TITLE:   GCN CIRCULAR
NUMBER:  22889
SUBJECT: GRB150101B: INTEGRAL prompt gamma-ray signal from a possible GRB170817A-analogue
DATE:    18/07/04 10:24:47 GMT
FROM:    Carlo Ferrigno at IAAT/ISDC  <carlo.Ferrigno@unige.ch>

J. Rodi, A. Bazzano, P. Ubertini (IAPS-Roma)
E. Bozzo, C. Ferrigno, V. Savchenko (ISDC, University of Geneva, CH)
E. Kuulkers (ESTEC/ESA, The Netherlands)
D. Gotz (DRF/Irfu/DAp Saclay/CEA)
L. Hanlon, A. Martin-Carrillo (UCD, Ireland)
J. M. Mas-Hesse (CSIC-INTA, Spain)
S. Mereghetti (INAF IASF-Milano, Italy)
L. Natalucci (IAPS-Roma)
A. Lutovinov, R. Sunyaev (IKI, Russia)
report on behalf of the INTEGRAL Gravitational Wave Team

We have analyzed INTEGRAL archival data of the SPI-ACS and IBIS/PICsIT
in coincidence with GRB150101B (GCN 17267, GCN 17276). Troja et al.
(2018, arXiv:1806.10624) suggest that GRB150101B is a kilonova event
comparable to GW170817/GRB170817A, but at cosmological distance and
without the observations of a gravitational-wave trigger. The INTEGRAL
orientation was 24.9 degrees from the GRB location and implies a
somewhat suppressed response for SPI-ACS, but an improved response for
IBIS, especially IBIS/PICsIT (Savchenko et al. 2017, A&A 603, A46).

We confirm the independent detection by SPI-ACS and IBIS/PICsIT of a
short duration (~0.012 sec) event, consistent with that reported in
Troja et al. The signal in SPI-ACS (75 keV-10 MeV) and in IBIS/PICsIT
(200 keV-1.2 MeV) has a S/N of 5.1, and 4.2, respectively.

 From the SPI-ACS observation, we estimate a 75 keV-2 MeV fluence of
GRB150101B in the time interval T_0-0.05s - T_0+0.1s of (1.3 ±
0.3)e-7 erg/cm2, assuming a simple power-law spectrum with a slope of
1.2 (as measured by Swift/BAT and Fermi/GBM).

Analysis is on-going to constrain any possible soft gamma-ray
afterglow with contemporaneous INTEGRAL observations.

A plot of the light curve can be found at
https://zenodo.org/record/1304812#.WzyLLa14VGw