Fermi-LAT Gamma-ray Detection of Nova V1405 Cas 2021
ATel #14658; S. Buson (Univ. of Wuerzburg), C. C. Cheung (NRL), P. Jean (IRAP, Toulouse), on behalf of the Fermi Large Area Telescope Collaboration
on 25 May 2021; 02:39 UT
Credential Certification: Teddy Cheung (Teddy.Cheung@nrl.navy.mil)
Subjects: Gamma Ray, >GeV, Nova, Transient
The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has detected faint gamma-ray emission from a source positionally consistent with the nova V1405 Cas. The optical nova was discovered by Y. Nakamura on 2021-03-18.4236 UT (see ATel #14471, #14472) and is notable because it is only 1.7 kpc distant.
Preliminary analysis using 4-day time bins indicates its first detection with 4.1-sigma significance in data from 2021-05-20 15:01:17 to 2021-05-24 15:01:17 UTC with a (E >100 MeV) flux of (1.4 +/- 0.8) x 10^-7 photons cm^-2 s^-1 (photon index fixed at 2.3; statistical uncertainties only). The gamma-ray detection was preceded by non-detections (see also ATel #14620) with typical flux upper limits (95% confidence) on 4-day intervals of ~(0.6-0.8) x 10^-7 photons cm^-2 s^-1 from 2021-04-26 15:01:17 to 2021-05-20 15:01:17. The gamma-ray detection follows the recent optical brightening event approximately 50 days after discovery (ATel #14614, #14615), that peaked at V ~ 5.3 mag between May 10-11 and returned to its baseline value of V ~ 7.3-7.7 since May 17 (according to observations reported to the AAVSO; see link in Alert Notice 742: https://www.aavso.org/aavso-alert-notice-742).
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multi-wavelength observations. For this source the Fermi LAT contact people are S. Buson (sara.buson@gmail.com) and C.C. Cheung (Teddy.Cheung@nrl.navy.mil).
The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
