Chandra Observations of NuSTAR Serendipitous Sources near the Galactic Plane. (arXiv:1811.05492v1 [astro-ph.HE])

Chandra Observations of NuSTAR Serendipitous Sources near the Galactic Plane. (arXiv:1811.05492v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tomsick_J/0/1/0/all/0/1">John A. Tomsick</a> (SSL/UCB), <a href="http://arxiv.org/find/astro-ph/1/au:+Lansbury_G/0/1/0/all/0/1">George B. Lansbury</a> (Cambridge), <a href="http://arxiv.org/find/astro-ph/1/au:+Rahoui_F/0/1/0/all/0/1">Farid Rahoui</a> (Harvard), <a href="http://arxiv.org/find/astro-ph/1/au:+Aird_J/0/1/0/all/0/1">James Aird</a> (Cambridge), <a href="http://arxiv.org/find/astro-ph/1/au:+Alexander_D/0/1/0/all/0/1">David M. Alexander</a> (Univ. of Durham), <a href="http://arxiv.org/find/astro-ph/1/au:+Clavel_M/0/1/0/all/0/1">Maica Clavel</a> (Univ. Grenoble Alpes), <a href="http://arxiv.org/find/astro-ph/1/au:+Cuturilo_A/0/1/0/all/0/1">AnaSofija Cuturilo</a> (Seattle Pacific Univ.), <a href="http://arxiv.org/find/astro-ph/1/au:+Fornasini_F/0/1/0/all/0/1">Francesca M. Fornasini</a> (CfA), <a href="http://arxiv.org/find/astro-ph/1/au:+Hong_J/0/1/0/all/0/1">JaeSub Hong</a> (CfA), <a href="http://arxiv.org/find/astro-ph/1/au:+Klindt_L/0/1/0/all/0/1">Lizelke Klindt</a> (Univ. of Durham), <a href="http://arxiv.org/find/astro-ph/1/au:+Stern_D/0/1/0/all/0/1">Daniel Stern</a> (JPL)

The NuSTAR serendipitous survey has already uncovered a large number of
Active Galactic Nuclei (AGN), providing new information about the composition
of the Cosmic X-ray Background. For the AGN off the Galactic plane, it has been
possible to use the existing X-ray archival data to improve source
localizations, identify optical counterparts, and classify the AGN with optical
spectroscopy. However, near the Galactic Plane, better X-ray positions are
necessary to achieve optical or near-IR identifications due to the higher
levels of source crowding. Thus, we have used observations with the Chandra
X-ray Observatory to obtain the best possible X-ray positions. With eight
observations, we have obtained coverage for 19 NuSTAR serendips within 12 deg
of the plane. One or two Chandra sources are detected within the error circle
of 15 of the serendips, and we report on these sources and search for optical
counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical
spectrum and detected the presence of hydrogen emission lines. The source is
Galactic, and we argue that it is likely a Cataclysmic Variable. For the other
sources, the Chandra positions will enable future classifications in order to
place limits on faint Galactic populations, including high-mass X-ray binaries
and magnetars.

The NuSTAR serendipitous survey has already uncovered a large number of
Active Galactic Nuclei (AGN), providing new information about the composition
of the Cosmic X-ray Background. For the AGN off the Galactic plane, it has been
possible to use the existing X-ray archival data to improve source
localizations, identify optical counterparts, and classify the AGN with optical
spectroscopy. However, near the Galactic Plane, better X-ray positions are
necessary to achieve optical or near-IR identifications due to the higher
levels of source crowding. Thus, we have used observations with the Chandra
X-ray Observatory to obtain the best possible X-ray positions. With eight
observations, we have obtained coverage for 19 NuSTAR serendips within 12 deg
of the plane. One or two Chandra sources are detected within the error circle
of 15 of the serendips, and we report on these sources and search for optical
counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical
spectrum and detected the presence of hydrogen emission lines. The source is
Galactic, and we argue that it is likely a Cataclysmic Variable. For the other
sources, the Chandra positions will enable future classifications in order to
place limits on faint Galactic populations, including high-mass X-ray binaries
and magnetars.

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