Journal Article

Recent torque reversal of 4U 1907+09

S. Ç. İnam, Ş. Şahiner and A. Baykal

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 2, pages 1015-1020
Published in print May 2009 | ISSN: 0035-8711
Published online April 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14596.x
Recent torque reversal of 4U 1907+09

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We present timing and spectral analysis of RXTE-PCA (Proportional Counter Array) observations of the accretion powered pulsar 4U 1907+09 between 2007 June and 2008 August. 4U 1907+09 had been in a spin-down episode with a spin-down rate of −3.54 × 10−14 Hz s−1 before 1999. From RXTE observations after 2001 March, the source showed a ∼60 per cent decrease in spin-down magnitude, and INTEGRAL observations after 2003 March showed that source started to spin-up. We found that the source recently entered into a new spin-down episode with a spin-down rate of −3.59 × 10−14 Hz s−1. This spin-down rate is pretty close to the previous long-term spin-down rate of the source measured before 1999. From the spectral analysis, we showed that hydrogen column density varies with the orbital phase.

Keywords: accretion, accretion discs; stars: neutron; pulsars: individual: 4U 1907+09; X-rays: binaries

Journal Article.  3347 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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