THEKEPLERLIGHT CURVES OF V1504 CYGNI AND V344 LYRAE: A STUDY OF THE OUTBURST PROPERTIES

Abstract

We examine the Kepler light curves of V1504 Cyg and V344 Lyr, encompassing ∼736 d at 1 min cadence. During this span each system exhibited ∼64 − 65 outbursts, including six superoutbursts. We find that, in both systems, the normal outbursts lying between two superoutbursts increase in duration over time by a factor ∼1.2−1.9, and then reset to a small value after the following superoutburst. In both systems the trend of quiescent intervals between normal outbursts is to increase to a local maximum about half way through the supercycle − the interval from one superoutburst to the next − and then to decrease back to a small value by the time of the next superoutburst. This is inconsistent with Osaki's thermal-tidal model, which predicts a monotonic increase in the quiescent intervals between normal outbursts during a supercycle. Also, most of the normal outbursts have an asymmetric, fast-rise/slower-decline shape, which would be consistent with outbursts triggered at large radii. The exponential rate of decay of the plateau phase of the superoutbursts is 8 d mag −1 for V1504 Cyg and 12 d mag −1 for V344 Lyr. This time scale gives a direct measure of the viscous time scale in the outer accretion disk given the expectation that the entire disk is in the hot, viscous state during superoutburst. The resulting constraint on the Shakura-Sunyaev parameter, α hot 0.1, is consistent with the value inferred from the fast dwarf nova decays. By looking at the slow decay rate for superoutbursts, which occur in systems below the period gap, in combination with the slow decay rate in one long outburst above the period gap (in U Gem), we infer a steep dependence of the decay rate on orbital period for long outbursts. We argue that this relation implies a steep dependence of α cold on orbital period, which may be consistent with recent findings of Patterson, and is consistent with tidal torquing as being the dominant angular momentum transport mechanism in quiescent disks in interacting binary systems.

The remarkable outburst of the highly-evolved post period-minimum dwarf nova SSS J122221.7−311525

“…We note, however, that in contrast to SSS J122222, the maximum light of precursors is usually lower by 0.5-1 mag than that of the following superoutbursts (see e.g. the very detailed high-fidelity Kepler light curves of several superoutbursts of two SU UMa stars; Cannizzo et al 2012), thus the origin of A superoutburst segment of the light curve in the V and uvm2 filters. Black points are the individual observations in the V filter.…”

“…We do not have simultaneous optical photometry which would enable us to verify such a behaviour, although the detailed Kepler observations of many CV superoutbursts (e.g. Cannizzo et al 2012) do not seem to show such drops at optical wavelengths. On the other hand, the drops of the UV flux in the beginning of outbursts were reported for several DNe (Wu & Panek 1983;Verbunt 1987).…”

Fast stochastic variability study of two SU UMa systems V1504 Cyg and V344 Lyr observed byKeplersatellite

“…Fig. 2 in Cannizzo et al (2012) suggests that all normal outbursts have a fairly consistent duration, which justifies the use of the same time interval for every outburst. In the subsequent analysis we denote as "outburst 0.10/0.10" a light curve extracted 0.10 days before and 0.10 days after the outburst peak.…”

“…3 For a long-term light curves (first 740 days) see Figs. 1 and 2 in Cannizzo et al (2012). 4 For V1504 Cyg in Dobrotka & Ness (2015) we used a value of 7000 electrons/s.…”

Reversibility of time series: revealing the hidden messages in X-ray binaries and cataclysmic variables

“…Table 1 shows a log of the available Kepler data for these sources. All three sources have already been subject to previous studies with Kepler data (Kato & Maehara 2013;Scaringi et al 2012aScaringi et al ,2012bScaringi 2014;Cannizzo et al 2012).…”