Gamma-ray Burst 250331B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN/BACODINE POSITION NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:20:35 UT
  NOTICE_TYPE:     Swift-BAT GRB Position
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  GRB_RA:           71.381d {+04h 45m 31s} (J2000),
                    71.832d {+04h 47m 20s} (current),
                    70.488d {+04h 41m 57s} (1950)
  GRB_DEC:         +43.805d {+43d 48' 17"} (J2000),
                   +43.849d {+43d 50' 57"} (current),
                   +43.714d {+43d 42' 50"} (1950)
  GRB_ERROR:       3.00 [arcmin radius, statistical only]
  GRB_INTEN:       9790 [cnts]    Image_Peak=253 [image_cnts]
  TRIGGER_DUR:     4.096 [sec] 
  TRIGGER_INDEX:   448     E_range: 15-50 keV
  BKG_INTEN:       87148 [cnts]
  BKG_TIME:        15524.65 SOD {04:18:44.65} UT
  BKG_DUR:         40 [sec]
  GRB_DATE:        20765 TJD;    90 DOY;   25/03/31
  GRB_TIME:        15583.47 SOD {04:19:43.47} UT
  GRB_PHI:         -179.81 [deg]
  GRB_THETA:        39.82 [deg]
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     9.21 [sigma]
  IMAGE_SIGNIF:    7.17 [sigma]
  MERIT_PARAMS:     +1  +0  +0  +2  +1  -3  +0  +1 -39  +0 
  SUN_POSTN:         9.85d {+00h 39m 24s}   +4.24d {+04d 14' 22"}
  SUN_DIST:         67.11 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.78d {+02h 07m 06s}  +16.20d {+16d 12' 06"}
  MOON_DIST:        43.67 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.13 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:       75.68, 21.29 [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 = 67.82,17.39 [deg].  
  

• red DSS finding chart ps-file
  
  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:23:34 UT
  NOTICE_TYPE:     Swift-BAT GRB Lightcurve
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  GRB_RA:           71.381d {+04h 45m 31s} (J2000),
                    71.832d {+04h 47m 20s} (current),
                    70.488d {+04h 41m 57s} (1950)
  GRB_DEC:         +43.805d {+43d 48' 17"} (J2000),
                   +43.849d {+43d 50' 57"} (current),
                   +43.714d {+43d 42' 50"} (1950)
  GRB_DATE:        20765 TJD;    90 DOY;   25/03/31
  GRB_TIME:        15583.47 SOD {04:19:43.47} UT
  TRIGGER_INDEX:   448
  GRB_PHI:         -179.81 [deg]
  GRB_THETA:        39.82 [deg]
  DELTA_TIME:      39.00 [sec]
  TRIGGER_DUR:     4.096 [sec] 
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     9.21 [sigma]
  IMAGE_SIGNIF:    7.17 [sigma]
  LC_URL:          sw01299965000msb.lc
  SUN_POSTN:         9.85d {+00h 39m 24s}   +4.24d {+04d 14' 25"}
  SUN_DIST:         67.10 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.81d {+02h 07m 13s}  +16.21d {+16d 12' 52"}
  MOON_DIST:        43.64 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.13 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:       75.68, 21.29 [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 = 67.82,17.39 [deg].  
  

  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:25:05 UT
  NOTICE_TYPE:     Swift-XRT Nack-Position
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.380d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.801d {+43d 48' 05"} (J2000)
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  15897.34 SOD {04:24:57.34} UT,   313.9 [sec] since BAT Trigger Time
  COUNTS:          2    Min_needed= 20
  STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
  PH2_ITER:        1    Max_iter_allowed= 4
  ERROR_CODE:      1
  COMMENTS:        SWIFT-XRT Nack Position.  
  COMMENTS:        No source found in the image.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:28:12 UT
  NOTICE_TYPE:     Swift-BAT GRB Lightcurve
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  GRB_RA:           71.381d {+04h 45m 31s} (J2000),
                    71.832d {+04h 47m 20s} (current),
                    70.488d {+04h 41m 57s} (1950)
  GRB_DEC:         +43.805d {+43d 48' 17"} (J2000),
                   +43.849d {+43d 50' 57"} (current),
                   +43.714d {+43d 42' 50"} (1950)
  GRB_DATE:        20765 TJD;    90 DOY;   25/03/31
  GRB_TIME:        15583.47 SOD {04:19:43.47} UT
  TRIGGER_INDEX:   448
  GRB_PHI:         -179.81 [deg]
  GRB_THETA:        39.82 [deg]
  DELTA_TIME:      1677.00 [sec]
  TRIGGER_DUR:     4.096 [sec] 
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     9.21 [sigma]
  IMAGE_SIGNIF:    7.17 [sigma]
  LC_URL:          sw01299965000msb.lc
  SUN_POSTN:         9.85d {+00h 39m 25s}   +4.24d {+04d 14' 30"}
  SUN_DIST:         67.10 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.85d {+02h 07m 24s}  +16.23d {+16d 14' 02"}
  MOON_DIST:        43.59 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.13 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:       75.68, 21.29 [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 = 67.82,17.39 [deg].  
  COMMENTS:        The 3rd packet (of 3) was missing in the lightcurve data stream.  
  

  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:33:38 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.801d {+43d 48' 05"} (J2000)
  POINT_ROLL:      252.538d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  15900.65 SOD {04:25:00.65} UT,   317.2 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        8.614
  N_STARS:         158
  X_OFFSET:        471 [pixels]
  Y_OFFSET:        576 [pixels]
  X_MAX:           1430 [pixels]
  Y_MAX:           1535 [pixels]
  DET_THRESH:      26
  PHOTO_THRESH:    16
  SL_URL:          sw01299965000msufc0317.fits
  SUN_POSTN:         9.86d {+00h 39m 26s}   +4.24d {+04d 14' 35"}
  SUN_DIST:         67.10 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.91d {+02h 07m 37s}  +16.26d {+16d 15' 25"}
  MOON_DIST:        43.54 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:33:49 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.801d {+43d 48' 05"} (J2000)
  POINT_ROLL:      252.538d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  15900.65 SOD {04:25:00.65} UT,   317.2 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        8.614
  N_STARS:         158
  X_OFFSET:        471 [pixels]
  Y_OFFSET:        576 [pixels]
  X_MAX:           1430 [pixels]
  Y_MAX:           1535 [pixels]
  DET_THRESH:      26
  PHOTO_THRESH:    16
  SL_URL:          sw01299965000msufc0317.fits
  SUN_POSTN:         9.86d {+00h 39m 26s}   +4.24d {+04d 14' 35"}
  SUN_DIST:         67.10 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.91d {+02h 07m 38s}  +16.26d {+16d 15' 28"}
  MOON_DIST:        43.54 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [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:     Mon 31 Mar 25 04:36:11 UT
  NOTICE_TYPE:     Swift-UVOT Image
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.801d {+43d 48' 05"} (J2000)
  ROLL:            252.538d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  15900.65 SOD {04:25:00.65} UT,   317.2 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     765087935
  X_OFFSET:        790 [pixels]
  Y_OFFSET:        895 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       950
  Y_GRB_POS:       1055
  BINNING_INDEX:   1
  IM_URL:          sw01299965000msuni0353.fits
  SUN_POSTN:         9.86d {+00h 39m 26s}   +4.24d {+04d 14' 37"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.93d {+02h 07m 44s}  +16.27d {+16d 16' 04"}
  MOON_DIST:        43.52 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [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:     Mon 31 Mar 25 04:36:24 UT
  NOTICE_TYPE:     Swift-UVOT Processed Image
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.801d {+43d 48' 05"} (J2000)
  ROLL:            252.538d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  15900.65 SOD {04:25:00.65} UT,   317.2 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     765087935
  X_OFFSET:        790 [pixels]
  Y_OFFSET:        895 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       950
  Y_GRB_POS:       1055
  BINNING_INDEX:   1
  IM_URL:          sw01299965000msuni0353.fits
  SUN_POSTN:         9.86d {+00h 39m 26s}   +4.24d {+04d 14' 38"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.93d {+02h 07m 44s}  +16.27d {+16d 16' 07"}
  MOON_DIST:        43.51 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [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:     Mon 31 Mar 25 04:41:18 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.802d {+43d 48' 07"} (J2000)
  POINT_ROLL:      252.536d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  16453.95 SOD {04:34:13.95} UT,   870.5 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        7.226
  N_STARS:         190
  X_OFFSET:        231 [pixels]
  Y_OFFSET:        336 [pixels]
  X_MAX:           1670 [pixels]
  Y_MAX:           1775 [pixels]
  DET_THRESH:      23
  PHOTO_THRESH:    14
  SL_URL:          sw01299965000msufc0870.fits
  SUN_POSTN:         9.86d {+00h 39m 27s}   +4.25d {+04d 14' 42"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.98d {+02h 07m 56s}  +16.29d {+16d 17' 22"}
  MOON_DIST:        43.47 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:41:35 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.802d {+43d 48' 07"} (J2000)
  POINT_ROLL:      252.536d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  16453.95 SOD {04:34:13.95} UT,   870.5 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        7.226
  N_STARS:         190
  X_OFFSET:        231 [pixels]
  Y_OFFSET:        336 [pixels]
  X_MAX:           1670 [pixels]
  Y_MAX:           1775 [pixels]
  DET_THRESH:      23
  PHOTO_THRESH:    14
  SL_URL:          sw01299965000msufc0870.fits
  SUN_POSTN:         9.86d {+00h 39m 27s}   +4.25d {+04d 14' 43"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.99d {+02h 07m 56s}  +16.29d {+16d 17' 26"}
  MOON_DIST:        43.46 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [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:     Mon 31 Mar 25 04:41:55 UT
  NOTICE_TYPE:     Swift-XRT Position
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  GRB_RA:           71.3736d {+04h 45m 29.66s} (J2000),
                    71.8251d {+04h 47m 18.02s} (current),
                    70.4811d {+04h 41m 55.45s} (1950)
  GRB_DEC:         +43.8108d {+43d 48' 38.8"} (J2000),
                   +43.8552d {+43d 51' 18.5"} (current),
                   +43.7198d {+43d 43' 11.3"} (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:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  15904.00 SOD {04:25:04.00} UT,   320.5 [sec] since BAT Trigger Time
  TAM[0-3]:        100.00 100.00 100.00 100.00
  AMPLIFIER:       1
  WAVEFORM:        31
  SUN_POSTN:         9.86d {+00h 39m 27s}   +4.25d {+04d 14' 43"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       31.99d {+02h 07m 57s}  +16.29d {+16d 17' 31"}
  MOON_DIST:        43.46 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.92, -1.13 [deg] galactic lon,lat of the burst
  ECL_COORDS:       75.68, 21.29 [deg] ecliptic lon,lat of the burst
  COMMENTS:        SWIFT-XRT Coordinates.  
  COMMENTS:        This Notice was ground-generated -- not flight-generated.  
  COMMENTS:        TAM values, flux and significance fields are not valid.  
  COMMENTS:        This position was automatically generated on the ground using  
  COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
  COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
  COMMENTS:        This position was enhanced using UVOT field astrometry.  
  COMMENTS:        The probability that this is a serendipitous source in the  
  COMMENTS:        SPER window is 2.8% < P(seren) < 6.6%.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Mon 31 Mar 25 04:42:57 UT
  NOTICE_TYPE:     Swift-UVOT Image
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.802d {+43d 48' 07"} (J2000)
  ROLL:            252.536d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  16453.95 SOD {04:34:13.95} UT,   870.5 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     765088489
  X_OFFSET:        790 [pixels]
  Y_OFFSET:        895 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       950
  Y_GRB_POS:       1055
  BINNING_INDEX:   1
  IM_URL:          sw01299965000msuni0906.fits
  SUN_POSTN:         9.86d {+00h 39m 27s}   +4.25d {+04d 14' 44"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       32.00d {+02h 08m 00s}  +16.30d {+16d 17' 47"}
  MOON_DIST:        43.45 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [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:     Mon 31 Mar 25 04:43:13 UT
  NOTICE_TYPE:     Swift-UVOT Processed Image
  TRIGGER_NUM:     1299965,   Seg_Num: 0
  POINT_RA:         71.379d {+04h 45m 31s} (J2000)
  POINT_DEC:       +43.802d {+43d 48' 07"} (J2000)
  ROLL:            252.536d
  IMG_START_DATE:  20765 TJD;    90 DOY;   25/03/31
  IMG_START_TIME:  16453.95 SOD {04:34:13.95} UT,   870.5 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     765088489
  X_OFFSET:        790 [pixels]
  Y_OFFSET:        895 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       950
  Y_GRB_POS:       1055
  BINNING_INDEX:   1
  IM_URL:          sw01299965000msuni0906.fits
  SUN_POSTN:         9.86d {+00h 39m 27s}   +4.25d {+04d 14' 44"}
  SUN_DIST:         67.09 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
  MOON_POSTN:       32.00d {+02h 08m 00s}  +16.30d {+16d 17' 51"}
  MOON_DIST:        43.45 [deg]
  MOON_ILLUM:      5 [%]
  GAL_COORDS:      160.93, -1.14 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:       75.68, 21.28 [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 #39958
  S. B. Cenko (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
  At 04:19:43 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250331B (trigger=1299965). Swift slewed to the burst after a brief delay to clear an observing constraint. The BAT on-board calculated location is RA, Dec 71.381, +43.805 which is

     RA(J2000) = 04h 45m 31s
     Dec(J2000) = +43d 48' 17"
  

  with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peak structure with a duration of about 8 sec. The peak count rate was ~1400 counts/sec (15-350 keV), at ~2 sec after the trigger.
  The XRT began observing the field at 04:24:57.3 UT, 313.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 71.37364, 43.81080 which is equivalent to:

     RA(J2000)  = 04h 45m 29.67s
     Dec(J2000) = +43d 48' 38.9"
  

  with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 28 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 does not constrain the column density.
  UVOT took a finding chart exposure of 150 seconds with the White filter starting 317 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 large, but uncertain, extinction expected.
  Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)
• GCN Circular #39962
  Damien Dornic (CPPM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Ny Avo Rakotondrainibe (LAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:
  We imaged the field of Swift/BAT GRB 250331B (Cenko et al., GCN Circ. 39958) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
  We started observing at 2025-03-31 04:21:10 UTC (87 s after the trigger) and obtained a total of 100 s exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction.
  At the XRT localization, we do not find any optical counterpart to a 3-sigma limiting magnitude of:
  i > 20.96
  We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
• GCN Circular #39974
  J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
  Using 824 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250331B, 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 = 71.37215, +43.81257 which is equivalent to:

  RA (J2000): 04h 45m 29.32s
  Dec (J2000): +43d 48' 45.2"
  

  with an uncertainty of 3.6 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 #39980
  V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
  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 250331B ( S. B. Cenko et al., GCN 39958) errorbox 47556 sec after notice time and 47612 sec after trigger time at 2025-03-31 17:33:15 UT, with upper limit up to 16.9 mag. Observations started at twilight. The observations began at zenith distance = 85 deg. The sun altitude is -13.0 deg.
  The galactic latitude b = -1 deg., longitude l = 161 deg.
  Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828939
  We obtain a following upper limits.

  Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
  _________|_____________________|_____|_______|______|________
  
     47702 |         MASTER-SAAO |   C |   180 | 16.5 |        
     47902 |         MASTER-SAAO |   C |   180 | 16.7 |        
     48101 |         MASTER-SAAO |   C |   180 | 16.9 |        
  

  Filter C is a clear (unfiltred) band.
  The observation and reduction will continue. The message may be cited.
• GCN Circular #39995
  T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:
  We have analysed 5.5 ks of XRT data for GRB 250331B, from 321 s to 35.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode.
  The light curve can be modelled with a power-law decay with a decay index of alpha=1.11 (+0.17, -0.14).
  A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.9, -0.8). The best-fitting absorption column is 2.1 (+1.5, -1.1) x 10^22 cm^-2, in excess of the Galactic value of 6.6 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 5.7 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1.
  A summary of the PC-mode spectrum is thus:

  Total column:	     2.1 (+1.5, -1.1) x 10^22 cm^-2
  Galactic foreground: 6.6 x 10^21 cm^-2
  Excess significance: 2.2 sigma
  Photon index:	     2.2 (+0.9, -0.8)
  

  If the light curve continues to decay with a power-law decay index of 1.11, the count rate at T+24 hours will be 7.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-14 (1.2 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/01299965.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #39996
  P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) and P.A. Evans report on behalf of the Swift-XRT team:
  We have analysed 5.5 ks of XRT data for GRB 250331B, from 321 s to 35.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode.
  The light curve can be modelled with a power-law decay with a decay index of alpha=1.11 (+0.17, -0.14).
  A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.9, -0.8). The best-fitting absorption column is 2.1 (+1.5, -1.1) x 10^22 cm^-2, in excess of the Galactic value of 6.6 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 5.7 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1.
  A summary of the PC-mode spectrum is thus:

  Total column:	     2.1 (+1.5, -1.1) x 10^22 cm^-2
  Galactic foreground: 6.6 x 10^21 cm^-2
  Excess significance: 2.2 sigma
  Photon index:	     2.2 (+0.9, -0.8)
  

  If the light curve continues to decay with a power-law decay index of 1.11, the count rate at T+24 hours will be 7.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-14 (1.2 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/01299965.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #40002
  M. H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team:
  The Swift/UVOT began settled observations of the field of GRB 250331B 317 s after the BAT trigger (Cenko et al., GCN Circ. 39958). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 39974) 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           317          467          147         >19.5
  white              317         1020          334         >19.9
  v                  474         1070           78         >18.3
  b                  572          764           39         >18.3
  u                  547         1144           58         >18.6
  w1                 523         1120           58         >18.0
  m2                 670          690           19         >17.7
  w2                 621         1046           58         >18.4
  

  The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.979 in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #40056
  S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team):
  Using the data set from T-240 to T+842 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250331B (trigger #1299965) (Cenko, et al., GCN Circ. 39958). The BAT ground-calculated position is RA, Dec = 71.377, 43.794 deg which is

     RA(J2000)  =  04h 45m 30.4s
     Dec(J2000) = +43d 47' 39.1"
  

  with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 55%.
  The mask-weighted light curve displays a single dim pulse. The T90 (15-350 keV) is 3.95 +- 0.77 sec (estimated error including systematics).
  The time-averaged spectrum from T-0.72 to T+3.76 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.61 +- 0.38. The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+1.28 sec in the 15-150 keV band is 0.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
  The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1299965