Quiescent thermal emission from the neutron star in Aquila X-1

被引:95
作者
Rutledge, RE
Bildsten, L
Brown, EF
Pavlov, GG
Zavlin, VE
机构
[1] CALTECH, Space Radiat Lab, Pasadena, CA 91125 USA
[2] Univ Calif Santa Barbara, Inst Theoret Phys, Santa Barbara, CA 93106 USA
[3] Univ Calif Santa Barbara, Dept Phys, Santa Barbara, CA 93106 USA
[4] Univ Chicago, Enrico Fermi Inst, Chicago, IL 60637 USA
[5] Penn State Univ, Davey Lab 525, University Pk, PA 16802 USA
[6] Max Planck Inst Extraterr Phys, D-85740 Garching, Germany
关键词
stars : atmospheres; stars : individual (Aquila X-1); stars : neutron; X-rays : binaries;
D O I
10.1086/322361
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report on the quiescent spectrum measured with Chandra ACIS-S of the transient, type I, X-ray-bursting neutron star Aq1 X-1, immediately following an accretion outburst. The neutron star radius, assuming a pure hydrogen atmosphere and a hard power-law spectrum, is R-infinity = 13.4(-4)(+5)(d/5 kpc) km. Based on the historical outburst record of the Rossi X-Ray Timing Explorer All-Sky Monitor, the quiescent luminosity is consistent with that predicted by Brown, Bildsten, and Rutledge from deep crustal heating, lending support to this theory for providing a minimum quiescent luminosity of transient neutron stars. While not required by the data, the hard power-law component can account for 18%+/-8% of the 0.5-10 keV thermal flux. Short-timescale intensity variability during this observation is less than 15% rms (3 sigma; 0.0001-1 Hz, 0.2-8 keV). Comparison between the Chandra spectrum and three X-ray spectral observations made between 1992 October and 1996 October find all spectra consistent with a pure H atmosphere, but with temperatures ranging from 145 to 168 eV, spanning a factor of 1.87 +/-0.21 in observed flux. The source of variability in the quiescent luminosity on long timescales (greater than years) remains a puzzle. If from accretion, then it remains to be explained why the quiescent accretion rate provides a luminosity so nearly equal to that from deep crustal heating.
引用
收藏
页码:1054 / 1059
页数:6
相关论文
共 43 条
[1]  
Arnaud KA, 1996, ASTR SOC P, V101, P17
[2]   ASCA observations of transient x-ray sources in quiescence [J].
Asai, K ;
Dotani, T ;
Hoshi, R ;
Tanaka, Y ;
Robinson, CR ;
Terada, K .
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 1998, 50 (06) :611-619
[3]   ASCA observations of soft X-ray transients in quiescence: X1608-52 and Cen X-4 [J].
Asai, K ;
Dotani, T ;
Mitsuda, K ;
Hoshi, R ;
Vaughan, B ;
Tanaka, Y ;
Inoue, H .
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 1996, 48 (02) :257-263
[4]   THE FATE OF ACCRETED CNO ELEMENTS IN NEUTRON-STAR ATMOSPHERES - X-RAY-BURSTS AND GAMMA-RAY LINES [J].
BILDSTEN, L ;
SALPETER, EE ;
WASSERMAN, I .
ASTROPHYSICAL JOURNAL, 1992, 384 (01) :143-176
[5]  
BILDSTEN L, 2000, IN PRESS NATO ASI C
[6]  
BRANDT S, 1992, 5664 IAU
[7]   Crustal heating and quiescent emission from transiently accreting neutron stars [J].
Brown, EF ;
Bildsten, L ;
Rutledge, RE .
ASTROPHYSICAL JOURNAL, 1998, 504 (02) :L95-L98
[8]  
Callanan P. J., 1999, 7086 IAU
[9]  
Campana S, 1997, ASTRON ASTROPHYS, V324, P941
[10]  
Campana S, 2000, ASTRON ASTROPHYS, V358, P583