Luminosity dependent changes in the X-ray pulse profile of the transient pulsar Cepheus X-4 during its declining phase of the 1997 outburst

Mukerjee, K. ; Agrawal, P. C. ; Paul, B. ; Rao, A. R. ; Seetha, S. ; Kasturirangan, K. (2000) Luminosity dependent changes in the X-ray pulse profile of the transient pulsar Cepheus X-4 during its declining phase of the 1997 outburst Astronomy & Astrophysics, 353 . pp. 239-243. ISSN 0004-6361

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Official URL: http://articles.adsabs.harvard.edu/cgi-bin/nph-iar...

Abstract

The transient X-ray pulsar Cepheus X-4 underwent its latest outburst in 1997, during July-August, which lasted for about 30 days. The Pointed mode Proportional Counters (PPCs) of the Indian X-ray Astronomy Experiment (IXAE) on board IRS-P3 satellite observed the source in its declining phase during 1997 July 28 to July 30. The timing analysis of the data confirms the 66 seconds pulsation of the neutron star. The X-ray pulse profile obtained in two energy bands between 2 and 18 keV, shows energy dependent variations. The pulse profile obtained by us in the declining phase of the outburst when the X-ray luminosity of the source was about 6x1035 ergs s-1, is distinctly different from the one observed with the RXTE in the earlier phase of the outburst. It is found that near the end of the outburst, the relative strength of the two pulses of the double-pulse profile got reversed and the inter-pulse became more dominant compared to the main pulse. The observations can be interpreted in terms of a luminosity dependent emission profile of the pulsar, where depending on the pulsar geometry with respect to line of sight, one of the emission patterns, either a pencil-beam or a fan-beam, becomes more dominant. This is due to the changes in the pulsar magneto-sphere below a specific luminosity, which may cause relative changes in accretion process onto the two poles of the neutron star.

Item Type:Article
Source:Copyright of this article belongs to EDP Sciences.
Keywords:Accretion; Accretion Disks; X-rays: Stars; Stars: Pulsars: Individual: CEP X-4
ID Code:85574
Deposited On:03 Mar 2012 14:48
Last Modified:19 May 2016 01:33

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