X-ray Spectroscopy of the gamma-ray Brightest Nova V906 Car (ASASSN-18fv)

Abstract

Shocks in gamma-ray emitting classical novae are expected to produce bright thermal and non-thermal X-rays. We test this prediction with simultaneous NuSTAR and Fermi/LAT observations of nova V906 Car, which exhibited the brightest GeV gamma-ray emission to date. The nova is detected in hard X-rays while it is still gamma-ray bright, but contrary to simple theoretical expectations, the detected 3.5-78 keV emission of V906 Car is much weaker than the simultaneously observed >100 MeV emission. No non-thermal X-ray emission is detected, and our deep limits imply that the gamma-rays are likely hadronic. After correcting for substantial absorption (N_H ~ 2 x 10^23 cm^-2), the thermal X-ray luminosity (from a 9 keV optically-thin plasma) is just ~2% of the gamma-ray luminosity. We consider possible explanations for the low thermal X-ray luminosity, including the X-rays being suppressed by corrugated, radiative shock fronts or the X-rays from the gamma-ray producing shock are hidden behind an even larger absorbing column (N_H >10^25 cm^-2). Adding XMM-Newton and Swift/XRT observations to our analysis, we find that the evolution of the intrinsic X-ray absorption requires the nova shell to be expelled 24 days after the outburst onset. The X-ray spectra show that the ejecta are enhanced in nitrogen and oxygen, and the nova occurred on the surface of a CO-type white dwarf. We see no indication of a distinct super-soft phase in the X-ray lightcurve, which, after considering the absorption effects, may point to a low mass of the white dwarf hosting the nova.

19 pages, 6 figures, 7 tables; accepted to MNRAS

References in corpus (34)

• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• The DArk Matter Particle Explorer mission
• 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
• Towards a unified view of inhomogeneous stellar winds in isolated supergiant stars and supergiant high mass X-ray binaries
• Gamma-ray novae as probes of relativistic particle acceleration at non-relativistic shocks
• Comparative performance of selected variability detection techniques in photometric time series
• Shocks in nova outflows. I. Thermal emission
• An Expanding Shell and Synchrotron Jet in RS Ophiuchi
• X-ray Spectroscopy of the 2006 Outburst of RS Oph
• A Nova Outburst Powered by Shocks
• Observations of Galactic and Extragalactic Novae
• NLTE model atmospheres for the hottest white dwarfs: Spectral analysis of the compact component in nova V4743 Sgr
• The BRITE Constellation nanosatellite mission: Testing, commissioning and operations
• Supernova Remnants Interacting with Molecular Clouds: X-ray and Gamma-ray Signatures
• Highly Enriched 7Be in the ejecta of Nova Sagittarii 2015 No. 2 (V5668 Sgr) and the Galactic Lithium origin
• High-resolution X-ray spectroscopy of the evolving shock in the 2006 outburst of RS Ophiuchi
• BRITE-Constellation: Data processing and photometry
• A NuSTAR observation of the fast symbiotic nova V745 Sco in outburst
• NuSTAR Detection of X-rays Concurrent with Gamma Rays in the Nova V5855 Sgr
• X-Ray Flashes in Recurrent Novae: M31N 2008-12a and the Implications of the Swift Non-detection
• The Distance to Nova V959 Mon from VLA Imaging
• Internal Shocks from Variable Outflows in Classical Novae
• Chemical and physical parameters from X-ray high resolution spectra of the Galactic nova V959 Mon
• V723 Cas (Nova Cassiopeiae 1995): MERLIN observations from 1996 to 2001
• Evolution of X-ray spectra and light curves of V1494 Aquilae
• Spectroscopic and geometrical evolution of the ejecta of the classical nova ASASSN-18fv
• The unusual Nova Cygni 2006 (V2362 Cyg)
• Novalike Cataclysmic Variables in the Infrared
• Early multiwavelength analysis of the recurrent nova V745 Sco
• Radio Frequency Models of Novae in eruption. I. The Free-Free Process in Bipolar Morphologies
• A Radio Emission Analysis of Classical Nova V351 Pup (1991)
• Classical Nova Carinae 2018: Discovery of circumbinary iron and oxygen
• Mass-loss from Red Giants

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