A Compton reflection dominated spectrum in a peculiar accreting neutron star

Abstract

We report on a puzzling event occurred during a long BeppoSAX observation of the slow-rotating binary pulsar GX 1+4. During this event, lasting about 1 day, the source X-ray flux was over a factor 10 lower than normal. The low-energy pulsations disappeared while at higher energies they were shifted in phase. The spectrum taken outside this low-intensity event was well fitted by an absorbed cut-off power law, and exhibited a broad iron line at ~6.5 keV probably due to the blending of the neutral (6.4 keV) and ionised (6.7 keV) K_alpha iron lines. The spectrum during the event was Compton reflection dominated and it showed two narrow iron lines at ~6.4 keV and ~7.0 keV, the latter never revealed before in this source. We also present a possible model for this event in which a variation of the accretion rate thickens a torus-like accretion disc which hides for a while the direct neutron star emission from our line of sight. In this scenario the Compton reflected emission observed during the event is well explained in terms of emission reflected by the side of the torus facing our line of sight.

arXiv comment10 pages; to be published in MNRAS

References in corpus (18)

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• The nature of the hard state of Cygnus X-3
• Spin period evolution of GX 1+4
• INTEGRAL observation of the accreting pulsar GX 1+4
• Study of the many fluorescent lines and the absorption variability in GX 301-2 with XMM-Newton
• Relativistic X-Ray Reflection and Photoionised Absorption in the Neutron-Star Low-Mass X-ray Binary GX 13+1
• The first detection of Compton Reflection in the Low-Mass X-ray Binary 4U1705-44 with INTEGRAL and BeppoSAX
• Discovery of radio emission from the symbiotic X-ray binary system GX 1+4
• A Suzaku View of Accretion Powered X-ray Pulsar GX 1+4
• Comprehensive Timing and X-ray Spectral Analysis of GX 1+4
• The puzzling symbiotic X-ray system 4U1700+24
• A curious case of the accretion-powered X-ray pulsar GX 1+4
• The Intensity Modulation of Fluorescent Line by a Finite Light Speed Effect in Accretion-Powered X-ray Pulsars
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• A Two-Stage Kick Scenario for the Peculiar LMXB GX 1+4