Hard X-ray Excess from the Magnificent Seven Neutron Stars. (arXiv:1910.02956v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Dessert_C/0/1/0/all/0/1">Christopher Dessert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Foster_J/0/1/0/all/0/1">Joshua W. Foster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Safdi_B/0/1/0/all/0/1">Benjamin R. Safdi</a>
We report significant hard X-ray excesses in the energy range 2-8 keV for two
nearby isolated neutron stars RX J1856.6-3754 and RX J0420.0-5022. These
neutron stars have previously been observed in soft X-rays to have nearly
thermal spectra at temperatures ~100 eV, which are thought to arise from the
warm neutron star surfaces. We find non-trivial hard X-ray spectra well above
the thermal surface predictions with archival data from the XMM-Newton and
Chandra X-ray telescopes. We analyze possible systematic effects that could
generate such spurious signals, such as nearby X-ray point sources and pileup
of soft X-rays, but we find that the hard X-ray excesses are robust to these
systematics. We also investigate possible sources of hard X-ray emission from
the neutron stars and find no satisfactory explanation with known mechanisms,
suggesting that a novel source of X-ray emission is at play. We do not find
high-significance hard X-ray excesses from the other five Magnificent Seven
isolated neutron stars.
We report significant hard X-ray excesses in the energy range 2-8 keV for two
nearby isolated neutron stars RX J1856.6-3754 and RX J0420.0-5022. These
neutron stars have previously been observed in soft X-rays to have nearly
thermal spectra at temperatures ~100 eV, which are thought to arise from the
warm neutron star surfaces. We find non-trivial hard X-ray spectra well above
the thermal surface predictions with archival data from the XMM-Newton and
Chandra X-ray telescopes. We analyze possible systematic effects that could
generate such spurious signals, such as nearby X-ray point sources and pileup
of soft X-rays, but we find that the hard X-ray excesses are robust to these
systematics. We also investigate possible sources of hard X-ray emission from
the neutron stars and find no satisfactory explanation with known mechanisms,
suggesting that a novel source of X-ray emission is at play. We do not find
high-significance hard X-ray excesses from the other five Magnificent Seven
isolated neutron stars.
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