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 |
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Authors: | Altan Baykal Tod Strohmayer Jean Swank M. Ali Alpar Michael J. Stark |
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Affiliation: | Physics Department, Middle East Technical University, Ankara 06531, Turkey;Laboratory for High Energy Astrophysics NASA/GSFC Greenbelt, MD 20771, USA;Department of Physics, SabancıUniversity, Istanbul, Turkey;Department of Physics and Astronomy, Denison University, Granville, OH 43023, USA |
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Abstract: | 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 ∼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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Keywords: | accretion, accretion discs binaries: general stars: individual: 1E 1048.1−5937 stars: individual: 1E 2259+586 stars: low-mass, brown dwarfs |
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