Gamma-ray Burst 230420A

(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 20 Apr 23 10:19:40 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1164980,   Seg_Num: 0
GRB_RA:          161.013d {+10h 44m 03s} (J2000),
                 161.338d {+10h 45m 21s} (current),
                 160.314d {+10h 41m 15s} (1950)
GRB_DEC:         +32.087d {+32d 05' 11"} (J2000),
                 +31.964d {+31d 57' 49"} (current),
                 +32.349d {+32d 20' 57"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       6310 [cnts]    Image_Peak=257 [image_cnts]
TRIGGER_DUR:     4.096 [sec] 
TRIGGER_INDEX:   298     E_range: 25-100 keV
BKG_INTEN:       49004 [cnts]
BKG_TIME:        37080.86 SOD {10:18:00.86} UT
BKG_DUR:         40 [sec]
GRB_DATE:        20054 TJD;   110 DOY;   23/04/20
GRB_TIME:        37141.08 SOD {10:19:01.08} UT
GRB_PHI:         -162.79 [deg]
GRB_THETA:        10.48 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     11.87 [sigma]
IMAGE_SIGNIF:    7.98 [sigma]
MERIT_PARAMS:     +1  +0  +0  +2  +2  -2  +0  +0 +46  +0 
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 08"}
SUN_DIST:        117.71 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.13d {+02h 04m 31s}  +12.68d {+12d 40' 31"}
MOON_DIST:       114.72 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.01, 61.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      149.91, 22.19 [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 = 150.82,-8.29 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:20:57 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1164980,   Seg_Num: 0
GRB_RA:          161.0505d {+10h 44m 12.11s} (J2000),
                 161.3752d {+10h 45m 30.04s} (current),
                 160.3520d {+10h 41m 24.46s} (1950)
GRB_DEC:         +32.1064d {+32d 06' 23.0"} (J2000),
                 +31.9836d {+31d 59' 00.9"} (current),
                 +32.3692d {+32d 22' 08.9"} (1950)
GRB_ERROR:       5.0 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       3.05e-09 [erg/cm2/sec]
GRB_SIGNIF:      9.59 [sigma]
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37232.90 SOD {10:20:32.90} UT,   91.8 [sec] since BAT Trigger Time
TAM[0-3]:        327.63 237.12 261.59 243.65
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 09"}
SUN_DIST:        117.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.14d {+02h 04m 34s}  +12.68d {+12d 40' 50"}
MOON_DIST:       114.72 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      194.96, 62.01 [deg] galactic lon,lat of the burst
ECL_COORDS:      149.93, 22.22 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 2.24 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:21:07 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
GRB_RA:          161.0505d {+10h 44m 12.1s} (J2000),
                 161.3752d {+10h 45m 30.0s} (current),
                 160.3520d {+10h 41m 24.4s} (1950)
GRB_DEC:         +32.1064d {+32d 06' 23.0"} (J2000),
                 +31.9836d {+31d 59' 00.9"} (current),
                 +32.3692d {+32d 22' 08.9"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       92 [cnts]
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37232.90 SOD {10:20:32.90} UT,   91.8 [sec] since BAT Trigger Time
CENTROID_X:      331.52,  raw= 332  [pixels]
CENTROID_Y:      250.10,  raw= 250  [pixels]
ROLL:            306.19 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -113.14
GRB_POS_XRT_Z:   56.88
IMAGE_URL:       sw01164980000msxps_rw.img
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 09"}
SUN_DIST:        117.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.14d {+02h 04m 34s}  +12.68d {+12d 40' 52"}
MOON_DIST:       114.72 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      194.96, 62.01 [deg] galactic lon,lat of the burst
ECL_COORDS:      149.93, 22.22 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:21:09 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
GRB_RA:          161.0505d {+10h 44m 12.1s} (J2000),
                 161.3752d {+10h 45m 30.0s} (current),
                 160.3520d {+10h 41m 24.4s} (1950)
GRB_DEC:         +32.1064d {+32d 06' 23.0"} (J2000),
                 +31.9836d {+31d 59' 00.9"} (current),
                 +32.3692d {+32d 22' 08.9"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       92 [cnts]
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37232.90 SOD {10:20:32.90} UT,   91.8 [sec] since BAT Trigger Time
CENTROID_X:      331.52,  raw= 332  [pixels]
CENTROID_Y:      250.10,  raw= 250  [pixels]
ROLL:            306.19 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -113.14
GRB_POS_XRT_Z:   56.88
IMAGE_URL:       sw01164980000msxps_rw.img
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 09"}
SUN_DIST:        117.72 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.14d {+02h 04m 34s}  +12.68d {+12d 40' 53"}
MOON_DIST:       114.72 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      194.96, 62.01 [deg] galactic lon,lat of the burst
ECL_COORDS:      149.93, 22.22 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:23:21 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1164980,   Seg_Num: 0
GRB_RA:          161.013d {+10h 44m 03s} (J2000),
                 161.338d {+10h 45m 21s} (current),
                 160.314d {+10h 41m 15s} (1950)
GRB_DEC:         +32.087d {+32d 05' 11"} (J2000),
                 +31.964d {+31d 57' 49"} (current),
                 +32.349d {+32d 20' 57"} (1950)
GRB_DATE:        20054 TJD;   110 DOY;   23/04/20
GRB_TIME:        37141.08 SOD {10:19:01.08} UT
TRIGGER_INDEX:   298
GRB_PHI:         -162.79 [deg]
GRB_THETA:        10.48 [deg]
DELTA_TIME:      57.00 [sec]
TRIGGER_DUR:     4.096 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     11.87 [sigma]
IMAGE_SIGNIF:    7.98 [sigma]
LC_URL:          sw01164980000msb.lc
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 11"}
SUN_DIST:        117.71 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.16d {+02h 04m 39s}  +12.69d {+12d 41' 25"}
MOON_DIST:       114.69 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.01, 61.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      149.91, 22.19 [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 = 150.82,-8.29 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:23:42 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.013d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.090d {+32d 05' 25"} (J2000)
POINT_ROLL:      306.190d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37240.61 SOD {10:20:40.61} UT,   99.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.064
N_STARS:         15
X_OFFSET:        456 [pixels]
Y_OFFSET:        536 [pixels]
X_MAX:           1415 [pixels]
Y_MAX:           1495 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01164980000msufc0099.fits
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 12"}
SUN_DIST:        117.71 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.16d {+02h 04m 39s}  +12.69d {+12d 41' 30"}
MOON_DIST:       114.68 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:23:59 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.013d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.090d {+32d 05' 25"} (J2000)
POINT_ROLL:      306.190d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37240.61 SOD {10:20:40.61} UT,   99.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.064
N_STARS:         15
X_OFFSET:        456 [pixels]
Y_OFFSET:        536 [pixels]
X_MAX:           1415 [pixels]
Y_MAX:           1495 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01164980000msufc0099.fits
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 12"}
SUN_DIST:        117.71 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.17d {+02h 04m 40s}  +12.69d {+12d 41' 34"}
MOON_DIST:       114.68 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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 20 Apr 23 10:25:03 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.013d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.090d {+32d 05' 25"} (J2000)
ROLL:            306.190d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37240.61 SOD {10:20:40.61} UT,   99.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     703678871
X_OFFSET:        802 [pixels]
Y_OFFSET:        1120 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       962
Y_GRB_POS:       1280
BINNING_INDEX:   1
IM_URL:          sw01164980000msuni0131.fits
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 13"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.18d {+02h 04m 42s}  +12.70d {+12d 41' 50"}
MOON_DIST:       114.67 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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:     Thu 20 Apr 23 10:25:09 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.013d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.090d {+32d 05' 25"} (J2000)
ROLL:            306.190d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37240.61 SOD {10:20:40.61} UT,   99.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     703678871
X_OFFSET:        802 [pixels]
Y_OFFSET:        1120 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       962
Y_GRB_POS:       1280
BINNING_INDEX:   1
IM_URL:          sw01164980000msuni0131.fits
SUN_POSTN:        28.00d {+01h 52m 00s}  +11.50d {+11d 30' 13"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.18d {+02h 04m 43s}  +12.70d {+12d 41' 51"}
MOON_DIST:       114.67 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_image.fits.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:30:52 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.014d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
POINT_ROLL:      306.192d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37399.07 SOD {10:23:19.07} UT,   258.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.539
N_STARS:         16
X_OFFSET:        482 [pixels]
Y_OFFSET:        800 [pixels]
X_MAX:           1441 [pixels]
Y_MAX:           1759 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01164980000msufc0257.fits
SUN_POSTN:        28.01d {+01h 52m 01s}  +11.50d {+11d 30' 18"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.23d {+02h 04m 55s}  +12.72d {+12d 43' 15"}
MOON_DIST:       114.62 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:31:02 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.014d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
POINT_ROLL:      306.192d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37399.07 SOD {10:23:19.07} UT,   258.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.539
N_STARS:         16
X_OFFSET:        482 [pixels]
Y_OFFSET:        800 [pixels]
X_MAX:           1441 [pixels]
Y_MAX:           1759 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01164980000msufc0257.fits
SUN_POSTN:        28.01d {+01h 52m 01s}  +11.50d {+11d 30' 18"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.23d {+02h 04m 55s}  +12.72d {+12d 43' 17"}
MOON_DIST:       114.62 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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 20 Apr 23 10:32:00 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.014d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
ROLL:            306.192d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37399.07 SOD {10:23:19.07} UT,   258.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     703679030
X_OFFSET:        802 [pixels]
Y_OFFSET:        1120 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       962
Y_GRB_POS:       1280
BINNING_INDEX:   1
IM_URL:          sw01164980000msuni0289.fits
SUN_POSTN:        28.01d {+01h 52m 02s}  +11.51d {+11d 30' 19"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.24d {+02h 04m 57s}  +12.73d {+12d 43' 31"}
MOON_DIST:       114.61 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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:     Thu 20 Apr 23 10:32:07 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.014d {+10h 44m 03s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
ROLL:            306.192d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37399.07 SOD {10:23:19.07} UT,   258.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     703679030
X_OFFSET:        802 [pixels]
Y_OFFSET:        1120 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       962
Y_GRB_POS:       1280
BINNING_INDEX:   1
IM_URL:          sw01164980000msuni0289.fits
SUN_POSTN:        28.01d {+01h 52m 02s}  +11.51d {+11d 30' 19"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.24d {+02h 04m 57s}  +12.73d {+12d 43' 33"}
MOON_DIST:       114.61 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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 Circular #33658
N. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB), R. A. J. Eyles-Ferris (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester), T. M. Parsotan (GSFC/UMBC/CRESSTII), C. Salvaggio (INAF-OAB) and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team:
At 10:19:01 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 230420A (trigger=1164980). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 161.013, +32.087 which is
```
   RA(J2000) = 10h 44m 03s
   Dec(J2000) = +32d 05' 11"
```
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 30 sec. The peak count rate was ~800 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 10:20:32.9 UT, 91.8 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source with an enhanced position: RA, Dec 161.04899, 32.10766 which is equivalent to:
```
   RA(J2000)  = 10h 44m 11.76s
   Dec(J2000) = +32d 06' 27.6"
```
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 132 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. We cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.71 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.1 (+2.19/-1.93) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 3.05e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 99 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.017.
Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu). 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:     Thu 20 Apr 23 10:38:03 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.015d {+10h 44m 04s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
POINT_ROLL:      306.193d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  38004.63 SOD {10:33:24.63} UT,   863.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.005
N_STARS:         27
X_OFFSET:        242 [pixels]
Y_OFFSET:        560 [pixels]
X_MAX:           1681 [pixels]
Y_MAX:           1999 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01164980000msufc0863.fits
SUN_POSTN:        28.01d {+01h 52m 02s}  +11.51d {+11d 30' 24"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.29d {+02h 05m 10s}  +12.75d {+12d 44' 59"}
MOON_DIST:       114.55 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Apr 23 10:39:28 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.015d {+10h 44m 04s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
ROLL:            306.193d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  38004.63 SOD {10:33:24.63} UT,   863.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     703679635
X_OFFSET:        801 [pixels]
Y_OFFSET:        1119 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       961
Y_GRB_POS:       1279
BINNING_INDEX:   1
IM_URL:          sw01164980000msuni0895.fits
SUN_POSTN:        28.01d {+01h 52m 03s}  +11.51d {+11d 30' 25"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.30d {+02h 05m 13s}  +12.76d {+12d 45' 20"}
MOON_DIST:       114.54 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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 20 Apr 23 10:38:12 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.015d {+10h 44m 04s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
POINT_ROLL:      306.193d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  38004.63 SOD {10:33:24.63} UT,   863.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.005
N_STARS:         27
X_OFFSET:        242 [pixels]
Y_OFFSET:        560 [pixels]
X_MAX:           1681 [pixels]
Y_MAX:           1999 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01164980000msufc0863.fits
SUN_POSTN:        28.01d {+01h 52m 02s}  +11.51d {+11d 30' 24"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.29d {+02h 05m 10s}  +12.75d {+12d 45' 02"}
MOON_DIST:       114.55 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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 20 Apr 23 10:39:42 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1164980,   Seg_Num: 0
POINT_RA:        161.015d {+10h 44m 04s} (J2000)
POINT_DEC:       +32.091d {+32d 05' 29"} (J2000)
ROLL:            306.193d
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  38004.63 SOD {10:33:24.63} UT,   863.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     703679635
X_OFFSET:        801 [pixels]
Y_OFFSET:        1119 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       961
Y_GRB_POS:       1279
BINNING_INDEX:   1
IM_URL:          sw01164980000msuni0895.fits
SUN_POSTN:        28.01d {+01h 52m 03s}  +11.51d {+11d 30' 25"}
SUN_DIST:        117.70 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.31d {+02h 05m 14s}  +12.76d {+12d 45' 23"}
MOON_DIST:       114.54 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      195.00, 61.98 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      149.91, 22.20 [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 20 Apr 23 10:31:54 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1164980,   Seg_Num: 0
GRB_RA:          161.0486d {+10h 44m 11.66s} (J2000),
                 161.3733d {+10h 45m 29.58s} (current),
                 160.3500d {+10h 41m 24.01s} (1950)
GRB_DEC:         +32.1077d {+32d 06' 27.7"} (J2000),
                 +31.9849d {+31d 59' 05.6"} (current),
                 +32.3705d {+32d 22' 13.6"} (1950)
GRB_ERROR:       1.9 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20054 TJD;   110 DOY;   23/04/20
IMG_START_TIME:  37343.00 SOD {10:22:23.00} UT,   201.9 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        28.01d {+01h 52m 01s}  +11.51d {+11d 30' 19"}
SUN_DIST:        117.71 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:       31.24d {+02h 04m 57s}  +12.72d {+12d 43' 30"}
MOON_DIST:       114.62 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      194.96, 62.01 [deg] galactic lon,lat of the burst
ECL_COORDS:      149.93, 22.22 [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 0.11% < P(seren) < 0.58%.

GCN Circular #33661
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 1619 s of XRT Photon Counting mode data and 3 UVOT images for GRB 230420A, 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 = 161.04816, +32.10769 which is equivalent to:
```
RA (J2000): 10h 44m 11.56s
Dec (J2000): +32d 06' 27.7"
```
with an uncertainty of 2.2 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 #33662
R. Strausbaugh (University of Minnesota), A. Cucchiara (NASA) report on behalf of a larger collaboration:
We observed the GRB 230420A (Klingler et al., GCN 33658) field with the LCOGT 1-meter Sinistro instrument at the Teide Observatory, Tenerife site, on April 20, from 20:28 to 20:55 UT (corresponding to 11.15 to 11.72 hours from the GRB trigger time) with the SDSS r and i filters.
We performed a series of 3x300s exposures in each band. We do not detect a source within the Swift-XRT enhanced error region (Osborne et al., GCN 33661) in either band.
The following upper limits are calculated using the PanSTARRS catalog as reference:
```
r > 22.3
i > 21.8
```
These magnitudes are not corrected for galactic extinction.
GCN Circular #33663
Y.-D. Hu, E. Fernandez-Garcia, A. J. Castro-Tirado, I. Perez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), D. Hiriart and W. H. Lee (UNAM), C. J. Perez del Pulgar (UMA) and I. Carrasco (SMA) and I. H. Park (SKKU), on behalf of a larger collaboration, report:
Following the detection of GRB 230420A by Swift (Klingler et al. GCNC 33658), the BOOTES-5/JGT 0.6m robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically observed the GRB location starting on Apr. 20, 10:21:03 UT (~ 122 s after trigger). A series of images in clear filter were gathered. A new optical transient was found within the enhanced Swift/XRT position (Osborne et al. GCNC 33661) for which we measure a magnitude of 17.7 on the initial 10 s exposure frame, which we propose to be the optical afterglow for GRB 230420A.
We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for their excellent support.
GCN Circular #33664
S.Y. Fu, S.Q. Jiang, X. Liu, T.H. Lu, D Xu (NAOC), Z.P. Zhu (NAOC, HUST), S.W. Luo, M.M. Yang, Z. K. Feng (GYZO, NAOC) report
We observed the field of GRB 230420A detected by Swift (Klingler et al., GCN 33658) with the 0.5-meter Gaoyazi Optical Telescope (GOT) located at Gaoyazi, Xinjiang, China. Observations started at 17:23:51 UT on 2023-04-20, i.e., 0.30 days after the Swift/BAT trigger, and 20 x 180 s images were obtained in the Sloan r filter.
No optical source is detected in our stacked image at the enhanced XRT position (Osborne et al,. GCN 33661), down to a limiting (3-sigma) magnitude of r > 21.6 at 0.32 days post-burst, calibrated with nearby PanSTARRS stars.
GCN Circular #33665
S.Y. Fu (NAOC), K.E. Heintz (DAWN/NBI), D.B. Malesani (Radboud, DAWN/NBI), D. Xu (NAOC), M. Linares (NTNU & UPC), M. Turchetta (NTNU) report on behalf of a larger collaboration:
We observed the field of GRB 230420A detected by Swift (Klingler et al., GCN 33658) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 00:31:32 UT on 2023-04-21, i.e., ~14.2 hr after the Swift/BAT trigger, and 3 x 300 s images in the Sloan r-filter and 5 x 200 s images in the Sloan z-filter were obtained, respectively.
We detect an uncatalogued source in the stacked images within the enhanced XRT error circle (Osborne et al., GCN 33661) at coordinates:
```
R.A. (J2000) = 10:44:11.55
Dec. (J2000) = +32:06:28.34
```
with an uncertainty of ~0.3 arcsec. The source has m(r) = 23.2 +/- 0.2 (AB) at 14.34 hr post-burst and m(z) = 22.3 +/- 0.2 (AB) at 14.64 hr post-burst, calibrated with nearby field stars from the Pan-STARRS catalog.
This source is likely the same as the one observed by BOOTES-5/JGT (Hu et al., GCN 33663), as both sources lie within the very small XRT error circle. The fading confirms that this source is the optical afterglow of GRB 230420A.
GCN Circular #33666
N. Higuchi, I. Takahashi, M. Sasada, S. Sato, R. Hosokawa, M. Niwano, Y. Yatsu (Tokyo Tech), K. L. Murata (Kyoto U) and N. Kawai (Riken) report on behalf of the MITSuME collaboration:
We observed the field of GRB 230420A (N. J. Klingler et al. #33658, J.P. Osborne et al. #33661,R. Strausbaugh et al. #33662, Y.-D. Hu et al. #33663, S.Y. Fu et al. #33664, S.Y. Fu et al. #33665) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno.
The observation with a series of 60 sec exposures started at 2023-04-20 10:23:41 UT (280 seconds after the Swift/BAT detection). We stacked the images with good conditions. Here we report the Rc and Ic band magnitudes by the forced-photometry at the enhanced Swift/XRT position (J.P. Osborne et al. GCN Circular #33661), and the 5-sigma limit of the stacked images in the g' band.
```
T0+[sec] |MID-UT | T-EXP[sec] | magnitudes of forced-photometry

------------------------------------------------------------------------------------------------

 588 | 2023-04-20 10:28:49| 540 | g'>18.3, Rc=18.3+/- 0.3, Ic=17.3 +/- 0.2

------------------------------------------------------------------------------------------------
```
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).
GCN Circular #33667
E. Ambrosi (INAF-IASFPA) , S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR) and report on behalf of the Swift-XRT team: report on behalf of the Swift-XRT team:
We have analysed 7.2 ks of XRT data for GRB 230420A, from 98 s to 84.8 ks after the BAT trigger. The data comprise 102 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with an initial power-law decay with an index of alpha=4.13 (+0.26, -0.18), followed by a break at T+316 s to an alpha of 0.83 (+0.10, -0.07).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.59 (+/-0.09). The best-fitting absorption column is 4.6 (+2.5, -2.3) x 10^20 cm^-2, in excess of the Galactic value of 1.7 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.82 (+0.21, -0.11) 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 3.5 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.7 (+4.0, -0.0) x 10^20 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.82 (+0.21, -0.11)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01164980.
This circular is an official product of the Swift-XRT team.
GCN Circular #33670
T. Sakamoto (AGU), S. D. Barthelmy (GSFC), 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), M. Stamatikos (OSU) (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 230420A (trigger #1164980) (Klingler, et al., GCN Circ. 33658). The BAT ground-calculated position is RA, Dec = 161.040, 32.111 deg which is
```
   RA(J2000)  =  10h 44m 09.5s
   Dec(J2000) = +32d 06' 38.3"
```
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).The partial coding was 100%.
The mask-weighted light curve shows possible pre-trigger activity with extended emission out to ~100 seconds. T90 (15-350 keV) is 111.75 +- 12.02 sec (estimated error including systematics).
The time-averaged spectrum from T-34.75 to T+100.80 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.96 +- 0.46, and Epeak of 70.6 +- 28.2 keV (chi squared 53.29 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.7 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+1.41 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.64 +- 0.10 (chi squared 60.99 for 57 d.o.f.). 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/1164980/BA/
GCN Circular #33671
H. Fausey (GWU), B. Schneider (MIT), C. C. Thoene (ASU-CAS), D. B. Malesani (Radboud Univ. and DAWN/NBI), and S. Campana (INAF-OAB) report on behalf of the Stargate collaboration:
We observed the field of GRB230420A (Klinger et al., GCN33658) with the ESO VLT UT3 (Melipal) using the acquisition camera of the X-shooter spectrograph. We took a 300s r-band image on 2023 April 20.105 UT (16 hours after the BAT trigger).
At the coordinates of the optical afterglow (Hu et al., GCN 33663; Fu et al., GCN 33665), we detect a faint source with magnitude r' = 23.2 +/- 0.1 (AB). The magnitude is consistent, within the errors, to the value reported by Fu et al. (GCN 33665). We note the presence of a marginally-detected object in the Legacy Survey at the same coordinates, which, if real, could be the GRB host galaxy.
We acknowledge the excellent support from the ESO observing staff in Paranal, in particular Zahed Wahhaj.
GCN Circular #33673
S. R. Oates (U.Birmingham) and N. J. Klingler (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 230420A 99 s after the BAT trigger (Klingler et al., GCN Circ. 33658). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 33661) 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            99          249          147         >21.1
u_FC               258          508          246         >20.5
white               99         1190          353         >21.7
v                  590         4885          255         >19.5
b                  514         1165           58         >19.9
u                  258         1141          285         >20.6
w1                 814         5109           52         >19.1
w2                4481         4681          197         >19.8
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.017 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #33680
B. O'Connor (UMD, GWU), E. Hammerstein (UMD), S.B. Cenko (UMD, NASA-GSFC), report on behalf of a larger collaboration:
We observed GRB 230420A (Klingler et al. GCN 33658) with the Large Monolithic Imager (LMI) on the 4.3m Lowell Discovery Telescope (LDT). Observations began on 2023-04-23 at 05:14:37 UT corresponding to ~2.8 d after the GRB trigger. Observations were carried out in r-band and i-band for 1800 s each at airmass 1.05 under seeing of ~1.6".
At the location of the optical counterpart (Hu et al. GCN 33663, Fu et al. GCN 33665, Fausey et al. GCN 33671) we detect a weak source in each filter. We measure magnitudes r~25.0+/-0.4 AB mag and i~24.2+/-0.2 AB mag. This is likely dominated by the contribution from the possible host galaxy (Fausey et al. GCN 33671).
Magnitudes are calibrated against the PS1 catalog and are not corrected for Galactic extinction.
We thank the staff of the Lowell Discovery Telescope for assistance with these observations.
GCN Circular #33717
Y. Koyanagi, T. Sakamoto (AGU)
We observed the field of GRB 230420A detected by Swift (Klingler et al., GCN Circ. 33658) with the 14-inch AGU Robotic Optical Monitor for Astrophysical object - Narrow (AROMA-N) located at the Sagamihara campus of Aoyama Gakuin University.
13 images of 60 sec exposures were taken in the R filter starting from April 20 11:41:42 (UT) about 1.37 hours after the trigger and stopped on April 20 11:59:16 (UT). We do not detect the optical afterglow both in the individual images and the stacked image. The estimated five sigma upper limit of the combined image (total exposure of 780 sec) is ~17.1 mag using the USNO-B1 catalog.
GCN Circular #33725
N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), I. Reva (FAPI), V. Rumyantsev (CrAO), S. Belkin (IKI) report on behalf of GRB IKI FuN:
We observed the field of Swift GRB 230420A (Klingler et al. GCN 33658) with AZT-33IK telescope of Mondy observatory in R-filter on 2023-04-20 starting (UT) 13:31:08, with Zeiss-1000 telescope of of Tien Shan Astronomical Observatory on 2023-04-20 starting (UT) 22:11:07, with Shajn 2.6m telescope of CrAO on 2023-04-22 and 2023-04-23. We detect the afterglow (Hu et al., GCN 33663; Fu et al., GCN 33665; Fausey et al., GCN 33671; O'Connor et al., GCN 33680) in Mondy observatory and obtained upper limits in TSHAO and CrAO observatories. The afterglow is detected at coordinates of (J2000) 10 44 11.53 +32 06 28.4 which are compatible with NOT estimated coordinates (Fu et al., GCN 33665) and are within Swift XRT enhanced position (Osborneet al. GCN 33661).
Preliminary photometry of stacked images is following
```
Date       UT start t-T0     Exp.  Filter  OT   Err.  UL(3sigma) Observ.
                   (mid, days)  (s)
2023-04-20 13:31:08 0.15424 30*120 R       22.0 0.1   22.8      Mondy
2023-04-20 16:49:25 0.28431 20*120 R       22.7 0.3   22.7      Mondy
2023-04-20 22:11:07 0.36494 31*120 R       n/d  n/d   22.1      TSHAO
2023-04-21 15:23:44 1.25189 27*120 R       n/d  n/d   22.5      Mondy
2023-04-22 18:33:32 2.52854 49*120 R       n/d  n/d   22.6      CrAO
2023-04-23 19:22:36 3.41915 60*120 R       n/d  n/d   23.1      CrAO
2023-04-22+2023-04-23 2.97385 109*120 R    n/d  n/d   23.5      CrAO
```
The photometry is based on nearby USNO-B1.0 R2 stars.

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Jochen Greiner, last update: 06-May-2023 [Disclaimer]