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Astron. Astrophys. 332, 165-172 (1998)


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The SIGMA pulse profiles of GX 1+4: four years of monitoring

P. David 1, P. Laurent 1, M. Denis 2, J. PaulL. Bouchet 1, 3, J.-P. Roques 3, E. Jourdain 3, G. Vedrenne 3, M. Gilfanov 4, M. Churazov 4, R.A. Sunyaev 4, N. Khavenson 4, B. Novikov 4, I. Chulkov 4 and A. Kuznetzov 4

1 Service d'Astrophysique, DAPNIA/DSM/CEA, Centre d'Etudes de Saclay, F-91191 Gif-sur-Yvette, France
2 Space Research Centre-Polish Academy of Sciences, Bartycka 18A, PL-00716 Warsaw, Poland
3 Centre d'Etudes Spatiale des Rayonnements, 9 avenue du Colonel Roche, BP 4346, F-31029 Toulouse Cedex, France
4 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117810 Moscow, Russia

Received 30 July 1997 / Accepted 11 December 1997

Abstract

The soft [FORMULA] -ray source GX 1+4 has been regularly monitored by the SIGMA telescope on board GRANAT since 1990. The accumulated data provides both period and spectral information on this source in the 35-150 keV range. The SIGMA telescope also allows a determination of a pulsed fraction. We report here on the last six years of the SIGMA data on GX 1+4. The general spin down trend is confirmed and the derived periods are consistent with those obtained at other energies. The pulse profiles are shown to be roughly divided into two groups. One including those instances when GX 1+4 presents a relatively high pulsed fraction ([FORMULA]), the other containing those when the source exhibits a low pulsed fraction ([FORMULA]). In an effort to understand this result, we construct an emission model which is based nearly entirely on the geometry of the system to describe the pulse profiles. It is found that the pulsed fraction might possibly be linked to the height of the accretion column.

Key words: X-rays: stars – individual: GX 1+4 – gamma-rays: observations

Send offprint requests to: P. David

© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998
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