Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

TL;DR

This paper reports the detection of high-energy gamma-ray emission from two classical novae by Fermi LAT, revealing extended emission periods and multiple optical peaks, with analysis of light curves, spectra, and models.

Contribution

It presents the first detailed gamma-ray observations of V1369 Centauri 2013 and V5668 Sagittarii 2015, including their light curves, spectra, and modeling, expanding understanding of nova gamma-ray emissions.

Findings

Gamma-ray emission detected 2 days after optical peaks

Extended gamma-ray emission lasting up to 55 days

Multiple optical peaks correlated with gamma-ray activity

Abstract

We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) gamma-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of gamma-ray onsets beginning ~2 days after their first optical peaks. Significant gamma-ray emission was found extending to 39-55 days after their initial LAT detections, with systematically fainter and longer duration emission compared to previous gamma-ray detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the timespans of the observed gamma rays. The gamma-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons to other novae detected by the LAT are discussed.