AstroNote 2025-328

We observed the field of TDE2025aarm (z = 0.01368, Faris et al., AstroNote 2025-311) with the MAGIC and LST-1 telescopes. A total 3.3 h of MAGIC and 1.1 h of LST-1 pointed observations were obtained on MJD 60991, MJD 60997 and MJD 60998, during the optical rising phase, complementing the earlier VHE gamma-ray observations by H.E.S.S. (Mohrmann et al., AstroNote 2025-322).

A preliminary offline analysis of the MAGIC and LST-1 dataset shows no excess of gamma rays above 200 GeV at the position of TDE2025aarm. Assuming a power-law spectrum with photon index = 2.0, we derive a 95% confidence-level preliminary upper-limit of < 6.20e-12 cm-2.s-1 and < 7.20e-12 cm-2.s-1 with the MAGIC and LST-1 telescopes, respectively. These results have been obtained using the MAGIC analysis software MARS (Zanin et al. 2013), and the LST analysis software, lstchain (https://zenodo.org/records/15804383 , v0.11.0). A more in-depth analysis of this data set is ongoing.

MAGIC and LST-1observations on TDE2025aarm will continue during the next weeks. Further multiwavelength observations are encouraged.

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 D. Paneque (dpaneque@mppmu.mpg.de) and Andrea Simongini (andrea.simongini@inaf.it). The preliminary offline analysis has been performed by Andrea Simongini (andrea.simongini@inaf.it) and Francesco Schiavone (francesco.schiavone@ba.infn.it).

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 M. Teshima (mteshima@mpp.mpg.de) and M. Kherlakian (kherlakian@astro.ruhr-uni-bochum.de). The preliminary offline analysis has been performed by Andrea Simongini, Hide Katagiri (hideaki.katagiri.sci@vc.ibaraki.ac.jp) and Sweta Menon (sweta.menon@inaf.it).