X-Ray Spectral Variability of Ultraluminous X-Ray Sources in Extragalactic Globular Clusters. (arXiv:1902.05073v1 [astro-ph.HE])

X-Ray Spectral Variability of Ultraluminous X-Ray Sources in Extragalactic Globular Clusters. (arXiv:1902.05073v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Dage_K/0/1/0/all/0/1">Kristen C. Dage</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zepf_S/0/1/0/all/0/1">Stephen E. Zepf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peacock_M/0/1/0/all/0/1">Mark B. Peacock</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bahramian_A/0/1/0/all/0/1">Arash Bahramian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Noroozi_O/0/1/0/all/0/1">Omid Noroozi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kundu_A/0/1/0/all/0/1">Arunav Kundu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maccarone_T/0/1/0/all/0/1">Thomas J. Maccarone</a>

A number of ultraluminous X-ray sources (ULXs) are physically associated with
extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis
of eight of the brightest of these sources. We fit the spectra of the GC ULXs
to single power law and single disk models. We find that the data never require
that any of the sources change between a disk and a power law across successive
observations. The GC ULXs best fit by a single disk show a bimodal
distribution: they either have temperatures well below 0.5 keV, or variable
temperatures ranging above 0.5 keV up to 2~keV. The GC ULXs with low kT have
significant changes in luminosity but show little or no change in kT. By
contrast, the sources with higher kT either change in both kT and $L_X$
together, or show no significant change in either parameter. Notably, the X-ray
characteristics may be related to the optical properties of these ULXs, with
the two lowest kT sources showing optical emission lines.

A number of ultraluminous X-ray sources (ULXs) are physically associated with
extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis
of eight of the brightest of these sources. We fit the spectra of the GC ULXs
to single power law and single disk models. We find that the data never require
that any of the sources change between a disk and a power law across successive
observations. The GC ULXs best fit by a single disk show a bimodal
distribution: they either have temperatures well below 0.5 keV, or variable
temperatures ranging above 0.5 keV up to 2~keV. The GC ULXs with low kT have
significant changes in luminosity but show little or no change in kT. By
contrast, the sources with higher kT either change in both kT and $L_X$
together, or show no significant change in either parameter. Notably, the X-ray
characteristics may be related to the optical properties of these ULXs, with
the two lowest kT sources showing optical emission lines.

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