A trio of month long flares in the nova-like variable V704 And

TL;DR

This paper reports the discovery of three month-long brightening flares in the nova-like variable V704 And, observed across multiple wavelengths, suggesting short-term mass transfer variations as the likely cause.

Contribution

It presents the first detailed observation of long-duration flares in V704 And and discusses their possible origin in mass transfer rate changes.

Findings

Flares increased brightness from ~13.5 to ~12.5 magnitude.

Flares lasted about a month with slow rise and faster decay.

X-ray, UV, and optical data support mass transfer variability.

Abstract

We present the discovery of an unusual set of flares in the nova-like variable V704 And. Using data from AAVSO, ASAS-SN, and ZTF, of the nova-like variable V704 And, we have discovered a trio of brightening events that occurred during the high state. These events elevate the optical brightness of the source from $\sim13.5$ magnitude to $\sim12.5$ magnitude. The events last for roughly a month, and exhibit the unusual shape of a slow rise and faster decay. Just after the third event we obtained data from regular monitoring with Swift, although by this time the flares had ceased and the source returned to its pre-flare level of activity in the high-state. The Swift observations confirm that during the high-state the source is detectable in the X-rays, and provide simultaneous UV and optical fluxes. As the source is already in the high-state prior to the flares, and thus the disc is expected to already be in the high-viscosity state, we conclude that the driver of the variations must be changes in the mass transfer rate from the companion star and we discuss possible mechanisms for such short-timescale mass transfer variations to occur.