Prolonged sub-luminous state of the new transitional pulsar candidate CXOU J110926.4-650224

Francesco Coti Zelati, Alessandro Papitto, Domitilla De Martino, David A.H. Buckley, Alida Odendaal, Jian Li, Thomas D. Russell, Diego F. Torres, Simona M. Mazzola, Enrico Bozzo, Mariusz Gromadzki, Sergio Campana, Nanda Rea, Carlo Ferrigno, Simone Migliari

    Producció científica: Contribució a una revistaArticleRecerca

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    © ESO 2019. We report on a multi-wavelength study of the unclassified X-ray source CXOU J110926.4-650224 (J1109). We identified the optical counterpart as a blue star with a magnitude of ∼20.1 (3300-10500 Å). The optical emission was variable on timescales from hundreds to thousands of seconds. The spectrum showed prominent emission lines with variable profiles at different epochs. Simultaneous XMM-Newton and NuSTAR observations revealed a bimodal distribution of the X-ray count rates on timescales as short as tens of seconds, as well as sporadic flaring activity. The average broad-band (0.3-79 keV) spectrum was adequately described by an absorbed power law model with photon index of Γ=1.63±0.01 (at 1σ c.l.), and the X-ray luminosity was (2.16±0.04)×10 34 erg s -1 for a distance of 4 kpc. Based on observations with different instruments, the X-ray luminosity has remained relatively steady over the past ∼15 years. J1109 is spatially associated with the gamma-ray source FL8Y J1109.8-6500, which was detected with Fermi at an average luminosity of (1.5±0.2)×10 34 erg s -1 (assuming the distance of J1109) over the 0.1-300 GeV energy band between 2008 and 2016. The source was undetected during ATCA radio observations that were simultaneous with NuSTAR, down to a 3σ flux upper limit of 18 μJy beam -1 (at 7.25 GHz). We show that the phenomenological properties of J1109 point to a binary transitional pulsar candidate currently in a sub-luminous accretion disk state, and that the upper limits derived for the radio emission are consistent with the expected radio luminosity for accreting neutron stars at similar X-ray luminosities.
    Idioma originalEnglish
    Número d’articleA211
    RevistaAstronomy and Astrophysics
    Estat de la publicacióPublicada - 1 de febr. 2019


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