Gamma-ray Burst 240916A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:22:59 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     748142580
GRB_RA:          164.150d {+10h 56m 36s} (J2000),
                 164.501d {+10h 58m 00s} (current),
                 163.437d {+10h 53m 45s} (1950)
GRB_DEC:         +43.017d {+43d 01' 00"} (J2000),
                 +42.884d {+42d 53' 03"} (current),
                 +43.284d {+43d 17' 03"} (1950)
GRB_ERROR:       9.40 [deg radius, statistical plus systematic]
GRB_INTEN:       136 [cnts/sec]
DATA_SIGNIF:     8.30 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         330.00 [deg]
GRB_THETA:       160.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.00
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:     100%  Below horizon
2nd_MOST_LIKELY:   0%  n/a
DETECTORS:       1,0,0, 1,0,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       174.20d {+11h 36m 47s}   +2.51d {+02d 30' 32"}
SUN_DIST:         41.29 [deg]   Sun_angle= 0.6 [hr] (West of Sun)
MOON_POSTN:      328.26d {+21h 53m 02s}  -16.52d {-16d 31' 25"}
MOON_DIST:       150.22 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      171.07, 61.86 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      147.13, 33.13 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 270.28,-8.42 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:23:07 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      59
TRIGGER_NUM:     748142580
GRB_RA:          247.933d {+16h 31m 44s} (J2000),
                 248.303d {+16h 33m 13s} (current),
                 247.187d {+16h 28m 45s} (1950)
GRB_DEC:         -22.417d {-22d 25' 00"} (J2000),
                 -22.468d {-22d 28' 04"} (current),
                 -22.310d {-22d 18' 37"} (1950)
GRB_ERROR:       8.63 [deg radius, statistical plus systematic]
GRB_INTEN:       243 [cnts/sec]
DATA_SIGNIF:     23.10 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         314.00 [deg]
GRB_THETA:        60.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.55
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       1,0,0, 1,0,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       174.20d {+11h 36m 47s}   +2.51d {+02d 30' 32"}
SUN_DIST:         76.34 [deg]   Sun_angle= -4.9 [hr] (East of Sun)
MOON_POSTN:      328.26d {+21h 53m 02s}  -16.52d {-16d 31' 23"}
MOON_DIST:        74.74 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      355.47, 17.29 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      249.68, -0.52 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 270.28,-8.42 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:23:14 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     748142580
GRB_RA:          231.540d {+15h 26m 10s} (J2000),
                 231.872d {+15h 27m 29s} (current),
                 230.868d {+15h 23m 28s} (1950)
GRB_DEC:          -8.220d {-08d 13' 11"} (J2000),
                  -8.305d {-08d 18' 18"} (current),
                  -8.046d {-08d 02' 43"} (1950)
GRB_ERROR:       5.49 [deg radius, statistical only]
DATA_SIGNIF:     19.40 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         317.00 [deg]
GRB_THETA:        81.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 47s}   +2.51d {+02d 30' 32"}
SUN_DIST:         58.51 [deg]   Sun_angle= -3.8 [hr] (East of Sun)
MOON_POSTN:      328.26d {+21h 53m 02s}  -16.52d {-16d 31' 22"}
MOON_DIST:        93.70 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      355.15, 38.49 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      231.28, 10.20 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_748142580.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
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:     Mon 16 Sep 24 01:24:00 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     748142580
GRB_RA:          232.400d {+15h 29m 36s} (J2000),
                 232.744d {+15h 30m 58s} (current),
                 231.705d {+15h 26m 49s} (1950)
GRB_DEC:         -13.910d {-13d 54' 35"} (J2000),
                 -13.994d {-13d 59' 36"} (current),
                 -13.739d {-13d 44' 19"} (1950)
GRB_ERROR:       3.56 [deg radius, statistical only]
DATA_SIGNIF:     24.50 [sigma]
DATA_INTERVAL:   6.144 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         320.00 [deg]
GRB_THETA:        76.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 48s}   +2.51d {+02d 30' 31"}
SUN_DIST:         60.31 [deg]   Sun_angle= -3.9 [hr] (East of Sun)
MOON_POSTN:      328.27d {+21h 53m 04s}  -16.52d {-16d 31' 10"}
MOON_DIST:        91.19 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      350.99, 33.82 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      233.53,  4.90 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_748142580.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:24:10 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     748142580
GRB_RA:          232.560d {+15h 30m 14s} (J2000),
                 232.901d {+15h 31m 36s} (current),
                 231.871d {+15h 27m 29s} (1950)
GRB_DEC:         -12.560d {-12d 33' 35"} (J2000),
                 -12.643d {-12d 38' 35"} (current),
                 -12.389d {-12d 23' 21"} (1950)
GRB_ERROR:       2.09 [deg radius, statistical only]
DATA_SIGNIF:     35.00 [sigma]
DATA_INTERVAL:   9.216 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         319.00 [deg]
GRB_THETA:        77.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 48s}   +2.51d {+02d 30' 31"}
SUN_DIST:         60.21 [deg]   Sun_angle= -3.9 [hr] (East of Sun)
MOON_POSTN:      328.27d {+21h 53m 04s}  -16.52d {-16d 31' 08"}
MOON_DIST:        91.45 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      352.25, 34.69 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      233.35,  6.24 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_748142580.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=10910).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:24:20 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      3
TRIGGER_NUM:     748142580
GRB_RA:          231.580d {+15h 26m 19s} (J2000),
                 231.912d {+15h 27m 39s} (current),
                 230.908d {+15h 23m 38s} (1950)
GRB_DEC:          -8.260d {-08d 15' 35"} (J2000),
                  -8.345d {-08d 20' 42"} (current),
                  -8.086d {-08d 05' 08"} (1950)
GRB_ERROR:       1.49 [deg radius, statistical only]
DATA_SIGNIF:     46.20 [sigma]
DATA_INTERVAL:   13.312 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         317.00 [deg]
GRB_THETA:        81.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 48s}   +2.51d {+02d 30' 31"}
SUN_DIST:         58.56 [deg]   Sun_angle= -3.8 [hr] (East of Sun)
MOON_POSTN:      328.27d {+21h 53m 05s}  -16.52d {-16d 31' 05"}
MOON_DIST:        93.66 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      355.15, 38.44 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      231.33, 10.17 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_748142580.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=10910).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:23:50 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     748142580
GRB_RA:          235.340d {+15h 41m 22s} (J2000),
                 235.682d {+15h 42m 44s} (current),
                 234.648d {+15h 38m 36s} (1950)
GRB_DEC:         -12.810d {-12d 48' 35"} (J2000),
                 -12.888d {-12d 53' 15"} (current),
                 -12.650d {-12d 39' 00"} (1950)
GRB_ERROR:       5.43 [deg radius, statistical only]
DATA_SIGNIF:     17.40 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         317.00 [deg]
GRB_THETA:        75.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 47s}   +2.51d {+02d 30' 32"}
SUN_DIST:         62.92 [deg]   Sun_angle= -4.1 [hr] (East of Sun)
MOON_POSTN:      328.27d {+21h 53m 04s}  -16.52d {-16d 31' 13"}
MOON_DIST:        88.78 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      354.36, 32.61 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      236.06,  6.64 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_748142580.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:24:30 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      4
TRIGGER_NUM:     748142580
GRB_RA:          231.650d {+15h 26m 36s} (J2000),
                 231.983d {+15h 27m 56s} (current),
                 230.978d {+15h 23m 55s} (1950)
GRB_DEC:          -8.340d {-08d 20' 23"} (J2000),
                  -8.425d {-08d 25' 29"} (current),
                  -8.166d {-08d 09' 57"} (1950)
GRB_ERROR:       1.20 [deg radius, statistical only]
DATA_SIGNIF:     52.30 [sigma]
DATA_INTERVAL:   19.456 [sec]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         317.00 [deg]
GRB_THETA:        81.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 48s}   +2.51d {+02d 30' 31"}
SUN_DIST:         58.64 [deg]   Sun_angle= -3.9 [hr] (East of Sun)
MOON_POSTN:      328.27d {+21h 53m 05s}  -16.52d {-16d 31' 03"}
MOON_DIST:        93.57 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      355.14, 38.33 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      231.42, 10.11 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_748142580.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=10910).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 16 Sep 24 01:32:16 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     748142580
GRB_RA:          233.170d {+15h 32m 41s} (J2000),
                 233.500d {+15h 34m 00s} (current),
                 232.502d {+15h 30m 01s} (1950)
GRB_DEC:          -7.070d {-07d 04' 11"} (J2000),
                  -7.152d {-07d 09' 07"} (current),
                  -6.902d {-06d 54' 06"} (1950)
GRB_ERROR:       1.20 [deg radius, statistical only]
GRB_DATE:        20569 TJD;   260 DOY;   24/09/16
GRB_TIME:        4975.77 SOD {01:22:55.77} UT
GRB_PHI:         315.00 [deg]
GRB_THETA:        81.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       174.20d {+11h 36m 49s}   +2.51d {+02d 30' 23"}
SUN_DIST:         59.95 [deg]   Sun_angle= -4.0 [hr] (East of Sun)
MOON_POSTN:      328.35d {+21h 53m 23s}  -16.49d {-16d 29' 08"}
MOON_DIST:        92.58 [deg]
MOON_ILLUM:      94 [%]
GAL_COORDS:      357.63, 38.12 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      232.59, 11.71 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_locplot_all_bn240916058.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=10910).

GCN Circular #37518
The Fermi GBM team reports the detection of a likely LONG GRB
At 01:22:55 UT on 16 Sep 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240916A (trigger 748142580.77199 / 240916058).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 233.2, Dec = -7.1 (J2000 degrees, equivalent to J2000 15h 32m, -7d 05'), with a statistical uncertainty of 1.2 degrees.
The angle from the Fermi LAT boresight is 81.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_skymap_all_bn240916058.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_healpix_all_bn240916058.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240916058/quicklook/glg_lc_medres34_bn240916058.gif
GCN Circular #37519
Devraj Pawar (R. J. College, Mumbai-86, India) on behalf of a collaboration studying transients.
The Fermi GBM team has reported a GRB in GCN 37518. We analyzed the INTEGRAL SPI ACS data around the T0 given in GCN 37518 and detected a peak in the count rate which lasts for about 50 s. The SPI ACS is sensitive above 80 keV; the peak of the burst is at ~4300 counts/s and the steady rate preceding the event is around 3800 counts/s. The peak count rate may be affected by the instruments orientation with respect to the direction of the source. The light curve and the profile is given in the link below :
[https://docs.google.com/document/d/1ypksdTUoXwB8_Lwr5zhiB-8ivEdobW_oeGTxN8B2Y_Y/edit?usp=sharing]()
This work is based on observations with INTEGRAL, an ESA project with instruments and a science data center funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.
GCN Circular #37522
B. P. Gompertz, A. Kumar, D. O=E2=80=99Neill, M. Kennedy, R. Starling, K. A= ckley, M. Dyer, F. Jim=C3=A9nez-Ibarra, J. Lyman, K. Ulaczyk, D. Steeghs, D= . Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Bre= ton, L. Nuttall, E. Palle, D. Pollacco and T. Killestein report on behalf o= f the GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Trans= ient Observer (GOTO; Steeghs et al. 2022) in response to GRB 240916A, detec= ted by Fermi/GBM and INTEGRAL SPI ACS (Fermi GBM Team, GCN 37518; Pawar et = al., GCN 37519).
Targeted observations were performed by GOTO South between 2024-09-16 09:06= :48 UT (t0+7.73h) and 2024-09-16 09:23:05 UT (t0+8.00h). In total, 48 image= s were taken across 6 unique pointings, covering 178.6 square degrees withi= n the GBM 90% localisation contour. This corresponds to ~78.3% coverage of = the total 2D localisation probability. Each observation consisted of 4x90s = exposures in the GOTO L-band (400-700 nm). The average 5-sigma limiting mag= nitude was L > 19.1 mag.
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of th= e same fields. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on a= ny candidates that passed the above checks.
We identify 2 new optical sources contained within the GBM 90% probability contour:
```
+-----------------------------------------------------------------------+

|  Internal name |  IAU name  |     ra     |    dec    |   L-band mag   |

+-----------------------------------------------------------------------+

|    GOTO24fzk   |     AT 2024vlo<https://www.wis-tns.org/object/2024vlo>  =
     | 234.873760 |  -6.94630 | 19.15 +/- 0.19 |

|    GOTO24fzn   |     AT 2024vlp<https://www.wis-tns.org/object/2024vlp>  =
     | 235.913454 |  -7.76478 | 17.80 +/- 0.05 |

+-----------------------------------------------------------------------+
```
GOTO24fzk/AT2024vlo is consistent with galaxy 6dF J1539293-065643 in the GL= ADE+ galaxy catalog (D=C3=A1lya et al., 2021), with a photometric redshift of z =3D 0.0267+/-0.0339 (121 Mpc).
We find no evidence of these sources prior to the GRB trigger time in previ= ous GOTO observations, the ZTF observations provided by the Lasair broker (= Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). However, pre-burst imaging to sufficient depth is not available for the week preceding the GRB.
We caution that due to the target field setting soon after twilight, only a= single epoch of observations could be obtained, and we therefore cannot as= sess the rate of evolution of either candidate. Manual checks for minor pla= nets revealed no matches consistent with the source properties at either po= sition.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is prin= cipally funded by the STFC and operated at the Roque de los Muchachos Obser= vatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash Univ= ersity, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Th= ailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular #37526
S.Q. Jiang, J. An, X. Liu, Z.P. Zhu, S.Y. Fu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the two GOTO optical counterpart candidates (Gompertz et al., GCN 37522) of GRB 240916A detected by Fermi/GBM (Fermi GBM Team, GCN 37518) and INTEGRAL SPI ACS (Pawar et al., GCN 37519), using the 100cm-C (100C) telescope of the JinShan project, located in Altay, Xinjiang, China. Observations started at 2024-09-16T13:38:03.01 UT, i.e., 12.25 hr after the Fermi/GBM trigger, and a series of Sloan r-band frames were obtained.
GOTO24fzk, also as AT 2024vlo, has r = 19.11 +/- 0.05 (AB) in our stacked image, via image subtraction and calibrated with Legacy Survey DR10. There is no apparent fading for this source, compared with L = 19.15 +/- 0.19 at the GOTO observational time. We thus think it's likely unrelated to the GRB.
GOTO24fzn, also as AT 2024vlp, has r = 18.69 +/- 0.05 (AB) in our stacked image, calibrated with Legacy Survey DR10. It has considerably faded, compared with L = 17.80 +/- 0.05 at the GOTO observational time. The decay rate is consistent with that for GRB optical afterglows.
We thus think GOTO24fzn/AT 2024vlp is likely the optical counterpart of GRB 240916A.
We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations.
GCN Circular #37529
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/GBM GRB 240916A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021717
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/GBM event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular #37531
A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 240916A, centred on the position of the candidate optical counterpart detected by GOTO: GOTO24fzn/AT2024vlp (Gompertz et al., GCN Circ. 37522), collecting 1.6 ks of Photon Counting (PC) mode data between T0+61.0 ks and T0+70.9 ks.
An uncatalogued X-ray source is spatially consistent with the GOTO position and is fading with 1.6 sigma significance and thus is believed to be the GRB afterglow. Using 687 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 235.91357, -7.76503 which is equivalent to:
```
RA (J2000): 15h 43m 39.26s
Dec(J2000): -07d 45' 54.1"
```
with an uncertainty of 3.2 arcsec (radius, 90% confidence). This position is 1.0 arcsec from the GOTO position.
The light curve can be modelled with a power-law decay with a decay index of alpha=2.96 (+0.03, -2.88).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.9 (+0.8, -0.6). The best-fitting absorption column is 3.3 (+2.2, -1.7) x 10^21 cm^-2, in excess of the Galactic value of 1.4 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.6 x 10^-11 (7.1 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.3 (+2.2, -1.7) x 10^21 cm^-2
Galactic foreground: 1.4 x 10^21 cm^-2
Excess significance: 1.8 sigma
Photon index:	     2.9 (+0.8, -0.6)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021717. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021717.
This circular is an official product of the Swift-XRT team.
GCN Circular #37532
D. Pieterse (Radboud Univ.), B. Schneider (MIT), A. Saccardi (GEPI/Obs. de Paris), B. P. Gompertz (U. Birmingham), J. P. U. Fynbo (DAWN/NBI), A. de Ugarte Postigo (LAM/OCA, CNRS), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), N. R. Tanvir (Univ. Leicester), D. Xu (NAOC) report on behalf of the Stargate collaboration:
We observed AT 2024vlp (GOTO24fzn), the likely afterglow (Gompertz et al., GCN 37522; Jiang et al., GCN 37526; Beardmore et al., GCN 37531) of GRB 240916A (Fermi GBM team, GCN 37518; Pawar, GCN 37519) using the X-shooter spectrograph mounted on the ESO VLT UT3 (Melipal). The observation was performed on 2024 September 16 (23.1 hr after the GRB), and consisted of 4 exposures of 600 s each covering the wavelength range 3000-21000 AA.
In images taken with the acquisition camera, the optical afterglow is well detected. In the r band, we measure an AB magnitude of r ~ 19.4, calibrated against three nearby stars from the Pan-STARRS catalog. This magnitude is significantly fainter than that reported by Jiang et al. (GCN 37526), confirming the fading nature of this object and thus the identification of this source as the afterglow of GRB 240916A.
In a preliminary analysis of the spectra, we clearly detect continuum over the entire wavelength range. A trough is visible around 4350 AA, which we identify as due to HI Lyman-alpha absorption. In addition, from detection of a plethora of absorption features, which we interpret as being due to O I, O I*, Si II, Si II*, C II, C II*, Si IV, C IV, Fe II, Fe II*, Cr II, Zn II, Ni II, Ni II*, Mn II, Mg II, we infer a common redshift of z = 2.610, which we conclude is the redshift of GRB 240916A. There is a tentative detection of H-beta emission at z=2.610 from the underlying host galaxy. We also note the presence of an additional intervening absorption system at z = 2.214.
We acknowledge expert support from the ESO staff in Paranal, in particular Claudia Cid, Thomas Rivinius and Zahed Wahhaj.
GCN Circular #37535
O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:22:55.77 UT on 16 September 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240916A (trigger 748142580/240916058), which was later detected by Swift XRT (Beardmore et al. 2024, GCN 37531) after two optical afterglows were initially discovered by GOTO (Gompertz et al., 2024, GCN 37522), of which GOTO24fzn/AT 2024vlp was reported to decay in the optical by the JinShan project (Jiang et al., 2024, GCN 37526), with a redshift measured by VLT/X-shooter of z=2.610 (Pieterse et al., 2024, GCN 37532).
The Fermi GBM on-ground location is consistent with the Swift XRT position.
The angle from the Fermi LAT boresight is 79 degrees.
The GBM light curve consists of a bright FRED-like pulse with a duration (T90) of about 32 s (50-300 keV). The time-averaged spectrum from T0-5.6 to T0+55.8 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.16 +/- 0.03 and the cutoff energy, parameterized as Epeak, is 710 +/- 80 keV.
The event fluence (10-1000 keV) in this time interval is (2.78 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 5.5 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak= 580 +/- 80 keV, alpha = -1.12 +/- 0.03 and beta = -2.2 +/- 0.2.
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 #37540
S.Q. Jiang (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), D. Xu (NAOC), B. N. Hauptmann (NOT) report on behalf of a large collaboration:
We observed the optical counterpart (AT 2024vlp / GOTO24fzn: Gompertz et al., GCN 37522; Jiang et al., GCN 37526; Pieterse et al., GCN 37532) of GRB 240916A, detected by Fermi/GBM (Fermi GBM Team, GCNs 37518, 37535) and INTEGRAL SPI/ACS (Pawar et al., GCN 37519) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera, and obtained 3 x 300 s frames in the Sloan r-band, starting at 20:03:23.239 UT on 2024-09-17, i.e., 42.675 hr after the Fermi/GBM trigger.
The afterglow is clearly detected in our stacked image, with a magnitude r = 20.58 +/- 0.04 (AB), calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction.
GCN Circular #37543
M. Dafcikova, J. Ripa, M. Kolar (Masaryk U.), A. Pal (Konkoly Observatory),= N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros,= B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Dur= iskova, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M.= Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (= Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Ha= nak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Cen= ter/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (IS= AS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.),= Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hirosh= ima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos= U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakaz= awa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torig= oe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Morit= aki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 240916A (Fermi/GBM detection: GCN 37518; INTEGRAL/SPI= -ACS detection: GCN 37519) was observed by the GRBAlpha 1U CubeSat (Pal et = al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A.= .40P/abstract).
The detection was confirmed at the peak time 2024-09-16 01:23:10.8 UTC. The= T90 duration measured by GRBAlpha is 27 s and the overall significance dur= ing T90 reaches 13 sigma.
The light curve obtained by GRBAlpha is available here: https://grbalpha.ko= nkoly.hu/static/share/GRB240916A_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/he= a/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a futur= e CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GR= BAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM ar= ray, covering the energy range from ~50 keV to ~1000 keV. To increase the d= uty cycle and the downlink rate, the upgrade of the on-board data acquisiti= on software stack is in progress. The ground segment is also supported by t= he radio amateur community and it takes advantage of the SatNOGS network fo= r increased data downlink volume.
GCN Circular #37788
S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB)
At 00:43:57 UT on 2024 Sept 18 (T_mid = 2.00 days post-burst) the Karl G. Jansky VLA observed the field of GRB 240916A (Fermi GBM team, GCN 37518; Pawar et al., GCN 37519; Dafcikova et al. 37543) at a central frequency of 6, 10 and 15 GHz.
The standard 3C286 was used as bandpass and flux density calibrator, while J1543-0757 was used as phase calibrator.
From a preliminary analysis, an unresolved radio source is clearly detected at a position:
```
RA: 15:43:39.205 +- 0.001
Dec: -07:45:53.30 +- 0.02
```
consistent with the optical (GOTO collaboration, GCN 37522; Jiang et al., GCN 37526; Jiang et al., GCN 37540) and X-ray (Beardmore et al., GCN 37531) transient.
The surface brightness peak is 35 uJy/beam, 44 uJy/b and 135 uJy/beam at 6, 10 and 15 GHz, respectively. The r.m.s. noise level of the image is 8 uJy/beam at all frequencies.
The synthesized beams are 1.25x0.72 arcsec (PA: 42deg) at 6 GHz, 1.10x0.52 arcsec (PA: 37deg) at 10 GHz and 0.56x0.33 arcsec (PA: 26deg) at 15 GHz.
No source is detected with a 3sigma confidence at the aforementioned position in previous radio surveys (FIRST, NVSS, VLASS, RACS), with r.m.s. noise levels (1sigma) above 100 uJy/b.
We would like to thank the staff of the VLA for approving, executing, and processing the observations.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
These observations were carried out as part of project SF171028, approved in the framework of the Fermi - NRAO joint program agreement.

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