Return of the King: Time-Series Photometry of FO Aquarii's Initial Recovery from its Unprecedented 2016 Low State

Abstract

In 2016 May, the intermediate polar FO~Aqr was detected in a low state for the first time in its observational history. We report time-resolved photometry of the system during its initial recovery from this faint state. Our data, which includes high-speed photometry with cadences of just 2 sec, shows the existence of very strong periodicities at 22.5 min and 11.26 min, equivalent to the spin-orbit beat frequency and twice its value, respectively. A pulse at the spin frequency is also present but at a much lower amplitude than is normally observed in the bright state. By comparing our power spectra with theoretical models, we infer that a substantial amount of accretion was stream-fed during our observations, in contrast to the disk-fed accretion that dominates the bright state. In addition, we find that FO~Aqr's rate of recovery has been unusually slow in comparison to rates of recovery seen in other magnetic cataclysmic variables, with an $e$-folding time of 115$\pm 7$ days. The recovery also shows irregular variations in the median brightness of as much as 0.2~mag over a 10-day span. Finally, we show that the arrival times of the spin pulses are dependent upon the system's overall brightness.

Accepted for publication at ApJ. The paper now includes ASAS-SN observations of what we believe is the initial decline from the high state. New co-authors have been added

References in corpus (1)

• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates

Cited by in corpus (11)

• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• The Spin-Period History of Intermediate Polars
• The disappearance and reformation of the accretion disc during a low state of FO Aquarii
• The true nature of Swift J0746.3-1608: a possible Intermediate Polar showing accretion state changes
• Hitting a New Low: The Unique 28 h Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)
• New observations of DW Cnc: where is the 38 min signal?
• Optical spectra of FO Aquarii during low and high accretion rates
• Variable stars with the Kepler space telescope
• Investigating the low-flux states in six Intermediate Polars
• Confirmation of SRGt 062340.2-265751 as a nova-like cataclysmic variable with a possible magnetic nature
• OAUNI astronomical photometry: Stellar variability of FO Aqr on 2016 low state