GCN Circular 31354

A. Ursi, E. Menegoni (INAF/IAPS), F. Longo (Univ. Trieste and INFN
Trieste), C. Pittori, F. Verrecchia (SSDC, and INAF/OAR), P. Tempesta
(TeleSpazio), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Argan,
M. Cardillo, C. Casentini, Y. Evangelista, L. Foffano, G. Piano
(INAF/IAPS), F. Lucarelli (SSDC, and INAF/OAR), A. Bulgarelli, A. Di Piano,
V. Fioretti, F. Fuschino, N. Parmiggiani (INAF/OAS-Bologna), M. Marisaldi
(INAF/OAS-Bologna, and Bergen University), M. Pilia, A. Trois
(INAF/OA-Cagliari), I. Donnarumma (ASI), A. Giuliani (INAF/IASF-Mi), report
on behalf of the AGILE Team:

The AGILE satellite detected the long GRB 220101A at T0 = 2022-01-01
05:11:22 (UTC), reported by Swift  BAT (GCN #31347, #31348), Swift XRT (GCN
#31349), Swift UVOT (GCN #31351), and Fermi LAT (GCN #31350).

The burst is clearly visible in the AGILE scientific ratemeters of the
SuperAGILE (SA; 20-60 keV), MiniCALorimeter (MCAL; 0.4-100 MeV), and
AntiCoincidence (AC; 50-200 keV) detectors. The event lasted about 80 s and
it released a total number of 14577 counts in the SA detector (above a
background rate of 100 Hz), 95830 counts in the MCAL detector (above a
background rate of 1140 Hz), and 256390 counts in the AC detector (above a
background rate of 3215 Hz). The AGILE ratemeters light curves can be found
at http://www.agilescienceapp.it/notices/GRB220101A_AGILE_RM.png .

The event also triggered a partial high time resolution MCAL data
acquisition, from T1 = 2022-01-01 05:11:21.50 +/- 0.01 s (UTC) to T2 =
2022-01-01 05:11:55.74 +/- 0.01 s (UTC), and released 10934 counts in the
detector, above a background rate of 570 Hz. The time-integrated spectrum
of the burst in this time interval can be fitted in the energy range
0.4-100 MeV with a power-law with ph. ind. = -1.28 (-0.11/+0.11), resulting
in a reduced chi-squared of 0.96 (84 d.o.f.) and a fluence of 7.8e-05
ergs/cm^2 (90% confidence level), in the same energy range.

We divided the data acquisition into four time intervals: interval a
[T0-0.5 s, T0+10.0 s], interval b [T0+10.0 s, T0+17.0 s], interval c
[T0+17.0 s, T0+24.0 s], and interval d [T0+24.0 s, T0+34.0 s]. The spectral
analysis in the energy range 0.4-100 MeV shows an evolution of the power
law photon index in the first stages of the burst, passing from -0.98 to
-1.70. Details are reported below:

  | model | ph. ind.           | red chi^2 (dof) | fluence (erg/cm^2)
a | PL    | 0.98 (-0.29/+0.19) | 1.00 (75)       | (1.8+/-0.2)e-5
b | PL    | 0.93 (-0.40/+0.22) | 0.98 (75)       | (8.3+/-0.8)e-6
c | PL    | 1.31 (-0.22/+0.23) | 0.99 (75)       | (1.1+/-0.1)e-5
d | PL    | 1.70 (-0.13/+0.29) | 1.05 (75)       | (2.6+/-0.3)e-5

The MCAL light curve can be found at:
http://www.agilescienceapp.it/notices/GRB220101A_AGILE_MCAL.png .

Additional analysis of AGILE data is in progress. Automatic MCAL GRB alert
Notices can be found at: https://gcn.gsfc.nasa.gov/agile_mcal.html.