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 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.