Radio and optical observations of the possible AE Aqr twin, LAMOST J024048.51+195226.9

Abstract

It was recently proposed that the cataclysmic variable (CV) LAMOST J024048.51+195226.9 may be a twin to the unique magnetic propeller system AE Aqr. If this is the case, two predictions are that it should display a short period white dwarf spin modulation, and that it should be a bright radio source. We obtained follow-up optical and radio observations of this CV, in order to see if this holds true. Our optical high-speed photometry does not reveal a white dwarf spin signal, but lacks the sensitivity to detect a modulation similar to the 33-s spin signal seen in AE Aqr. We detect the source in the radio, and measure a radio luminosity similar to that of AE Aqr and close to the highest so far reported for a CV. We also find good evidence for radio variability on a time scale of tens of minutes. Optical polarimetric observations produce no detection of linear or circular polarization. While we are not able to provide compelling evidence, our observations are all consistent with this object being a propeller system.

Confirmation of a Second Propeller: A High-inclination Twin of AE Aquarii

“…We unsuccessfully searched for a photometric signature of the spinning WD as is seen in AE Aqr. We placed a 4 mmag upper limit on the g-band spin amplitude for periods between 6.3 s and 85 s. This is consistent with the nondetection of a spin signal noted by Pretorius et al (2021).…”

“…The propellers and AR Sco appear to efficiently extract spin energy from their WDs, and are unusually strong radio emitters, implying a significant nonthermal power source derived from an interaction with the rapidly spinning magnetic WD. (Bookbinder & Lamb 1987;Stanway et al 2018;Pretorius et al 2021).…”

Found: a rapidly spinning white dwarf in LAMOST J024048.51+195226.9

“…Two subsequent studies have added additional weight to the connection between J0240+1952 and AE Aqr. Pretorius et al (2021) detected radio emission, with a radio luminosity close to the highest measured of any CV, higher even than AE Aqr, while Garnavich et al (2021) found that the Balmer emission lines broadened up to ±3000 km/s during flares, and showed that a P Cygni-like component in H𝛼, also seen by Thorstensen (2020), was consistent with Wynn et al (1997)'s magnetic propeller model.…”

“…The flares are also seen spectroscopically in increased fluxes and widths of the Balmer lines (Reinsch & Beuermann 1994). Rounding off the list of notable properties, AE Aqr was one of the first CVs to be detected at radio frequencies (Bookbinder & Lamb 1987), and is one of the most luminous of all CVs in terms of radio power (Pretorius et al 2021). The radio flux is thought to be generated by synchrotron emission from expanding clouds of plasma (Meintjes & Venter 2003).…”

“…Thorstensen (2020) found no evidence of pulsations in 23.3 s-cadence photometry. Pretorius et al (2021) searched for optical pulsations down to a period of 10 s, but found no signals above their detection threshold of 1%. Finally, and most stringently of all, Garnavich et al (2021) presented 𝑔 and 𝑖-band photometry taken with the Hale 5 m telescope and Caltech HIghspeed Multi-color camERA (CHIMERA) which had the cadence and the signal-to-noise to detect spin periods with amplitudes as low as 4 mmag (0.43%) in the 𝑔-band over a period range of 6.3 to 85 s, but again found nothing of significance.…”