Detection of X-rays from the jet-driving symbiotic star MWC 560

Abstract

Aims. We report the detection of X-ray emission from the jet-driving symbiotic star MWC 560. Methods. We observed MWC 560 with XMM-Newton for 36 ks. We fitted the spectra from the EPIC pn, MOS1 and MOS2 instruments with XSPEC and examined the light curves with the package XRONOS. Results. The spectrum can be fitted with a highly absorbed hard X-ray component from an optically thin hot plasma, a Gaussian emission line with an energy of 6.1 keV and a less absorbed soft thermal component. The best fit is obtained with a model in which the hot component is produced by optically thin thermal emission from an isobaric cooling flow with a maximum temperature of 61 keV, which might be created inside an optically thin boundary layer on the surface of the accreting with dwarf. The derived parameters of the hard component detected from MWC 560 are in good agreement with similar objects such as CH Cyg, SS7317, RT Cru and T CrB, which all form a new sub-class of symbiotic stars emitting hard X-rays. Our previous numerical simulations of the jet of MWC 560 showed that it should produce detectable soft X-ray emission. We infer a temperature of 0.17 keV for the observed soft component, i.e. less than expected from our models. The total soft X-ray flux (i.e. at <3 keV) is more than a factor 100 less than predicted for the propagating jet soon after its birth (<0.3 yr), but consistent with the value expected due its decrease with age. The ROSAT upper limit is also consistent with such a decrease. We find aperiodic or quasi-periodic variability on timescales of minutes and hours, but no periodic rapid variability. Conclusions. All results are consistent with an accreting white dwarf powering the X-ray emission and the existence of an optically thin boundary layer around it.

Broad absorption line symbiotic stars: highly ionized species in the fast outflow from MWC 560

“…The ionization parameter in AS 304's outflow was therefore large, contributing to the absence of low-ionization (and in this case, optical) absorption. In MWC 560, optical and UV flickering (Bond et al 1984;Tomov et al 1996;Zamanov et al 2011b;Lucy et al, in preparation;though see Zamanov et al 2011a) and hard X-rays sometimes observed from the boundary layer (Stute & Sahai 2009) indicate an accretion disk without WD surface burning (see Luna et al 2013). Thus, both hot burning (AS 304) and cooler non-burning (MWC 560) symbiotics can sustain persistent BAL outflows.…”

Orbital eccentricity of the symbiotic star MWC 560

“…The orbital period is supposed to be P orb ≈ 5.3 yr (Doroshenko, Goranskij & Efimov 1993). The most spectacular features of this object are the collimated ejections of matter with velocities of up to ∼ 6000 km s −1 (Tomov et al 1992;Stute & Sahai 2009) and the resemblance of its emission line spectrum to that of the low-redshift quasars (Zamanov & Marziani 2002).…”

The 2016 outburst of the unique symbiotic star MWC 560 (= V694 Mon), its long-term BVRI evolution and a marked 331 days periodicity

“…The situation could now reverse following our recent discovery (Munari et al 2016) that MWC 560 is going through a new outburst phase, brighter than that of 1990. This has immediately prompted deep X-ray observations by Lucy et al (2016) that found a dramatic enhancement in the soft (<2 keV) X-rays, compared to the observations by Stute & Sahai (2009) obtained in 2007 when MWC 560 was in quiescence. The report on the optical outburst also prompted VLA observations that detected for the first time radio emission from MWC 560 (Lucy, Weston, & Sokoloski 2016), at least an order of magnitude enhanced over a VLA non-detection on 2014 October 2, during the quiescence preceding the current outburst.…”

“…Tomov et al (1992) and Michalitsianos et al (1993) modelled MWC 560 with a non-variable M4 giant and an accreting -and probably magnetic -white dwarf (WD), surrounded by an (outer) accretion disk, and subject to a steady optically thick wind outflow and a complex pattern of mass ejection into discrete blobs. Stute & Sahai (2009) deduced however a non-magnetic WD from their X-ray observations. A fit with a variable collimated outflow that originates at the surface of the accretion disk and that is accellerated with far greater efficiency than in normal stellar atmospheres was considered by Shore, Aufdenberg, & Michalitsianos (1994).…”