Investigating the Low-flux States in Intermediate Polars

Magnetic fields in accreting compact objects are responsible for a number of astrophysical phenomena, ranging from accretion powered pulsars to driving outflows in X-ray binaries and AGN. Intermediate Polars (IPs) are a subclass of cataclysmic variables containing an accreting white dwarf with a magnetic field that is strong enough to disrupt the innermost regions of the accretion disk, leaving a residual disk that terminates at the magnetospheric radius. Some of these systems show puzzling transitions to so-called “low-states,” characterized by a significant fading in both optical and X-rays, the physical mechanisms behind which are uncertain. Studies of the timing properties of optical and X-ray light curves of IPs in and out of low states will allow us to probe the underlying physics of the accretion flow. Here, we present timing analysis of AAVSO optical photometry of several IPs that have exhibited transitions to a low-flux state. For at least two systems, we see changes in the dominant periodicities present in the light curves as the flux decreases, which we interpret as a change in the accretion mechanism. In another case, we see the onset of a series of short outbursts that are not consistent with the typical mechanism associated with dwarf novae but are instead linked to the white dwarf’s magnetic field. We discuss the variety of behaviors seen in IP low states and how we are able to use optical monitoring to trigger X-ray studies of the next low state in order to probe the inner-most regions of the changing accretion flow.