Swift XRT observations of BD Cam
ATel #15332; I. J. Lima (IAFE/Conicet, Argentina), G. J. M. Luna (IAFE/Conicet, Argentina), N. E. Nu\~{n}ez (ICATE-Conicet, UNSJ, Argentina)
on 14 Apr 2022; 20:51 UT
Credential Certification: Isabel de Jesus Lima (isabellima01@gmail.com)
Subjects: X-ray, Cataclysmic Variable, Variables
BD Cam is a symbiotic binary system in which a white dwarf accretes from a Barium-enhanced red giant. In order to look for X-ray emission from symbiotic stars, our group started a survey under multi-cycle-approved Swift Fill-in programs (Luna et al., 2013, A&A, 559, A6). BD Cam was observed with SWIFT XRT in PC mode on April 13, 16, and 17, 2012 with exposure times of 2.1, 6.6, and 3.0 ks, respectively. However, due to the intense brightness in optical wavelengths (V = 5.11 mag, J = 1.31 mag), the X-ray spectrum was significantly distorted by optical loading precluding any meaningful analysis. In order to determine if BD Cam is indeed a X-ray source and the nature of its spectrum, on March 17 2022 we obtained a SWIFT XRT observation in WT mode (exposure time 2.1 ks), which should minimize the effects of optical loading (SWIFT, see https://www.swift.ac.uk/analysis/xrt/optical_loading.php). We also blocked the UVOT for optical photometry. The source was detected with a count rate of 0.082 +- 0.006 counts/s. We model the spectrum in the range of 0.6-10 keV because the background dominates at lower energies. Our preliminary analysis favors a model that includes a combination of an absorbed (NH < 9.51e22 cm^-2) and a optically thin thermal plasma with a temperature of 8.09(+0.05 -0.06) keV. This model gives an estimated unabsorbed flux of 6.2e-12(+0.3 -0.2) ergs/s/cm^2. The Gaia Early Data Release 3 (EDR3) distance of BD Cam is 235 +- 15 pc (Bailer-Jones et al. 2021, AJ, 161, 147). Therefore, the luminosity at this distance is 4.10e31 ergs/s, within the range of most beta-type symbiotics. We thank the Swift team and Kim Page for assistance and quick planning of the observations.
