The Soft X-ray Spectrum of the High Mass X-Ray Binary V0332+53 in Quiescence

K. Elshamouty; C. Heinke; R. Chouinard

doi:10.1093/mnras/stw1940

paper

The Soft X-ray Spectrum of the High Mass X-Ray Binary V0332+53 in Quiescence

arXiv:1604.07808 · doi:10.1093/mnras/stw1940

Abstract

The propeller effect should cut off accretion in fast-spinning neutron star high mass X-ray binaries (HMXBs) at low mass transfer rates. However, accretion continues in some HMXBs at $L_{x} < 1 0^{34}$ erg s $^{- 1}$ , as evidenced by continuing pulsations. Indications of spectral softening in systems in the propeller regime suggest that some HMXBs are undergoing fundamental changes in their accretion regime. A 39 ks \textit{XMM-Newton} observation of the transient HMXB V0332+53 found it at a very low X-ray luminosity ( $L_{x} \sim 4 \times 1 0^{32}$ erg s $^{- 1}$ ). A power-law spectral fit requires an unusually soft spectral index ( $4. 4_{- 0.6}^{+ 0.9}$ ), while a magnetized neutron star atmosphere model, with temperature \lt\ 6.7 $\pm 0.2$ K and inferred emitting radius of $\sim 0.2 - 0.3$ km, gives a good fit. We suggest that the quiescent X-ray emission from V0332+53 is mainly from a hot spot on the surface of the neutron star. We could not detect pulsations from V0332+53, due to the low count rate. Due to the high $N_{H}$ , thermal emission from the rest of the neutron star could be only weakly constrained, to \lt\ $<$ 6.14 $_{- 6.14}^{+ 0.05}$ K, or $< 3 \times 1 0^{33}$ erg s $^{- 1}$ .

arXiv comment6 pages, 3 figures, 1 table, submitted to MNRAS

The Soft X-ray Spectrum of the High Mass X-Ray Binary V0332+53 in Quiescence

Abstract

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