TITLE:   GCN CIRCULAR
NUMBER:  24181
SUBJECT: LIGO/Virgo S190425z: INTEGRAL IBIS prompt observation
DATE:    19/04/25 14:19:28 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

I. Chelovekov, A. Pozanenko, P. Minaev, S. Grebenev on behalf of the IKI
GRB FuN collaboration report:

We used public data (observations of Inner Galaxy, proposal 1620021, PI 
A. Bodaghee) of IBIS-ISGRI/INTEGRAL to search for a possible 
EM-counterpart of the LIGO/Virgo S190425z event (LVC GCN #24168). We 
present our preliminary analysis of the prompt off-axis observation of 
the event with IBIS-ISGRI.

Around trigger time of S190425z (=G330561) the boresight angle was 30.8 
degrees. We found no significant emission above the background in the
time window -100 s + 100 s around the LIGO/Virgo S190425z trigger time.

In particular, we did not detect any positive signal near the time of a 
hard X-ray pulse detected by SPI-ACS/INTEGRAL(Martin-Carillo et al. GCN 
#24169; Minaev et al., GCN #24170; Savchenko et al., GCN #24178).

The upper limit of any possible emission with a duration of 1 s was (1.7 
+/- 0.8) x 10^{-6} erg / cm2 and (1.3 +/- 0.8) x 10^{-6} erg / cm2 in 
the energy ranges 30-100 and 100-500 keV, respectively. To estimate the 
flux we used our calibration based on several hundreds of GRBs 
synchronously detected by GBM/Fermi and on/off-axis by IBIS/ISGRI 
(Chelovekov et al, 2019, in press).

The light curves of IBIS/ISGRI and SPI-ACS can be found in

http://grb.rssi.ru/S190425z/S190425z_SPI-ACS.png
http://grb.rssi.ru/S190425z/S190425z_IBIS_1s.png