吸積毫秒脈衝星XTE J0929-314之不同能量間脈衝相位關係之研究;Energy Dependent Pulse Arrival Times of Accretion-Powered Millisecond Pulsar XTE J0929-314

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题名:	吸積毫秒脈衝星XTE J0929-314之不同能量間脈衝相位關係之研究;Energy Dependent Pulse Arrival Times of Accretion-Powered Millisecond Pulsar XTE J0929-314
作者:	鄭寶玲;PAO-LING CHENG
贡献者:	天文研究所
关键词:	不同能量間脈衝相位關係;吸積毫秒脈衝星;Energy Dependent Pulse Arrival Times;Accretion-Powered Millisecond Pulsar
日期:	2009-04-07
上传时间:	2009-09-22 10:13:13 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	XTE J0929-314於2002年爆發時被RXTE發現，它是第三顆被發現的吸積毫秒脈衝星，其具有較高的銀緯及較低的X光強度。由於XTE J0929-314是顆較暗X光源，因此本論文將選用RXTE資料組態中，時間解析度最高的Good Xenon mode作為觀測資料的來源。　　本論文主要目的在於研究XTE J0929-314不同能量間脈衝相位關係，為此則需不同能量間之精確的脈衝波形以玆比較。我們嘗試利用相位分析的方法來求出足以精確描述XTE J0929-314之軌道與自轉行為的參數，以消除軌道都卜勒效應及長時間下脈衝星自轉的相位變化。不幸的是，由於此脈衝星的熱點可能在脈衝星表面做飄移的緣故，導致無法找出一組精確的軌道與自轉參數。退而求其次的，改由一一地求得每次觀測資料(即obsID，曝光時間約1~2小時)之最佳軌道與自轉參數，進而得出每個obsID在2keV~14keV中七個不同能帶間之精確的脈衝波形，並透過互相關得出不同能帶間的脈衝相位關係。將MJD 52406~MJD 52410的觀測資料加權平均後，發現能量範園介於2 keV ~8 keV的脈衝中，能量較低的脈衝比能量較高的脈衝，最大約延遲了810μs(0.15相位)，能量高於8 keV以後延遲情況則趨於平坦。　　XTE J0929-314相較於其他吸積毫秒脈衝星，其低能量的脈衝有最大的延遲量。根據二分量模型，低能延遲是由於黑體幅射分量的脈衝與逆康普吞分量的脈衝，兩者間之角分佈的不同，在考慮都卜勒加速(Doppler boosting)的情況下，前者的脈衝會因而延遲到達所致使。因此推測XTE J0929-314其X光光譜有較多低能量X光光子。 XTE J0929-314 is the third known accretion-powered millisecond pulsar, which was first identified by Rossi X-ray Timing Explorer ( RXTE ) during its outburst. The follow-up RXTE pointing observations of the source was made between May 2 to June 24 2002. It is a faint, high Galactic latitude, transient, ultracompace X-ray binary. Our analysis is based on the data collected by RXTE Proportional Counter Array (PCA) in GoodXenon mode with 1 μs resolution because of its weak x-ray intensity. The purpose of this thesis is to investigate the energy dependent pulse arrival time of this source. Therefore, the fine pulse profiles, which require precise ephemeris to compensate the effects from orbital motion and other long-term phase drifts for the observed pulses, are essential. We applied pulse phase analysis method to find the ephemeris. Unfortunately, because of possible hot spot movements on the surface of neutron star, no simple model can well-describe the pulse phase modulation for the whole 40 days’ observations. We alternatively attempted to find the local best ephemeris and extracted pulse profiles in seven distinct energy bands between 2 and 14 keV for each observation ID (~1 to 2 hrs exposure). The energy dependent pulse arrival time differences were obtained through cross-correlating these pulse profiles. The weighted-average result for the observations shows that hard X-ray pulses arrived up to 810μs (0.15 cycles) earlier than the soft ones from 2 to 8 keV and the lead saturates beyond 8 keV. Being compared with other accretion-powered millisecond pulsars, XTE J0929-314 has the largest soft lag. According to the two-component model, the Comptonized component has a broader (fan-like) angular distribution than the blackbody component. The Doppler boosting then significantly shifts the peak of the hard pulse producing the soft lag. Therefore, this source probably has a relatively stronger blackbody component than other millisecond pulsars which indicates that XTE J0929-314 has a softer spectrum.
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