Investigating the Low-flux States in Six Intermediate Polars

Abstract

We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four of these systems, DW Cnc, V515 And, V1223 Sgr, and RX J2133.7+5107, we are able to perform timing analysis in and out of the low states. We find that, for DW Cnc and V515 And, the dominant periodicities in the light curves change as the flux decreases, indicating a change in the sources’ accretion properties as they transition to the low state. For V1223 Sgr, we find that the variability is almost completely quenched at the lowest flux, but we do not find evidence for a changing accretion geometry. For RX J2133.7+5107, the temporal properties do not change in the low state, but we do see a period of enhanced accretion that is coincident with increased variability on the beat frequency, which we do not associate with a change in the accretion mechanisms in the system.

Hitting a New Low: The Unique 28 hr Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)

“…FO Aqr is the best example of this, as optical (Littlefield et al 2016(Littlefield et al , 2020, X-ray (Kennedy et al 2017), and spectroscopic (Kennedy et al 2020) studies have all agreed that the system's mode of accretion changes at reduced mass-transfer rates. This is also true of DW Cnc and V515 And (Covington et al 2022). With just one exception, these studies have not detected a total interruption of accretion during low states.…”

“…More recently, low-accretion states have been detected in several confirmed or suspected IPs, including V1323 Her (Andronov et al 2014), FO Aqr (Littlefield et al 2016;Kennedy et al 2017), DW Cnc (Segura Montero et al 2020), Swift J0746.3-1608(Bernardini et al 2019Beuermann et al 2022), and YY Dra itself (Breus et al 2017), though as we noted in Section 3.3, the previously observed YY Dra low states do not show evidence of a cessation of accretion. Additionally, Covington et al (2022) have identified low states in V1223 Sgr, V1025 Cen, V515 And, and RX J2133.7 + 5107, and they conclude that low states in IPs are more common than previously realized.…”

“…The low states in FO Aqr lasted 5-6 months in 2016, 4-5 months in 2017, and only 2-3 months in 2018 (Littlefield et al 2020). Additionally, V1025 Cen (Covington et al 2022;Littlefield et al 2022) declined 2.5 mag over the course of 4 yr and remained in that low state for a little under 2 yr. DW Cnc has significant gaps in the data, but it has shown a nearly 3 yr low state with a depth of 2.3 mag (Covington et al 2022). The lengths of these low states are substantially longer than those of YY Dra, underscoring the remarkable brevity of YY Dra's deep low state.…”

“…11 Covington et al (2022) examined archival observations of YY Dra from 2018 and identified a 3 mag fade in Swift ultraviolet UVW-and UVM-band observations that coincided with a nondetection of YY Dra in X-ray observations. Likewise, Shaw et al (2020) found no X-ray emission in a 55.4 ks NuSTAR observation of YY Dra in 2018 July.…”

Magnetically-gated accretion model: application to short bursts in the intermediate polar V1223 Sgr

“…The situation changed with the observation by TESS of V1025 Cen, which showed a rapid succession (recurrence time ranging between one and 3 days) of short (less than six hours) outbursts (Littlefield et al 2022). Covington et al (2022) also reported the detection of many short outbursts in V1223 Sgr that we explore in detail here. Cataclysmic variables not classified as magnetic have also shown short outbursts; MV Lyr experienced a series of 30 minutes outbursts every two hours (Scaringi et al 2017).…”