Gamma-ray Burst 220427A

(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:     Wed 27 Apr 22 21:01:59 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1104343,   Seg_Num: 0
GRB_RA:          275.869d {+18h 23m 29s} (J2000),
                 276.340d {+18h 25m 22s} (current),
                 274.813d {+18h 19m 15s} (1950)
GRB_DEC:         -56.253d {-56d 15' 09"} (J2000),
                 -56.240d {-56d 14' 22"} (current),
                 -56.279d {-56d 16' 42"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=2770 [image_cnts]
TRIGGER_DUR:     72.000 [sec] 
TRIGGER_INDEX:   20000     E_range: 15-50 keV
BKG_INTEN:       0 [cnts]
BKG_TIME:        0.00 SOD {00:00:00.00} UT
BKG_DUR:         0 [sec]
GRB_DATE:        19696 TJD;   117 DOY;   22/04/27
GRB_TIME:        75634.96 SOD {21:00:34.96} UT
GRB_PHI:           6.06 [deg]
GRB_THETA:        35.18 [deg]
SOLN_STATUS:     0x113
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    11.95 [sigma]
MERIT_PARAMS:     +1  +0  +0  +6  +1  +1  +0  +0 +46  +0 
SUN_POSTN:        35.23d {+02h 20m 54s}  +14.04d {+14d 02' 19"}
SUN_DIST:        117.52 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.86d {+00h 15m 27s}   -2.69d {-02d 41' 29"}
MOON_DIST:        86.39 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      273.88,-32.89 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.)  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This matches a source in the ground catalog: IGR J18244-5622, delta=0.154 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 40.03,-20.39 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:04:02 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.858d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.253d {-56d 15' 11"} (J2000)
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75813.08 SOD {21:03:33.08} UT,   178.1 [sec] since BAT Trigger Time
COUNTS:          45    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many iterations.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:05:01 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1104343,   Seg_Num: 0
GRB_RA:          275.869d {+18h 23m 29s} (J2000),
                 276.340d {+18h 25m 22s} (current),
                 274.813d {+18h 19m 15s} (1950)
GRB_DEC:         -56.253d {-56d 15' 09"} (J2000),
                 -56.240d {-56d 14' 22"} (current),
                 -56.279d {-56d 16' 42"} (1950)
GRB_DATE:        19696 TJD;   117 DOY;   22/04/27
GRB_TIME:        75634.96 SOD {21:00:34.96} UT
TRIGGER_INDEX:   20000
GRB_PHI:           6.06 [deg]
GRB_THETA:        35.18 [deg]
DELTA_TIME:      0.00 [sec]
TRIGGER_DUR:     72.000 [sec] 
SOLN_STATUS:     0x113
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    11.95 [sigma]
LC_URL:          sw01104343000msb.lc
SUN_POSTN:        35.23d {+02h 20m 55s}  +14.04d {+14d 02' 21"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.89d {+00h 15m 33s}   -2.68d {-02d 40' 44"}
MOON_DIST:        86.41 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      273.88,-32.89 [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 an image trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This matches a source in the ground catalog: IGR J18244-5622, delta=0.154 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 40.03,-20.39 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:06:54 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.859d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.253d {-56d 15' 11"} (J2000)
POINT_ROLL:      107.154d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75816.69 SOD {21:03:36.69} UT,   181.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.169
N_STARS:         190
X_OFFSET:        507 [pixels]
Y_OFFSET:        535 [pixels]
X_MAX:           1466 [pixels]
Y_MAX:           1494 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01104343000msufc0181.fits
SUN_POSTN:        35.23d {+02h 20m 55s}  +14.04d {+14d 02' 23"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.90d {+00h 15m 37s}   -2.67d {-02d 40' 16"}
MOON_DIST:        86.43 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:07:08 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.859d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.253d {-56d 15' 11"} (J2000)
POINT_ROLL:      107.154d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75816.69 SOD {21:03:36.69} UT,   181.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.169
N_STARS:         190
X_OFFSET:        507 [pixels]
Y_OFFSET:        535 [pixels]
X_MAX:           1466 [pixels]
Y_MAX:           1494 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01104343000msufc0181.fits
SUN_POSTN:        35.23d {+02h 20m 55s}  +14.04d {+14d 02' 23"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.90d {+00h 15m 37s}   -2.67d {-02d 40' 13"}
MOON_DIST:        86.43 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:08:21 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.859d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.253d {-56d 15' 11"} (J2000)
ROLL:            107.154d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75816.69 SOD {21:03:36.69} UT,   181.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     672786245
X_OFFSET:        826 [pixels]
Y_OFFSET:        854 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       986
Y_GRB_POS:       1014
BINNING_INDEX:   1
IM_URL:          sw01104343000msuni0211.fits
SUN_POSTN:        35.23d {+02h 20m 55s}  +14.04d {+14d 02' 24"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.91d {+00h 15m 39s}   -2.67d {-02d 39' 55"}
MOON_DIST:        86.44 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:08:29 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.859d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.253d {-56d 15' 11"} (J2000)
ROLL:            107.154d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75816.69 SOD {21:03:36.69} UT,   181.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     672786245
X_OFFSET:        826 [pixels]
Y_OFFSET:        854 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       986
Y_GRB_POS:       1014
BINNING_INDEX:   1
IM_URL:          sw01104343000msuni0211.fits
SUN_POSTN:        35.23d {+02h 20m 55s}  +14.04d {+14d 02' 24"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.92d {+00h 15m 40s}   -2.66d {-02d 39' 53"}
MOON_DIST:        86.44 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:10:55 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     1104343,   Seg_Num: 0
GRB_RA:          275.8888d {+18h 23m 33.31s} (J2000),
                 276.3597d {+18h 25m 26.32s} (current),
                 274.8332d {+18h 19m 19.95s} (1950)
GRB_DEC:         -56.2550d {-56d 15' 18.0"} (J2000),
                 -56.2417d {-56d 14' 30.2"} (current),
                 -56.2810d {-56d 16' 51.6"} (1950)
GRB_ERROR:       0.6 [arcsec radius, statistical only]
GRB_MAG:         17.22 +/- 0.14 [mag]
FILTER:          10, White
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75813.00 SOD {21:03:33.00} UT,   178.0 [sec] since BAT Trigger Time
SUN_POSTN:        35.23d {+02h 20m 56s}  +14.04d {+14d 02' 26"}
SUN_DIST:        117.52 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.94d {+00h 15m 44s}   -2.65d {-02d 39' 17"}
MOON_DIST:        86.45 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.61 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      273.89,-32.90 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT UVOT Position Notice.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        Result based on Genie data.  
COMMENTS:        Notice generated automatically.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:11:59 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 05"} (J2000)
POINT_ROLL:      107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75974.86 SOD {21:06:14.86} UT,   339.9 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.673
N_STARS:         190
X_OFFSET:        267 [pixels]
Y_OFFSET:        295 [pixels]
X_MAX:           1706 [pixels]
Y_MAX:           1734 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01104343000msufc0339.fits
SUN_POSTN:        35.23d {+02h 20m 56s}  +14.04d {+14d 02' 27"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.94d {+00h 15m 46s}   -2.65d {-02d 39' 01"}
MOON_DIST:        86.47 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:13:28 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 05"} (J2000)
ROLL:            107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75974.86 SOD {21:06:14.86} UT,   339.9 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     672786403
X_OFFSET:        826 [pixels]
Y_OFFSET:        854 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       986
Y_GRB_POS:       1014
BINNING_INDEX:   1
IM_URL:          sw01104343000msuni0369.fits
SUN_POSTN:        35.23d {+02h 20m 56s}  +14.04d {+14d 02' 28"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.96d {+00h 15m 49s}   -2.64d {-02d 38' 39"}
MOON_DIST:        86.48 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:12:23 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 05"} (J2000)
POINT_ROLL:      107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75974.86 SOD {21:06:14.86} UT,   339.9 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.673
N_STARS:         190
X_OFFSET:        267 [pixels]
Y_OFFSET:        295 [pixels]
X_MAX:           1706 [pixels]
Y_MAX:           1734 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01104343000msufc0339.fits
SUN_POSTN:        35.23d {+02h 20m 56s}  +14.04d {+14d 02' 27"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.95d {+00h 15m 47s}   -2.65d {-02d 38' 55"}
MOON_DIST:        86.47 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:19:20 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 04"} (J2000)
POINT_ROLL:      107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  76505.62 SOD {21:15:05.62} UT,   870.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.203
N_STARS:         190
X_OFFSET:        267 [pixels]
Y_OFFSET:        295 [pixels]
X_MAX:           1706 [pixels]
Y_MAX:           1734 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01104343000msufc0870.fits
SUN_POSTN:        35.24d {+02h 20m 57s}  +14.04d {+14d 02' 33"}
SUN_DIST:        117.54 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        4.00d {+00h 16m 01s}   -2.62d {-02d 37' 12"}
MOON_DIST:        86.53 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:19:38 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 04"} (J2000)
POINT_ROLL:      107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  76505.62 SOD {21:15:05.62} UT,   870.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.203
N_STARS:         190
X_OFFSET:        267 [pixels]
Y_OFFSET:        295 [pixels]
X_MAX:           1706 [pixels]
Y_MAX:           1734 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01104343000msufc0870.fits
SUN_POSTN:        35.24d {+02h 20m 57s}  +14.04d {+14d 02' 33"}
SUN_DIST:        117.54 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        4.01d {+00h 16m 01s}   -2.62d {-02d 37' 08"}
MOON_DIST:        86.53 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:21:05 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 04"} (J2000)
ROLL:            107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  76505.62 SOD {21:15:05.62} UT,   870.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     672786934
X_OFFSET:        826 [pixels]
Y_OFFSET:        854 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       986
Y_GRB_POS:       1014
BINNING_INDEX:   1
IM_URL:          sw01104343000msuni0900.fits
SUN_POSTN:        35.24d {+02h 20m 57s}  +14.04d {+14d 02' 34"}
SUN_DIST:        117.54 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        4.02d {+00h 16m 04s}   -2.61d {-02d 36' 46"}
MOON_DIST:        86.54 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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:     Wed 27 Apr 22 21:21:19 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 04"} (J2000)
ROLL:            107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  76505.62 SOD {21:15:05.62} UT,   870.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     672786934
X_OFFSET:        826 [pixels]
Y_OFFSET:        854 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       986
Y_GRB_POS:       1014
BINNING_INDEX:   1
IM_URL:          sw01104343000msuni0900.fits
SUN_POSTN:        35.24d {+02h 20m 57s}  +14.04d {+14d 02' 34"}
SUN_DIST:        117.54 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        4.02d {+00h 16m 05s}   -2.61d {-02d 36' 43"}
MOON_DIST:        86.54 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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 #31960
A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), C. Gronwall (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), S. Laha (GSFC/UMBC), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team:
At 21:00:34 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220427A (trigger=1104343). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 275.869, -56.253 which is
```
   RA(J2000) = 18h 23m 29s
   Dec(J2000) = -56d 15' 09"
```
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 80 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~10 sec after the trigger.
The XRT began observing the field at 21:03:33.0 UT, 178.1 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 275.88860, -56.25508 which is equivalent to:
```
   RA(J2000)  = 18h 23m 33.26s
   Dec(J2000) = -56d 15' 18.3"
```
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This location is 39 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 https://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 (1.02 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.9 (+3.18/-2.73) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 181 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at
```
RA(J2000) = 18:23:33.32 = 275.88882    
DEC(J2000) = -56:15:18.3 = -56.25507    
```
with a 90%-confidence error radius of about 0.61 arc sec. This position is 1.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.23 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.097.
The original BAT Position Notice found an approximate coincidence (~10 arcmin) with the position of IGR J18244-5622 (which in turn is coincident with the Sey2 galaxy IC 4709 at z=0.017). However, the position of the X-ray and Optical counterpart excludes this source and galaxy, indicating that this is a new GRB.
Burst Advocate for this burst is A. D'Ai (antonino.dai AT 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/)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Apr 22 21:13:41 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1104343,   Seg_Num: 0
POINT_RA:        275.860d {+18h 23m 26s} (J2000)
POINT_DEC:       -56.252d {-56d 15' 05"} (J2000)
ROLL:            107.152d
IMG_START_DATE:  19696 TJD;   117 DOY;   22/04/27
IMG_START_TIME:  75974.86 SOD {21:06:14.86} UT,   339.9 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     672786403
X_OFFSET:        826 [pixels]
Y_OFFSET:        854 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       986
Y_GRB_POS:       1014
BINNING_INDEX:   1
IM_URL:          sw01104343000msuni0369.fits
SUN_POSTN:        35.23d {+02h 20m 56s}  +14.04d {+14d 02' 28"}
SUN_DIST:        117.53 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:        3.96d {+00h 15m 50s}   -2.64d {-02d 38' 36"}
MOON_DIST:        86.48 [deg]
MOON_ILLUM:      9 [%]
GAL_COORDS:      338.51,-18.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      273.87,-32.89 [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 #31962
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team.
Using 1603 s of XRT Photon Counting mode data and 3 UVOT images for GRB 220427A, 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 = 275.88811, -56.25541 which is equivalent to:
```
RA (J2000): 18h 23m 33.15s
Dec (J2000): -56d 15' 19.5"
```
with an uncertainty of 2.5 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 #31963
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto) and A. D'Ai report on behalf of the Swift-XRT team:
We have analysed 6.1 ks of XRT data for GRB 220427A (D'Ai et al. GCN Circ. 31960), from 162 s to 30.4 ks after the BAT trigger. The data comprise 37 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 31962).
The light curve can be modelled with a power-law decay with a decay index of alpha=1.05 (+0.05, -0.04).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.01 (+/-0.15). The best-fitting absorption column is 1.6 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 1.0 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.6 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 1.0 x 10^21 cm^-2
Excess significance: 2.1 sigma
Photon index:	     2.01 (+/-0.15)
```
If the light curve continues to decay with a power-law decay index of 1.05, the count rate at T+24 hours will be 6.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x 10^-13 (2.8 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/01104343.
This circular is an official product of the Swift-XRT team.
GCN Circular #31964
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long GRB 220427A (Swift detection: D'Ai et al., GCN Circ. 31960) triggered Konus-Wind (KW) at T0=75645.009 s UT (21:00:45.009).
The burst light curve shows a single pulse, which starts at ~T0-3 s and has a total duration of ~15 s. The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB220427_T75645/
As observed by Konus-Wind, the burst had a fluence of (1.0 � 0.3)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.256 s, of (2.5 � 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
A time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is well fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.04(-0.30,+0.43) and Ep = 503(-204,+757) keV (chi2 = 77/97 dof). A fit to this spectrum by the Band GRB function is poorly constrained, it results in the best fit values of alpha~-0.6, Ep~260 keV, and the high energy photon index beta ~ -2.0 (chi2 = 77/96 dof).
All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.
GCN Circular #31967
A. de Ugarte Postigo (Artemis/OCA), H. Fausey (George Washington University), D. A. Kann (HETH/IAA-CSIC), D. B. Malesani (Radboud Univ. and DAWN/NBI), P. Jakobsson (U. of Iceland), A. Saccardi (GEPI, Observatoire de Paris) and B. Schneider (CEA Paris-Saclay), report on behalf of the Stargate Consortium:
We observed the field of GRB 220427A (D'Ai et al., GCN 31960) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In images taken with the acquisition camera 7.9 hr after the GRB we measure for the optical afterglow the following AB magnitudes (calibrated against 2 field stars from the SkyMapper catalogue):
```
g' = 22.40 +/- 0.09 mag
r' = 22.04 +/- 0.08 mag
z' = 20.81 +/- 0.08 mag
```
No useful spectroscopy could be secured.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Jonathan Smoker and Rob van Holstein.
GCN Circular #31968
M. Stamatikos (OSU) S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU) (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 220427A (trigger #1104343) (D'Ai et al., GCN Circ. 31960). The BAT ground-calculated position is RA, Dec = 275.922, -56.257 deg which is
```
   RA(J2000)  =  18h 23m 41.2s
   Dec(J2000) = -56d 15' 23.7"
```
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 62%.
The mask-weighted light curve shows a single-peaked structure that starts at ~T+3 s and peaks at ~T+8 s, and followed by a long tail emission that ends at ~T+70 s. T90 (15-350 keV) is 57.2 +- 12.2 sec (estimated error including systematics).
The time-averaged spectrum from T+3.09 to T+68.06 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.23 +- 0.13. The fluence in the 15-150 keV band is 2.1 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+7.83 sec in the 15-150 keV band is 3.0 +- 0.3 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/1104343/BA/
GCN Circular #31991
A. Klotz (CNRS-OMP-IRAP), M. Blazek (FZU), N. Christensen (OCA/Artemis), D. Datashvili (AbAO), P. A. Duverne (IJCLAB), F. Z. Guo (THU), N. Kochiashvili (AbAO), M. Lamoureux (UCLouvain), N. Leroy (IJCLAB), T. Sadibekova (AIM/CEA-UPS), P. Thierry (AGORA), A. Simon (Kyiv Univ), L. Eymar, S. Antier, M. Boer, A. de Ugarte Postigo (all CNRS-OCA-ARTEMIS), D. A. Kann (IAA-CSIC), A. Iskandar (XAO), A. Baransky (Kyiv Univ), N. Sasaki (NEPA/UEA), W. Corradi (LNA), I. Tosta e Melo (INFN-LNS), J. P. Vignes (KNC), V. Godunova (IC ICAMER) report on behalf of GRANDMA collaboration:
The GRANDMA telescope network responded promptly to the alert of GRB 220427A (A. D'Ai et al. GCN 31960, M. R. Goad et al. GCN 31962, A. P. Beardmore et al. GCN 31963, M. Stamatikos et al. GCN 31968).
The first observations with TAROT La Reunion started 2.35 min after the Swift/BAT trigger time, and were followed by observations with the Les Makes T60. Later observations were obtained by the CDK40 0.4m telescope that is part of the Kilonova-Cather citizen science programme. The light curve peaked around 4.5 min after the burst and then decayed steadily with a decay slope of alpha ~ 1.3, where F ~ t^-alpha.
The following table displays part of our photometry with magnitudes given in the AB system and calibrated with respect to field stars from the SkyMapper catalogue, using the MUPHOTEN pipeline (Duverne et al. 2021).
```
T-T0 (hr)| MJD   | Obser.     |Exposure| Filter| Mag +/- err (AB)
_________________________________________________________________
0.04 |59696.878276| TRE       |     60s| Clear | 15.7 +/- 0.2
1.38 |59696.932836| Makes-T60 | 15x120s| Clear | 20.1 +/- 0.1
1.65 |59696.944294| Makes-T60 | 15x120s| Clear | 20.4 +/- 0.2
11.37|59697.3491  | KNC-CDK400| 10x300s| R     | > 21.0
```
T-T0 is the mid-time of observations related to the BAT trigger time.
These detections are consistent with the previous report of detections by the VLT (A. de Ugarte Postigo et al. GCN 31967).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular #31995
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (College of Marin) report on behalf of a larger collaboration:
We observed Swift GRB220427A (D'Ai et al. GCN 31960) with the LCO 1-m Sinistro instrument at the South African Astronomical Observatory site, on April 27, from 22:57 to 23:24 UT (corresponding to 1.95 to 2.40 hours from the GRB trigger time) with the Bessel R and I filters.
We performed a series of 3x300s exposures in I and R bands. We detect an optical counterpart at the location of the Swift optical counterpart that is consistent with other optical detections (Ugarte Postigo, et al., GCN 31967; Klotz, et al., GCN 31991). The following magnitudes are calculated using the USNO-B.1 catalog as reference:
```
R=20.35+/-0.12
I=20.15+/-0.30
```
These magnitudes are not corrected for galactic extinction.
R.S. is funded by NSF AST grant #1831682
GCN Circular #32032
S. de Wet (UCT), D.B. Malesani (Radboud), P.M. Vreeswijk (Radboud) and P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT consortium:
Following the detection of GRB 220427A by Swift and its X-ray counterpart (D'Ai et al., GCN 31960), the 0.6m MeerLICHT telescope, located at Sutherland, South Africa obtained a repeating series of 60 s images in the q,u,q,g,q,r,q,i,q,z bands. Observations began at 2022-04-27, 23:41:48 UT, 2 hours 41 minutes after the Swift detection, and continued for a further 4.5 hours. The median seeing was 2" under clear skies.
No source is detected at the optical transient position (D'Ai et al., GCN 31960) in any individual 60 s exposure, hence we co-added all the images in each filter and performed forced photometry at the transient position. The afterglow is detected with a SNR of at least 7 in the g,r,i,z and q bands. We report the following upper limit and AB magnitudes, at 3 hours 50 minutes post-trigger:
```
u > 21.83
g = 21.26 +/- 0.11
q = 21.14 +/- 0.09
r = 20.88 +/- 0.12
i = 20.49 +/- 0.13
z = 19.59 +/- 0.15
```
MeerLICHT is built and run by a consortium consisting of Radboud University, University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam.

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