GRB 250717B

The Fermi GBM team reports the detection of a likely LONG GRB

At 13:44:22 UT on 17 Jul 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250717B (trigger 774452667.945704 / 250717572).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 44.4, Dec = 20.9 (J2000 degrees, equivalent to J2000 02h 57m, 20d 53'), with a statistical uncertainty of 3.8 degrees.

The angle from the Fermi LAT boresight is 70.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250717572/quicklook/glg_skymap_all_bn250717572.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/bn250717572/quicklook/glg_healpix_all_bn250717572.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250717572/quicklook/glg_lc_medres34_bn250717572.gif

Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU) report:

Swift/BAT did not localize GRB 250717B onboard (T0: 2025-07-17T13:44:22 UTC, Fermi GCN 41107
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 ).

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 position is found with the newly developed pipeline BAT-GLIMPSE: Gamma-ray Localization using Imaging and Mosaic techniques for Pointing and Slew Epochs (Ronchini et. al, in prep). The pipeline makes use of the tools from BatAnalysis ([Parsotan et al. 2025](https://iopscience.iop.org/article/10.3847/1538-4357/ade240)). The source is found with an SNR = 26.3.

The BAT position is:

RA, Dec = 44.1179, 26.3789 deg which is

RA(J2000) = 02h 56m 28.30s 

Dec(J2000) = 26d 22’ 44.0″

with an estimated uncertainty of 3 arcmin radius.

More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=774452698

XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.

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/

Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 13:44:22.95 UT on 17 July 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250717B (trigger 774452667/250717572).
which was also detected by Swift/BAT-GUANO (Samuele Ronchini et al. 2025, GCN 41110
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 ).
The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 74 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 6.4 s (50-300 keV). The time-averaged spectrum
from T0+0.002 to T0+7.360 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.9 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 75 +/- 5 keV.
A Band function fits equally well with Epeak = 72 +/- 6 keV, alpha = -0.9 +/- 0.2 and beta = -3.2 +/- 0.9.

The event fluence (10-1000 keV) in this time interval is
(1.36 +/- 0.05)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.13 s in the 10-1000 keV band is 6.1 +/- 0.3 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/"

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a ToO observation of the Fermi/GBM-detected event
GRB 250717B. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021846
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.

S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester), S. Campana (INAF-OAB), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), D.N. Burrows (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 250717B, collecting  2.8 ks of Photon
Counting (PC) mode data between T0+27.9 ks and T0+34.0 ks. 

One uncatalogued X-ray source has been detected within the estimated
BAT-GUANO error region (3 arcmin), it is below the RASS limit and shows
no definitive signs of fading. Therefore, at the present time we cannot
confirm this as the afterglow. Details of this source are given below:

Source 1:
  RA (J2000.0):  44.1037  =  02:56:24.88
  Dec (J2000.0): +26.3758  =  +26:22:32.8
  Error: 8.9 arcsec (radius, 90% conf.)
  Count-rate: (1.90 [+1.27, -0.91])e-3 ct s^-1	 
  Distance: 47 arcsec from BAT-GUANO position.

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021846.

This circular is an official product of the Swift-XRT team.