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請使用永久網址來引用或連結此文件:
http://ir.lib.ncu.edu.tw/handle/987654321/6116
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| 題名: | 吸積毫秒脈衝星SAX J1808.4-3658於2002年爆發之不同能量間脈衝相位關係之研究;Energy Dependent Pulse Arrival Time for the Accretion-powered Millisecond Pulsar SAX J1808.4-3658 in its 2002 Outburst |
| 作者: | 李姿蓉;TZU-JUNG LI |
| 貢獻者: | 天文研究所 |
| 關鍵詞: | X光雙星;吸積毫秒脈衝星;X-ray binary;millisecond pulsar;SAX J1808.4-3658 |
| 日期: | 2009-07-01 |
| 上傳時間: | 2009-09-22 10:13:28 (UTC+8) |
| 出版者: | 國立中央大學圖書館 |
| 摘要: | 本論文針對第一顆發現的吸積毫秒脈衝星 (accretion-powered millisecond pulsar) SAX J1808.4-3658，於2002年爆發期間RXTE PCA的觀測，研究其能量間的脈衝相位變化，並與1998年爆發期間的現象比較。 SAX J1808.4-3658為一低質量X光雙星系統，為了要分析中子星不同能量間的脈衝相位差，必須先掌握其自轉與軌道參數以解析出中子星的脈衝波形。我們先取2 – 10 keV，使用加入中子星自轉頻率的圓軌道模型，採取軌道都卜勒效應以及相位分析的方法，進行軌道與自轉參數的分析。一開始我們找不到適用於整段的軌道與自轉參數，後來發現在爆發後第14天發生了參數不連續的情形，Burderi等人 (2006) 也發表其在第14 – 17天發生了相位劇變，因而避開2002年相位劇變期間的資料，並將相位劇變前後分別處理。以各自求得的最佳軌道與自轉參數，疊合2 – 60 keV所劃分成的11個能量區段，並將所有的能量區段與最低能進行互相關分析。相位劇變前，低於9 keV的脈衝相位，有系統地呈現出低能脈衝較高能脈衝延遲的現象，達0.08個相位，即約200 μs，而高於9 keV此現象便消失；相位劇變後，低能脈衝的延遲更高達近0.12個相位，約300 μs，但在擁有足夠訊噪比的資料內，尚未觀察到這個現象的趨勢消失或發生變化。 不同能量間脈衝相位關係的成因，主要是由於脈衝星熱點區域的光譜組成差異所致。相位劇變前的低能延遲現象與1998年爆發的結果十分相似，但相位劇變後的現象則與前二者差異甚大，有著較長的延遲時間甚至沒有看到延遲消失的情形，這顯示著對於2002年爆發，在相位劇變後脈衝星熱點附近的低能量光子相對較多。藉由這樣的結果，我們大概能相信低能延遲現象，即使在同一個光源上也可能會有不同的表現，而其表現似乎與中子星熱點區域的光譜組成有所關聯。 In this thesis, I present the result of the phase shifts of the X-ray pulses in different energy ranges of the first known accretion-powered millisecond pulsar SAX J1808.4-3658 in its 2002 outburst observed by Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA), and compare to the similar phenomenon seen in 1998 outburst. To compare the pulse arrival times of different energy ranges, the precise orbital and spin parameters which reveal the correct pulse profiles are required. These parameters were refined through minimizing the variation of the pulse peak phases, yielded by folding the non-burst, 2 – 10 keV events with a model consisting of orbital Doppler Effect plus possible pulse phase drift described as a polynomial. I found the discontinuity in parameters after day 14, hence it was hard to get the orbital and spin parameters for whole 2002 outburst. Moreover, Burderi et al. (2006) reported that there was a “phase jump” during the day 14 – 17 of the 2002 outburst. Thus, I decided to remove the data in the phase jump and divided 2002 outburst into two sections, before and after the phase jump, then obtained their parameters separately. I subsequently applied these parameters to fold the 11 energy bands of data allocated by event energy to obtain their fine pulse profiles. The phase delays relative to the softest band were derived through cross-correlating the corresponding pulse profiles. The results show a soft pulse lag in the first ~14 days’ data up to 0.08 spin phase (~200 μs) and it saturates at > 9 keV, consistent with the one in 1998 outburst. On the other hand, the similar phenomenon is also seen after the phase jump but the soft lag is up to 0.12 spin phase (~300 μs), much more than the one we found in first 14 days, and the phase lag doesn’t saturate. It is believed that the energy dependent phase pulse arrival time would be caused by the spectrum on the pulsar’s hotspot. The energy dependent pulse phase behavior before the phase jump in 2002 outburst is consistent with it in 1998 outburst, but the case after the phase jump shows a huge difference – in which it shows longer soft pulse lags and no sign of saturation. It seems that the spectrum around the hotspot after the phase jump in 2002 outburst might be softer. Based on this result, we conclude that even in the same source, it might have different behaviors due to the construction of the spectra of the hotspot environments. |
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