Abstract
Context. Polars (AM Herculis binaries) are a prominent class of bright soft X-ray sources, many of which were discovered with ROSAT. Aims. We present a homogenous analysis of all the pointed ROSAT PSPC observations of polars subdivided into two papers that discuss the prototype polar AM Her in detail and summarize the class properties of all other polars. Methods. We derive the high-state soft X-ray flux and short-term spectral variability of AM Her using a new detector response matrix and a confirmed flux calibration of the ROSAT PSPC below 0.28 keV. Results. The best-fit mean single-blackbody temperature and integrated bright-phase energy flux of AM Her in its April 1991 high state are 27.2 ± 1. 0e V and (2.6 ± 0.6) × 10 −9 erg cm −2 s −1 , respectively. The total blackbody flux of a multi-temperature model that fits both the soft X-ray and the fluctuating far-ultraviolet components is Fbb = (4.5 ± 1.5) × 10 −9 erg cm −2 s −1 . The total accretion luminosity at a distance of 80 pc, Lbb = (2.1 ± 0.7) × 10 33 erg s −1 , implies an accretion rate of u
Highlights
Research on polars, the synchronized magnetic variety of cataclysmic variables (CVs), has greatly benefited from the discovery of numerous new members of the class during the ROSAT All Sky Survey and the subsequent pointed observations with the position sensitive proportional counter (PSPC) (Beuermann & Thomas 1993)
After the decommissioning of the PSPC, AM Her was repeatedly observed with the high-resolution imager (HRI), on 13–17 March 1994 and 8–10 March 1995 during high states and between 26 January and 30 May 1996, when it declined from a high state into a deep low with zero detectable flux
The soft part of the PSPC spectrum is consistent with a single blackbody of k Tbb = 27.4 eV and a total blackbody flux of Fbb = 2.6 × 10−9 erg cm−2 s−1
Summary
The synchronized magnetic variety of cataclysmic variables (CVs), has greatly benefited from the discovery of numerous new members of the class during the ROSAT All Sky Survey and the subsequent pointed observations with the position sensitive proportional counter (PSPC) (Beuermann & Thomas 1993). The second paper of this short series of two summarizes the spectral analysis of all other polars observed with the ROSAT PSPC. Before embarking on this project, we have investigated the putative absolute miscalibration of the PSPC by up to a factor of two at photon energies below the interstellar carbon edge at 0.28 keV (Napiwotzki et al 1993; Jordan et al 1994; Wolff et al 1996, 1999), where most of the energy flux of polars resides.
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