
GCN Circular #26553
Title: GRB 191221B: VLT/X-shooter redshift
J.-B. Vielfaure (CNRS, Paris Obs.), M. Arabsalmani (ICRAR/UWA), K. E. Heintz (Univ. Iceland), N. R. Tanvir (Univ. Leicester), A. de Ugarte Postigo (HETH/IAA-CSIC), D. B. Malesani (DTU Space), J. P. U. Fynbo (DAWN/NBI), K. Wiersema (Univ. Warwick), S. D. Vergani (CNRS, Paris Obs.), D. Xu (NAO/CAS), G. Pugliese (Univ. Amsteram), S. Schulze (WIS), D. Burgarella (AMU, CNRS, CNES, LAM), report on behalf of the Stargate collaboration:
We observed the optical afterglow of GRB 191221B (Laha et al., GCN 26534; Longo et al., GCN 26549; Lipunov et al., GCN 26537). using the ESO VLT UT2 (Kueyen) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 2 exposures by 600 s each. The observation mid time was 2019 Dec 22.2707 UT (9.843 hr after the GRB).
In a 15 s image taken with the acquisition camera on Dec 22.2592 UT, we detect the optical afterglow, for which we measure a magnitude r = 17.13 +- 0.01 AB (calibrated against nearby stars from the Skymapper catalog; Wolf et al. 2018, PASA, 35, 010; https:doi.org/10.4225/41/593620ad5b574).
We detect several absorption profiles in the GRB spectrum including MgII, MgI, SiII, CIV, AlII, NiII, and FeII lines. From these metal lines we infer a redshift z=1.148 for the GRB, consistent with the redshift reported by Swift/UVOT tram (GCN 26538). We also detect the MgII absorption profile corresponding to an intervening system at z=0.961.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Pascale Hibon, Francisco Belmar, and Trystyn Berg.
GCN Circular #26555
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa,A.Kuznetsov,F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov(Lomonosov Moscow State University, SAI, Physics Department), D. Buckley(South African Astronomical Observatory), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), R. Podesta, C.Lopez, F. Podesta, C.Francile(Observatorio Astronomico Felix Aguilar OAFA), H.Levato(Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), V. Yurkov, A. Gabovich, Yu. Sergienko(Blagoveschensk Educational State University)
We found first image with error box at 2019-12-21 20:40:15 (62 sec after trigger time).
MASTER-OAFA Very Wide Field Camera detected OT in Swift GRB 191221B (Laha et al GCN 26534; Lipunov et al., GCN 26537; Kuin, GCN 26538; Gokuldass et al., GCN 26551; Vielfaure et al., GCN 26553;) error-box at coordinates at 2019-12-21 20:41:35 UT (142 s after trigger time). with m_OT~10.5 mag.
The observation and reduction will be continued. The message may be cited.
GCN Circular #26559
P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), A. Tohuvavohu (U. Toronto), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) and S Laha report on behalf of the Swift-XRT team:
We have analysed 7.8 ks of XRT data for GRB 191221B (S Laha et al. GCN Circ. 26534), from 74 s to 58.6 ks after the BAT trigger. The data comprise 1.3 ks in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 26540).
The late-time light curve (from T0+4.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.03 (+0.09, -0.08).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.097 (+/-0.014). The best-fitting absorption column is consistent with the Galactic value of 8.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.86 (+0.07, -0.06) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Galactic foreground: 8.6 x 10^20 cm^-2
Intrinsic column:    8.6 (+5.8, -0.0) x 10^20 cm^-2 at z=1.148
Photon index:	     1.86 (+0.07, -0.06)
```
If the light curve continues to decay with a power-law decay index of 1.03, the count rate at T+24 hours will be 0.087 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.1 x 10^-12 (3.6 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00945521.
This circular is an official product of the Swift-XRT team.
GCN Circular #26560
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:
We observed Swift GRB 191221B (Laha et al., GCN 26534) with the LCO 1-m Sinistro instrument at the Sutherland South African Astronomical Observatory site on December 22, from 00:30 to 01:11 UT (corresponding to 3.5 to 4.2 hours after the GRB trigger time) with the Bessel R and I filters.
We performed a series of 10x90s exposures in each band. We detect a bright source in the Swift-BAT refined error region (Laha et al., GCN 26536) that is not present in either USNO-B1.0 or 2MASS surveys with the following magnitudes:
R = 16.50 +/- 0.01
I = 15.86 +/- 0.01
This flux measurement is calibrated against several USNO-B1.0 objects near the GRB location and is not corrected for Galactic Extinction.
GCN Circular #26561
B. Gendre (OzGrav-UWA), H. Crisp (OzGrav-UWA), J. Moore (OzGrav-UWA), D. Coward (OzGrav-UWA), A. Klotz (IRAP-CNRS-OMP), P. Thierry (Aragne Observatory), A. Burrell (OzGrav-UWA), J. Zadko (Claire Energy), M. Boer, (UNS-CNRS-OCA) report:
We imaged the field of GRB 191221B detected by Swift (trigger 945521, Laha et al. GCN 26534) with the Zadko robotic telescope (D=100cm) located at the Zadko observatory - Gingin, Australia.
The observations started 19 hours after the GRB trigger. The elevation of the field was at 32 degrees above horizon and weather conditions were good. We performed 6 long exposures of 180s in Clear filter.
We detected the candidate couterpart mentioned by Lipunov et al. (GCNC 26537) in each of the images.
OT was R~17.6+/-0.2 at that time. Further analysis and observations are ongoing.
Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction.
This message may be cited.
GCN Circular #26562
T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), 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 191221B (trigger #945521) (Laha et al., GCN Circ. 26534). The BAT ground-calculated position is RA, Dec = 154.831, -38.152 deg which is
```
   RA(J2000)  =  10h 19m 19.3s
   Dec(J2000) = -38d 09' 07.1"
```
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 12%.
The mask weighted light curve shows complex structures with a duration of ~30 s. The overall structure starts at ~T-10 s and lasts till ~T+20s. There is some hint of weak emission extending up to ~ T+60 s. T90 (15-350 keV) is 48.00 +- 16.00 sec (estimated error including systematics).
The time-averaged spectrum from T-15.28 to T+96.72 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.24 +- 0.05. The fluence in the 15-150 keV band is 1.9 +- 0.1 x 10^-05 erg/cm2. the fluence of this burst is among the brightest ~3% of all BAT-detected GRBs (based on fluences from the BAT GRB catalog https://swift.gsfc.nasa.gov/results/batgrbcat/). The 1-sec peak photon flux measured from T+8.22 sec in the 15-150 keV band is 4.8 +- 0.7 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/945521/BA/
GCN Circular #26564
T. Laskar (University of Bath), W. Fong (Northwestern), K. D. Alexander (Northwestern), E. Berger (Harvard), S. Bhandari (CSIRO), G. Hosseinzadeh (Harvard), R. Margutti (Northwestern), C. G. Mundell (University of Bath), and P. Schady (University of Bath) report on behalf of a larger collaboration:
"We observed GRB 191221B (Laha et al. GCN 26534) with the Atacama Large Millimeter/Submillimeter Array (ALMA) beginning on 2019 December 22 at 07:43:55 UT (11.1 hr after the burst) at 97.5 GHz under good weather conditions. Preliminary analysis reveals a bright (S/N > 300) mm source at position:
10:19:19.225 (+/- 0.005), -38:09:27.45 (+/- 0.01)
consistent with the X-ray position (Beardmore et al. GCN 26540) and optical position (Lipunov et al., GCN 26537). Follow-up observations are planned.
We thank the JAO staff, AoD, P2G, and the entire ALMA team for their help with these observations."
GCN Circular #26565
```
SUBJECT: GRB 191221B: iTelescope optical observations
DATE:    19/12/23 00:21:24 GMT 
FROM:    Filipp Dmitrievich Romanov at Amateur astronomer 
```
I observed the optical afterglow of GRB 191221B (Laha et al., GCN Circ. 26534) with remote telescope T32 (0.43-m f/6.8 reflector + FLI Proline 16803 CCD) of iTelescope.Net in Siding Spring Observatory (Australia) on 2019-12-22 since 13:28:52 UT (~16.8 hours after the trigger). Two images were obtained in each band with Astrodon luminance filter and Johnson/Cousins V filter for 180 and 120 seconds (Binx2). I detected the optical afterglow in three images in the enhanced Swift-XRT position (Beardmore et al., GCN Circ. 26540); it not present in images from DSS Plate Finder.
The following magnitudes (mag. error ~ 0.2) were measured from comparison to nearby stars from APASS DR9 catalogue (Henden et al., 2016):
```
Time of start  Exp.time  Mag.   Comp.star band  Filter
----------------------------------------------------------
13:28:52 UT    180 s     18.1        r'         Luminance
13:32:58 UT    180 s     18.3        V          V
13:36:51 UT    120 s     18.3        r'         Luminance
13:39:46 UT    120 s     <17.9       V          V
----------------------------------------------------------
```
Magnitudes were not corrected for Galactic extinction.
GCN Circular #26566
A.K.H. Kong (NTHU, Taiwan) reports
We observed the field of GRB 191221B (Laha et al., GCN 26534) with the T17 0.43m telescope of iTelescope.Net in Siding Spring, Australia. The observation was done with a SDSS r filter beginning at 2019-12-22 14:56:51 UT (about 18 hours after the trigger) for 300 sec. The optical counterpart (Laha et al., GCN 26534) was detected with r=18.4+/-0.1 (AB) by calibrating with the SkyMapper Southern Sky Survey.
GCN Circular #26567
R. Gaikwad, S. Gupta, V. Sharma, A. Vibhute and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data showed the detection of a GRB 191221B, which was also detected by Swift (Laha S. et al., GCN #26534), Global MASTER-Net (Lipunov V. et al., GCN #26536), Swift/UVOT (Kuin N. et al., GCN #26538), Swift-XRT (Beardmore A. et al., GCN #26540), AGILE/MCAL (Longo F. et al., GCN #26549), VIRT (Gokuldass P. et al., GCN #26551), VLT/X-shooter (Vielfaure J. et al., GCN #26553), MASTER VWFC (Lipunov V. et al., GCN #26555), LCO (Strausbaugh R. et al., GCN #26560), Zadko (Gendre B. et al., GCN #26561), ALMA (Laskar T. et al., GCN #26564) and iTelescope (Romanov F. et al., GCN #26565).
The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with the strongest peak at 2019-12-21 20:39:12.0 UT. The measured peak count rate associated with the burst is 708 cts/s above the background in the combined data of four quadrants, with a total of 4829 cts. The local mean background count rate was 515 cts/s. Using cumulative rates, we measure a T90 of 11.16 s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
GCN Circular #26573
W. C. Xue, Y. G. Zheng, C. Cai, Q. Luo, S. Xiao, Q. B. Yi, Y. Huang, C. K. Li, G. Li, X. B. Li, J. Y. Liao, S. L. Xiong, C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:
At 2019-12-21T20:39:10.70 (T0), Insight-HXMT/HE detected GRB 191221B (trigger ID: HEB191221860) in a routine search of the data, which was also triggered by Swift/BAT (GCN #26534).
The Insight-HXMT/HE light curve mainly consists of multiple pulses with a duration (T90) of 8.85 s measured from T0-0.62 s. The 1-ms peak rate, measured from T0+5.37 s, is 8262 cnts/sec. The total counts from this burst is 38429 counts. URL_LC: http://www.hxmt.org/images/GRB/HEB191221860_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 (deposited 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.
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.
GCN Circular #26574
N. P. M. Kuin (UCL-MSSL) and S. L. Laha (GSFC/UMBC/CRESST) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 191221B 92 s after the BAT trigger (Laha et al., GCN Circ. 26534). A source consistent with the XRT position (Beardmore et al. GCN Circ. 26540) and ALMA position (Laskar et al., GCN Circ. 26564) was detected in the initial UVOT exposures.
The preliminary UVOT position is:
```
    RA  (J2000) =  10:19:19.24 = 154.83017 (deg.)
    Dec (J2000) = -38:09:27.64 = -38.15768 (deg.)
```
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white               92          241          147         see below
u                  304          554          246         12.30 +/- 0.02
b                  560          579           20         13.54 +/- 0.04
uvw2               610          630           20         13.20 +/- 0.06
v                  635          655           20         13.42 +/- 0.05
uvm2               659          679           20         12.79 +/- 0.06
uvw1               684          704           20         12.82 +/- 0.05
```
Aperture photometry shows initially a completely saturated detector, leading to wh < 13.8 mag. The first exposure in the white filter (tstart=T0+92s) shows a readout streak but the readout streak traverses also another relatively bright star which leads to a saturated readout streak and precludes using that method of determining the magnitude (Page et al, 2013 MNRAS 436, 1684). Analysis continues.
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.08 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #26576
D. Frederiks, S. Golenetskii, R.Aptekar, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long GRB 191221B (Swift detection: Laha et al., GCN 26534; AGILE/MCAL detection: Longo et al., GCN 26549; AstroSat CZTI detection: Gaikwad et al., GCN 26567) triggered Konus-Wind (KW) at T0=74349.647 s UT (20:39:09.647).
The burst light curve shows a bright pulse with a complex, multi-peaked structure. The total duration of the burst is ~35 s. The emission is seen up to ~15 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB191221_T74349/
As observed by Konus-Wind, the burst had a fluence of (1.0 � 0.1)x10^-4 erg/cm^2 and a 64-ms peak energy flux, measured from T0+8.064, of (1.9 � 0.2)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+21.760 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.81 (-0.06,+0.06), the high energy photon index beta = -2.47 (-0.24,+0.16), the peak energy Ep = 377 (-29,+30) keV, chi2 = 99/97 dof.
The spectrum near the peak count rate (measured from T0+6.912 s to T0+8.448 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.51 (-0.11,+0.13), the high energy photon index beta = -2.72 (-0.50,+0.26), the peak energy Ep = 338 (-36,+38) keV, chi2 = 64/66 dof.
Assuming the redshift z=1.148 (Vielfaure et al., GCN 26553) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso = (3.6 � 0.4)x10^53 erg, the peak luminosity L_iso = (1.5 � 0.16)x10^53 erg/s, and the rest-frame peak energy of the time-integrated spectrum Ep,z=(810 � 65) keV. With these values, GRB 191221B is within 68% prediction bands for both 'Amati' and 'Yonetoku' relations built for the sample of 138 long KW GRBs with known redshifts (Tsvetkova et al., ApJ 850 161, 2017), see http://www.ioffe.ru/LEA/GRBs/GRB191221_T74349/GRB191221B.pdf
All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.
GCN Circular #26580
T. Laskar (University of Bath), S. Bhandari (CSIRO), K. D. Alexander (Northwestern), E. Berger (Harvard), R. Chornock (Ohio U.), D. Coppejans (Northwestern), M. Drout (U. Toronto), H. van Eerten (University of Bath), Wen-fai Fong (Northwestern), C. Guidorzi (U. Ferrara), G. Hosseinzadeh (Harvard), R. Margutti (Northwestern), C. G. Mundell (University of Bath), and P. Schady (University of Bath) report:
"We observed GRB 191221B (Laha et al., GCN 26534) with the Australia Telescope Compact Array (ATCA) at multiple frequencies and multiple epochs beginning on 2019 December 22 14:17 UT (0.73 days after the burst). We detect a varying radio counterpart at 5.5, 9.0, 16.7, and 21.2 GHz at a position consistent with the X-ray position (Beardmore et al., GCN 26540) and optical position (Lipunov et al., GCN 26537). We identify this source as the radio afterglow of GRB 191221B.
Further analysis and observations are on-going.
We thank the CSIRO staff for approving these observations."
GCN Circular #26616
S. Sugita, A. Yoshida, T. Sakamoto, V. Pal'shin (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), Y. Asaoka, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:
The long GRB 191221B (Swift detection: Barthelmy et al., GCN Circ. 26534, Sakamoto et al., GCN Circ. 26562; AGILE/MCAL observations: Longo et al., GCN Circ. 26549; AstroSat CZTI detection: Gaikwad et al., GCN Circ. 26567; Insight-HXMT/HE detection: Xue et al., GCN Circ. 26573; Konus-Wind observation: Frederiks et al., GCN Circ. 26576; https://gcn.gsfc.nasa.gov/other/191221B.gcn3) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 20:39:04.868 UTC on 21 December 2019. The burst signal was seen by all CGBM detectors.
The burst light curve shows a multi-peaked pulse which starts at T+1.8 sec, peaks at T+11.3 sec and ends at T+23.4 sec. The T90 and T50 durations measured by the SGM data are 13.0 +- 1.6 sec and 4.4 +- 0.4 sec (40-1000 keV), respectively.
The ground processed light curve will be available at
http://cgbm.calet.jp/cgbm_trigger/ground/1260995788/
The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.
GCN Circular #26990
Dear GCN circular admin,
This email serves to submit details of the radio observation of GRB191221B with MeerKAT. Please see the detail of the GCN draft below.
I. Monageng (UCT/SAAO), M. Boettcher (NWU), D.A.H Buckley (SAAO), R. Britto (UFS), S. Razzaque (UJ), B. van Soelen (UFS)
We observed GRB 191221B with the MeerKAT radio telescope on 21 January 2020 from 20:26 to 21:26 UTC (~30 days after the trigger) at a position consistent with the X-ray position reported by Beardmore et al. (GCN 26540). We used J0408-6545 as the bandpass and flux calibrator, which was observed for 10 minutes at the start of the observation. The phase calibrator used was J1120-2508, which was observed for 2 minutes before and after the two ~20 minute scans on GRB 191221B (20:41:04.0 - 21:00:55.5 and 21:03:51.5 - 21:23:50.9 UTC). The observation was performed with 60 antennas and is centered at a frequency of 1.28 GHz with a bandwidth of 856 MHz over 4096 channels. The GRB afterglow was not detected, and we report a 3-sigma upper limit of 64 micro Jy at the position of GRB 191221B.
We thank the team at the South African Radio Astronomy Observatory (SARAO) for observing this DDT request.
Best regards, Itu

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