Title:	Pulse characteristics of the X-Ray pulsar 4U 1907+09
Authors:	Mukerjee, K. Agrawal, P.C. Paul, Biswajit Rao, A.R. Yadav, J.S. Seetha, S. Kasturirangan, K.
Issue Date:	Feb-2001
Publisher:	IOP Publishing Ltd.
Citation:	Astrophysical Journal, 2001, Vol. 548, p368-376
Abstract:	The X-ray pulsar 4U 1907+09 was observed in the 2-18 keV energy band with the Indian X-Ray Astronomy Experiment (IXAE) during 1996 August and again in 1998 June. From the timing measurements, the spin-down rate of the neutron star is measured to be +0.23+/-0.01 s yr-1. A straight-line fit to the historical pulse period data indicates that the pulsar has been in a monotonic phase of spin-down since its discovery. The day-to-day pulse profile indicates some variations during its 8.4 day binary period. The average profile obtained from these observations shows a double-pulse shape with a pronounced asymmetric primary separated by a dip from a relatively weaker but broad secondary. These profiles show a closer resemblance to the pulse shape obtained with the recent observations with the Rossi X-Ray Timing Explorer (RXTE) during 1996 February, as compared to the earlier observations carried out six to 13 years earlier. A secondary flare of 88 mcrab intensity was detected during the IXAE observations in 1996 August. A detailed analysis of the flare data shows the presence of transient 14.4 s oscillations, which may be quasi-periodic during the flaring activity but have a period different from the earlier reported oscillations of 18.2 s as detected by RXTE during the flare of 1996 February. These results, therefore, strengthen the evidence for the presence of a transient accretion disk around the neutron star during the flare, which may be responsible for the continuous slowing down of the pulsar. The studies of such transient quasi-periodic oscillations during flaring activities of 4U 1907+09 thus provide opportunities for understanding the transient behavior of the accretion disk and its physical characteristics.
Description:	Restricted Access
URI:	http://hdl.handle.net/2289/4951
ISSN:	0004-6256 1538-3881(Online)
Alternative Location:	http://adsabs.harvard.edu/abs/2001ApJ...548..368M http://dx.doi.org/10.1086/318655
Copyright:	2001 The American Astronomical Society
Appears in Collections:	Research Papers (A&A)

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