Fermi-Lat Gamma-Ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

Abstract

We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) γ-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 γ-ray onsets beginning ∼2 days after their first optical peaks. Significant γ-ray emission was found extending to 39-55 days after their initial LAT detections, with systematically fainter and longerduration emission compared to previous γ-ray-detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the time spans of the observed γ-rays. The γ-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons with other novae detected by the LAT are discussed.

A Detailed Observational Analysis of V1324 Sco, the Most Gamma-Ray-luminous Classical Nova to Date

“…It should be noted that, of the gamma-ray-detected novae, at least two-V1369 Cen and V5668 Sgr-had a similar flattening of the optical light curve near maximum (Cheung et al 2016), though both exhibited large (D > V 1 mag) fluctuations in brightness during their period of flattening (unlike V1324 Sco; Figure 2). In both systems, the evolution of optical spectral line profiles around the maximum imply that several episodes of mass ejection transpire over the course of the variegated plateau .…”

“…As can be see in Cheung et al (2016), V1324Sco is the most gamma-ray-luminous classical nova discovered to date. Note, however, that Cheung et al assume a distance of 4.5 kpc to V1324Sco, while Finzell et al (2015) showed that its distance is substantially farther (>6.5 kpc).…”

“…Note, however, that Cheung et al assume a distance of 4.5 kpc to V1324Sco, while Finzell et al (2015) showed that its distance is substantially farther (>6.5 kpc). Therefore, V1324Sco is even more gamma-ray luminous than presented in Cheung et al (2016), registering at ǵ L 2 10 36 erg s −1 . In V1324Sco, there is strong observational evidence for shock interaction, both from the gamma-rays and from the radio (in particular, the initial maximum; Section 3.2).…”

“…These models, however, could not explain the subsequent novae detected by Fermi/LAT: V1324 Sco, V959 Mon, V339 Del (Ackermann et al 2014), and V1369 Cen and V5668 Sgr (Cheung et al 2016). These systems do not have a detectable red-giant companion (see, e.g., Hornoch 2013;Munari & Henden 2013;Finzell et al 2015; although note that the underlying binary of V5668 Sgr has yet to be identified).…”

“…These outbursts give rise to an increase in luminosity across the electromagnetic spectrum and eject~-Area Telescope (LAT; see, e.g., Cheung et al 2010Cheung et al , 2012bCheung et al , 2012aCheung et al , 2015Hays et al 2013;Ackermann et al 2014;Cheung et al 2016). They show gamma-ray luminosities (>100 MeV) of -10 10 34 36 erg s −1 , lasting for 2-8 weeks around optical maximum (Ackermann et al 2014;Cheung et al 2016).…”