What determines the $\gamma$-ray luminosities of classical novae?

Abstract

Classical novae in the Milky Way have now been well-established as high-energy GeV $\gamma$-ray sources. In novae with main-sequence companions, this emission is believed to result from shocks internal to the nova ejecta, as a later fast wind collides with an earlier slow outflow. To test this model and constrain the $\gamma$-ray production mechanism, we present a systematic study of a sample of recent Galactic novae, comparing their $\gamma$-ray properties ($\gamma$-ray luminosity and duration) with their outflow velocities, peak $V$-band magnitudes, and the decline times of their optical light curves ($t_2$). We uniformly estimate distances in a luminosity-independent manner, using spectroscopic reddening estimates combined with three-dimensional Galactic dust maps. Across our sample, $\gamma$-ray luminosities ($>$100 MeV) vary by three orders of magnitude, spanning $10^{34}-10^{37}$ erg s${}^{-1}$. Novae with larger velocity of the fast outflow (or larger differential between the fast and slow outflow) have larger $\gamma$-ray luminosities, but are detectable for a shorter duration. The optical and $\gamma$-ray fluxes are correlated, consistent with substantial thermal emission in the optical from shock-heated gas. Across six novae with $\gamma$-ray and infrared light curves, evidence for dust formation appears soon after the end of the detected $\gamma$-ray emission. Dusty and non-dusty novae appear to have similar $\gamma$-ray luminosities, though novae that have more material processed by the shocks may be more likely to form dust. We find that the properties of the $\gamma$-ray emission in novae depend heavily on the ejecta properties, and are consistent with expectations for internal shocks.

58 pages, 76 figures, Accepted by MNRAS

References in corpus (29)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Incremental Fermi Large Area Telescope Fourth Source Catalog
• The Optical to Mid-Infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS and WISE Surveys
• 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
• First science with SALT: peering at the accreting polar caps of the eclipsing polar SDSS J015543.40+002807.2
• 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
• Early spectral evolution of classical novae: consistent evidence for multiple distinct outflows
• Comprehensive Catalogue of the Overall Best Distances and Properties of 402 Galactic Novae
• Binary Interaction Dominates Mass Ejection in Classical Novae
• Surveying the X-ray Behavior of Novae as They Emit $\gamma$-rays
• Classical Novae at Radio Wavelengths
• NuSTAR Detection of X-rays Concurrent with Gamma Rays in the Nova V5855 Sgr
• The first nova eruption in a novalike variable: YZ Ret as seen in X-rays and gamma-rays
• X-ray Spectroscopy of the gamma-ray Brightest Nova V906 Car (ASASSN-18fv)
• Recurrent and symbiotic novae in the OGLE data
• The multi-wavelength view of shocks in the fastest nova V1674 Her
• Nova-produced Common Envelope: Source of the Non-solar Abundances and an Additional Frictional Angular Momentum Loss in Cataclysmic Variables
• The Galactic Nova Rate: Estimates from the ASAS-SN and Gaia Surveys
• Fermi-LAT Observations of V549 Vel 2017: a Sub-Luminous Gamma-Ray Nova?
• Infrared spectroscopy of the remnant of Nova Sco 2014: a symbiotic star with too little circumstellar matter to decelerate the ejecta
• Shocks and dust formation in nova V809 Cep
• Optical and NIR data and modelling of nova V5668 Sgr
• $\gamma$-ray Emission from Classical Nova V392 Per: Measurements from Fermi and HAWC
• Evidence of the gamma-ray counterpart from nova FM Cir with Fermi-LAT