Gamma-ray Burst 250504A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:26:15 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1310284,   Seg_Num: 0
GRB_RA:          269.612d {+17h 58m 27s} (J2000),
                 270.057d {+18h 00m 14s} (current),
                 268.735d {+17h 54m 56s} (1950)
GRB_DEC:         -40.349d {-40d 20' 57"} (J2000),
                 -40.350d {-40d 20' 58"} (current),
                 -40.345d {-40d 20' 42"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       3399 [cnts]    Image_Peak=237 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   155     E_range: 50-350 keV
BKG_INTEN:       13669 [cnts]
BKG_TIME:        84340.45 SOD {23:25:40.45} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84357.47 SOD {23:25:57.47} UT
GRB_PHI:         -97.59 [deg]
GRB_THETA:        10.42 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     37.02 [sigma]
IMAGE_SIGNIF:    10.17 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +3  +0  +0  +1 +67  +0 
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 27"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.01d {+09h 32m 03s}  +17.98d {+17d 58' 53"}
MOON_DIST:       129.54 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.45, -8.04 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      269.69,-16.91 [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 = 84.21,-19.46 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(3.0<100sec) coincident with the FERMI_GBM event (trignum=768093959).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:26:25 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     768093959
GRB_RA:          197.483d {+13h 09m 56s} (J2000),
                 197.882d {+13h 11m 32s} (current),
                 196.703d {+13h 06m 49s} (1950)
GRB_DEC:         -59.867d {-59d 52' 00"} (J2000),
                 -60.001d {-60d 00' 03"} (current),
                 -59.601d {-59d 36' 01"} (1950)
GRB_ERROR:       7.13 [deg radius, statistical plus systematic]
GRB_INTEN:       514 [cnts/sec]
DATA_SIGNIF:     11.30 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         204.00 [deg]
GRB_THETA:       155.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.02
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      98%  GRB
2nd_MOST_LIKELY:   2%  Generic SGR
DETECTORS:       0,0,0, 0,0,0, 0,0,1, 0,0,1, 0,0,
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 27"}
SUN_DIST:        132.81 [deg]   Sun_angle= -10.4 [hr] (East of Sun)
MOON_POSTN:      143.01d {+09h 32m 03s}  +17.98d {+17d 58' 51"}
MOON_DIST:        89.64 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      305.25,  2.92 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      225.21,-47.18 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 78.10,16.77 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:26:33 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     768093959
GRB_RA:          197.500d {+13h 10m 00s} (J2000),
                 197.898d {+13h 11m 36s} (current),
                 196.720d {+13h 06m 53s} (1950)
GRB_DEC:         -59.767d {-59d 46' 00"} (J2000),
                 -59.901d {-59d 54' 03"} (current),
                 -59.501d {-59d 30' 01"} (1950)
GRB_ERROR:       6.07 [deg radius, statistical plus systematic]
GRB_INTEN:       398 [cnts/sec]
DATA_SIGNIF:     16.60 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         204.00 [deg]
GRB_THETA:       155.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.37
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,1, 0,0,1, 0,0,
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 28"}
SUN_DIST:        132.90 [deg]   Sun_angle= -10.4 [hr] (East of Sun)
MOON_POSTN:      143.01d {+09h 32m 04s}  +17.98d {+17d 58' 49"}
MOON_DIST:        89.58 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      305.27,  3.02 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      225.14,-47.09 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 78.10,16.77 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:26:43 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     768093959
GRB_RA:          264.290d {+17h 37m 10s} (J2000),
                 264.735d {+17h 38m 56s} (current),
                 263.413d {+17h 33m 39s} (1950)
GRB_DEC:         -40.510d {-40d 30' 35"} (J2000),
                 -40.523d {-40d 31' 24"} (current),
                 -40.480d {-40d 28' 48"} (1950)
GRB_ERROR:       3.85 [deg radius, statistical only]
DATA_SIGNIF:     20.30 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         227.00 [deg]
GRB_THETA:       113.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 28"}
SUN_DIST:        136.08 [deg]   Sun_angle= 9.2 [hr] (West of Sun)
MOON_POSTN:      143.02d {+09h 32m 04s}  +17.98d {+17d 58' 47"}
MOON_DIST:       125.50 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      349.24, -4.63 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      265.46,-17.16 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_768093959.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:27:14 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     768093959
GRB_RA:          264.300d {+17h 37m 12s} (J2000),
                 264.745d {+17h 38m 59s} (current),
                 263.423d {+17h 33m 42s} (1950)
GRB_DEC:         -40.530d {-40d 31' 47"} (J2000),
                 -40.543d {-40d 32' 35"} (current),
                 -40.500d {-40d 30' 00"} (1950)
GRB_ERROR:       2.83 [deg radius, statistical only]
DATA_SIGNIF:     17.50 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         227.00 [deg]
GRB_THETA:       113.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 28"}
SUN_DIST:        136.07 [deg]   Sun_angle= 9.2 [hr] (West of Sun)
MOON_POSTN:      143.02d {+09h 32m 05s}  +17.98d {+17d 58' 41"}
MOON_DIST:       125.50 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      349.23, -4.65 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      265.47,-17.18 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_768093959.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:27:24 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     768093959
GRB_RA:          265.370d {+17h 41m 29s} (J2000),
                 265.817d {+17h 43m 16s} (current),
                 264.489d {+17h 37m 57s} (1950)
GRB_DEC:         -40.940d {-40d 56' 23"} (J2000),
                 -40.951d {-40d 57' 02"} (current),
                 -40.915d {-40d 54' 54"} (1950)
GRB_ERROR:       2.61 [deg radius, statistical only]
DATA_SIGNIF:     22.90 [sigma]
DATA_INTERVAL:   6.144 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         228.00 [deg]
GRB_THETA:       113.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 28"}
SUN_DIST:        135.16 [deg]   Sun_angle= 9.1 [hr] (West of Sun)
MOON_POSTN:      143.02d {+09h 32m 05s}  +17.98d {+17d 58' 39"}
MOON_DIST:       126.26 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      349.31, -5.55 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      266.33,-17.56 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_768093959.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:27:39 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     768093959
GRB_RA:          265.360d {+17h 41m 26s} (J2000),
                 265.807d {+17h 43m 14s} (current),
                 264.479d {+17h 37m 55s} (1950)
GRB_DEC:         -40.930d {-40d 55' 47"} (J2000),
                 -40.941d {-40d 56' 26"} (current),
                 -40.905d {-40d 54' 18"} (1950)
GRB_ERROR:       2.60 [deg radius, statistical only]
DATA_SIGNIF:     27.50 [sigma]
DATA_INTERVAL:   10.240 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         228.00 [deg]
GRB_THETA:       113.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 28"}
SUN_DIST:        135.17 [deg]   Sun_angle= 9.1 [hr] (West of Sun)
MOON_POSTN:      143.02d {+09h 32m 06s}  +17.98d {+17d 58' 35"}
MOON_DIST:       126.25 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      349.31, -5.54 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      266.32,-17.55 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_768093959.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:27:53 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      3
TRIGGER_NUM:     768093959
GRB_RA:          264.270d {+17h 37m 05s} (J2000),
                 264.715d {+17h 38m 52s} (current),
                 263.393d {+17h 33m 34s} (1950)
GRB_DEC:         -40.490d {-40d 29' 23"} (J2000),
                 -40.504d {-40d 30' 12"} (current),
                 -40.460d {-40d 27' 35"} (1950)
GRB_ERROR:       2.21 [deg radius, statistical only]
DATA_SIGNIF:     30.70 [sigma]
DATA_INTERVAL:   15.360 [sec]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         227.00 [deg]
GRB_THETA:       113.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 29"}
SUN_DIST:        136.10 [deg]   Sun_angle= 9.2 [hr] (West of Sun)
MOON_POSTN:      143.03d {+09h 32m 06s}  +17.98d {+17d 58' 33"}
MOON_DIST:       125.48 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      349.25, -4.61 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      265.44,-17.14 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_768093959.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 04 May 25 23:35:20 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     768093959
GRB_RA:          265.370d {+17h 41m 29s} (J2000),
                 265.817d {+17h 43m 16s} (current),
                 264.489d {+17h 37m 57s} (1950)
GRB_DEC:         -40.940d {-40d 56' 23"} (J2000),
                 -40.951d {-40d 57' 02"} (current),
                 -40.915d {-40d 54' 54"} (1950)
GRB_ERROR:       2.14 [deg radius, statistical only]
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84354.78 SOD {23:25:54.78} UT
GRB_PHI:         228.00 [deg]
GRB_THETA:       113.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        42.28d {+02h 49m 08s}  +16.26d {+16d 15' 34"}
SUN_DIST:        135.17 [deg]   Sun_angle= 9.1 [hr] (West of Sun)
MOON_POSTN:      143.09d {+09h 32m 22s}  +17.95d {+17d 57' 01"}
MOON_DIST:       126.19 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      349.31, -5.55 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      266.33,-17.56 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_locplot_all_bn250504976.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the SWIFT_BAT event (trignum=1310284).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:27:25 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1310284,   Seg_Num: 0
POINT_RA:        269.628d {+17h 58m 31s} (J2000)
POINT_DEC:       -40.349d {-40d 20' 55"} (J2000)
IMG_START_DATE:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84435.37 SOD {23:27:15.37} UT,   77.9 [sec] since BAT Trigger Time
COUNTS:          13    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:     Sun 04 May 25 23:30:21 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1310284,   Seg_Num: 0
GRB_RA:          269.612d {+17h 58m 27s} (J2000),
                 270.057d {+18h 00m 14s} (current),
                 268.735d {+17h 54m 56s} (1950)
GRB_DEC:         -40.349d {-40d 20' 57"} (J2000),
                 -40.350d {-40d 20' 58"} (current),
                 -40.345d {-40d 20' 42"} (1950)
GRB_DATE:        20799 TJD;   124 DOY;   25/05/04
GRB_TIME:        84357.47 SOD {23:25:57.47} UT
TRIGGER_INDEX:   155
GRB_PHI:         -97.59 [deg]
GRB_THETA:        10.42 [deg]
DELTA_TIME:      57.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     37.02 [sigma]
IMAGE_SIGNIF:    10.17 [sigma]
LC_URL:          sw01310284000msb.lc
SUN_POSTN:        42.28d {+02h 49m 07s}  +16.26d {+16d 15' 30"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.05d {+09h 32m 11s}  +17.97d {+17d 58' 02"}
MOON_DIST:       129.50 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.45, -8.04 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      269.69,-16.91 [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 = 84.21,-19.46 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:31:55 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1310284,   Seg_Num: 0
GRB_RA:          269.6179d {+17h 58m 28.29s} (J2000),
                 270.0625d {+18h 00m 15.00s} (current),
                 268.7408d {+17h 54m 57.78s} (1950)
GRB_DEC:         -40.3660d {-40d 21' 57.5"} (J2000),
                 -40.3664d {-40d 21' 59.0"} (current),
                 -40.3620d {-40d 21' 43.2"} (1950)
GRB_ERROR:       3.5 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84488.00 SOD {23:28:08.00} UT,   130.5 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        42.28d {+02h 49m 08s}  +16.26d {+16d 15' 31"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.06d {+09h 32m 15s}  +17.96d {+17d 57' 43"}
MOON_DIST:       129.49 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.44, -8.05 [deg] galactic lon,lat of the burst
ECL_COORDS:      269.70,-16.93 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN Circular #40341
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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 GRB250504.98 (trigger No 1310284,17h 58m 26.88s , -40d 20m 56.4s, R=0.05) errorbox 14 sec after notice time and 40 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg.
The galactic latitude b = -9 deg., longitude l = 352 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860822
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      46 |         MASTER-SAAO |   C |    10 | 16.7 |        
      75 |         MASTER-SAAO |   C |    10 | 16.7 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #40342
The Fermi GBM team reports the detection of a likely LONG GRB
At 23:25:54 UT on 4 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959.78286 / 250504976).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 265.4, Dec = -40.9 (J2000 degrees, equivalent to J2000 17h 41m, -40d 53'), with a statistical uncertainty of 2.1 degrees.
The angle from the Fermi LAT boresight is 113.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_skymap_all_bn250504976.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_healpix_all_bn250504976.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:36:43 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1310284,   Seg_Num: 0
GRB_RA:          269.6169d {+17h 58m 28.05s} (J2000),
                 270.0615d {+18h 00m 14.76s} (current),
                 268.7398d {+17h 54m 57.54s} (1950)
GRB_DEC:         -40.3662d {-40d 21' 58.3"} (J2000),
                 -40.3666d {-40d 21' 59.7"} (current),
                 -40.3622d {-40d 21' 43.9"} (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:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84488.00 SOD {23:28:08.00} UT,   130.5 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        42.29d {+02h 49m 08s}  +16.26d {+16d 15' 35"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.10d {+09h 32m 24s}  +17.95d {+17d 56' 45"}
MOON_DIST:       129.45 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.44, -8.05 [deg] galactic lon,lat of the burst
ECL_COORDS:      269.69,-16.93 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:37:46 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1310284,   Seg_Num: 0
POINT_RA:        269.626d {+17h 58m 30s} (J2000)
POINT_DEC:       -40.349d {-40d 20' 55"} (J2000)
ROLL:            106.399d
IMG_START_DATE:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84494.87 SOD {23:28:14.87} UT,   137.4 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     768094130
X_OFFSET:        744 [pixels]
Y_OFFSET:        930 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       904
Y_GRB_POS:       1090
BINNING_INDEX:   1
IM_URL:          sw01310284000msuni0173.fits
SUN_POSTN:        42.29d {+02h 49m 09s}  +16.26d {+16d 15' 36"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.11d {+09h 32m 27s}  +17.94d {+17d 56' 32"}
MOON_DIST:       129.45 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.46, -8.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.70,-16.91 [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:     Sun 04 May 25 23:38:01 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1310284,   Seg_Num: 0
POINT_RA:        269.626d {+17h 58m 30s} (J2000)
POINT_DEC:       -40.349d {-40d 20' 55"} (J2000)
ROLL:            106.399d
IMG_START_DATE:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84494.87 SOD {23:28:14.87} UT,   137.4 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     768094130
X_OFFSET:        744 [pixels]
Y_OFFSET:        930 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       904
Y_GRB_POS:       1090
BINNING_INDEX:   1
IM_URL:          sw01310284000msuni0173.fits
SUN_POSTN:        42.29d {+02h 49m 09s}  +16.26d {+16d 15' 36"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.11d {+09h 32m 27s}  +17.94d {+17d 56' 29"}
MOON_DIST:       129.45 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.46, -8.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.70,-16.91 [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 #40343
M. J. Moss (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 23:25:57 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250504A (trigger=1310284). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.612, -40.349 which is
```
   RA(J2000) = 17h 58m 27s
   Dec(J2000) = -40d 20' 57"
```
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 60 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 23:27:15.3 UT, 77.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 269.61691, -40.36642 which is equivalent to:
```
   RA(J2000)  = 17h 58m 28.06s
   Dec(J2000) = -40d 21' 59.1"
```
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 64 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 consistent with the Galactic value of 2.12 x 10^21 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 250 seconds with the U filter starting 137 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 0.00% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.191.
Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)

GCN Circular #40344
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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) started inspect of the Fermi GRB 250504A ( Fermi GBM team, GCN 40342) errorbox 1 sec after notice time and 43 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg.
The galactic latitude b = -6 deg., longitude l = 350 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860892
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      49 | 2025-05-04 23:26:38 |         MASTER-SAAO | (17h 56m 41.66s , -40d 35m 44.3s) |   C |    10 | 16.7 |        
      77 | 2025-05-04 23:27:07 |         MASTER-SAAO | (17h 56m 41.67s , -40d 35m 44.8s) |   C |    10 | 16.7 |        
     111 | 2025-05-04 23:27:36 |         MASTER-SAAO | (17h 56m 41.71s , -40d 35m 45.1s) |   C |    20 | 17.0 |        
     151 | 2025-05-04 23:28:15 |         MASTER-SAAO | (17h 56m 41.72s , -40d 35m 45.3s) |   C |    20 | 17.0 |        
     249 | 2025-05-04 23:29:43 |         MASTER-SAAO | (17h 56m 41.65s , -40d 35m 44.1s) |   C |    40 | 17.2 |        
     313 | 2025-05-04 23:30:42 |         MASTER-SAAO | (17h 56m 41.63s , -40d 35m 43.6s) |   C |    50 | 17.2 |        
     387 | 2025-05-04 23:31:51 |         MASTER-SAAO | (17h 56m 41.55s , -40d 35m 43.1s) |   C |    60 | 17.3 |        
     466 | 2025-05-04 23:33:10 |         MASTER-SAAO | (17h 56m 41.50s , -40d 35m 42.3s) |   C |    60 | 17.3 |        
     545 | 2025-05-04 23:34:29 |         MASTER-SAAO | (17h 56m 41.40s , -40d 35m 41.4s) |   C |    60 | 17.3 |        
     624 | 2025-05-04 23:35:48 |         MASTER-SAAO | (17h 56m 41.29s , -40d 35m 40.5s) |   C |    60 | 17.3 |        
     703 | 2025-05-04 23:37:08 |         MASTER-SAAO | (17h 56m 41.19s , -40d 35m 39.7s) |   C |    60 | 17.3 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:36:18 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1310284,   Seg_Num: 0
POINT_RA:        269.626d {+17h 58m 30s} (J2000)
POINT_DEC:       -40.349d {-40d 20' 55"} (J2000)
POINT_ROLL:      106.399d
IMG_START_DATE:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84494.87 SOD {23:28:14.87} UT,   137.4 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.628
N_STARS:         190
X_OFFSET:        185 [pixels]
Y_OFFSET:        371 [pixels]
X_MAX:           1624 [pixels]
Y_MAX:           1810 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw01310284000msufc0137.fits
SUN_POSTN:        42.28d {+02h 49m 08s}  +16.26d {+16d 15' 35"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.10d {+09h 32m 24s}  +17.95d {+17d 56' 50"}
MOON_DIST:       129.46 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.46, -8.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.70,-16.91 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 04 May 25 23:36:33 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1310284,   Seg_Num: 0
POINT_RA:        269.626d {+17h 58m 30s} (J2000)
POINT_DEC:       -40.349d {-40d 20' 55"} (J2000)
POINT_ROLL:      106.399d
IMG_START_DATE:  20799 TJD;   124 DOY;   25/05/04
IMG_START_TIME:  84494.87 SOD {23:28:14.87} UT,   137.4 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.628
N_STARS:         190
X_OFFSET:        185 [pixels]
Y_OFFSET:        371 [pixels]
X_MAX:           1624 [pixels]
Y_MAX:           1810 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw01310284000msufc0137.fits
SUN_POSTN:        42.29d {+02h 49m 08s}  +16.26d {+16d 15' 35"}
SUN_DIST:        132.29 [deg]   Sun_angle= 8.8 [hr] (West of Sun)
MOON_POSTN:      143.10d {+09h 32m 24s}  +17.95d {+17d 56' 47"}
MOON_DIST:       129.46 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      351.46, -8.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.70,-16.91 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN Circular #40345
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 940 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250504A, 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 = 269.61806, -40.36676 which is equivalent to:
```
RA (J2000): 17h 58m 28.34s
Dec (J2000): -40d 22' 00.3"
```
with an uncertainty of 4.0 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 #40346
S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 23:25:54.78 UT on 04 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959/250504976), which was also detected by Swift BAT (M. J. Moss et al. 2025, GCN 40343). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 111 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 49 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+59.393 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 621 +/- 130 keV.
The event fluence (10-1000 keV) in this time interval is (1.20 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 3.6 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular #40347
S. de Wet (DTU Space), P.M. Vreeswijk (Radboud) and P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT consortium:
The 0.6 m wide-field MeerLICHT optical telescope located in Sutherland, South Africa, obtained a repeating series of 60 s exposures in the q,u,g,r,i,z bands of GRB 250504A following the Swift detection (Moss et al., GCN 40343). Observations started at 23:29:27 UT on 2025 May 5 (210 seconds post-trigger) and continued for a further 3 hours, following the filter sequence quqgqrqiqz.
We find a new transient candidate in our first q-band exposure at the following coordinates:
```
   
RA (J2000) = 17:58:28.38 (269.61827d)
Dec (J2000) = -40:21:59.58 (-40.36655d)
```
calibrated against Gaia DR2. The astrometric uncertainty is ~0.3" in each coordinate. This position is outside the initial XRT error circle reported by Moss et al. (GCN 40343) but within the updated XRT error circle reported by Osborne et al. (GCN 40345). We regard this object as the optical afterglow to GRB250504A. We report the following AB magnitudes and non detections from our first exposures:
```
q = 19.32 +/- 0.05 at 23:29:59 UT
u > 19.34 (3sigma) at 23:31:20 UT
g = 19.69 +/- 0.10 at 23:34:04 UT
r = 19.52 +/- 0.11 at 23:36:48 UT
i = 19.32 +/- 0.13 at 23:39:31 UT
z = 18.85 +/- 0.20 at 23:42:14 UT
```
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.
GCN Circular #40350
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 250504A detected by Fermi/GBM (Fermi GBM team, GCN 40342) and Swift/BAT (Moss et al., GCN 40343) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 05 at 01:09:20 UT (i.e. 1.7 hr after the burst), and lasted for about 1 hour.
From preliminary inspection, we do not detect any counterpart at the position of the optical afterglow (de Wet et al., GCN. 40347) down to the following 3sigma limits:
r > 19.3 (AB; calibrated against the SkyMapper catalogue), at a mid-time of 2.2 hours after the trigger;
H > 15.7 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 2.1 hours after the trigger.
GCN Circular #40351
L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, D.H. Zhao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT Instrument Center:
SVOM/VT conducted ToO follow-up observations of GRB 250504A detected by Fermi (Fermi/GBM team, GCN 40342; Bala et al., GCN 40346) and Swift (Moss et al., GCN 40343). The observation started on 2025-05-05T01:11:01 UT, 2025 May 05, ~1.75 hr after the burst.
Our preliminary analysis shows no detection of an optical counterpart in VT_B-band stacked images (3975 s total effective exposure) at both the de Wet et al. (GCN 40347) position and the enhanced XRT position (4.0 arcsec error radius; Osborne et al. GCN 40345), with a 3 sigma upper limit of VT_B > 22.0 mag (AB) at 2.74 hr post-burst.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.
GCN Circular #40353
A. Saccardi (CEA/Irfu), M. Garnichey (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (Leicester), A. de Ugarte Postigo (LAM) report on behalf of the Stargate collaboration:
We observed the field of GRB 250504A detected by Fermi/GBM (Fermi GBM team, GCN 40342; Bala et al., GCN 40346) and Swift/BAT (Moss et al., GCN 40343) using the ESO VLT UT3 (Melipal) with the X-shooter acquisition camera.
A short sequence of imaging was secured in the r (3x30 s), g (3x60 s), and z (3x40 s) bands. No afterglow is detected consistent with the optical position reported by de Wet et al. (GCN 40347) with the following 5 sigma upper limit calibrated against nearby SkyMapper stars:
r > 23.4 (AB) on 2025 May 05 at 03:21:58 UT (3.93 hr after the burst).
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Abigail Frost, Florian Rodler, Marco Berton, and Rodrigo Palominos.
GCN Circular #40354
J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M. A. Williams (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.9 ks of XRT data for GRB 250504A, from 81 s to 56.7 ks after the BAT trigger. The data comprise 47 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with a power-law decay with a decay index of alpha=1.26 (+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 1.60 (+0.24, -0.22). The best-fitting absorption column is 2.9 (+1.4, -0.7) x 10^21 cm^-2, consistent with the Galactic value of 2.1 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 4.8 x 10^-11 (6.0 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     2.9 (+1.4, -0.7) x 10^21 cm^-2
Galactic foreground: 2.1 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.60 (+0.24, -0.22)
```
If the light curve continues to decay with a power-law decay index of 1.26, the count rate at T+24 hours will be 1.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.3 x 10^-14 (1.0 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/01310284.
This circular is an official product of the Swift-XRT team.
GCN Circular #40357
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), T. Parsotan (GSFC), D. Sadaula (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 250504A (trigger #1310284) (Moss, et al., GCN Circ. 40343). The BAT ground-calculated position is RA, Dec = 269.605, -40.345 deg which is
```
   RA(J2000)  =  17h 58m 25.3s 
   Dec(J2000) = -40d 20' 41.8" 
```
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 98%.
The mask-weighted light curve shows a complex light curve with several pulses. T90 (15-350 keV) is 52.39 +- 2.31 sec (estimated error including systematics).
The time-averaged spectrum from T-2.96 to T+55.10 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.27 +- 0.08. The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+7.70 sec in the 15-150 keV band is 1.6 +- 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/1310284
GCN Circular #40372
P. McDermott, D. Murphy, C. McKenna, C. de Barra, A. Ulyanov, G. Finneran, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team:
EIRSAT-1 reports the detection of the long gamma-ray burst GRB 250504A by the Gamma-ray Module (GMOD) instrument, which was also detected by Fermi GBM (GCN [40342](https://gcn.nasa.gov/circulars/40342) and [40346](https://gcn.nasa.gov/circulars/40346)) and Swift-BAT (GCN [40343](https://gcn.nasa.gov/circulars/40343)). The GMOD detection was made starting at 2025-05-04 23:25:56.5 UTC.
The GMOD light curve for GRB 250405A, with 1.2s binning, shows multiple peaks consistent with the detections by Fermi GBM and Swift-BAT.
The spacecraft location at time of detection was 9.886º S, 164.567° E and an altitude of 386 km.
The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250504A/250504A_LC_onboard_preliminary.png
EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023.

Back to JG's homepage

Jochen Greiner, last update: 06-May-2025 [Disclaimer]