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Detection of enhanced very-high-energy gamma-ray emission from the radio-galaxy NGC1275 with the LST-1

ATel #15819; Juan Cortina (CIEMAT) for the CTA LST collaboration
on 21 Dec 2022; 22:29 UT
Credential Certification: Juan Cortina (Juan.Cortina@ciemat.es)

Subjects: Gamma Ray, TeV, VHE, AGN, Transient

Referred to by ATel #: 15820, 15823, 15852, 15856, 15938, 17020

The LST-1 telescope has observed an increase in the very-high-energy (VHE; >100 GeV) gamma-ray flux from the radio-galaxy NGC1275 (RA=03:19:48.1, DEC=+41:30:42, J2000.0). The LST-1 observed NGC1275 on the night of December 20 to December 21, 2022 (MJD 59934), triggered by an increase in gamma-ray flux detected by MAGIC and Fermi-LAT. In the preliminary offline analysis of the LST-1 data, NGC1275 has been detected with a significance of more than 10 sigma with an average flux of approximately 3.0 x 10^-10 cm^-2 s^-1 above 100 GeV, i.e. 70% that of the Crab Nebula, varying from 140% to below 30% at the beginning and at the end of the observation, respectively. Note though that this is the result of a quick-look analysis. The LST-1 observations were performed during commissioning which began in 2018. LST-1 is a prototype of the Large-Sized Telescope for the Cherenkov Telescope Array and is located on the Canary island of La Palma, Spain. The LST-1 is designed to perform gamma-ray astronomy in the energy range from 20 GeV to 3 TeV. LST-1 observations on NGC1275 will continue during the next few nights, multi-wavelength observations are encouraged. The preliminary offline analysis has been performed by Chaitanya Priyadarshi (cpriyadarshi@ifae.es) and Seiya Nozaki (nozaki@mpp.mpg.de). The LST-1 contact persons for these observations are Juan Cortina (juan.cortina@ciemat.es), Masahiro Teshima (mteshima@mppmu.mpg.de) and Mireia Nievas (mnievas@iac.es).