TITLE: GCN CIRCULAR NUMBER: 38443 SUBJECT: LIGO/Virgo/KAGRA S241125n: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes DATE: 24/12/05 15:33:48 GMT FROM: David Paneque at Max Planck Institute for Physics <dpaneque@mppmu.mpg.de> D. Paneque (MPP Munich), M. Teshima (MPP Munich), M. Seglar Arroyo (IFAE Barcelona), D. Miceli (INFN Padova), A. Stamerra (INAF Rome), J. Jimenez (IFAE Barcelona), S. Menon (University & INAF Rome), A. Simongini (University & INAF Rome) on behalf of the LST and MAGIC Collaborations report: We observed the Swift/BAT-GUANO gamma-ray counterpart candidate (GRB 241125A, DeLaunay, GCNC 38308) presumably related to the GW S241125n (LVK Collaboration, GCNC 38305, 38315). A total of 4h of pointed observations towards the gamma-ray counterpart candidate position were obtained, starting approximately on Nov 25, 20 UT (i.e. about 19h post trigger time). A preliminary offline analysis of the LST-1 and MAGIC dataset shows no excess of gamma-rays above 300 GeV at the position of the Swift/BAT-GUANO candidate. These results have been obtained using the LST analysis software, lstchain (https://zenodo.org/records/14227973 , v0.10.13), and the MAGIC analysis software MARS (Zanin et al. 2013). Observations were affected by the presence of clouds and by reduced atmospheric transparency. A more in-depth analysis of this data set is ongoing. LST-1 is the first telescope of the Large-Sized Telescope (LST) for the Cherenkov Telescope Array Observatory. It is located on the Canary island of La Palma, Spain. The telescope design is optimized for observing gamma rays in the range from 20 GeV to 3 TeV. The LST-1 contact persons for these observations are Masahiro Teshima (mteshima@mpp.mpg.de) and Monica Seglar-Arroyo (mseglar@ifae.es). The preliminary offline analysis has been performed by Sweta Menon (sweta.menon@inaf.it) and Juan Jimenez (juan.jimenez@ifae.es). MAGIC is a system of two 17m-diameter Imaging Atmospheric Cherenkov Telescopes located on the Canary island of La Palma, Spain, and designed to perform gamma-ray astronomy in the energy range from 50 GeV to greater than 50 TeV. The MAGIC contact persons for these observations are David Paneque (dpaneque@mpp.mpg.de), Antonio Stamerra (antonio.stamerra@inaf.it) and Davide Miceli (davide.miceli@pd.infn.it). The preliminary offline analysis has been performed by Andrea Simongini (andrea.simongini@inaf.it). View this GCN Circular online at https://gcn.nasa.gov/circulars/38443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...