GRB 250226B
GCN Circular 39503
Subject
GRB 250226B: Fermi GBM Final Real-time Localization
Date
2025-02-26T22:40:51Z (3 months 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 22:30:23 UT on 26 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250226B (trigger 762301828.12293 / 250226938).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 284.4, Dec = -10.8 (J2000 degrees, equivalent to J2000 18h 57m, -10d 48'), with a statistical uncertainty of 1.9 degrees.
The angle from the Fermi LAT boresight is 71.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226938/quicklook/glg_skymap_all_bn250226938.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/bn250226938/quicklook/glg_healpix_all_bn250226938.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226938/quicklook/glg_lc_medres34_bn250226938.gif
GCN Circular 39505
Subject
Fermi GRB 250226B: Global MASTER-Net observations report
Date
2025-02-26T23:31:13Z (3 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
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 250226B ( Fermi GBM team, GCN 39503) errorbox 99 sec after notice time and 134 sec after trigger time at 2025-02-26 22:32:37 UT, with upper limit up to 16.4 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -13.9 deg.
The galactic latitude b = -7 deg., longitude l = 24 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2792989
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
150 | 2025-02-26 22:32:37 | MASTER-Tunka | (18h 59m 50.08s , -12d 13m 54.5s) | C | 30 | 16.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 39519
Subject
GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection
Date
2025-02-27T14:32:17Z (3 months ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
James Craig Rodi(a), Aishwarya Linesh Thakur(a), Patrizia Barria(a,b), Giulia Gianfagna(a), Lorenzo Natalucci(a,b), Luigi Piro(a), report:
GRB 250226B was discovered by Fermi/GBM (GCN 39503) at 2025-02-26T22:30:23 (UTC).
In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with the GBM detection, having an approximate duration of ~ 20 sec. The signal consists of multiple pulses over this duration. The strongest pulse of this signal is also detected in the IBIS/PICsIT data.
The approximate peak count rate in SPI-ACS is 95,000 cts/s for E>80 keV, over a median background rate of 63,000 cts/s.
This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.
-----
(a) INAF/IAPS-Rome
(b) ICSC National Research Centre for High-Performance Computing
GCN Circular 39673
Subject
GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
Date
2025-03-11T20:10:47Z (3 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250226B onboard (T0: 2025-02-26T22:30:23.12 UTC, Fermi GCN 39503, INTEGRAL GCN 39519)
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 15.1 in a 1.024 s analysis time bin, starting at T0 + 1.79 s.
Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)
The 90% credible area is 3,416 deg2 and the 50% credible area is 994 deg2.
The integrated probability inside the coded field of view is 6%.
The joint NITRATES+GBM localization has a 90% credible area of 165 deg2 and a 50% credible area of 36 deg2
A plot of the probability skymap can be viewed here:
[skymap_plot](https://guano.swift.psu.edu/trigger_report?id=762301858/#:~:text=Probability%20Skymap)
The probability skymap and joint skymap files can be downloaded from the links here
[skymap_fits_file](https://guano.swift.psu.edu/files/762301858/0_n_PROBMAP)
[joint_skymap_fits_file](https://guano.swift.psu.edu/files/762301858/0_n_JOINTMAP)
Instructions on how to read and manipulate this map can be found here:
https://guano.swift.psu.edu/documentation
More details about this burst can be found on the trigger report page here:
https://guano.swift.psu.edu/trigger_report?id=762301858
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at:
https://www.swift.psu.edu/guano/
GCN Circular 39690
Subject
GRB 250226B: Fermi GBM Observation
Date
2025-03-12T20:16:32Z (3 months ago)
From
Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>
Via
Web form
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
At 22:30:23.12 UT on 26 February 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250226B (trigger 762301828/250226938).
which was also detected by INTEGRAL SPI-ACS (J. Rodi, et al. 2025, GCN 39519) and Swift/BAT-GUANO (S. Ronchini, et al., 2025, GCN 39673).
The angle from the Fermi LAT boresight is 71 degrees.
The GBM light curve consists of multiple peaks with a duration (T90)
of about 26 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+27.457 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.09 +/- 0.03 and the cutoff energy,
parameterized as Epeak, is 1688 +/- 250 keV.
The event fluence (10-1000 keV) in this time interval is
(1.60 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.7 s in the 10-1000 keV band is 9.7 +/- 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/