Evidence of a Change in the Long Term Spin-down Rate of the X-ray Pulsar 4U 1907+09

Abstract

We analyzed RXTE archival observations of 4U 1907+09 between 17 February 1996 and 6 March 2002. The pulse timing analysis showed that the source stayed at almost {\bf{constant}} period around August 1998 and then started to spin-down at a rate of $(-1.887\mp 0.042)\times 10^{-14}$ Hz s${}^{-}1$ which is $\sim$ 0.60 times lower than the long term ($\sim 15$ years) spin-down rate (Baykal et al. 2001). Our pulse frequency measurements for the first time resolved significant spin-down rate variations since the discovery of the source. We also presented orbital phase resolved X-ray spectra during two stable spin down episodes during November 1996 - December 1997 and March 2001 - March 2002. The source has been known to have two orbitally locked flares. We found that X-ray flux and spectral parameters except Hydrogen column density agreed with each other during the flares.We interpreted the similar values of X-ray fluxes as an indication of the fact that the source accretes not only via transient retrograde accretion disc (in't Zand et al. 1998) but also via the stellar wind of the companion (Roberts et al. 2001), so that the variation of the accretion rate from the disc does not cause significant variation in the observed X-ray flux. Lack of significant change in spectral parameters except Hydrogen column density was interpreted as a sign of the fact that the change in the spin-down rate of the source was not accompanied by a significant variation in the accretion geometry.

arXiv commentRevised version. Accepted for publication in MNRAS

References in corpus (4)

• RXTE Measurement of the Diffuse X-ray Emission From the Galactic Ridge: Implications for the Energetics of the Interstellar Medium
• Recent X-ray measurements of the accretion-powered pulsar 4U 1907+09
• X-ray Flux Related Timing and Spectral Features of 2S 1417-62
• The Steady Spin Down Rate of 4U 1907+09

Cited by in corpus (13)

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• Five years of SGR 1900+14 observations with BeppoSAX
• A Comprehensive Study on RXTE & INTEGRAL Observations of the X-ray Pulsar 4U 1907+09
• Firm Detection of a Cyclotron Resonance Feature with Suzaku in the X-ray Spectrum of GRO J1008-57 during a Giant Outburst in 2012
• Recent Torque Reversal of 4U 1907+09
• Pulse Phase Variation of Cyclotron Line in HMXB 4U 1907+09 with ASTROSAT LAXPC
• A high-mass X-ray binary pulsar 4U 1907+09 with multiple absorption-line features in the spectrum
• Comprehensive Timing and X-ray Spectral Analysis of GX 1+4
• Change in spin-down rate and detection of emission line in HMXB 4U 2206+54 with AstroSat observation
• Variability study of classical supergiant X-ray binary 4U 1907+09 using NuSTAR