GRB 250527C
GCN Circular 40653
Subject
GRB 250527C: CrAO Optical Upper Limit
Date
2025-06-09T10:19:33Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), S. Nazarov (CrAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 250527C detected by Fermi/GBM (Trigger 770047117) and further localized by Swift/BAT-GUANO (Delaunay et. al, GCN 40563). The field has also been observed by Swift/XRT (Evans, GCN 40564), and Swift/UVOT (Klingler, GCN 40574). Our observations were carried out using the Sintez-Newton 0.36-meter telescope installed at the Crimean Astrophysical Observatory (CrAO). The series of images has taken in the R-filter. We do not detect candidate transients in comparison with USNO-B1.0, and PS1 catalogs in the stacked image of 22*120 sec. Particularly, we were searching for candidates inside localization circles of X-Ray sources provided in (Evans, GCN 40564). The preliminary upper limit is given below:
Date UTstart T-T0 Exposure Filter OT Err UL
(n*T) (3-sigma)
2025-05-28 23:46:57 1.42390 22*120 R n/d n/d 19.1
The photometry was calibrated using nearby USNO-B1.0 stars (R2 magnitudes) and has not been corrected for the Galactic extinction.
GCN Circular 40574
Subject
GRB 250527C: Swift/UVOT Upper Limits
Date
2025-05-29T21:29:30Z (9 months ago)
From
noelklin@umbc.edu
Via
Web form
N. Klingler (UMBC / NASA-GSFC / CRESST II) reports on behalf of the Swift/UVOT team:
Swift/UVOT has performed observations of GRB 250527C centered on the BAT position, RA, Dec = 21h 18m 31.92s, +52d 44' 13.2" (= 319.633, 52.737 deg; 90% uncertainty of 5 arcmin) (DeLaunay et al.; GCN 40563). UVOT collected 4536 s of data between 96 ks and 113 ks post-trigger, using the White filter.
No uncatalogued/transient sources are detected, with an approximate 3 sigma upper limit > 22.56 (AB) in the 90% BAT localization region.
For the X-ray sources detected by XRT (https://www.swift.ac.uk/ToO_GRBs/00021843/): sources 3, 4, and 6 fall outside the UVOT field of view. XRT source 2 is not detected. XRT source 1 is a star: TYC 3953-1190-2. XRT 5 has an optical counterpart (AB mag 17.99 +/- 0.07), but it is seen in archival DSS images and thus does not appear to be a transient.
No correction has been made for the expected Galactic extinction due to the reddening of E(B-V) = 3.43 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 40564
Subject
GRB 250527C: Swift ToO observations
Date
2025-05-28T16:37:51Z (9 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT-detected event
GRB 250527C. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021843
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 Swift/BAT 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.
GCN Circular 40563
Subject
GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
Date
2025-05-28T15:52:17Z (9 months ago)
From
Jimmy DeLaunay at Penn State <delauj2@gmail.com>
Via
Web form
James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250527C onboard (T0: 2025-05-27T13:58:32.41 UTC, Fermi Trig 770047117).
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), detects the burst in a 8.192 s analysis time bin starting at T0 - 4.096 s with a sqrt(TS) of 11.6.
An arcminute localization is found with DeltaLLHOut of 29.5 and a DeltaLLHPeak of 17.4.
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
The BAT position is
RA, Dec = 319.633, 52.737 deg which is
RA(J2000) = 21h 18m 31.92s
Dec(J2000) = 52d 44’ 13.2″
with an estimated uncertainty of 5 arcmin radius.
More details about this burst can be found on the trigger report page here:
https://guano.swift.psu.edu/trigger_report?id=770047148
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/