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GRB 250718A

GCN Circular 41115

Subject

Swift Trigger 1334535: a possible GRB 250718A

Date

2025-07-18T00:47:35Z (a day ago)

From

Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>

Via

M. H. Siegel (PSU), R. Gupta (NASA GSFC), S. Lanava (PSU),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB) and M. A. Williams (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 00:14:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 250718A (trigger=1334535). 
The BAT on-board calculated location is 
RA, Dec 241.998, -11.993 which is 
   RA(J2000) = 16h 07m 59s
   Dec(J2000) = -11d 59' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a sharp rise with
a duration of just a few milliseconds.  The peak count rate was ~1070
counts/sec (15-350 keV), at ~0 sec after the trigger.

Due to an observing constraint, Swift will not slew to the burst until
01:07 UT. Due to the marginal significance of the BAT image (6.85
sigma), and the lack of prompt XRT and UVOT data, this trigger may be
due to a noise fluctuation. Further data are required to determine the
nature of this trigger.

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)

GCN Circular 41116

Subject

Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits

Date

2025-07-18T05:24:16Z (a day ago)

From

Alan Watson at UNAM <alan@astro.unam.mx>

Via

Web form

Enrique Moreno Méndez (UNAM), Francis Fortin (IRAP), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Kin Ocelotl López (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM):

We imaged the field of Swift Trigger 1334535 (Siegel et al, GCN Circ. 41115Loading...
 
 ), possibly GRB 250718A, using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-07-18 03:52 to 04:30 UTC (from 3:38 to 4:16 hours after the trigger at 00:14 UTC) and obtained 32 minutes of exposure in the i filter.

The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

In the stacked image, after subtracting the a template image from Legacy Survey DR10 (Dey et al. 2019), we do not detect any new source in the BAT uncertainty region (Siegel et al, GCN Circ. 41115Loading...
 
 ) down to the following 5-sigma limit:

i > 22.7

Our results are compatible with the earlier upper limit reported by Lipunov et al. (GCN Circ. 41114Loading...
 
 ).

We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

GCN Circular 41117

Subject

GRB 250718A: Fermi GBM Final Real-time Localization

Date

2025-07-18T07:16:14Z (a day ago)

From

Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>

Via

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

At 07:05:40 UT on 18 Jul 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250718A (trigger 774515145.094648 / 250718296).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 233.0, Dec = -26.0 (J2000 degrees, equivalent to J2000 15h 31m, -26d 00'), with a statistical uncertainty of 20.3 degrees.

The angle from the Fermi LAT boresight is 119.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250718296/quicklook/glg_skymap_all_bn250718296.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/bn250718296/quicklook/glg_healpix_all_bn250718296.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250718296/quicklook/glg_lc_medres34_bn250718296.gif