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.

arXiv commentAccepted 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

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Cited by in corpus (15)

• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• Dwarf nova outbursts in intermediate polars
• The Rise and Fall of the King: The Correlation between FO Aquarii's Low States and the White Dwarf's Spindown
• The Spin-Period History of Intermediate Polars
• High-Time-Resolution Photometry of AR Scorpii: Confirmation of the White Dwarf's Spin-Down
• X-ray observations of FO Aqr during the 2016 low state
• The true nature of Swift J0746.3-1608: a possible Intermediate Polar showing accretion state changes
• The disappearance and reformation of the accretion disc during a low state of FO Aquarii
• 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
• OAUNI astronomical photometry: Stellar variability of FO Aqr on 2016 low state
• Confirmation of SRGt 062340.2-265751 as a nova-like cataclysmic variable with a possible magnetic nature
• Investigating the low-flux states in six Intermediate Polars