WZ Sge-Type Dwarf Novae with Multiple Rebrightenings: MASTER OT J211258.65+242145.4 and MASTER OT J203749.39+552210.3

Abstract

We report on photometric observations of two WZ Sge-type dwarf novae, MASTER OT J211258.65+242145.4 and MASTER OT J203749.39+552210.3, which underwent outbursts in 2012. Early superhumps were recorded in both systems. During the superoutburst plateau, ordinary superhumps with a period of 0.060291(4) d (MASTER J211258) and with 0.061368(11) d (MASTER J203749) on average were observed. MASTERJ211258 and MASTERJ203749 exhibited eight post-superoutburst rebrightenings and more than four, respectively. In the final part of the superoutburst, an increase in superhump period was seen in both systems. We made a survey of WZSge-type dwarf novae with multiple rebrightenings, and confirmed that the superhump periods of WZSge-type dwarf novae with multiple rebrightenings were longer than those of WZSge-type dwarf novae without a rebrightening. Although WZSge-type dwarf novae with multiple rebrightenings have been thought to be likely candidates for period bouncers based on their low mass ratio (q), inferred from the period of fully grown (stage B) superhumps, our new method of using the period of growing superhumps (stage A superhumps), however, implies higher q's than those expected from stage B superhumps. These q values appear to be consistent with the duration of the stage A superoutbursts, which likely reflects the growth time of the 3W1 resonance. We present a working hypothesis that the small fractional superhump excesses for stage B superhumps in these systems may be explained by a gas pressure effect that works more efficiently in these systems than in ordinary SU UMa-type dwarf novae. This result forms a new picture that WZSge-type dwarf novae with multiple rebrightenings and SU UMa-type ones without a rebrightening (they are not period bouncers) are located in the same place on the evolutionary track.

Delimiting the black hole mass in the X-ray transient MAXI J1659-152 with H$α$ spectroscopy

“…The apparent doublewave R-band variability identified by Kuroda et al (2010) had a ∼0.05 mag amplitude and was present during at least the first 18 days after the discovery of the transient. Both characteristics are compatible with the properties of early superhumps in WZ Sge systems with the majority showing amplitudes < 0.05 mag (although they can reach 0.35 mag; Kato 2015) and observed durations of up to ∼15 day (Table 9 in Nakata et al 2013). With regards to ordinary superhumps, their shape is generally described as saw-tooth, but it can significantly differ as the outburst evolves (Kato et al 2009;Zurita et al 2008).…”

Statistical properties of dwarf novae-type cataclysmic variables: the outburst catalogue

“…As the light curve is averaged by day, and not sampled on consecutive days, a turnover is not expected within an outburst. Although some WZ Sge-type DN do show post superoutburst re-brightenings (e.g Kato et al 2009;Nakata et al 2013),. few turnovers are expected in the dataset due to the CRTS sampling cadence.…”

Investigation of WZ Sge-type Dwarf Nova ASASSN-19oc: Optical Spectroscopy and Multicolor Light Curve Analysis

“…Based on the light curve shape, rebrightenings can be classified as long-duration, multiple, or single events (Imada et al 2006). For example, EZ Lyn showed 11 rebrightenings (Kato et al 2009b), ASASSN-15po had 10 rebrightenings (Kato 2015;Namekata et al 2017), EG Cnc exhibited 6 rebrightenings (Kimura et al 2021), and MASTER OT J211258.65+242145.4 displayed 8 rebrightenings (Nakata et al 2013), among others. The occurrence of rebrightenings can be associated with the behavior of the accretion disk.…”