Soft phase lags of pulsed emission from the millisecond X-ray pulsar SAX J1808.4-3658

被引:76
作者
Cui, W [1 ]
Morgan, EH
Titarchuk, LG
机构
[1] MIT, Ctr Space Res, Cambridge, MA 02139 USA
[2] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[3] George Mason Univ, Inst Computat Sci & Informat, Fairfax, VA 22030 USA
基金
美国国家航空航天局;
关键词
accretion; accretion disks; pulsars : individual (SAX J1808.4-3658); stars : neutron; X-rays : stars;
D O I
10.1086/311569
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report the discovery of phase shifts between X-ray pulses at different energies in the newly discovered millisecond X-ray pulsar SAX J1808.4-3658. The results show that low-energy pulses lag high-energy pulses by as much as similar to 0.2 ms (or similar to 8% of the pulse period). The measurements were made in two different ways: (1) computing cross-power spectra between different energy bands, and (2) cross-correlating the folded pulse profiles in different energy bands; consistent results were obtained. We speculate that the observed soft lags might be related to the lateral expansion and subsequent cooling of a "hot spot" on the neutron star surface in which the pulsed X-ray emission originates. Also presented is the possibility of producing soft lags via Compton downscattering of hard X-ray photons from the hot spot in the cool surrounding atmosphere. We will discuss possible X-ray production mechanisms for SAX J1808.4-3658 and constraints on the emission environment, based on the observed soft lags, pulse profiles, and energy spectrum.
引用
收藏
页码:L27 / L30
页数:4
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