RT Cru: a look into the X-ray emission of a peculiar symbiotic star

Abstract

Symbiotic stars are a heterogeneous class of interacting binaries. Among them, RT Cru has been classified as prototype of a subclass that is characterised by hard X-ray spectra extending past ~20 keV. We analyse ~8.6 Ms of archival INTEGRAL data collected in the period 2003-2014, ~140 ks of Swift/XRT data, and a Suzaku observation of 39 ks, to study the spectral X-ray emission and investigate the nature of the compact object. Based on the 2MASS photometry, we estimate the distance to the source of 1.2-2.4 kpc. The X-ray spectrum obtained with Swift/XRT, JEM-X, IBIS/ISGRI, and Suzaku data is well fitted by a cooling flow model modified by an absorber that fully covers the source and two partial covering absorbers. Assuming that the hard X-ray emission of RT Cru originates from an optically thin boundary layer around a non-magnetic white dwarf, we estimated a mass of the WD of about 1.2 M_Sun. The mass accretion rate obtained for this source might be too high for the optically thin boundary layer scenario. Therefore we investigate other plausible scenarios to model its hard X-ray emission. We show that, alternatively, the observed X-ray spectrum can be explained with the X-ray emission from the post-shock region above the polar caps of a magnetised white dwarf with mass ~0.9-1.1 M_Sun.

Accepted for publication in Astronomy & Astrophysics. 6 pages

References in corpus (5)

• Optimal binning of X-ray spectra and response matrix design
• Variable stars across the observational HR diagram
• The Nature of the Hard-X-Ray Emitting Symbiotic Star RT Cru
• The defining characteristics of Intermediate Polars - the case of three candidate systems
• Modeling the EUV spectra of optically thick boundary layers of dwarf novae in outburst

Cited by in corpus (9)

• Suzaku and NuSTAR X-Ray Spectroscopy of gamma Cas and HD110432
• INTEGRAL view on Cataclysmic Variables and Symbiotic Binaries
• X-ray, UV, and optical observations of the accretion disk and boundary layer in the symbiotic star RT Cru
• Taking a break: paused accretion in the symbiotic binary RT Cru
• Long-term X-ray Variability of the Symbiotic System RT Cru based on Chandra Spectroscopy
• X-ray Variability in the Symbiotic Binary RT Cru: Principal Component Analysis
• Classification of low-luminosity stellar X-ray sources in the field of the Draco dwarf spheroidal galaxy
• A novel approach to detect line emission under high background in high-resolution X-ray spectra
• Further evidence for natal kick segregation by spectral type in high-mass X-ray binaries