The broad-band noise characteristics of selected anomalous X-ray pulsars and soft gamma-ray repeaters |
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| Authors: | B Külebi † &#; Balman |
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| Institution: | Department of Physics, Middle East Technical University, InönüBulvar?, 06531 Ankara, Turkey;Astrophysics Missions Division, Research and Scientific Support Department of ESA, ESTEC, Postbus 299 SCI-SA, Keplerlaan 1, 2201 AZ Noorwijk ZH, The Netherlands |
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| Abstract: | We present the broad-band noise structure of selected anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) in the 2–60 keV energy band. We have analysed Rossi X-Ray Timing Explorer Proportional Counter Array archival light curves for four AXPs and one SGR. We detect that the persistent emission of these sources shows band-limited noise at low frequencies in the range 0.005–0.05 Hz varying from 2.5 to 70 per cent integrated rms in times of prolonged quiescence and following outbursts. We discovered band-limited red noise in 1E 2259+586 only for ～2 yr after its major 2002 outburst. The system shows no broad-band noise otherwise. Although this rise in noise in 1E 2259+586 occurred following an outburst which included a rotational glitch, the other glitching AXPs showed no obvious change in broad-band noise, thus it does not seem that this noise is correlated with glitches. The only source that showed significant variation in broad-band noise was 1E 1048.1?5937 , where the noise gradually rose for 1.95 yr at a rate of ～3.6 per cent per year. For this source the increases in broad-band noise was not correlated with the large increases in persistent and pulsed flux, or its two short SGR-like bursts. This rise in noise did commence after a long burst, however, given the sparsity of this event, and the possibility that similar bursts went unnoticed the trigger for the rise is noise in 1E 1048.1?5937 is not as clear as for 1E 2259+586. The other three sources indicate a persistent band-limited noise at low levels in comparison. |
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| Keywords: | stars: coronae stars: neutron stars: oscillations X-rays: stars |
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