GRB 180720A

AGILE/MCAL detection of GRB 180720A

A.Ursi (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), F.
Verrecchia (SSDC and INAF/OAR), N. Parmiggiani, A. Bulgarelli
(INAF/IASF-Bo), A. Trois, M. Pilia (INAF/OA-Cagliari), C. Pittori, F.
Lucarelli (SSDC and INAF/OAR), M. Marisaldi (University of Bergen), F.
Longo (Univ. Trieste and INFN Trieste), M. Cardillo, G. Piano (INAF/IAPS),
G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), V. Fioretti, F.
Fuschino (INAF/IASF-Bo), , I. Donnarumma (ASI), A. Giuliani (INAF/IASF-Mi),
report on behalf of the AGILETeam:

The AGILE Mini-CALorimeter (MCAL) detected a burst at T0 = 2018-07-20
05:06:03.29 +/- 0.01 s (UTC), lasting about ~ 3.6 s in the 0.4-100 MeV
energy range. The light curve is composed of a single smooth peak and
released a total of ~3000 counts at E> 400 keV in the detector, above an
average background rate of 20 counts / 32 ms.

Further analysis is still in progress.

The AGILE-MCAL detector has a full solid angle acceptance, and is
operational in the range 0.4 - 100 MeV.

E. Bissaldi (Politecnico & INFN Bari)
reports on behalf of the Fermi GBM Team:


"At 05:06:02.06 UT on 20 July 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180720A (trigger 553755967 / 180720213),
which was also detected by the AGILE/MCAL (Ursi et al. 2018, GCN 22970
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 ).

The on-ground calculated location, using the GBM trigger data, is

RA, Dec = 127.0, -0.4 (J2000 degrees),

with an uncertainty of 1 degree (radius, 1-sigma containment,
statistical only; there is additionally a systematic error
which we have characterized as a core-plus-tail model,
with 90% of GRBs having a 3.7 deg error and a small tail
suffering a larger than 10 deg systematic error.
[Connaughton et al. 2015, ApJS, 216, 32]).

The angle from the Fermi LAT boresight at the GBM trigger time is 74 degrees.

The GBM light curve consists of single FRED-like peak
with a duration (T90) of about 9 s (50-300 keV).
The time-averaged spectrum from T0 to T0+10 s is
best fit by a Band function with Epeak = 260 +/- 15 keV,
alpha = -1.08 +/- 0.02 and beta = -2.13 +/- 0.06.

The event fluence (10-1000 keV) in this time interval is
(2.563 +/- 0.026)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.3 s in the 10-1000 keV band
is 36.5 +/- 0.5 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."