GRB 250619B

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

At 23:36:17 UT on 19 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250619B (trigger 772068982.168064 / 250619984).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 25.4, Dec = -24.8 (J2000 degrees, equivalent to J2000 01h 41m, -24d 48'), with a statistical uncertainty of 13.4 degrees.

The angle from the Fermi LAT boresight is 48.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250619984/quicklook/glg_skymap_all_bn250619984.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/bn250619984/quicklook/glg_healpix_all_bn250619984.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250619984/quicklook/glg_lc_medres34_bn250619984.gif

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

Swift/BAT did not localize GRB 250619B onboard (T0: 2025-06-19T23:36:17.17 UTC, Fermi/GBM trig 772068982) 

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 7.9 in a 8.192 s analysis time bin, starting at T0 - 2.048 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 10,760 deg2 and the 50% credible area is 1,197 deg2.
The integrated probability inside the coded field of view is 30%. 

The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 40788
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 ). The combined Fermi/GBM+NITRATES 90% credible area is 652 deg2 and the 50% credible area is 146 deg2.

A plot of the probability skymap can be viewed here:

[skymap_plot](https://guano.swift.psu.edu/trigger_report?id=772069012/#:~: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/772069012/0_n_PROBMAP)

[joint_skymap_fits_file](https://guano.swift.psu.edu/files/772069012/0_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=772069012

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 23:36:17.17 UT on 19 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250619B (trigger 772068982/250619984).
which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 40795
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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 48 degrees.

The GBM light curve consists of a double emission episode with a duration (T90)
of about 29 s (50-300 keV). The time-averaged spectrum
from T0-1 to T0+28.7 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.1 +/- 0.2 and the cutoff energy,
parameterized as Epeak, is 67 +/- 9 keV. A Band function fits the spectrum 
equally well with Epeak = 57 +/- 13 keV, alpha = -1 +/- 0.4 and beta = -2.5 +/- 0.4.

The event fluence (10-1000 keV) in this time interval is
(1.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.32 s in the 10-1000 keV band is 2.2 +/- 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/