Gamma-ray Burst 250721A

(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 21 Jul 25 09:38:05 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     774783471
GRB_RA:           81.400d {+05h 25m 36s} (J2000),
                  81.666d {+05h 26m 40s} (current),
                  80.879d {+05h 23m 31s} (1950)
GRB_DEC:         -23.550d {-23d 33' 00"} (J2000),
                 -23.529d {-23d 31' 44"} (current),
                 -23.593d {-23d 35' 33"} (1950)
GRB_ERROR:       28.48 [deg radius, statistical plus systematic]
GRB_INTEN:       56 [cnts/sec]
DATA_SIGNIF:     4.90 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20877 TJD;   202 DOY;   25/07/21
GRB_TIME:        34666.53 SOD {09:37:46.53} UT
GRB_PHI:          54.00 [deg]
GRB_THETA:        70.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.97
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      62%  GRB
2nd_MOST_LIKELY:  35%  Distant Particles
DETECTORS:       0,1,1, 0,0,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       121.02d {+08h 04m 06s}  +20.38d {+20d 22' 41"}
SUN_DIST:         58.30 [deg]   Sun_angle= 2.6 [hr] (West of Sun)
MOON_POSTN:       71.83d {+04h 47m 18s}  +27.53d {+27d 31' 52"}
MOON_DIST:        51.94 [deg]
MOON_ILLUM:      15 [%]
GAL_COORDS:      226.29,-28.73 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       78.48,-46.65 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_lc_medres34_bn250721401.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 121.73,-19.72 [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 21 Jul 25 09:38:23 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     774783471
GRB_RA:           76.760d {+05h 07m 02s} (J2000),
                  77.076d {+05h 08m 18s} (current),
                  76.142d {+05h 04m 34s} (1950)
GRB_DEC:          -4.740d {-04d 44' 23"} (J2000),
                  -4.708d {-04d 42' 27"} (current),
                  -4.805d {-04d 48' 18"} (1950)
GRB_ERROR:       19.20 [deg radius, statistical only]
DATA_SIGNIF:     5.90 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20877 TJD;   202 DOY;   25/07/21
GRB_TIME:        34666.53 SOD {09:37:46.53} UT
GRB_PHI:          50.00 [deg]
GRB_THETA:        89.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       121.02d {+08h 04m 06s}  +20.38d {+20d 22' 41"}
SUN_DIST:         49.91 [deg]   Sun_angle= 2.9 [hr] (West of Sun)
MOON_POSTN:       71.83d {+04h 47m 19s}  +27.53d {+27d 31' 54"}
MOON_DIST:        32.63 [deg]
MOON_ILLUM:      15 [%]
GAL_COORDS:      204.89,-25.33 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       75.09,-27.50 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_lc_medres34_bn250721401.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_774783471.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 21 Jul 25 09:47:11 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     774783471
GRB_RA:           86.360d {+05h 45m 26s} (J2000),
                  86.642d {+05h 46m 34s} (current),
                  85.809d {+05h 43m 14s} (1950)
GRB_DEC:         -17.860d {-17d 51' 35"} (J2000),
                 -17.851d {-17d 51' 04"} (current),
                 -17.879d {-17d 52' 43"} (1950)
GRB_ERROR:       16.93 [deg radius, statistical only]
GRB_DATE:        20877 TJD;   202 DOY;   25/07/21
GRB_TIME:        34666.53 SOD {09:37:46.53} UT
GRB_PHI:          47.00 [deg]
GRB_THETA:        73.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       121.03d {+08h 04m 07s}  +20.38d {+20d 22' 36"}
SUN_DIST:         50.98 [deg]   Sun_angle= 2.3 [hr] (West of Sun)
MOON_POSTN:       71.93d {+04h 47m 43s}  +27.54d {+27d 32' 35"}
MOON_DIST:        47.58 [deg]
MOON_ILLUM:      15 [%]
GAL_COORDS:      222.25,-22.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       85.39,-41.24 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_lc_medres34_bn250721401.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_locplot_all_bn250721401.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 21 Jul 25 10:26:00 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     774783471
GRB_RA:           75.940d {+05h 03m 46s} (J2000),
                  76.231d {+05h 04m 55s} (current),
                  75.372d {+05h 01m 29s} (1950)
GRB_DEC:         -14.960d {-14d 57' 35"} (J2000),
                 -14.926d {-14d 55' 31"} (current),
                 -15.029d {-15d 01' 43"} (1950)
GRB_ERROR:       10.95 [deg radius, statistical only]
GRB_DATE:        20877 TJD;   202 DOY;   25/07/21
GRB_TIME:        34666.53 SOD {09:37:46.53} UT
GRB_PHI:          55.00 [deg]
GRB_THETA:        79.98 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:       121.06d {+08h 04m 14s}  +20.37d {+20d 22' 17"}
SUN_DIST:         56.44 [deg]   Sun_angle= 3.0 [hr] (West of Sun)
MOON_POSTN:       72.36d {+04h 49m 26s}  +27.59d {+27d 35' 33"}
MOON_DIST:        42.68 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      214.95,-30.46 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       72.78,-37.56 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_lc_medres34_bn250721401.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_locplot_all_bn250721401.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 has human-in-the-loop processing.

GCN Circular #41128
The Fermi GBM team reports the detection of a likely LONG GRB
"At 09:37:46.53 UT on 21 July 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250721A (trigger 774783471/250721401).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 76.94, Dec = -12.37 (J2000 degrees, equivalent to J2000 5h 7m, -12d 22'), with a statistical uncertainty of 10.20 degrees.
The angle from the Fermi LAT boresight is 82 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_skymap_all_bn250721401.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/bn250721401/quicklook/glg_healpix_all_bn250721401.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250721401/quicklook/glg_lc_medres34_bn250721401.gif"
GCN Circular #41129
C. Kang (Ehime U.), M. Serino, Y. Kawakubo (AGU), H. Negoro (Nihon U.), M. Nakajima, K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.), M. Shidatsu, Y. Niida, T. Nakamoto (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U)
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 09:38:05 UT on July 21, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = ( 82.805, -25.592) = (05 31 13, -25 35 31) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.37 deg and 0.32 deg, respectively. The roll angle of long axis from the north direction is 24.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 119 +- 23 mCrab (4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners:
```
(81.815, -25.748) deg = (05 27 15, -25 44 52) (J2000)
(82.171, -26.333) deg = (05 28 41, -26 19 58) (J2000)
(84.986, -24.908) deg = (05 39 56, -24 54 28) (J2000)
(84.621, -24.329) deg = (05 38 29, -24 19 44) (J2000)
```
There was no significant excess flux in the next transit at 11:10 UT with an upper limit of 20 mCrab.
We also note that a transient was detected by Fermi (GCN Circular #41128), which is probably associated with the event.
GCN Circular #41130
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a series of observations, tiled on the sky, of the MAXI GRB 250721A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/xrt_products/TILED_GRB00137
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the MAXI event is high: 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 #41136
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the MAXI-detected burst GRB 250721A in a series of observations tiled on the sky. The total exposure time is 1.4 ks, distributed over 5 tiles; the maximum exposure at a single sky location in the tiling was 569 s. The data were collected between T0+16.2 ks and T0+22.9 ks, and are entirely in Photon Counting (PC) mode.
No X-ray sources have been detected. The 3-sigma upper limit in the field (not including the regions where the tiles overlap) ranges from ~0.02 to ~0.05 ct s^-1, corresponding to a 0.3-10 keV observed flux of 6.5e-13 to 2.2e-12 erg cm^-2 s^-1 (assuming a typical GRB spectrum).
The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00137.
This circular is an official product of the Swift-XRT team.
GCN Circular #41141
A. Holzmann Airasca (UniTrento and INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 09:37:46.53 UT on 21 July 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250721A (trigger 774783471/250721401). which was also detected by MAXI (M. Nakajima et al. 2025, GCN 41129). The Fermi GBM on-ground location is consistent with the MAXI position.
The angle from the Fermi LAT boresight is 70 degrees.
The GBM light curve consists of a single emission episode with a duration (T90) of about 54 s (50-300 keV). The time-averaged spectrum from T0-3.1 to T0+1.5 s is best fit by a simple power law function with index -1.46 +/- 0.07.
The event fluence (10-1000 keV) in this time interval is (9.8 +/- 1.6)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0-2.5 s in the 10-1000 keV band is 1.7 +/- 0.2 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/"

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Jochen Greiner, last update: 23-Jul-2025 [Disclaimer]