Browsing by Author "Cerri-Serim, D."

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    Discovery of a glitch in the accretion- powered pulsar SXP 1062
    (2017) Imam, Sıtkı Cagdas; Serim, M.M.; Sahiner, S.; Cerri-Serim, D.; Baykal, A.; 0000-0003-0820-9186
    We present timing analysis of the accretion-powered pulsar SXP 1062, based on the observations of Swift, XMM-Newton and Chandra satellites covering a time span of about 2 yr. We obtain a phase coherent timing solution that shows that SXP 1062 has been steadily spinning down with a rate-4.29(7) x10(-14) Hz s(-1) leading to a surface magnetic field estimate of about 1.5 x 10(14) G. We also resolve the binary orbital motion of the system from X-ray data that confirms an orbital period of 656(2) d. On MJD 56834.5, a sudden change in pulse frequency occurs with Delta v = 1.28(5) x 10(-6) Hz, which indicates a glitch event. The fractional size of the glitch is Delta v/v similar to 1.37(6) x 10(-3) and SXP 1062 continues to spin-down with a steady rate after the glitch. A short X-ray outburst 25 d prior to the glitch does not alter the spin-down of the source; therefore, the glitch should be associated with the internal structure of the neutron star. While glitch events are common for isolated pulsars, the glitch of SXP 1062 is the first confirmation of the observability of this type of events among accretion-powered pulsars. Furthermore, the value of the fractional change of pulse frequency ensures that we discover the largest glitch reported up to now.
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    Pulse frequency fluctuations of magnetars
    (2019) Cerri-Serim, D.; Serim, M. M.; Sahiner, S.; Inam, S.C.; Baykal, A.; 0000-0003-0820-9186
    Using RXTE, Chandra, XMM-Newton and Swift observations, we construct the power spectra and torque noise strengths of magnetars for the first time. For some of the sources, on time-scales of months to years, we measure strong red noise that might be a consequence of their outbursts. We compare the noise strengths of magnetars with those of radio pulsars by investigating the possible correlations of noise strength with spin-down rate, magnetic field and age. Using these correlations, we find that the noise strengths of magnetars obey similar trends as radio pulsars. However, we do not find any correlation between noise strength and X-ray luminosity, a correlation that has been seen in accretion-powered pulsars. Our findings suggest that the noise behaviour of magnetars resembles that of radio pulsars, but magnetars possess higher noise levels likely because of their stronger magnetic fields.