GRB 240118C

T. Preis, B. Biltzinger, J. Burgess & J. Greiner (all MPE Garching) report:

The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
727291408 at 17:23:23 on 18 Jan. 2024 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).

The best-fit position is:
RA(2000.0) = 305.3 deg
Decl.(2000.0) = -9.8 deg
The 1 sigma statistical error radius is 1.6 deg.
We estimate an additional systematic error of 1 deg.

Further details are available at:
https://grb.mpe.mpg.de/grb/GRB240118725/

The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB240118725/healpix

The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB240118725/json

                        

V. Sharma (NASA-GSFC/UMBC) and R. Hamburg (CNRS/IN2P3) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

At 17:23:23.93 UT on 18 January 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240118C (trigger 727291408/240118725).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 305.33, Dec = -12.39 (J2000 degrees, equivalent to J2000 20h 21m, 12d 23'), with a statistical uncertainty of 1.8 degrees.

The angle from the Fermi LAT boresight is 90.00 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240118725/quicklook/glg_skymap_all_bn240118725.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240118725/quicklook/glg_healpix_all_bn240118725.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240118725/quicklook/glg_lc_medres34_bn240118725.gif

James DeLaunay (PSU), 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 240118C onboard (T0: 2024-01-18T17:23:23.93 UTC, Fermi GBM Trig 727291408, INTEGRAL SPI-ACS Trig 10480). 

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 10.2 in a 16.384 s analysis time bin, starting at T0 + 12.288 s. 

NITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a DeltaLLHOut of 9.6.

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/

V. Sharma (NASA-GSFC/UMBC) and C. Meegan (UAH) report on behalf of the 
Fermi Gamma-ray Burst Monitor Team:

"At 17:23:23.93 UT on 18 January 2024, the Fermi Gamma-ray Burst Monitor (GBM) 
triggered and located GRB 240118C (trigger 727291408/240118725), which was also 
detected by Swift/BAT-GUANO (DeLaunay et al. 2024, GCN 35581
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 ).
The Fermi Final Real-time Localization is reported in GCN 35576
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 .

The angle from the Fermi LAT boresight is 90 degrees.

The GBM light curve consists of multiple pulses with a duration (T90)
of about 31 s (50-300 keV). The time-averaged spectrum from 
T0-0.6 to T0+32.5 s is best fit by a power law function with 
an exponential high-energy cutoff.
The power law index is -1.39 +/- 0.03 and the cutoff energy,
parameterized as Epeak, is 144 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is (1.23 +/- 0.04)E-05 erg/cm^2. 
The 1-sec peak photon flux measured starting from T0+29.7 s in the 10-1000 keV band 
is 13.6 +/- 0.5 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/."

Wen-Long Zhang, Shao-Lin Xiong, Yan-Qiu Zhang report on behalf of the GECAM team:

GECAM-B was triggered on-ground by a long burst, GRB 240118C, at 2024-01-18T17:23:24.000 UTC (T0), which was also observed by Fermi/GBM (GCN #35576
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  and GCN #35586
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 ) and Swift/BAT-GUANO（GCN #35581）. 

According to the GECAM-B light curve, this burst consists of  roughly three pulses with a total duration of ~40 sec. 

The GECAM-B ground calculated location (J2000) is:
Ra: 308.64 deg   
Dec: -1.56 deg
Err: 4.65 deg (1-sigma, statistical only)
This GECAM-B localization is consistent with that of Fermi/GBM within the error.

We note that these results are very preliminary. Refined analysis will be reported later.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).