Fermi-LAT observation of V1405 Cas

ATel #14620; Yi-Huan Gong and Kwan-Lok Li (National Cheng Kung University)
on 11 May 2021; 14:30 UT
Credential Certification: K. L. Li (lilirayhk@gmail.com)

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We report the Fermi-LAT gamma-ray observation of the classical nova V1405 Cas, which was discovered by Yuji Nakamura (Japan) on 2021-03-18.4236 UTC (CBET 4945; Atel #14471). We have been monitoring the nova with LAT since the discovery, and no significant gamma-ray emission has been found so far. Recently, a rapid brightening was observed in optical since 2021-05-05 (ATel #14614), and the maximum brightness is around V = 5.2 mag according to the AAVSO light curve. By extracting the LAT data taken from 2021-05-04 to 2021-05-10 with 10 deg of radius centered at V1405 Cas, we obtained TS=0 (photon index = 2.1 was assumed), indicating that the gamma ray emission was still undetected. The inferred 95% upper limit is 4.2e-11 erg/cm^2/s or 1.5e34 erg/s if the Gaia distance of 1.7 kpc (ATel #14530) is assumed.