Time-Resolved Photometry of the Optical Counterpart of Swift J2319.4+2619

Time-resolved CCD photometry is presented of the V~17 optical counterpart of the newly-discovered, hard-X-ray-emitting polar Swift J2619.4+2619. A total of ~20 hr of data obtained over five nights in various bandpasses (B, V, R, and I) reveals a strong quasi-sinusoidal modulation in the light curve at a best-fitting period of 0.1254 d (3.01 hr), which we associate with the orbital period of the system (one-day aliases of this period at 0.1114 d and 0.1435 d are considered, but appear to be ruled out by our analysis). The amplitude of the modulation increases with wavelength from ~0.8 mag in B to ~1.1 mag in R and I. The increase in amplitude with wavelength is typical of polar systems where the modulated radiation comes from cyclotron emission. The combination of the relatively long orbital period and the emission of hard X-rays suggest that Swift J2619.4+2619 may be a good candidate for an asynchronous polar system.