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Post Info TOPIC: EXO 2030+375
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V2246 Cygni
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Title: Possible regular phenomena in EXO 2030+375
Author: Eva Laplace, Tatehiro Mihara, Yuki Moritani, Motoki Nakajima, Toshihiro Takagi, Kazuo Makishima, Andrea Santangelo

In the last 10 years, since its last giant outburst in 2006, regular X-ray outbursts (type I) were detected every periastron passage in the Be X-ray binary EXO 2030+375. Recently, however, it was reported that the source started to show a peculiar behaviour: its X-ray flux decreased significantly and type I outbursts were missed in several cases. At the same time, the spin frequency of the neutron star, which had been increasing steadily since the end of the 2006 giant outburst, reached a plateau. Very recent observations indicate that the source is now starting to spin down. These observed phenomena have a striking similarity with those which took place 20 years ago, just before the source displayed a sudden orbital phase shift of the outburst peak (1995). This historical event occurred at the time exactly between the two giant outbursts (1985 and 2006). These phenomena suggest the system to have an underlying periodicity of 10.5 years between orbital phase shifts and/or giant outbursts. The suggested periodicity may reflect some long-period dynamics in the circumstellar disk of the Be star, due, e.g., to the Kozai-Lidov effect. A model generating such a periodic change of the Be disk, namely Kozai-Lidov oscillations in the Be disk, is discussed. If this behaviour is really periodical, another phase shift of the X-ray outburst peak is predicted to occur around 2016 December.

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Blobrana


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RE: EXO 2030+375
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ATel 9485: EXO 2030+375 restarts in reverse



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Blobrana


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Title: Analysing X-Ray Pulsar Profiles: Geometry and Beam Pattern of EXO 2030+375
Authors: Manami Sasaki, Dmitry Klochkov, Ute Kraus, Isabel Caballero, Andrea Santangelo

The pulse profiles of the transient Be/X-ray binary EXO 2030+375 show strong dependence on energy, as well as on its luminosity state, and are asymmetric in shape. We want to identify the emission components of the two magnetic poles in the pulsed emission to understand the geometry of the neutron star and its beam pattern. We utilize a pulse-profile decomposition method that enables us to find two symmetric pulse profiles from the magnetic poles of the neutron star. The symmetry characteristics of these single-pole pulse profiles give information about the position of the magnetic poles of the neutron star relative to its rotation axis. We find a possible geometry for the neutron star in EXO 2030+375 through the decomposition of the pulse profiles, which suggests that one pole gets closer to the line of sight than the other and that, during the revolution of the neutron star, both poles disappear behind the horizon for a short period of time. A considerable fraction of the emission arises from a halo while the pole is facing the observer and from the accretion stream of the other pole while it is behind the neutron star, but the gravitational line bending makes the emission visible to us.

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Title: Giant outburst of EXO 2030+375: pulse-phase resolved analysis of INTEGRAL data
Authors: D. Klochkov, A. Santangelo, R. Staubert, C. Ferrigno

In June-September 2006 the Be/X-ray binary EXO 2030+375 experienced the second giant outburst since its discovery. The source was shown to have a complicated pulse-averaged X-ray spectral continuum with possible evidence of cyclotron absorption features. In this paper we present the first pulse-phase resolved analysis of the broad band X-ray spectra of EXO 2030+375 obtained with the INTEGRAL observatory close to the maximum and during the decay phase of the giant outburst. We report a strong variability of the spectrum with pulse phase. Alternative spectral continuum models are discussed. The dependence of the spectral parameters on pulse phase during the maximum of the outburst and the evolution of the pulse profiles with time are qualitatively consistent with the pulsar's emission diagram changing from the fan-beam geometry close to the maximum of the outburst to a combination of pencil and fan beams (of comparable intensities) at the end of the decay phase. Evidence of a cyclotron absorption line around 63 keV at the pulse phase interval preceding the main peak of the pulse profile is present in the spectrum obtained close to the maximum of the outburst.

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