GRB 180416A

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


"At 08:09:26.47 UT on 16 April 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180416A (trigger 545558971 / 180416340).
The on-ground calculated location, using the GBM trigger data, is

RA = 113.65, Dec = -49.12 (J2000 degrees)

with an uncertainty of 1.0 degrees (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 21 degrees.

The GBM light curve consists of multiple separated peaks
with a duration (T90) of about 103 s (50-300 keV).
The time-averaged spectrum from T0 s to T0+100 s is
adequately by a power law function with an exponential
high-energy cutoff. The power law index is -1.19 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 153 +/- 4 keV.

The event fluence (10-1000 keV) in this time interval is
(3.61 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+87.2 s in the 10-1000 keV band
is 22.2 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak = 145 +/- 5 keV, alpha = -1.16 +/- 0.02 and
beta = -2.89 +/- 0.26.


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

V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration:

Analysis of Astrosat CZTI data showed the detection of a long GRB 180416A, which was also detected by Fermi-GBM (Bissaldi E. et al, GCN # 22644).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 08:10:54.5 UT, ~87 s after GBM trigger. The measured peak count rate is 420.5 cts/s above the background in combined data of four quadrants, with a total of 3904 cts. The local mean background count rate was 508.5 cts/s. Using cumulative rates, we measure a T90 of 92.6 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.