The correlation timescale of the X-ray flux during the outbursts of soft X-ray transients  

作　　者：WU YuXiang1,2,YU WenFei1 & LI TiPei2 1 Shanghai Astronomical Observatory,Shanghai 100012,China 2 Department of Engineering Physics & Center for Astrophysics,Tsinghua University,Beijing 100084,China 

出　　处：《Science China(Physics,Mechanics & Astronomy)》2010年第S1期161-167,共7页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Natural Science Foundation of China (Grant Nos. 10533020,10773023,and 10833002);the One Hundred Talents project of the Chinese Academy of Sciences,the Shanghai Pujiang Program (Grant No. 08PJ14111);the National Basic Research Program of China (Grant No. 2009CB824800);the Starting Funds at the Shanghai Astronomical Observatory

摘　　要：Recent studies of black hole and neutron star low mass X-ray binaries(LMXBs) show a positive correlation between the X-ray flux at which the low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the following HS state.By analyzing the data from the All Sky Monitor(ASM) onboard the Rossi X-ray Timing Explorer(RXTE),we show that the HS state flux after the source reaches its HS flux peak still correlates with the transition flux during soft X-ray transient(SXT) outbursts.By studying large outbursts or flares of GX 339-4,Aql X-1 and 4U 1705-44,we have found that the correlation holds up to 250,40,and 50 d after the LH-to-HS state transition,respectively.These time scales correspond to the viscous time scale in a standard accretion disk around a stellar mass black hole or a neutron star at a radius of-104-5 Rg,indicating that the mass accretion rates in the accretion flow either correlate over a large range of radii at a given time or correlate over a long period of time at a given radius.If the accretion geometry is a two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow in the LH state,the disk flow with a radius up to-105 Rg would have contributed to the nearly instantaneous non-thermal radiation directly or indirectly,and therefore affects the time when the state transition occurs.Recent studies of black hole and neutron star low mass X-ray binaries(LMXBs) show a positive correlation between the X-ray flux at which the low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the following HS state.By analyzing the data from the All Sky Monitor(ASM) onboard the Rossi X-ray Timing Explorer(RXTE),we show that the HS state flux after the source reaches its HS flux peak still correlates with the transition flux during soft X-ray transient(SXT) outbursts.By studying large outbursts or flares of GX 339-4,Aql X-1 and 4U 1705-44,we have found that the correlation holds up to 250,40,and 50 d after the LH-to-HS state transition,respectively.These time scales correspond to the viscous time scale in a standard accretion disk around a stellar mass black hole or a neutron star at a radius of-104-5 Rg,indicating that the mass accretion rates in the accretion flow either correlate over a large range of radii at a given time or correlate over a long period of time at a given radius.If the accretion geometry is a two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow in the LH state,the disk flow with a radius up to-105 Rg would have contributed to the nearly instantaneous non-thermal radiation directly or indirectly,and therefore affects the time when the state transition occurs.

关 键 词：ACCRETION DISKS black hole physics star:individual(Aquila X-1 GX 339-4 4U 1705-44) 

分 类 号：P172.2[天文地球—天文学]