The First Candidate Colliding-Wind Binary in M33. (arXiv:1906.03274v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Garofali_K/0/1/0/all/0/1">Kristen Garofali</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Levesque_E/0/1/0/all/0/1">Emily M. Levesque</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Massey_P/0/1/0/all/0/1">Philip Massey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Williams_B/0/1/0/all/0/1">Benjamin F. Williams</a>
We present the detection of the first candidate colliding-wind binary (CWB)
in M33, located in the giant H II region NGC 604. The source was first
identified in archival {it Chandra} imaging as a relatively soft X-ray point
source, with the likely primary star determined from precise astrometric
alignment between archival {it Hubble Space Telescope} and {it Chandra}
imaging. The candidate primary star in the CWB is classified for the first time
in this work as a carbon-rich Wolf-Rayet star with a likely O star companion
based on spectroscopy obtained from Gemini-North. We model the X-ray spectrum
using {it Chandra} and {it XMM-Newton} observations, and find the CWB is
well-fit as a $sim$ 1 keV thermal plasma with a median unabsorbed luminosity
in the 0.5–2.0 keV band of $L_{rm X}$ $sim$ 3 $times$ 10$^{35}$ erg
s$^{-1}$, making this source among the brightest of CWBs observed to date. We
present a long term light curve for the candidate CWB from archival {it
Chandra} and {it XMM-Newton} observations, and discuss the constraints placed
on the binary by this light curve, as well as the X-ray luminosity at maximum.
Finally, we compare this candidate CWB in M33 to other well-studied, bright
CWBs in the Galaxy and Magellanic Clouds, such as $eta$ Car.
We present the detection of the first candidate colliding-wind binary (CWB)
in M33, located in the giant H II region NGC 604. The source was first
identified in archival {it Chandra} imaging as a relatively soft X-ray point
source, with the likely primary star determined from precise astrometric
alignment between archival {it Hubble Space Telescope} and {it Chandra}
imaging. The candidate primary star in the CWB is classified for the first time
in this work as a carbon-rich Wolf-Rayet star with a likely O star companion
based on spectroscopy obtained from Gemini-North. We model the X-ray spectrum
using {it Chandra} and {it XMM-Newton} observations, and find the CWB is
well-fit as a $sim$ 1 keV thermal plasma with a median unabsorbed luminosity
in the 0.5–2.0 keV band of $L_{rm X}$ $sim$ 3 $times$ 10$^{35}$ erg
s$^{-1}$, making this source among the brightest of CWBs observed to date. We
present a long term light curve for the candidate CWB from archival {it
Chandra} and {it XMM-Newton} observations, and discuss the constraints placed
on the binary by this light curve, as well as the X-ray luminosity at maximum.
Finally, we compare this candidate CWB in M33 to other well-studied, bright
CWBs in the Galaxy and Magellanic Clouds, such as $eta$ Car.
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