Hflares from V404 Cyg in quiescence

Abstract

A B S T R A C TWe present a spectrophotometric study of short-term optical variability in the quiescent black hole X-ray transient V404 Cyg. This includes two nights of high-time-resolution Ha spectroscopy with which we resolve much of the time variability, and a further six nights of archival spectroscopy with lower time resolution but higher spectral resolution. We find significant variability in most of the data considered, with both the Ha line and the continuum often varying in a correlated way. This includes both dramatic flares lasting a few hours in which the line flux nearly doubles and lower-level flickering. The strongest flares involve development of asymmetry in the line profile, with the red wing usually strongest independent of orbital phase. It is unclear why this is the case, but we discuss several possible explanations. We consider the energetics of the flares and compare with plausible models including chromospheric activity on the companion star, local magnetic reconnection events within the disc and varying irradiation from close to the black hole. Based on the line profile changes during the flares, we conclude that the most likely origin for the variability is variable photoionization by the central source, although local flares within the disc cannot be ruled out.

Evidence for Optical Flares in Quiescent Soft X‐Ray Transients

“…Therefore, the maximum flare duration should be limited by the outer disk radius. If this is correct, then V404 Cyg should also show short-timescale (roughly tenths of minutes) variability superimposed on the major 3-6 hr flares, and, indeed, this is detected in Figure 2 and is also noted by Hynes et al (2002).…”

“…Our data rule out this possibility since no correlation with inclination is evident and, most important, no dependence with the orbital phase is found. In addition, H velocity information of flares has been presented by Zurita & Casares (1998) and Hynes et al (2002) showing no correspondence with the expected velocity of the hot spot or gas stream.…”

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

“…Mass transfer instabilities, magnetic reconnection events, and X-ray reprocessing in the accretion disc (Hynes et al 2002;Zurita et al 2003) might in principle also explain a strong flaring activity in LMXBs. No enhanced X-ray activity has been detected in IGR J00291+5934 near the epoch of our observations in 2014.…”

“…Magnetic reconnection events in the disc could also trigger the flares (Hynes et al 2002;Zurita et al 2003). In particular, differential motions in the accretion disc plasma may produce magnetic fields, and when the reconnection between vertical field lines of opposite signs occurs, some energy is dissipated, leading to the emission of flares.…”

Doppler tomography of the black hole binary A0620-00 and the origin of chromospheric emission in quiescent X-ray binaries

“…This means that almost 92% of the incident X-ray radiation would have to be reprocessed to Hα photons in order to power the observed Hα emission. Following Hynes et al (2002), F Hα, = f 1 f 2 F X, , where f 1 is the fraction of X-ray emission intercepted by the companion; i.e., the solid angle subtended by the companion from the compact object ( f 1 = [R /(2a)] 2 ), and f 2 0.3 is the fraction of input energy emitted in Hα (Hynes et al 2002, and references therein). Adopting R = 1.1 R from González Hernández et al (2004), we obtain F Hα, 4.5 × 10 −3 F X, .…”