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X-ray and optical monitoring of the December 2017 outburst of the Be/X-ray binary AXJ0049.4-7323

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dc.abstract.enAXJ0049.4-7323 (SXP 756) is a Be/X-ray binary that shows an unusual and poorly understood optical variability that consists of periodic and bright optical outbursts, simultaneous with X-ray outbursts, characterised by a highly asymmetric profile. The periodicity of the outbursts is thought to correspond to the orbital period of the neutron star. To understand the peculiar behaviour shown by this source, we performed the first multi-wavelength monitoring campaign during the periastron passage of December 2017. The monitoring lasted for about 37 days and consisted of X-ray, near-ultraviolet, and optical data from the Neil Gehrels Swift Observatory, the optical I band from the OGLE survey, and spectroscopic observations of the Hα line performed with the 3.9 m Anglo-Australian Telescope. These observations revealed AXJ0049.4-7323 during an anomalous outburst having remarkably different properties compared to the previous ones. In the I band, it showed a longer rise timescale (∼60 days instead of 1-5 days) and a longer decay timescale. At the peak of the outburst, it showed a sudden increase in luminosity in the I band, corresponding to the onset of the X-ray outburst. The monitoring of the Hα emission line showed a fast and highly variable profile composed of three peaks with variable reciprocal brightness. To our knowledge, this is the second observation of a variable three-peak Hα profile of a Be/X-ray binary, after A0535+26. We interpreted these results as a circumstellar disc warped by tidal interactions with the neutron star in a high eccentricity orbit during its periastron passage. The fast jump in optical luminosity at the peak of the outburst and the previous asymmetric outbursts might be caused by the reprocessing of the X-ray photons in the circumstellar disc or the tidal displacement of a large amount of material from the circumstellar disc or the outer layers of the donor star during the periastron passage of the neutron star, which led to an increase in size of the region emitting in the I band. Further multi-wavelength observations are necessary to discriminate among the different scenarios proposed to explain the puzzling optical and X-ray properties of AXJ0049.4-7323.
dc.affiliationUniwersytet Warszawski
dc.contributor.authorDucci, L.
dc.contributor.authorMalacaria, C.
dc.contributor.authorRomano, P.
dc.contributor.authorJi, L.
dc.contributor.authorBozzo, E.
dc.contributor.authorSaathoff, I.
dc.contributor.authorSantangelo, A.
dc.contributor.authorUdalski, Andrzej
dc.date.accessioned2024-01-26T12:17:41Z
dc.date.available2024-01-26T12:17:41Z
dc.date.copyright2018-11-30
dc.date.issued2019
dc.description.accesstimeBEFORE_PUBLICATION
dc.description.financeNie dotyczy
dc.description.versionORIGINAL_AUTHOR
dc.description.volume621
dc.identifier.doi10.1051/0004-6361/201834432
dc.identifier.issn0004-6361
dc.identifier.urihttps://repozytorium.uw.edu.pl//handle/item/125636
dc.identifier.weblinkhttp://adsabs.harvard.edu/abs/2019A&A...621A..94D
dc.languageeng
dc.pbn.affiliationastronomy
dc.relation.ispartofAstronomy and Astrophysics
dc.relation.pagesA94
dc.rightsOther
dc.sciencecloudnosend
dc.titleX-ray and optical monitoring of the December 2017 outburst of the Be/X-ray binary AXJ0049.4-7323
dc.typeJournalArticle
dspace.entity.typePublication