Fermi-LAT Observations of V549 Vel 2017: a Sub-Luminous Gamma-Ray Nova?

Abstract

We report on the Fermi-LAT detection (with ~5.7 sigma significance) as well as the multi-wavelength analysis of the 2017 nova eruption V549 Vel. Unlike the recent shock-powered novae ASASSN-16ma and V906 Car, the optical and gamma-ray light curves of V549 Vel show no correlation, likely implying relatively weak shocks in the eruption. Gaia detected a candidate progenitor of V549 Vel and found a parallax measurement of 1.91+/-0.39 mas, equivalent to a mode distance of d=560 pc (90% credible interval of 380-1050 pc). The progenitor was also observed by the 2MASS and WISE surveys. When adopting the Gaia distance, the spectral energy distribution of the progenitor is close to that of a G-type star. Swift/XRT detected the supersoft X-ray emission of the nova (kT=30-40 keV) since day 236, and the inferred blackbody size is comparable to that of other novae assuming d=560 pc (i.e., R_bb~5*10^8 cm). However, there is also an unknown astrometric excess noise of 3.2 mas found in the Gaia data, and the inferred distance becomes controversial. If the Gaia distance is accurate, the gamma-ray luminosity of V549 Vel will be as low as L_gamma~4*10^33 erg/s, making it the least luminous gamma-ray nova known so far. This may imply that the shock properties responsible for the gamma-ray emission in V549 Vel are different from those of the more luminous events. If the nova is located farther away, it is likely a symbiotic system with a giant companion as the observed progenitor.

10 pages, including 5 figures and 1 tables. Accepted for publication in ApJ

References in corpus (14)

• Three-dimensional mapping of the local interstellar medium with composite data
• Gamma-Ray Emission Concurrent with the Nova in the Symbiotic Binary V407 Cygni
• Fermi Establishes Classical Novae as a Distinct Class of Gamma-Ray Sources
• The Super-Soft X-ray Phase of Nova RS Ophiuchi 2006
• Shock-powered light curves of luminous red novae as signatures of pre-dynamical mass loss in stellar mergers
• Gamma-ray novae as probes of relativistic particle acceleration at non-relativistic shocks
• Shocks in nova outflows. I. Thermal emission
• A Nova Outburst Powered by Shocks
• The BRITE Constellation nanosatellite mission: Testing, commissioning and operations
• NuSTAR Detection of X-rays Concurrent with Gamma Rays in the Nova V5855 Sgr
• The Distance to Nova V959 Mon from VLA Imaging
• X-ray Spectroscopy of the gamma-ray Brightest Nova V906 Car (ASASSN-18fv)
• Very Long Baseline Interferometry imaging of the advancing ejecta in the first gamma-ray nova V407 Cyg
• The sustained post-outburst brightness of Nova Per 2018, the evolved companion, and the long orbital period

Cited by in corpus (9)

• Surveying the X-ray Behavior of Novae as They Emit $\gamma$-rays
• The first nova eruption in a novalike variable: YZ Ret as seen in X-rays and gamma-rays
• The multi-wavelength view of shocks in the fastest nova V1674 Her
• A strong shock during a nova outburst: an origin of multiple velocity systems in optical spectra and of high-energy emissions
• An update on Fermi-LAT transients in the Galactic plane, including strong activity of Cygnus X-3 in mid-2020
• Search for sub-TeV Neutrino Emission from Novae with IceCube-DeepCore
• The Luminosity Phase Space of Galactic and Extragalactic X-ray Transients Out to Intermediate Redshifts
• What determines the $\gamma$-ray luminosities of classical novae?
• Discovery and Detailed Study of the M31 Classical Nova AT 2023tkw: Evidence for Internal Shocks