Differences between the two anomalous X-ray pulsars: variations in the spin-down rate of 1E 1048.1-5937 and an extended interval of quiet spin-down in 1E 2259+586
Baykal, Altan and Strohmayer, Tod and Swank, Jean and Alpar, M. Ali and Stark, Michael J. (2000) Differences between the two anomalous X-ray pulsars: variations in the spin-down rate of 1E 1048.1-5937 and an extended interval of quiet spin-down in 1E 2259+586. Monthly Notices of the Royal Astronomical Society, 319 (1). pp. 205-208. ISSN 0035-8711
Official URL: http://dx.doi.org/10.1046/j.1365-8711.2000.03845.x
We analysed the Rossi X-ray Timing Explorer (RXTE) archival data of 1E 1048.1-5937 covering a time-span of more than one year. The spin-down rate of this source decreases by similar to 30 per cent during the observation. We could not resolve the X-ray flux variations because of contamination by eta Carinae. We find that the level of pulse frequency fluctuations of 1E 1048.1-5937 is consistent with typical noise levels of accretion-powered pulsars. Recent RXTE observations of 1E 2259+586 have shown a constant spin-down with a very low upper limit on timing noise. We used the RXTE archival X-ray observations of 1E 2259+586 to show that the intrinsic X-ray luminosity times-series is also stable, with an rms fractional variation of less than 15 per cent. The source could have been in a quiet phase of accretion with a constant X-ray luminosity and spin-down rate.
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