Effect of non-stationary accretion on spectral state transitions: An example of a persistent neutron star LMXB 4U1636–536

Abstract

Observations of the black hole and neutron star X-ray binaries show that the luminosity of the hard-to-soft state transition is usually higher than that of the soft-tohard state transition, indicating additional parameters other than the mass accretion rate is required to interpret spectral state transitions. It has been found in some individual black hole or neutron star soft X-ray transients that the luminosity corresponding to the hard-tosoft state transition is positively correlated with the peak luminosity of the following soft state. In this work, we report the discovery of the same correlation in a single persistent neutron star low mass X-ray binary (LMXB) 4U1636-536 based on the data from the All Sky Monitor(ASM) on board the RXTE, the Gas Slit Camera (GSC) on board the MAXI and the Burst Alert Telescope (BAT) on board the Swift. We also found such a positive correlation holds in the persistent neutron star LMXB in a luminosity range spanning by about a factor of four. Our results indicates that non-stationary accretion also plays an important role in driving X-ray spectral state transitions in persistent accreting systems with small accretion flares, which is much less dramatic compared with the bright outbursts seen in many Galactic LMXB transients.

The advection-dominated accretion flow for the origin of the thermal soft X-ray component in low-level accreting neutron stars

“…⋆ E-mail: qiaoel@nao.cas.cn 2016; Zhang & Yu 2018). So far, a great of effects have been made for exploring the accretion physics in the different spectral states of XRBs.…”

Hot Accretion Flow around Neutron Stars

“…When L < L c , the sources are in the low/hard state. Previous works show that L c is about 1 ∼ 4 percents of L Edd (e.g., Nowak et al 2002;Maccarone & Coppi 2003;Rodriguez et al 2003;Kubota & Done 2004;Meyer-Hofmeister et al 2005;Gladstone et al 2007;Qiao & Liu 2009;Zhang et al 2016;Zhang & Yu 2018). In the high/soft state, a geometrically thin and optically thick disk operates (Shakura & Sunyaev 1973).…”