X-ray analysis of high mass x-ray binary pulsars

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Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Fizik Bölümü, Türkiye

Tezin Onay Tarihi: 2015

Öğrenci: ŞEYDA ŞAHİNER

Danışman: ALTAN BAYKAL

Özet:

In this thesis, X-ray properties of three high mass X-ray binary (HMXB) pulsars are analysed, using the data of X-ray satellites such as RXTE, INTEGRAL and Swift. Selected sources belong to different subgroups of the HMXB family. The first system, 4U 1907+09 is a classical wind-fed supergiant system with persistent X-ray emission; although it shows irregular flares and dips. SWIFT J1729.9-3437 and SWIFT J0513.4-6547 are newly discovered transient systems. Although the counterpart of SWIFT J1729.9-3437 could not be detected, its properties are in agreement with highly obscured wind-fed supergiant systems. SWIFT J0513.4-6547 resides in a Be X-ray binary system. Timing studies of 4U 1907+09 shows that the pulsar entered to a new spin-down episode during the 4.5 years of monitoring campaign. Pulse period fluctuations of the source are consistent with noise processes implying a random walk. Orbital variations in spectral parameters and occurrence of dip states are also examined. Results show that the probability of observing a dip state is higher for certain orbital phases. The column density is also changing with orbital period, giving clues on the geometry of the accretion and the structural properties of the matter. Outburst observations of SWIFT J1729.9-3437 are used to identify the timing and spectral properties of the source. The pulse frequency and its derivative are measured as 1.8734(8)x10^{-3} Hz and 6.42(6)x10^{-12} Hz/s, respectively. In addition a possible orbital period is detected as 15.3 days. The pulse and orbit periods place SWIFT J1729.9-3437 among the wind-fed supergiant systems in the Corbet diagram. Furthermore, X-ray spectrum, defined by a power law with a high energy cut-off, is highly absorbed (n_H = 8.27x10^{22} cm^{-2}). The two outbursts from SWIFT J0513.4-6547 are investigated for temporal and pulse-phase dependent variations in X-ray spectral properties. Two different models equally fit well the overall spectrum of 2009 outburst, however spectral parameters are unusual for both. A power law with a high energy cut-off model gives the lowest cut-off energy (E_{cut} = 5.04 keV) among HMXBs, where as a power law plus blackbody model gives the highest blackbody temperature (kT = 1.89 keV).