Measuring the precise photometric period of the probable intermediate polar 1RXS J014549.6+514314 based on extensive photometry

TL;DR

The study confirms a coherent optical oscillation in 1RXS J014549.6+514314 with a precise period of $41.485867(26)$ min, measured from 25 nights totaling 139 hours over 18 months. Using FFT-based power spectra and an ephemeris anchored by times of maxima, the author demonstrates phase-coherent behavior and derives a long-term ephemeris valid for about 30 years, highlighting a large semi-amplitude of $0.154(2)$ mag and a sinusoidal pulse profile. The results strengthen the case for classifying the source as an intermediate polar, though the orbital period remains undetermined spectroscopically; no orbital sidebands are detected in the optical data. The work illustrates the value of extended, high-precision photometry for establishing spin-period coherence and enabling long-term period-change studies in IPs, with future spectroscopy suggested to measure the orbital period.

Abstract

Recently, in the VSX database, G. Murawski reported the discovery of an oscillation with a period of about 40 min in the probable cataclysmic variable 1RXS J014549.6+514314. To confirm the existence of this oscillation and precisely measure its period, I conducted extensive photometric observations of the object over 25 nights between 2022 and 2024. The total duration of these observations was 139 hr. The observations revealed the oscillation on each observation night. This oscillation was coherent throughout all the observations covering 18 months. Due to the large coverage of observations, I was able to determine the oscillation period with high precision. It was found to be 41.485867+\-0.000026 min. The semi-amplitude of the oscillation was large, averaging 0.154(2) mag. The pulse profile of the oscillation did not change during the observations and followed a perfect sinusoidal pattern. With the high precision of the period, I created an ephemeris for the oscillation with a validity time of 30 years. This ephemeris can be used in future studies of changes in the oscillation period. Although short-period X-ray oscillations have not yet been detected in 1RXS J014549.6+514314, the high coherence of its 41-minute oscillation suggests that this object is most likely to be an intermediate polar.

Figures (8)

• Figure 1: Longest light curves of J0145, in which the oscillation with a period of about 40 min is clearly visible.
• Figure 2: Averaged power spectrum calculated from 16 individual power spectra of nights that were longer than 5 hours each. In addition to the large peak corresponding to a period of 41 min seen on the left, truncated at the 30 per cent level, there is red noise at frequencies up to 20 mHz.
• Figure 3: Power spectra of two combined time series, consisting mostly of consecutive nights obtained in August 2022 and January 2023. The dashed lines indicate the expected frequencies corresponding to the first subharmonic and the first harmonic of the 41-min oscillation.
• Figure 4: Part of the power spectrum of the overall combined time series shown at frequencies around the frequency of the 41-min oscillation (bottom frame). It reveals a structure similar to that of the window function (top frame).
• Figure 5: Part of the power spectrum of the overall combined time series shown at frequencies around the main peak of the 41-min oscillation on an expanded frequency scale (bottom frame). This power spectrum reveals a fine structure that strikingly coincides with the fine structure of the window function (top frame).