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A Compton reflection dominated spectrum in a peculiar accreting neutron star

Nanda Rea·Luigi Stella·Gian Luca Israel·Giorgio Matt·Silvia Zane·Alberto Segreto·Tim Oosterbroek·Mauro Orlandini
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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.

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Nanda Rea, Luigi Stella, Gian Luca Israel, Giorgio Matt, Silvia Zane, Alberto Segreto, Tim Oosterbroek, Mauro Orlandini. 2005-09-22. A Compton reflection dominated spectrum in a peculiar accreting neutron star. https://doi.org/10.1111/j.1365-2966.2005.09646.x

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