GRB 230727A
GCN Circular 34275
Subject
GRB 230727A: Fermi GBM Final Real-time Localization
Date
2023-07-27T11:13:44Z (2 years 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 11:03:06 UT on 27 Jul 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230727A (trigger 712148591.84604 / 230727460).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 323.8, Dec = 73.7 (J2000 degrees, equivalent to J2000 21h 35m, 73d 42'), with a statistical uncertainty of 1.2 degrees.
The angle from the Fermi LAT boresight is 100.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230727460/quicklook/glg_skymap_all_bn230727460.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230727460/quicklook/glg_healpix_all_bn230727460.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230727460/quicklook/glg_lc_medres34_bn230727460.gif
GCN Circular 34280
Subject
GRB 230727A: Swift/BAT-GUANO detection of a burst
Date
2023-07-28T01:05:25Z (2 years ago)
From
Jimmy DeLaunay at University of Alabama <delauj2@gmail.com>
Via
Web form
James DeLaunay (UAlabama), Gayathri Raman (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 230727A onboard (T0: 2023-07-27T11:03:06.85 UTC, Fermi Trig 712148591, GCN 34275).
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 with a sqrt(TS) of 11 in a 2.048 s analysis time bin.
NITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a borderline DeltaLLHOut of 7.4.
The Fermi GBM localization (GCN 34275) has this burst significantly outside of the BAT coded FOV
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
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 34283
Subject
GRB 230727A: AstroSat CZTI detection
Date
2023-07-28T06:47:03Z (2 years ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
email
B. Pari (IITB), P K. Navaneeth (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 230727A which was also detected by Fermi (Fermi GBM Team, GCN Circ. 34275) and Swift/BAT-GUANO (DeLaunay et al., GCN Circ. 34280).
The source was clearly detected in the 20-200 keV energy range. The light curve peaks at 2023-07-27 11:03:09.45 UTC. The measured peak count rate associated with the burst is 709.2 (+211.2, -56.0) counts/s above the background in the combined data of all quadrants, with a total of 1916 (+278, -290) counts. The local mean background count rate was 522.1 (+5.0, -7.7) counts/s. Using cumulative rates, we measure a T90 of 11.8 (+2.5, -1.6) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2023-07-27 11:03:08.85 UTC. The measured peak count rate associated with the burst is 343.3 (+76.9, -79.7) counts/s above the background in the combined data of all quadrants, with a total of 1231 (+419, -444) counts. The local mean background count rate was 1992.2 (+5.8, -7.1) counts/s. We measure a T90 of 11.3 (+3.7, -5.1) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb