X-ray monitoring of the intermediate polar BG CMi during its low state
ATel #17089; Aarran W. Shaw (Butler U.), Craig O. Heinke (U. Alberta)
on 19 Mar 2025; 16:09 UT
Credential Certification: Aarran Shaw (awshaw@butler.edu)
Subjects: X-ray, Request for Observations, Cataclysmic Variable
As reported by Littlefield et al. (ATel #17050), the intermediate polar BG CMi is currently in a low state, exhibiting an average magnitude of V~15.5, about 0.5 magnitudes fainter than typical. Littlefield et al. also reported changes in the dominant periodicities in the optical light curves, indicative of changes to the accretion flow.
We report here on X-ray follow up of BG CMi with the Neil Gehrels Swift Observatory, which has performed 4 observations thus far. For each observation we fit a simple model to the X-ray spectrum consisting of interstellar absorption, a partial covering component and a thermal bremsstrahlung model (tbabs*pcfabs*bremss). We find a remarkably steady 0.5-10 keV unabsorbed flux of 4.6+3.7-1.1 x 10-11 erg cm-2 s-1 on 2025-03-05, 3.2+0.8-0.5 x 10-11 erg cm-2 s-1 on 2025-03-12, 2.9+0.7-0.6 x 10-11 erg cm-2 s-1 on 2025-03-15 and 2.8+0.9-0.6 x 10-11 erg cm-2 s-1 on 2025-03-18. The light curves show variability, as is expected from intermediate polars, but the observations were not long enough (texp≤1955 s) for us to perform meaningful timing analysis on them, thus we are unable to investigate the changing timing properties of the source at X-ray energies.
However, we have successfully requested a DDT observation of BG CMi with XMM-Newton, which is scheduled to take place from 2025-03-23 18:49:43 to 2025-03-24 03:51:22. With this observation we will be able to simultaneously measure the timing properties in the X-ray with EPIC, as well as in the V-band with the OM in fast mode.
We encourage simultaneous and quasi-simultaneous ground based time-series observations of BG CMi during the XMM-Newton window, particularly at wavelengths other than V-band. The source is bright (V~15.5), and thus should be accessible to 1m-class telescopes with sub-60s exposure times. We note that the first half of the XMM-Newton window is particularly accessible to telescopes in Europe or Africa, and the second half of the window is accessible to telescopes in the Eastern US/Canada and South America. Please contact the authors of this telegram if you would like to contribute to the observing campaign.
