The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton

TL;DR

This study uses XMM-Newton observations to analyze the quiescent spectrum of the black hole X-ray nova V404 Cygni, finding a power-law spectrum consistent with ADAF models, variability, and placing limits on iron emission lines.

Contribution

First detailed XMM-Newton spectral analysis of V404 Cygni in quiescence, confirming ADAF-like spectra and improving constraints on iron emission lines.

Findings

Spectrum fits a power-law with slope 2

Luminosity similar to previous Chandra observations

No significant iron emission detected

Abstract

We present XMM observations of the black hole X-ray nova V404 Cygni in quiescence. Its quiescent spectrum can be best fitted by a simple power-law with slope 2. The spectra are consistent with that expected for the advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in luminosity compared to the previous observation of Chandra. We see variability of a factor of 4 during the observation. We find no evidence for the presence of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and 110 eV respectively. The limit on the fluorescent emission is improved by a factor of 15 over the previous estimate, and the restriction on H-like/He-like emission is lower than predicted from models by a factor of roughly 2.