[vsnet-grb-info 23548] LIGO/Virgo S190901ap: Upper limits from CALET observations.

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25647
SUBJECT: LIGO/Virgo S190901ap: Upper limits from CALET observations.
DATE:    19/09/04 07:06:55 GMT
FROM:    Yuta Kawakubo at Louisiana State U./CALET  <kawakubo1 at lsu.edu>

N. Cannady (GSFC/UMBC), A. Yoshida, T. Sakamoto, V. Pal'shin, 
S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), 
S. Nakahira (RIKEN), Y. Asaoka, S. Torii (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), M. L. Cherry (LSU), 
S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) was operating at the trigger 
time of S190901ap T0 = 2019-09-01 23:31:01.838 UT (The LIGO Scientific
Collaboration and Virgo Collaboration, GCN Circ. 25606 and 25614).

No CGBM on-board trigger occurred around the event time.  Based
on the LIGO-Virgo localization sky map, the summed LIGO probabilities 
inside the CGBM HXM (7 - 3000 keV) and SGM (40 keV - 28 MeV) fields 
of view are 6 % and 61 %, respectively (and 82 % credible region 
of the updated localization map was above the horizon).  The HXM and 
SGM fields of view were centered at RA = 345.1 deg, Dec = 22.4 deg
and RA = 353.8 deg, Dec = 16.7 deg at T0, respectively.

Based on the analysis of the light curve data with 0.125 sec
time resolution from T0-60 sec to T0+60 sec, we found no
significant excess (signal-to-noise ratio >= 7) around the trigger
time in either the HXM or the SGM data.

The CALET Calorimeter (CAL) was operating in the low energy trigger
mode at the trigger time of S190901ap. Using the CAL data, we have 
searched for gamma-ray events in the 1-10 GeV band from -60 sec 
to +60 sec from the GW trigger time and found no candidates 
in the overwrap region with the LIGO-Virgo probability map. 
The 90% upper limit of CAL is 6.3x10^-5 erg/cm^2/s (1-10 GeV) when
the summed LIGO-Virgo probability reaches 5%.
The CAL FOV was centered at RA= 353.8 deg, Dec= 16.6 deg at T0.