吸積驅動毫秒脈衝星 XTE J1814-338 之軌道參數及不同能量間相位延遲之研究

Study of Orbital and Pulsation Properties of Accretion-Powered Millisecond Pulsar XTE J1814-338

鍾怡音(Yi-Ying Chung)

指導教授 ： 周翊

國立中央大學/理學院/天文研究所/碩士(2007年)

摘要

第五顆吸積驅動毫秒脈衝星 XTE J1814-338 在 2003 年 6 月爆發時被 RXTE 發現。本文利用 RXTE 的觀測資料，研究 XTE J1814-338 之軌道及脈衝特性。

中子星上的 X 射線發射，一般而言，包含康普敦與黑體輻射部份，而脈衝反應發射性質。在我們探討脈衝特性前，必須先求得精細的軌道和自轉參數，才能正確解析脈衝波形。首先我們以微分修正法，分析能量位於 2- 10 keV 之內，非 X 射線爆發 (X-ray burst) 時的光子抵達時間，求得最佳系統質心自轉頻率為 $
u = $ 314.35610897(9) Hz, 軌道週期為 4.27464545(7) hr, 及投影軌道半徑 390.623(2) lt-ms。 脈衝星相位在爆發前 23 日內隨時間變化，顯示其一階自轉頻率變化率為 $dot
u = -4.1(2) imes 10^{-13}
m Hz s^{-1}$，二階變化率為 $ddot
u = 2.9(1) imes 10^{-19}
m Hz s^{-2}$。

使用以上所得最佳軌道與自轉參數，我們疊合 2 - 50 keV 內 RXTE/PCA 及 HEXTE 所觀測的光子抵達時間，發現脈衝在不同能量間有延遲的現象。在 2 - 10 keV 能階內，能量較低的脈衝比較高能量脈衝晚抵達，總共延遲約 50 毫秒；此行為與其他已知吸積驅動毫秒脈衝星相同，主要由於受康普敦效應影響的脈衝其發射型態呈扇狀，因中子星自轉速度快，使其脈衝波型受都卜勒增強 (Doppler Boosting) 而被扭曲，造成 2-10 keV 內的 "低能延遲" 現象。在 10 - 50 keV 內， 高能量脈衝反而比低能量脈衝遲。本文提議， 10 - 50 keV 內之 "高能延遲" 現象是由吸積衝擊區域中高熱的電子雲對光子康普敦（增能）散射所造成的。

關鍵字

低能延遲 ； 吸積驅動毫秒波霎 ； 低質量X光雙星系統 ； 時變性質 ； 高能延遲

並列摘要

The fifth known accretion-powered millisecond pulsar (AMP) XTE J1814-338 was discovered by Rossi X-ray Timing Explorer (RXTE) in June 2003 during its outburst. In this thesis, we study its orbital and pulsation properties based on the observations by RXTE.

It is believed that emission on the neutron star surface is mainly composed of a Comptonized and blackbody components, and pulsar pulsations reflect the emission properties. Before we investigate pulsation properties, it is essential to determine fine orbital and spin parameters in order to resolve pulse structures. We first carried out pulse arrival-time analysis based on the non-burst events within energy range 2-10 keV using differential correction technique, and derived barycentric pulsar frequency $
u = $314.35610897(9) Hz, orbital period 4.27464545(7) hr, and 390.623(2) lt-ms projected radius. Our analysis of pulsar phase evolution in the initial 23 days shows that the pulsar has a spin frequency derivative $dot
u = -4.1(2) imes 10^{-13}
m Hz s^{-1}$, and a second frequency derivative $ddot
u = 2.9(1) imes 10^{-19}
m Hz s^{-2}$.

After folding RXTE/PCA and HEXTE photon events within 2 - 50 keV using the best orbital and spin ephemerids obtained in the first part of analysis, we were able to find the pulses show energy-dependent phase delays, where soft energy pulses lag high energy pulses for up to $sim$ 50 $mu
m s$ between 2-10 keV, which is common in known AMPs; in addition, we also found hard pulses lag soft ones between 10-50 keV. While the soft lags are mainly caused by Doppler boosting effect that distorts the Comptonizing pulse component with fan-like emission pattern, we propose that "hard lags" between 10 - 50 keV are likely attributed to Compton upscattering by the hot electron gas in accretion shock region.

並列關鍵字

RXTE ； Low Mass X-ray Binaries ； orbital parameters ； XTE J1814-338 ； millisecond pulsar ； soft lags ； hard lags

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