Gamma-ray Burst 250327A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:31:43 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1299088,   Seg_Num: 0
GRB_RA:          248.197d {+16h 32m 47s} (J2000),
                 248.280d {+16h 33m 07s} (current),
                 248.035d {+16h 32m 09s} (1950)
GRB_DEC:         +61.595d {+61d 35' 43"} (J2000),
                 +61.543d {+61d 32' 36"} (current),
                 +61.699d {+61d 41' 57"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=1424 [image_cnts]
TRIGGER_DUR:     88.000 [sec] 
TRIGGER_INDEX:   20000     E_range: 15-50 keV
BKG_INTEN:       0 [cnts]
BKG_TIME:        0.00 SOD {00:00:00.00} UT
BKG_DUR:         0 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27004.68 SOD {07:30:04.68} UT
GRB_PHI:         -143.77 [deg]
GRB_THETA:        50.63 [deg]
SOLN_STATUS:     0x20000013
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    8.75 [sigma]
MERIT_PARAMS:     +1  +0  +0  +6  +1  -1  +0  +0 +18  +0 
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 03"}
SUN_DIST:        100.48 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:      339.69d {+22h 38m 46s}  -10.44d {-10d 26' 26"}
MOON_DIST:        99.84 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       92.25, 39.93 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      197.39, 79.33 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.)  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 239.02,-18.50 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(2.0<100sec) coincident with the FERMI_GBM event (trignum=764753411).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:30:54 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     764753411
GRB_RA:          239.780d {+15h 59m 07s} (J2000),
                 239.878d {+15h 59m 31s} (current),
                 239.587d {+15h 58m 21s} (1950)
GRB_DEC:         +61.680d {+61d 40' 48"} (J2000),
                 +61.609d {+61d 36' 34"} (current),
                 +61.821d {+61d 49' 14"} (1950)
GRB_ERROR:       5.18 [deg radius, statistical only]
DATA_SIGNIF:     24.00 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         233.00 [deg]
GRB_THETA:        48.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 02"}
SUN_DIST:        103.90 [deg]   Sun_angle= 8.4 [hr] (West of Sun)
MOON_POSTN:      339.69d {+22h 38m 44s}  -10.44d {-10d 26' 40"}
MOON_DIST:       103.84 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       94.34, 43.61 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      186.20, 76.10 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_764753411.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:30:35 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     764753411
GRB_RA:          244.933d {+16h 19m 44s} (J2000),
                 244.915d {+16h 19m 40s} (current),
                 244.973d {+16h 19m 53s} (1950)
GRB_DEC:         +69.583d {+69d 34' 60"} (J2000),
                 +69.524d {+69d 31' 26"} (current),
                 +69.701d {+69d 42' 04"} (1950)
GRB_ERROR:       11.55 [deg radius, statistical plus systematic]
GRB_INTEN:       192 [cnts/sec]
DATA_SIGNIF:     9.50 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         235.00 [deg]
GRB_THETA:        40.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.84
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   2%  Cyg X-1
DETECTORS:       0,0,0, 0,0,0, 1,1,0, 0,0,0, 0,0,
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 02"}
SUN_DIST:         97.90 [deg]   Sun_angle= 8.1 [hr] (West of Sun)
MOON_POSTN:      339.68d {+22h 38m 44s}  -10.45d {-10d 26' 45"}
MOON_DIST:       101.45 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:      102.44, 38.18 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      150.72, 80.24 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 165.92,18.55 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:30:44 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      59
TRIGGER_NUM:     764753411
GRB_RA:          259.017d {+17h 16m 04s} (J2000),
                 258.988d {+17h 15m 57s} (current),
                 259.075d {+17h 16m 18s} (1950)
GRB_DEC:         +68.600d {+68d 35' 60"} (J2000),
                 +68.573d {+68d 34' 24"} (current),
                 +68.653d {+68d 39' 10"} (1950)
GRB_ERROR:       7.37 [deg radius, statistical plus systematic]
GRB_INTEN:       184 [cnts/sec]
DATA_SIGNIF:     20.60 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         243.00 [deg]
GRB_THETA:        40.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.70
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 1,1,0, 0,0,0, 0,0,
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 02"}
SUN_DIST:         93.69 [deg]   Sun_angle= 7.2 [hr] (West of Sun)
MOON_POSTN:      339.68d {+22h 38m 44s}  -10.45d {-10d 26' 42"}
MOON_DIST:        96.35 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       99.26, 33.77 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      149.03, 85.35 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 165.92,18.55 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:31:29 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     764753411
GRB_RA:          239.950d {+15h 59m 48s} (J2000),
                 240.038d {+16h 00m 09s} (current),
                 239.778d {+15h 59m 07s} (1950)
GRB_DEC:         +62.720d {+62d 43' 12"} (J2000),
                 +62.650d {+62d 38' 59"} (current),
                 +62.860d {+62d 51' 35"} (1950)
GRB_ERROR:       4.96 [deg radius, statistical only]
DATA_SIGNIF:     24.00 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         233.00 [deg]
GRB_THETA:        47.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 03"}
SUN_DIST:        103.25 [deg]   Sun_angle= 8.4 [hr] (West of Sun)
MOON_POSTN:      339.69d {+22h 38m 46s}  -10.44d {-10d 26' 30"}
MOON_DIST:       103.69 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       95.57, 43.08 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      182.61, 76.72 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_764753411.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:31:40 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     764753411
GRB_RA:          244.240d {+16h 16m 58s} (J2000),
                 244.340d {+16h 17m 22s} (current),
                 244.043d {+16h 16m 10s} (1950)
GRB_DEC:         +60.500d {+60d 30' 00"} (J2000),
                 +60.439d {+60d 26' 21"} (current),
                 +60.621d {+60d 37' 17"} (1950)
GRB_ERROR:       4.16 [deg radius, statistical only]
DATA_SIGNIF:     24.20 [sigma]
DATA_INTERVAL:   8.192 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         236.00 [deg]
GRB_THETA:        49.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 03"}
SUN_DIST:        102.68 [deg]   Sun_angle= 8.1 [hr] (West of Sun)
MOON_POSTN:      339.69d {+22h 38m 46s}  -10.44d {-10d 26' 27"}
MOON_DIST:       101.71 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       91.70, 42.10 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      195.83, 77.15 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_764753411.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:31:57 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     764753411
GRB_RA:          249.540d {+16h 38m 10s} (J2000),
                 249.603d {+16h 38m 25s} (current),
                 249.416d {+16h 37m 40s} (1950)
GRB_DEC:         +63.160d {+63d 09' 36"} (J2000),
                 +63.111d {+63d 06' 39"} (current),
                 +63.258d {+63d 15' 27"} (1950)
GRB_ERROR:       2.22 [deg radius, statistical only]
DATA_SIGNIF:     26.40 [sigma]
DATA_INTERVAL:   14.336 [sec]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         239.00 [deg]
GRB_THETA:        46.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:         6.33d {+00h 25m 18s}   +2.73d {+02d 44' 03"}
SUN_DIST:         99.24 [deg]   Sun_angle= 7.8 [hr] (West of Sun)
MOON_POSTN:      339.69d {+22h 38m 47s}  -10.44d {-10d 26' 22"}
MOON_DIST:        99.34 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       93.95, 38.87 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      191.88, 80.72 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_764753411.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(2.0<100sec) coincident with the SWIFT_BAT event (trignum=1299088).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:39:26 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     764753411
GRB_RA:          246.110d {+16h 24m 26s} (J2000),
                 246.189d {+16h 24m 45s} (current),
                 245.956d {+16h 23m 49s} (1950)
GRB_DEC:         +62.330d {+62d 19' 48"} (J2000),
                 +62.273d {+62d 16' 23"} (current),
                 +62.443d {+62d 26' 35"} (1950)
GRB_ERROR:       3.57 [deg radius, statistical only]
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27006.33 SOD {07:30:06.33} UT
GRB_PHI:         237.00 [deg]
GRB_THETA:        47.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:         6.33d {+00h 25m 19s}   +2.74d {+02d 44' 11"}
SUN_DIST:        101.02 [deg]   Sun_angle= 8.0 [hr] (West of Sun)
MOON_POSTN:      339.76d {+22h 39m 03s}  -10.41d {-10d 24' 19"}
MOON_DIST:       100.86 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       93.58, 40.63 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      191.21, 78.95 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_locplot_all_bn250327313.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(2.0<100sec) coincident with the SWIFT_BAT event (trignum=1299088).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 27 Mar 25 07:34:18 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1299088,   Seg_Num: 0
GRB_RA:          248.197d {+16h 32m 47s} (J2000),
                 248.280d {+16h 33m 07s} (current),
                 248.035d {+16h 32m 09s} (1950)
GRB_DEC:         +61.595d {+61d 35' 43"} (J2000),
                 +61.543d {+61d 32' 36"} (current),
                 +61.699d {+61d 41' 57"} (1950)
GRB_DATE:        20761 TJD;    86 DOY;   25/03/27
GRB_TIME:        27004.68 SOD {07:30:04.68} UT
TRIGGER_INDEX:   20000
GRB_PHI:         -143.77 [deg]
GRB_THETA:        50.63 [deg]
DELTA_TIME:      0.00 [sec]
TRIGGER_DUR:     88.000 [sec] 
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    8.75 [sigma]
LC_URL:          sw01299088000msb.lc
SUN_POSTN:         6.33d {+00h 25m 19s}   +2.73d {+02d 44' 06"}
SUN_DIST:        100.48 [deg]   Sun_angle= 7.9 [hr] (West of Sun)
MOON_POSTN:      339.72d {+22h 38m 52s}  -10.43d {-10d 25' 44"}
MOON_DIST:        99.84 [deg]
MOON_ILLUM:      7 [%]
GAL_COORDS:       92.25, 39.93 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      197.39, 79.33 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is an image trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 239.02,-18.50 [deg].

GCN Circular #39876
The Fermi GBM team reports the detection of a likely LONG GRB
At 07:30:06 UT on 27 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250327A (trigger 764753411.32631 / 250327313).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 246.1, Dec = 62.3 (J2000 degrees, equivalent to J2000 16h 24m, 62d 17'), with a statistical uncertainty of 3.6 degrees.
The angle from the Fermi LAT boresight is 47.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_skymap_all_bn250327313.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/bn250327313/quicklook/glg_healpix_all_bn250327313.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/quicklook/glg_lc_medres34_bn250327313.gif
GCN Circular #39877
T. M. Parsotan (GSFC), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team:
At 07:30:04 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250327A (trigger=1299088). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 248.197, +61.595 which is
```
   RA(J2000) = 16h 32m 47s
   Dec(J2000) = +61d 35' 43"
```
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 40 sec. The peak count rate was ~1648 counts/sec (15-350 keV), at ~3 sec after the trigger.
Due to an observing constraint, Swift did not get data immediately. We will report on XRT data in a later GCN.
Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular #39878
Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM) and Ny Avo Rakotondrainibe (LAM) report:
We observed the field of the Swift/BAT GRB 250327A (Parsotan et al., GCN 39877) also detected by Fermi/GBM (Fermi GBM Team, GCN 39876) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We obtained 23 minutes of exposure in the i filter from 2025-03-27 07:50 to 08:34 UTC (20.5 to 64.1 minutes after the trigger).
Within the Swift/BAT localization, we do not detect any credible uncatalogued source to a 5-sigma limiting magnitude of:
i > 22.9 mag (AB)
We also performed an image subtraction using HOTPANTS and the PanSTARRS i-band image as a reference, which did not reveal any credible residuals.
The data were coadded with the COLIBRI pipeline and analysed in STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the Pan-STARRS DR1 catalog and the magnitude is not corrected for Galactic extinction.
Further observations are ongoing.
We acknowledge the excellent support from the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
GCN Circular #39879
Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observed the field of the Swift/BAT GRB 250327A (Parsotan et al., GCN 39877) also detected by Fermi/GBM (Fermi GBM Team, GCN 39876) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-03-27 UTC.
DDOTI observed the Swift/BAT error region (Parsotan et al., GCN 39877) from 08:13 UTC to 10:43 UTC (from T+0.7 h to T+3.2 h after the trigger) with a total exposure of 1.4 hours.
Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues and after performed image subtraction against PanSTARRS PS1 DR2, we detect no evident uncatalogued sources within the observed field to a 5-sigma limiting AB magnitude of
w > 21.82
This non-detection is consistent with the reported by Ducoin et al. (GCN 39877).
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
GCN Circular #39880
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB 250327A ( T. M. Parsotan et al., GCN 39877) errorbox 22478 sec after notice time and 22599 sec after trigger time at 2025-03-27 13:46:44 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 56 deg. The sun altitude is -20.9 deg.
The galactic latitude b = 40 deg., longitude l = 92 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2825096
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   22690 |        MASTER-Tunka |   C |   180 | 19.1 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #39881
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250327A ( Fermi GBM team, GCN 39876) errorbox 22555 sec after notice time and 22597 sec after trigger time at 2025-03-27 13:46:44 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 56 deg. The sun altitude is -20.9 deg.
The galactic latitude b = 41 deg., longitude l = 93 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2825101
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   22688 | 2025-03-27 13:46:44 |        MASTER-Tunka | (16h 33m 04.03s , +61d 29m 19.4s) |   C |   180 | 19.1 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #39882
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:
"At 07:30:06.33 UT on 27 March 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 250327A (trigger 764753411 / 250327313), which was also detected by the Swift/BAT (Parsotan et al. 2025, GCN 39877). The Fermi GBM Final Real-time Localization (GCN 39876) is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 47 degrees.
The GBM light curve shows a structured emission episode with a duration (T90) of about 160 s (50-300 keV). The time-averaged spectrum from T0-1.024s to T0+90.114s is best fit by a Band function with Epeak = 480 +/- 50 keV, alpha = -1.08 +/- 0.03, and beta = -2.14 +/- 0.15.
The event fluence (10-1000 keV) in this time interval is (2.97 +/- 0.07)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.704 s in the 10-1000 keV band is 5.08 +/- 0.23 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 #39884
L.P. Xin (NAOC), J. T. Palmerio (CEA), L. Zhang (IHEP), Y.D. Hu (GXU), X.L. Chen (YNU), Y. L. Qiu, H.L. Li., C. Wu, Z.H. Yao, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei (NAOC), B. Cordier (CEA), report on behalf of the SVOM/VT team:
SVOM performed a Target of Opportunity observation of GRB 250327A (Fermi GBM team, GCN 39876; Parsotan et al., GCN 39877). SVOM/VT began observing the field at 2025-03-27T11:25:40.50 UT, ~3.9 hours after the Swift/BAT trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
An uncatalogued candidate is detected inside the Swift/BAT error circle at ra=248.18018, dec=61.63347 (J2000), corresponding to:
```
RA (J2000) = 16:32:43.2
Dec (J2000) = +61:38:00.5
```
with an uncertainty of 1.0 arcsec.
This source is not present in the archival Legacy Survey. The source is detected in the VT_R stacked image with exposure time of 47x60 seconds with VT_R = 22.8 +/- 0.3 mag (AB). The 3 sigma upper limit in the VT_B is 23.4 mag (AB).
We thank D.B. Malesani for helpful discussion.
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 #39885
Geoffrey Mo (MIT), Benjamin Schneider (LAM), Tomas Ahumada (Caltech), Danielle Frostig (CfA), Viraj Karambelkar (Caltech), Robert Stein (UMD), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 250327A (Fermi GBM Team, GCN 39876; Parsotan et al., GCN 39877, Kienlin et al., GCN 39882) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations were triggered automatically and began at 2025-03-27T07:41:48 UTC (12 min after the GRB), consisting of 5 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We do not detect a source at the SVOM/VT counterpart location (Xin et al., GCN 39884), and also do not detect any new sources in the Swift/BAT localization after visual comparison to archival PanSTARRS-1 (Chambers et al. 2016) y-band imaging. This is consistent with other observations (Ducoin et al., GCN 39878; Becerra et al., GCN 39879; Lipunov et al., GCN 39880; Lipunov et al., GCN 39881). We obtain the following 5-sigma upper limit: J ~ 18.3 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular #39892
D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 8.0 ks of XRT data for GRB 250327A, from 12.1 ks to 47.5 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 248.1950, +61.6164 which is equivalent to:
```
RA (J2000): 16 32 46.80
Dec(J2000): +61 36 58.9
```
with an uncertainty of 3.6 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay index of alpha=0.92 (+0.22, -0.21).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.38 (+0.32, -0.29). The best-fitting absorption column is 3.0 (+1.1, -1.0) x 10^21 cm^-2, in excess of the Galactic value of 2.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.0 (+1.1, -1.0) x 10^21 cm^-2
Galactic foreground: 2.6 x 10^20 cm^-2
Excess significance: 4.6 sigma
Photon index:	     2.38 (+0.32, -0.29)
```
If the light curve continues to decay with a power-law decay index of 0.92, the count rate at T+24 hours will be 0.016 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.1 x 10^-13 (9.3 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/01299088.
This circular is an official product of the Swift-XRT team.
GCN Circular #39899
H.L. Li(NAOC), L. Zhang (IHEP), Y.D. Hu (GXU), X.L. Chen (YNU), Y. L. Qiu, L.P. Xin, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, W. J. Xie, J.Y. Wei (NAOC), J. T. Palmerio (CEA)report on behalf of the SVOM/VT team:
SVOM performed a Target of Opportunity observation of GRB 250327A (Fermi GBM team, GCN 39876; Parsotan et al., GCN 39877). SVOM/VT began observing the field at 2025-03-27T11:25:40.50 UT, ~3.9 hours after the Swift/BAT trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With the full X-band data, no any source was detected in the stacked images within the errorbox of Swift/XRT (Burrows et al. GCNC39892).
The 3 sigma limits in AB magnitude were derived as follows:
```
---------------------------------------------------------
(t-T0)_mid(hr)  exptime(ks)   Band    upperlim (3sigma)
 5.9              7.32        VT_R       23.8
 5.9              7.38        VT_B       23.8
```
Deeper or redder observations are encouraged to investigate the nature of the 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 #39987
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), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+843 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250327A (trigger #1299088) (Parsotan, et al., GCN Circ. 39877). The BAT ground-calculated position is RA, Dec = 248.209, 61.610 deg which is
```
   RA(J2000)  =  16h 32m 50.1s 
   Dec(J2000) = +61d 36' 35.4" 
```
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 10%.
The mask-weighted light curve shows a single main pulse lasting ~60 sec composed of several shorter pulses. The remainder of the burst emission is included in a dim tail. The T90 (15-350 keV) is 91.008 +- 12.21 sec (estimated error including systematics).
The time-averaged spectrum from T+1.67 to T+109.928 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.28 +- 0.12. The fluence in the 15-150 keV band is 7.6 +- 0.5 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+24.49 sec in the 15-150 keV band is 2.1 +- 0.7 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/1299088
GCN Circular #40008
M. H. Siegel (PSU) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250327A 13.8 ks after the BAT trigger (Parsotan et al., GCN Circ. 39877). No optical afterglow consistent with the XRT position (Burrows et al., GCN Circ. 39892) GCN Circ. 39977) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

B                25500        43748         1714            >20.88
UVM2             47869        48769          885            >20.28
U                14704        42891         1711            >20.58
V                21282        21402          117            >18.30
UVW1             13797        49176         1885            >20.62
UVW2             20376        21275          885            >20.31
WHITE            26413        27065          633            >20.81
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.053 in the direction of the burst (Schlegel et al. 1998).

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Jochen Greiner, last update: 02-Apr-2025 [Disclaimer]