GRB 250521A
GCN Circular 40508
Subject
GRB 250521A: Fermi GBM Final Real-time Localization
Date
2025-05-21T04:37:01Z (9 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 04:27:02 UT on 21 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250521A (trigger 769494427.113864 / 250521185).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 213.0, Dec = 30.1 (J2000 degrees, equivalent to J2000 14h 11m, 30d 06'), with a statistical uncertainty of 4.6 degrees.
The angle from the Fermi LAT boresight is 74.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521185/quicklook/glg_skymap_all_bn250521185.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/bn250521185/quicklook/glg_healpix_all_bn250521185.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521185/quicklook/glg_lc_medres34_bn250521185.gif
GCN Circular 40514
Subject
GRB 250521A: DDOTI Optical Upper Limit
Date
2025-05-21T17:03:34Z (8 days ago)
From
sahil.atri@students.uniroma2.eu
Via
Web form
Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observed the field of the GRB 250521A detected by Fermi/GBM (Fermi GBM Team, GCN 40508) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-05-21 UTC.
DDOTI observed the Fermi/GBM error region, covering about 93% of the error region (Fermi GBM Team, GCN Circ. 40508). DDOTI observed the field of GRB 250521A from 04:41 UTC to 11:25 UTC (from T+0.2 h to T+ 6.7 h after the trigger) and obtained a total exposure of 2.5 hours, alternating with other scientific programs.
Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we
detect no uncatalogued fading sources within the observed field to a 10-sigma limiting AB magnitude of:
w > 20.91
This value is not corrected for the Galactic extinction.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
GCN Circular 40541
Subject
GRB 250521A: GRBAlpha detection
Date
2025-05-23T18:31:11Z (6 days ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
Via
Web form
M. Dafcikova, J. Ripa (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. Duriskova, M. Kolar, 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. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/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 (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 250521A (Fermi/GBM detection: GCN 40508) 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 2025-05-21 04:27:02.6 UTC. The T90 duration measured by GRBAlpha is 21 s and the overall significance during T90 reaches 8.6 sigma.
The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250521A_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/
GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.