Gamma-ray Burst 250516A

(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:     Fri 16 May 25 14:35:44 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1314210,   Seg_Num: 0
GRB_RA:          334.561d {+22h 18m 15s} (J2000),
                 334.896d {+22h 19m 35s} (current),
                 333.901d {+22h 15m 36s} (1950)
GRB_DEC:          -9.130d {-09d 07' 48"} (J2000),
                  -9.002d {-09d 00' 08"} (current),
                  -9.381d {-09d 22' 50"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       1539 [cnts]    Image_Peak=125 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   124     E_range: 25-100 keV
BKG_INTEN:       16474 [cnts]
BKG_TIME:        52516.38 SOD {14:35:16.38} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52528.92 SOD {14:35:28.92} UT
GRB_PHI:         -159.82 [deg]
GRB_THETA:        38.11 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     14.38 [sigma]
IMAGE_SIGNIF:    8.41 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +2  -1  +0  +0 -12  +0 
SUN_POSTN:        53.66d {+03h 34m 38s}  +19.25d {+19d 14' 51"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.80d {+18h 43m 12s}  -28.03d {-28d 01' 45"}
MOON_DIST:        54.21 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.05,-49.64 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      333.11,  1.32 [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 = 196.81,2.57 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=769098934).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 16 May 25 14:35:59 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     769098934
GRB_RA:          330.300d {+22h 01m 12s} (J2000),
                 330.617d {+22h 02m 28s} (current),
                 329.675d {+21h 58m 42s} (1950)
GRB_DEC:          +6.650d {+06d 39' 00"} (J2000),
                  +6.773d {+06d 46' 22"} (current),
                  +6.409d {+06d 24' 32"} (1950)
GRB_ERROR:       16.32 [deg radius, statistical plus systematic]
GRB_INTEN:       118 [cnts/sec]
DATA_SIGNIF:     6.00 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52529.28 SOD {14:35:29.28} UT
GRB_PHI:         270.00 [deg]
GRB_THETA:        20.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      1.16
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      97%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       0,0,0, 1,0,0, 1,0,0, 0,0,0, 0,0,
SUN_POSTN:        53.66d {+03h 34m 38s}  +19.25d {+19d 14' 51"}
SUN_DIST:         81.23 [deg]   Sun_angle= 5.5 [hr] (West of Sun)
MOON_POSTN:      280.80d {+18h 43m 12s}  -28.03d {-28d 01' 45"}
MOON_DIST:        59.32 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       65.96,-36.75 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      334.83, 17.58 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 221.00,-23.18 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1314210).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 16 May 25 14:36:07 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      59
TRIGGER_NUM:     769098934
GRB_RA:          330.500d {+22h 02m 00s} (J2000),
                 330.817d {+22h 03m 16s} (current),
                 329.875d {+21h 59m 30s} (1950)
GRB_DEC:          +6.600d {+06d 35' 60"} (J2000),
                  +6.723d {+06d 43' 23"} (current),
                  +6.358d {+06d 21' 30"} (1950)
GRB_ERROR:       6.37 [deg radius, statistical plus systematic]
GRB_INTEN:       452 [cnts/sec]
DATA_SIGNIF:     16.60 [sigma]
INTEG_TIME:      0.512 [sec]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52529.28 SOD {14:35:29.28} UT
GRB_PHI:         270.00 [deg]
GRB_THETA:        20.00 [deg]
DATA_TIME_SCALE: 0.5120 [sec]
HARD_RATIO:      0.42
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      93%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 1,0,0, 1,0,0, 0,0,0, 0,0,
SUN_POSTN:        53.66d {+03h 34m 38s}  +19.25d {+19d 14' 51"}
SUN_DIST:         81.06 [deg]   Sun_angle= 5.5 [hr] (West of Sun)
MOON_POSTN:      280.80d {+18h 43m 13s}  -28.03d {-28d 01' 44"}
MOON_DIST:        59.45 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       66.07,-36.93 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      335.00, 17.46 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 221.00,-23.18 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1314210).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 16 May 25 14:36:17 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     769098934
GRB_RA:          333.600d {+22h 14m 24s} (J2000),
                 333.946d {+22h 15m 47s} (current),
                 332.918d {+22h 11m 40s} (1950)
GRB_DEC:         -18.280d {-18d 16' 47"} (J2000),
                 -18.153d {-18d 09' 11"} (current),
                 -18.529d {-18d 31' 42"} (1950)
GRB_ERROR:       6.84 [deg radius, statistical only]
DATA_SIGNIF:     8.30 [sigma]
DATA_INTERVAL:   0.512 [sec]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52529.28 SOD {14:35:29.28} UT
GRB_PHI:         265.00 [deg]
GRB_THETA:        45.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        53.66d {+03h 34m 38s}  +19.25d {+19d 14' 51"}
SUN_DIST:         86.70 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.80d {+18h 43m 13s}  -28.03d {-28d 01' 44"}
MOON_DIST:        49.49 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       38.26,-52.88 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      328.95, -6.88 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_769098934.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1314210).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 16 May 25 14:37:11 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     769098934
GRB_RA:          333.310d {+22h 13m 14s} (J2000),
                 333.634d {+22h 14m 32s} (current),
                 332.672d {+22h 10m 41s} (1950)
GRB_DEC:          +1.220d {+01d 13' 12"} (J2000),
                  +1.346d {+01d 20' 47"} (current),
                  +0.972d {+00d 58' 19"} (1950)
GRB_ERROR:       2.60 [deg radius, statistical only]
DATA_SIGNIF:     20.70 [sigma]
DATA_INTERVAL:   10.240 [sec]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52529.28 SOD {14:35:29.28} UT
GRB_PHI:         273.00 [deg]
GRB_THETA:        26.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        53.66d {+03h 34m 38s}  +19.25d {+19d 14' 52"}
SUN_DIST:         80.14 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.81d {+18h 43m 15s}  -28.03d {-28d 01' 41"}
MOON_DIST:        58.52 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       63.13,-42.56 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      335.69, 11.43 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_769098934.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1314210).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 16 May 25 14:37:00 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     769098934
GRB_RA:          333.520d {+22h 14m 05s} (J2000),
                 333.855d {+22h 15m 25s} (current),
                 332.859d {+22h 11m 26s} (1950)
GRB_DEC:          -9.080d {-09d 04' 47"} (J2000),
                  -8.953d {-08d 57' 11"} (current),
                  -9.328d {-09d 19' 42"} (1950)
GRB_ERROR:       6.75 [deg radius, statistical only]
DATA_SIGNIF:     15.40 [sigma]
DATA_INTERVAL:   7.168 [sec]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52529.28 SOD {14:35:29.28} UT
GRB_PHI:         268.00 [deg]
GRB_THETA:        36.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        53.66d {+03h 34m 38s}  +19.25d {+19d 14' 52"}
SUN_DIST:         83.47 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.81d {+18h 43m 15s}  -28.03d {-28d 01' 42"}
MOON_DIST:        53.32 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       51.30,-48.73 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      332.16,  1.74 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_769098934.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1314210).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 16 May 25 14:44:49 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     769098934
GRB_RA:          333.170d {+22h 12m 41s} (J2000),
                 333.495d {+22h 13m 59s} (current),
                 332.530d {+22h 10m 07s} (1950)
GRB_DEC:          +0.140d {+00d 08' 24"} (J2000),
                  +0.266d {+00d 15' 58"} (current),
                  -0.108d {-00d 06' 27"} (1950)
GRB_ERROR:       8.52 [deg radius, statistical only]
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52529.28 SOD {14:35:29.28} UT
GRB_PHI:         272.00 [deg]
GRB_THETA:        27.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        53.67d {+03h 34m 40s}  +19.25d {+19d 14' 56"}
SUN_DIST:         80.64 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.89d {+18h 43m 33s}  -28.02d {-28d 01' 18"}
MOON_DIST:        57.73 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       61.87,-43.14 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      335.16, 10.47 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_locplot_all_bn250516608.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:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1314210).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:37:26 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.117d {-09d 07' 00"} (J2000)
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52633.26 SOD {14:37:13.26} UT,   104.3 [sec] since BAT Trigger Time
COUNTS:          37    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many iterations.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:39:09 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1314210,   Seg_Num: 0
GRB_RA:          334.561d {+22h 18m 15s} (J2000),
                 334.896d {+22h 19m 35s} (current),
                 333.901d {+22h 15m 36s} (1950)
GRB_DEC:          -9.130d {-09d 07' 48"} (J2000),
                  -9.002d {-09d 00' 08"} (current),
                  -9.381d {-09d 22' 50"} (1950)
GRB_DATE:        20811 TJD;   136 DOY;   25/05/16
GRB_TIME:        52528.92 SOD {14:35:28.92} UT
TRIGGER_INDEX:   124
GRB_PHI:         -159.82 [deg]
GRB_THETA:        38.11 [deg]
DELTA_TIME:      25.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     14.38 [sigma]
IMAGE_SIGNIF:    8.41 [sigma]
LC_URL:          sw01314210000msb.lc
SUN_POSTN:        53.66d {+03h 34m 39s}  +19.25d {+19d 14' 53"}
SUN_DIST:         82.53 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.83d {+18h 43m 20s}  -28.03d {-28d 01' 35"}
MOON_DIST:        54.18 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.05,-49.64 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      333.11,  1.32 [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 = 196.81,2.57 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:40:07 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.117d {-09d 07' 00"} (J2000)
POINT_ROLL:      69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52637.22 SOD {14:37:17.22} UT,   108.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.758
N_STARS:         27
X_OFFSET:        438 [pixels]
Y_OFFSET:        642 [pixels]
X_MAX:           1397 [pixels]
Y_MAX:           1601 [pixels]
DET_THRESH:      16
PHOTO_THRESH:    9
SL_URL:          sw01314210000msufc0108.fits
SUN_POSTN:        53.66d {+03h 34m 39s}  +19.25d {+19d 14' 53"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.84d {+18h 43m 22s}  -28.03d {-28d 01' 32"}
MOON_DIST:        54.19 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:40:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.117d {-09d 07' 00"} (J2000)
POINT_ROLL:      69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52637.22 SOD {14:37:17.22} UT,   108.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.758
N_STARS:         27
X_OFFSET:        438 [pixels]
Y_OFFSET:        642 [pixels]
X_MAX:           1397 [pixels]
Y_MAX:           1601 [pixels]
DET_THRESH:      16
PHOTO_THRESH:    9
SL_URL:          sw01314210000msufc0108.fits
SUN_POSTN:        53.66d {+03h 34m 39s}  +19.25d {+19d 14' 54"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.84d {+18h 43m 22s}  -28.03d {-28d 01' 32"}
MOON_DIST:        54.18 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN Circular #40466
The Fermi GBM team reports the detection of a likely LONG GRB
At 14:35:29 UT on 16 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250516A (trigger 769098934.27533 / 250516608).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 333.2, Dec = 0.1 (J2000 degrees, equivalent to J2000 22h 12m, 0d 06'), with a statistical uncertainty of 8.5 degrees.
The angle from the Fermi LAT boresight is 27.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_skymap_all_bn250516608.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/bn250516608/quicklook/glg_healpix_all_bn250516608.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/quicklook/glg_lc_medres34_bn250516608.gif

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:49:53 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.119d {-09d 07' 07"} (J2000)
ROLL:            69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52849.23 SOD {14:40:49.23} UT,   320.3 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     769099284
X_OFFSET:        757 [pixels]
Y_OFFSET:        961 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       917
Y_GRB_POS:       1121
BINNING_INDEX:   1
IM_URL:          sw01314210000msuni0356.fits
SUN_POSTN:        53.67d {+03h 34m 41s}  +19.25d {+19d 14' 59"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.94d {+18h 43m 44s}  -28.02d {-28d 01' 03"}
MOON_DIST:        54.10 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [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:     Fri 16 May 25 14:50:07 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.119d {-09d 07' 07"} (J2000)
ROLL:            69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52849.23 SOD {14:40:49.23} UT,   320.3 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     769099284
X_OFFSET:        757 [pixels]
Y_OFFSET:        961 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       917
Y_GRB_POS:       1121
BINNING_INDEX:   1
IM_URL:          sw01314210000msuni0356.fits
SUN_POSTN:        53.67d {+03h 34m 41s}  +19.25d {+19d 14' 59"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.94d {+18h 43m 45s}  -28.02d {-28d 01' 02"}
MOON_DIST:        54.10 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [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:     Fri 16 May 25 14:54:34 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1314210,   Seg_Num: 0
GRB_RA:          334.6097d {+22h 18m 26.32s} (J2000),
                 334.9444d {+22h 19m 46.65s} (current),
                 333.9495d {+22h 15m 47.88s} (1950)
GRB_DEC:          -9.1194d {-09d 07' 09.8"} (J2000),
                  -8.9916d {-08d 59' 29.8"} (current),
                  -9.3702d {-09d 22' 12.7"} (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:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52646.00 SOD {14:37:26.00} UT,   117.1 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        53.67d {+03h 34m 41s}  +19.25d {+19d 15' 02"}
SUN_DIST:         82.49 [deg]   Sun_angle= 5.2 [hr] (West of Sun)
MOON_POSTN:      280.98d {+18h 43m 55s}  -28.01d {-28d 00' 49"}
MOON_DIST:        54.10 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.10,-49.67 [deg] galactic lon,lat of the burst
ECL_COORDS:      333.15,  1.32 [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 Circular #40467
A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), R. Gupta (NASA GSFC), K. L. Page (U Leicester), S. P. R. Shilling (Lancaster U.) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 14:35:29 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250516A (trigger=1314210). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 334.561, -9.130 which is
```
   RA(J2000) = 22h 18m 15s
   Dec(J2000) = -09d 07' 48"
```
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 ~5000 counts/sec (15-350 keV), at ~5 sec after the trigger.
The XRT began observing the field at 14:37:13.2 UT, 104.3 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 334.60979, -9.11941 which is equivalent to:
```
   RA(J2000)  = 22h 18m 26.35s
   Dec(J2000) = -09d 07' 09.9"
```
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 177 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (5.84 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.8 (+1.47/-1.34) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 108 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 none of the XRT error circle. 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 0.062.
Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 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:     Fri 16 May 25 14:48:22 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.119d {-09d 07' 07"} (J2000)
POINT_ROLL:      69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52849.23 SOD {14:40:49.23} UT,   320.3 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.027
N_STARS:         49
X_OFFSET:        198 [pixels]
Y_OFFSET:        402 [pixels]
X_MAX:           1637 [pixels]
Y_MAX:           1841 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01314210000msufc0320.fits
SUN_POSTN:        53.67d {+03h 34m 40s}  +19.25d {+19d 14' 58"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.92d {+18h 43m 41s}  -28.02d {-28d 01' 08"}
MOON_DIST:        54.12 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:48:36 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.119d {-09d 07' 07"} (J2000)
POINT_ROLL:      69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52849.23 SOD {14:40:49.23} UT,   320.3 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.027
N_STARS:         49
X_OFFSET:        198 [pixels]
Y_OFFSET:        402 [pixels]
X_MAX:           1637 [pixels]
Y_MAX:           1841 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01314210000msufc0320.fits
SUN_POSTN:        53.67d {+03h 34m 40s}  +19.25d {+19d 14' 58"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.92d {+18h 43m 42s}  -28.02d {-28d 01' 07"}
MOON_DIST:        54.11 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [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:     Fri 16 May 25 14:42:00 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.117d {-09d 07' 00"} (J2000)
ROLL:            69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52637.22 SOD {14:37:17.22} UT,   108.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     769099072
X_OFFSET:        757 [pixels]
Y_OFFSET:        961 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       917
Y_GRB_POS:       1121
BINNING_INDEX:   1
IM_URL:          sw01314210000msuni0144.fits
SUN_POSTN:        53.66d {+03h 34m 39s}  +19.25d {+19d 14' 55"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.86d {+18h 43m 26s}  -28.02d {-28d 01' 27"}
MOON_DIST:        54.17 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [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:     Fri 16 May 25 14:42:03 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1314210,   Seg_Num: 0
GRB_RA:            0.0000d {+00h 00m 00.00s} (J2000),
                   0.3251d {+00h 01m 18.02s} (current),
                 359.3595d {+23h 57m 26.27s} (1950)
GRB_DEC:          +0.0000d {+00d 00' 00.0"} (J2000),
                  +0.1413d {+00d 08' 28.5"} (current),
                  -0.2784d {-00d 16' 42.2"} (1950)
GRB_ERROR:       0.0 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52646.00 SOD {14:37:26.00} UT,   117.1 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        53.66d {+03h 34m 39s}  +19.25d {+19d 14' 55"}
SUN_DIST:         55.63 [deg]   Sun_angle= 3.6 [hr] (West of Sun)
MOON_POSTN:      280.86d {+18h 43m 26s}  -28.02d {-28d 01' 27"}
MOON_DIST:        80.78 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       96.34,-60.19 [deg] galactic lon,lat of the burst
ECL_COORDS:        0.00,  0.00 [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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 May 25 14:41:54 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1314210,   Seg_Num: 0
POINT_RA:        334.568d {+22h 18m 16s} (J2000)
POINT_DEC:        -9.117d {-09d 07' 00"} (J2000)
ROLL:            69.103d
IMG_START_DATE:  20811 TJD;   136 DOY;   25/05/16
IMG_START_TIME:  52637.22 SOD {14:37:17.22} UT,   108.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     769099072
X_OFFSET:        757 [pixels]
Y_OFFSET:        961 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       917
Y_GRB_POS:       1121
BINNING_INDEX:   1
IM_URL:          sw01314210000msuni0144.fits
SUN_POSTN:        53.66d {+03h 34m 39s}  +19.25d {+19d 14' 54"}
SUN_DIST:         82.52 [deg]   Sun_angle= 5.3 [hr] (West of Sun)
MOON_POSTN:      280.86d {+18h 43m 26s}  -28.02d {-28d 01' 27"}
MOON_DIST:        54.17 [deg]
MOON_ILLUM:      86 [%]
GAL_COORDS:       52.07,-49.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      333.12,  1.33 [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 Circular #40468
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 1717 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250516A, 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 = 334.60978, -9.11949 which is equivalent to:
```
RA (J2000): 22h 18m 26.35s
Dec (J2000): -09d 07' 10.2"
```
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 #40471
S. P. R. Shilling (Lancaster U.) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250516A 108 s after the BAT trigger (Beardmore et al., GCN Circ. 40467). A source consistent with the enhanced XRT position (Evans et al., GCN Circ. 40468) is detected in the initial UVOT exposures.
The preliminary detection and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)        Mag

white              108         1715          411         20.5 +/- 0.3
v                  650         1765          136        >18.5
b                  576         1691          117        >19.2
u                  320         1838          362        >19.7
w1                 699         1814          117        >18.8
w2                 626         1741           97        >19.1
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.062 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #40472
A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), M.A. Williams (PSU), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.8 ks of XRT data for GRB 250516A, from 108 s to 23.8 ks after the trigger. The data comprise 151 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+5.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.45 (+0.18, -0.17).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.44 (+0.13, -0.12). The best-fitting absorption column is 3.5 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 5.8 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.98 (+/-0.12) and a best-fitting absorption column of 3.0 (+/-0.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.0 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 5.8 x 10^20 cm^-2
Excess significance: 8.2 sigma
Photon index:	     1.98 (+/-0.12)
```
If the light curve continues to decay with a power-law decay index of 1.45, the count rate at T+24 hours will be 5.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x 10^-13 (3.3 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/01314210.
This circular is an official product of the Swift-XRT team.
GCN Circular #40473
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 14:35:29.28 UT on 16 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250516A (trigger 769098934/250516608). which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 40467). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 36 degrees.
The GBM light curve consists of two peaks with a duration (T90) of about 21.8 s (50-300 keV). The time-averaged spectrum from T0-1.4 to T0+25.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 200 +/- 30 keV.
The event fluence (10-1000 keV) in this time interval is (4.8 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+5.1 s in the 10-1000 keV band is 5.8 +/- 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 #40475
M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long duration GRB 250516A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40466), and Swift/BAT (Beardmore et al., GCN Circ. 40467).
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a single burst of emission that peaked at 2025-05-16 14:35:33.81 UTC. The measured peak count rate associated with the burst is 333 (+66, -72) counts/s above the background in the combined data of all quadrants, with a total of 527 (+187, -195) counts. The local mean background count rate was 1349 (+8, -9) counts/s. We measure a T90 of 2.4 (+1.8, -1.2) s from the cumulative Veto light curve. We note that our T90 is low since we detect just the brightest burst episode from the lightcurve seen in other missions (Fermi/GBM, Swift/BAT). This is likely due to the unfavourable orientation of our detectors with respect to the GRB.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb
GCN Circular #40477
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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 250516A ( A. P. Beardmore et al., GCN 40467) errorbox 54907 sec after notice time and 54930 sec after trigger time at 2025-05-17 05:50:59 UT, with upper limit up to 15.5 mag. The observations began at zenith distance = 77 deg. The sun altitude is -68.5 deg.
The galactic latitude b = -50 deg., longitude l = 53 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2872228
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   55020 |         MASTER-OAFA |   C |   180 | 15.5 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN Circular #40482
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 State University), 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250516A ( Fermi GBM team, GCN 40466) errorbox 53236 sec after notice time and 53273 sec after trigger time at 2025-05-17 05:23:23 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 81 deg. The sun altitude is -73.4 deg.
The galactic latitude b = -43 deg., longitude l = 63 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2872281
We obtain a following upper limits.

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

   53354 | 2025-05-17 05:23:23 |         MASTER-OAFA | (22h 08m 57.57s , -09d 53m 16.4s) |   C |   160 | 16.3 |        
   54587 | 2025-05-17 05:43:56 |         MASTER-OAFA | (22h 08m 53.80s , -09d 49m 35.9s) |   C |   160 | 16.6 |        
   54724 | 2025-05-17 05:47:13 |         MASTER-OAFA | (22h 08m 48.08s , -09d 50m 58.9s) |   C |    40 | 16.7 |        
   55010 | 2025-05-17 05:50:59 |         MASTER-OAFA | (22h 09m 00.15s , -09d 50m 43.3s) |   C |   160 | 16.9 |        
   55020 | 2025-05-17 05:50:59 |         MASTER-OAFA | (22h 19m 10.53s , -09d 28m 33.4s) |   C |   180 | 15.5 |        
   55206 | 2025-05-17 05:54:15 |         MASTER-OAFA | (22h 08m 57.96s , -09d 49m 01.8s) |   C |   160 | 17.0 |        
   55216 | 2025-05-17 05:54:15 |         MASTER-OAFA | (22h 19m 08.28s , -09d 26m 54.9s) |   C |   180 | 16.0 |        
   55401 | 2025-05-17 05:57:30 |         MASTER-OAFA | (22h 08m 58.20s , -09d 49m 52.9s) |   C |   160 | 17.0 |        
   55411 | 2025-05-17 05:57:30 |         MASTER-OAFA | (22h 19m 08.56s , -09d 27m 47.0s) |   C |   180 | 16.7 |        
   55597 | 2025-05-17 06:00:46 |         MASTER-OAFA | (22h 09m 01.12s , -09d 48m 33.7s) |   C |   160 | 17.1 |        
   55607 | 2025-05-17 06:00:46 |         MASTER-OAFA | (22h 19m 11.35s , -09d 26m 29.4s) |   C |   180 | 16.9 |        
   56557 | 2025-05-17 06:16:46 |         MASTER-OAFA | (22h 08m 55.08s , -09d 48m 15.8s) |   C |   160 | 17.1 |        
   56568 | 2025-05-17 06:16:46 |         MASTER-OAFA | (22h 19m 06.24s , -09d 26m 09.9s) |   C |   180 | 17.9 |        
   56752 | 2025-05-17 06:20:01 |         MASTER-OAFA | (22h 08m 57.37s , -09d 46m 58.3s) |   C |   160 | 17.3 |        
   56763 | 2025-05-17 06:20:02 |         MASTER-OAFA | (22h 19m 08.29s , -09d 24m 56.6s) |   C |   180 | 18.0 |        
   56946 | 2025-05-17 06:23:15 |         MASTER-OAFA | (22h 09m 01.40s , -09d 47m 45.6s) |   C |   160 | 17.4 |        
   56956 | 2025-05-17 06:23:15 |         MASTER-OAFA | (22h 19m 12.42s , -09d 25m 45.4s) |   C |   180 | 18.3 |        
   57850 | 2025-05-17 06:39:19 |         MASTER-OAFA | (22h 08m 51.04s , -09d 48m 32.1s) |   C |    40 | 17.1 |        
   57860 | 2025-05-17 06:39:19 |         MASTER-OAFA | (22h 18m 01.41s , -09d 25m 06.5s) |   C |    60 | 18.3 |        
   58215 | 2025-05-17 06:44:23 |         MASTER-OAFA | (22h 09m 03.18s , -09d 45m 55.1s) |   C |   160 | 17.5 |        
   58225 | 2025-05-17 06:44:24 |         MASTER-OAFA | (22h 19m 14.38s , -09d 23m 59.1s) |   C |   180 | 18.8 |        
   59041 | 2025-05-17 06:59:10 |         MASTER-OAFA | (22h 08m 45.76s , -09d 46m 30.8s) |   C |    40 | 17.1 |        
   59051 | 2025-05-17 06:59:10 |         MASTER-OAFA | (22h 17m 56.74s , -09d 23m 08.5s) |   C |    60 | 18.5 |        
   59424 | 2025-05-17 07:04:33 |         MASTER-OAFA | (22h 08m 56.48s , -09d 46m 31.6s) |   C |   160 | 17.5 |        
   59434 | 2025-05-17 07:04:33 |         MASTER-OAFA | (22h 19m 08.49s , -09d 24m 38.0s) |   C |   180 | 18.9 |        
   60168 | 2025-05-17 07:17:57 |         MASTER-OAFA | (22h 08m 45.17s , -09d 46m 41.0s) |   C |    40 | 17.1 |        
   60179 | 2025-05-17 07:17:57 |         MASTER-OAFA | (22h 17m 56.70s , -09d 23m 17.5s) |   C |    60 | 18.7 |        
   60363 | 2025-05-17 07:21:11 |         MASTER-OAFA | (22h 08m 48.12s , -09d 44m 50.5s) |   C |    40 | 17.3 |        
   60373 | 2025-05-17 07:21:12 |         MASTER-OAFA | (22h 17m 59.64s , -09d 21m 30.3s) |   C |    60 | 18.9 |        
   60616 | 2025-05-17 07:24:25 |         MASTER-OAFA | (22h 09m 03.10s , -09d 43m 57.6s) |   C |   160 | 17.8 |        
   60626 | 2025-05-17 07:24:25 |         MASTER-OAFA | (22h 19m 14.88s , -09d 21m 57.0s) |   C |   180 | 19.1 |        
   62075 | 2025-05-17 07:48:44 |         MASTER-OAFA | (22h 08m 55.13s , -09d 42m 54.6s) |   C |   160 | 17.7 |        
   62086 | 2025-05-17 07:48:44 |         MASTER-OAFA | (22h 19m 08.48s , -09d 20m 53.2s) |   C |   180 | 19.3 |        
   62214 | 2025-05-17 07:52:02 |         MASTER-OAFA | (22h 08m 49.30s , -09d 44m 23.1s) |   C |    40 | 17.4 |        
   62224 | 2025-05-17 07:52:03 |         MASTER-OAFA | (22h 18m 01.84s , -09d 20m 58.6s) |   C |    60 | 19.2 |        
   63302 | 2025-05-17 08:09:10 |         MASTER-OAFA | (22h 08m 57.42s , -09d 43m 55.7s) |   C |   160 | 18.0 |        
   63312 | 2025-05-17 08:09:11 |         MASTER-OAFA | (22h 19m 11.59s , -09d 21m 56.1s) |   C |   180 | 19.6 |        
   65610 | 2025-05-17 08:47:39 |         MASTER-OAFA | (22h 08m 55.02s , -09d 41m 06.6s) |   C |   160 | 18.1 |        
   65620 | 2025-05-17 08:47:39 |         MASTER-OAFA | (22h 19m 09.74s , -09d 19m 09.9s) |   C |   180 | 19.6 |        
   66945 | 2025-05-17 09:09:53 |         MASTER-OAFA | (22h 08m 56.20s , -09d 42m 17.9s) |   C |   160 | 18.2 |        
   66955 | 2025-05-17 09:09:54 |         MASTER-OAFA | (22h 19m 12.01s , -09d 20m 14.9s) |   C |   180 | 19.8 |        
   68016 | 2025-05-17 09:28:45 |         MASTER-OAFA | (21h 54m 48.23s , -07d 54m 13.2s) |   C |    40 | 17.7 |        
   68155 | 2025-05-17 09:30:04 |         MASTER-OAFA | (22h 27m 36.59s , -08d 43m 27.0s) |   C |   160 | 18.4 |        
   68165 | 2025-05-17 09:30:04 |         MASTER-OAFA | (22h 17m 17.92s , -09d 03m 28.4s) |   C |   180 | 19.7 |        
   68957 | 2025-05-17 09:44:25 |         MASTER-OAFA | (21h 54m 46.25s , -07d 53m 07.2s) |   C |    40 | 17.7 |        
   69276 | 2025-05-17 09:49:45 |         MASTER-OAFA | (22h 27m 06.28s , +01d 35m 10.8s) |   C |    40 | 17.4 |        
   69286 | 2025-05-17 09:49:45 |         MASTER-OAFA | (22h 17m 55.04s , +01d 12m 56.3s) |   C |    60 | 18.7 |        
   69415 | 2025-05-17 09:51:03 |         MASTER-OAFA | (22h 27m 35.48s , -08d 42m 28.0s) |   C |   160 | 18.6 |        
   69425 | 2025-05-17 09:51:04 |         MASTER-OAFA | (22h 17m 16.20s , -09d 02m 35.8s) |   C |   180 | 19.7 |        
   69553 | 2025-05-17 09:54:21 |         MASTER-OAFA | (22h 26m 50.43s , -00d 18m 25.4s) |   C |    40 | 17.5 |        
   69563 | 2025-05-17 09:54:22 |         MASTER-OAFA | (22h 17m 38.98s , -00d 40m 37.2s) |   C |    60 | 19.2 |        
   69631 | 2025-05-17 09:55:39 |         MASTER-OAFA | (22h 11m 55.19s , +01d 37m 25.6s) |   C |    40 | 17.4 |        
   69641 | 2025-05-17 09:55:40 |         MASTER-OAFA | (22h 02m 43.70s , +01d 15m 10.5s) |   C |    60 | 19.4 |        
   69706 | 2025-05-17 09:56:55 |         MASTER-OAFA | (22h 28m 42.02s , +03d 30m 10.0s) |   C |    40 | 17.0 |        
   69716 | 2025-05-17 09:56:55 |         MASTER-OAFA | (22h 19m 30.05s , +03d 07m 48.2s) |   C |    60 | 18.1 |        
   69785 | 2025-05-17 09:58:14 |         MASTER-OAFA | (22h 42m 12.03s , +01d 36m 43.5s) |   C |    40 | 17.9 |        
   69795 | 2025-05-17 09:58:14 |         MASTER-OAFA | (22h 33m 00.73s , +01d 14m 23.6s) |   C |    60 | 19.3 |        
   69865 | 2025-05-17 09:59:33 |         MASTER-OAFA | (22h 43m 22.31s , -02d 12m 22.6s) |   C |    40 | 17.8 |        
   69875 | 2025-05-17 09:59:34 |         MASTER-OAFA | (22h 34m 10.40s , -02d 34m 34.0s) |   C |    60 | 19.3 |        
   69944 | 2025-05-17 10:00:52 |         MASTER-OAFA | (22h 27m 01.19s , +01d 35m 18.5s) |   C |    40 | 17.4 |        
   69954 | 2025-05-17 10:00:53 |         MASTER-OAFA | (22h 17m 49.81s , +01d 12m 59.9s) |   C |    60 | 18.8 |        
   70024 | 2025-05-17 10:02:12 |         MASTER-OAFA | (22h 30m 55.45s , -04d 06m 35.7s) |   C |    40 | 17.7 |        
   70034 | 2025-05-17 10:02:13 |         MASTER-OAFA | (22h 21m 42.26s , -04d 28m 41.7s) |   C |    60 | 19.2 |        
   70103 | 2025-05-17 10:03:31 |         MASTER-OAFA | (22h 12m 53.62s , -02d 10m 32.8s) |   C |    40 | 17.7 |        
   70113 | 2025-05-17 10:03:32 |         MASTER-OAFA | (22h 03m 41.57s , -02d 32m 40.4s) |   C |    60 | 19.3 |        
   70179 | 2025-05-17 10:04:48 |         MASTER-OAFA | (22h 26m 50.63s , -00d 18m 22.6s) |   C |    40 | 17.4 |        
   70189 | 2025-05-17 10:04:48 |         MASTER-OAFA | (22h 17m 39.16s , -00d 40m 35.4s) |   C |    60 | 19.0 |        
   70258 | 2025-05-17 10:06:07 |         MASTER-OAFA | (22h 11m 54.89s , +01d 37m 38.1s) |   C |    40 | 17.4 |        
   70268 | 2025-05-17 10:06:07 |         MASTER-OAFA | (22h 02m 43.38s , +01d 15m 22.1s) |   C |    60 | 19.3 |        
   70335 | 2025-05-17 10:07:24 |         MASTER-OAFA | (22h 28m 43.22s , +03d 30m 23.6s) |   C |    40 | 17.0 |        
   70346 | 2025-05-17 10:07:24 |         MASTER-OAFA | (22h 19m 31.24s , +03d 08m 01.5s) |   C |    60 | 18.1 |        
   70413 | 2025-05-17 10:08:42 |         MASTER-OAFA | (22h 42m 12.23s , +01d 36m 55.4s) |   C |    40 | 17.9 |        
   70423 | 2025-05-17 10:08:42 |         MASTER-OAFA | (22h 33m 00.93s , +01d 14m 35.7s) |   C |    60 | 19.3 |        
   70490 | 2025-05-17 10:09:59 |         MASTER-OAFA | (22h 43m 21.90s , -02d 12m 10.0s) |   C |    40 | 17.6 |        
   70500 | 2025-05-17 10:09:59 |         MASTER-OAFA | (22h 34m 09.98s , -02d 34m 21.8s) |   C |    60 | 19.1 |        
   70629 | 2025-05-17 10:11:18 |         MASTER-OAFA | (22h 27m 33.04s , -08d 43m 51.9s) |   C |   160 | 18.5 |        
   70639 | 2025-05-17 10:11:18 |         MASTER-OAFA | (22h 17m 13.64s , -09d 04m 01.9s) |   C |   180 | 19.6 |        
   70767 | 2025-05-17 10:14:36 |         MASTER-OAFA | (22h 27m 07.09s , +01d 35m 50.2s) |   C |    40 | 17.4 |        
   70777 | 2025-05-17 10:14:36 |         MASTER-OAFA | (22h 17m 55.62s , +01d 13m 33.1s) |   C |    60 | 18.7 |        
   70845 | 2025-05-17 10:15:54 |         MASTER-OAFA | (22h 30m 52.15s , -04d 04m 48.9s) |   C |    40 | 17.5 |        
   70856 | 2025-05-17 10:15:54 |         MASTER-OAFA | (22h 21m 38.89s , -04d 26m 54.1s) |   C |    60 | 19.0 |        
   70923 | 2025-05-17 10:17:12 |         MASTER-OAFA | (22h 12m 53.74s , -02d 11m 39.7s) |   C |    40 | 17.6 |        
   70933 | 2025-05-17 10:17:12 |         MASTER-OAFA | (22h 03m 41.60s , -02d 33m 46.9s) |   C |    60 | 19.3 |        
   70999 | 2025-05-17 10:18:28 |         MASTER-OAFA | (22h 26m 52.97s , -00d 16m 47.4s) |   C |    40 | 17.5 |        
   71009 | 2025-05-17 10:18:28 |         MASTER-OAFA | (22h 17m 41.41s , -00d 38m 59.6s) |   C |    60 | 19.0 |        
   71076 | 2025-05-17 10:19:44 |         MASTER-OAFA | (22h 11m 47.30s , +01d 37m 17.4s) |   C |    40 | 17.4 |        
   71086 | 2025-05-17 10:19:45 |         MASTER-OAFA | (22h 02m 35.75s , +01d 15m 02.1s) |   C |    60 | 19.0 |        
   71153 | 2025-05-17 10:21:02 |         MASTER-OAFA | (22h 28m 42.63s , +03d 31m 39.9s) |   C |    40 | 16.9 |        
   71164 | 2025-05-17 10:21:02 |         MASTER-OAFA | (22h 19m 30.49s , +03d 09m 19.0s) |   C |    60 | 17.9 |        
   71231 | 2025-05-17 10:22:20 |         MASTER-OAFA | (22h 42m 19.67s , +01d 36m 09.6s) |   C |    40 | 17.5 |        
   71241 | 2025-05-17 10:22:20 |         MASTER-OAFA | (22h 33m 08.20s , +01d 13m 51.0s) |   C |    60 | 18.7 |        
   71309 | 2025-05-17 10:23:38 |         MASTER-OAFA | (22h 43m 15.76s , -02d 12m 56.3s) |   C |    40 | 17.4 |        
   71319 | 2025-05-17 10:23:38 |         MASTER-OAFA | (22h 34m 03.65s , -02d 35m 05.9s) |   C |    60 | 18.8 |        
   71386 | 2025-05-17 10:24:55 |         MASTER-OAFA | (22h 27m 07.17s , +01d 36m 13.3s) |   C |    40 | 16.8 |        
   71396 | 2025-05-17 10:24:55 |         MASTER-OAFA | (22h 17m 55.54s , +01d 13m 57.3s) |   C |    60 | 18.3 |        
   71464 | 2025-05-17 10:26:13 |         MASTER-OAFA | (22h 30m 52.43s , -04d 04m 36.5s) |   C |    40 | 17.1 |        
   71475 | 2025-05-17 10:26:13 |         MASTER-OAFA | (22h 21m 38.98s , -04d 26m 39.6s) |   C |    60 | 18.5 |        
   71542 | 2025-05-17 10:27:31 |         MASTER-OAFA | (22h 12m 53.84s , -02d 11m 34.0s) |   C |    40 | 17.1 |        
   71552 | 2025-05-17 10:27:31 |         MASTER-OAFA | (22h 03m 41.51s , -02d 33m 39.0s) |   C |    60 | 18.5 |        
   71620 | 2025-05-17 10:28:49 |         MASTER-OAFA | (22h 26m 53.05s , -00d 16m 22.4s) |   C |    40 | 16.7 |        
   71631 | 2025-05-17 10:28:49 |         MASTER-OAFA | (22h 17m 41.27s , -00d 38m 32.2s) |   C |    60 | 18.3 |        
   71697 | 2025-05-17 10:30:06 |         MASTER-OAFA | (22h 11m 49.08s , +01d 37m 28.1s) |   C |    40 | 16.6 |        
   71708 | 2025-05-17 10:30:06 |         MASTER-OAFA | (22h 02m 37.28s , +01d 15m 16.2s) |   C |    60 | 18.3 |        
   71836 | 2025-05-17 10:31:25 |         MASTER-OAFA | (22h 27m 34.11s , -08d 41m 29.1s) |   C |   160 | 17.4 |        
   71974 | 2025-05-17 10:34:43 |         MASTER-OAFA | (22h 28m 49.55s , +03d 30m 54.7s) |   C |    40 | 15.9 |        
   72050 | 2025-05-17 10:35:59 |         MASTER-OAFA | (22h 42m 11.99s , +01d 35m 23.8s) |   C |    40 | 16.2 |        
   72127 | 2025-05-17 10:37:16 |         MASTER-OAFA | (22h 43m 23.70s , -02d 12m 28.1s) |   C |    40 | 16.0 |

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

GCN Circular #40485
D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report
The long GRB 250516A (Fermi GBM detection: Fermi GBM team, GCN 40466; Mukherjee & Meegan, GCN 40473; Swift detection: Beardmore et al., GCN 40467) was detected by Konus-Wind (KW) in the waiting mode.
A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~11 sigma count-rate increase in the interval from T0-2.757 s to T0+23.739 s where T0 = 14:35:29 UT.
The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250516A/
Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.21 (-0.10, + 0.10) and Ep = 164(-9,+10) keV.
Modelling the spectrum near the peak count rate (T0+3.131 s to T0+9.019 s) by a CPL function yields alpha = -1.35 (-0.10, + 0.11) and Ep = 403(-53,+82) keV.
In the 20 keV -10 MeV band, standard for the KW analysis, the burst fluence is (4.41 ± 1.33)x10^-6 erg/cm^2 and the 2.944 s peak energy flux, measured from T0+6.075 s, is (5.85 ± 0.42)x10^-7 erg/cm^2/s.
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
GCN Circular #40486
Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the GRB 250516A (Fermi GBM team GCN Circ. 40466; Beardmore et al., GCN Circ. 40467; Frederiks et al., GCN Circ. 40485) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-18 09:59 to 11:20 UTC (from 43.4 to 44.8 hours after the trigger) and obtained 64 minutes of exposure in the r filter.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the XRT source position (Evans et al., GCN Circ. 40468) down to the following 3-sigma limit:
r > 22.08
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular #40487
T. Sakamoto (AGU), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), (i.e. the Swift-BAT team):
Using the data set from T-240 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250516A (trigger #1314210) (Beardmore et al., GCN Circ. 40467). The BAT ground-calculated position is RA, Dec = 334.612, -9.120 deg which is
```
   RA(J2000)  =  22h 18m 26.8s
   Dec(J2000) = -09d 07' 11.9"
```
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 61%.
The mask-weighted light curve shows a multi-peaked structure that starts at ~T-20 s and ends at ~T+23 s. The highest peak occurs at ~T+20 s. T90 (15-350 keV) is 30.04 +- 6.01 sec (estimated error including systematics).
The time-averaged spectrum from T-19.96 to T+22.70 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.69 +- 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+19.39 sec in the 15-150 keV band is 3.8 +- 0.3 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/1314210

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Jochen Greiner, last update: 19-May-2025 [Disclaimer]