X-ray Pulsations from Nova Her 2021
Thomas J Maccarone (Texas Tech), Andy Beardmore (Leicester), Koji Mukai (NASA-GSFC), Kim Page (Leicester), Manuel Pichardo Marcano (Texas Tech), Liliana Rivera Sandoval (Alberta)
We report the discovery of X-ray pulsations from the supersoft emission of Nova Her 2021, at a period consistent with what was seen in ZTF optical data from before the nova (ATel #14720). This was found from a 10 kilosecond Chandra DDT observation with HRC-S with no gratings, made on July 10, 2021, at 1:12 AM UT. The feature is clearly present in a periodogram of the data, as a delta-function at the fundamental and several harmonics, so we follow this up with an epoch folding search. The strongest period is found at 503.9 seconds, consistent with the 8.4 minutes reported previously. The folded light curve shows variations from about 0.6 to 1.4 times the mean count rate, with two maxima per cycle. This result likely indicates that even during the fusion episode, accreted matter is at least partially constrained by the white dwarf's magnetic field. Suggestive evidence is seen for a sideband in the data at a period of about 542 seconds. If this is real, and is a beat between the orbital and spin periods, it implies an orbital period of about 2 hours, but given the short duration of the dataset, it must be confirmed with further observations of the system.
optical,x-ray,cataclysmic variable,nova,transient,variables