(All information courtesy of the instrument teams.)
Previous IAU Circulars
Results of Observations
GCN Circular #31501
Gayathri Raman (PSU), James DeLaunay (UAlabama), Aaron Tohuvavohu (U
Toronto), Jamie A. Kennea (PSU), report:
Swift/BAT did not localize GRB 220117C onboard (T0:
2022-01-17T04:45:55 UTC, Fermi/GBM trigger #664087560).
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,
arXiv:2111.01769), confidently detects the burst in a 8.192 s analysis
time bin with a sqrt(TS) of 19.5.
Estimated T90 in the detector is 8.55+/-0.07 s (10-350 keV).
An arcminute localization is found with DeltaLLHOut of 96.3 and a
DeltaLLHPeak of 58.7.
Using the conventional BAT imaging technique, we find an SNR of 6.1 at
the same location.
See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and
The BAT position is
RA, Dec = 286.457, +16.791 deg which is
with an estimated uncertainty of 2 arcmin.
The position is consistent with the Fermi/GBM localization.
No XRT/UVOT followup will take place (GCN 31500).
We encourage followup from other facilities.
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.
GCN Circular #31508
S. Lesage (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 04:45:55 UT on 17 January 2022, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 220117C (trigger 664087560/220117199)
which was also detected by Swift/BAT-GUANO (Raman et al. 2022, GCN 31501).
The Fermi GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 73 degrees.
The GBM light curve consists of multiple pulses with a duration (T90)
of about 115 s (10-1000 keV). The time-averaged spectrum
from T0-1.8 to T0+114.9 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is 0.1 +/- 0.3 and the cutoff energy,
parameterized as Epeak, is 82 +/- 6 keV.
The event fluence (10-1000 keV) in this time interval is
(4.6 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.7 s in the 10-1000 keV band is 6.4 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB
For Fermi GBM data and info, please visit the official Fermi GBM