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Blank Field X-Ray Sources

Ilaria Cagnoni·Annalisa Celotti·Martin Elvis·Dong-Woo Kim·Fabrizio Nicastro
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Abstract

The X-ray sky is not as well known as is sometimes thought. We report on our search of minority populations (Kim & Elvis 1999). One of the most intriguing is that of `blank field sources', i.e. bright ROSAT sources (F(X)>1e-13 erg/cm2/s) with no optical counterpart on the Palomar Sky Survey (to O=21.5) within their 39"(99%) radius error circle. The nature of Blank Field sources is unknown: no known extragalactic population has such extreme X-ray to optical ratios (f(X)/f(V) >60). Moreover blank field source tend to have much flatter PSPC spectra compared to radio-quiet AGN. Both properties suggest obscuration. `Blank field sources' could be: Quasar-2s, low-mass AGNs, isolated neutron stars, high redshift clusters of galaxies, failed clusters, AGNs with no big blue bump. Identification with any of these populations would be an interesting discovery.

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Ilaria Cagnoni, Annalisa Celotti, Martin Elvis, Dong-Woo Kim, Fabrizio Nicastro. 2000-06-19. Blank Field X-Ray Sources. https://arxiv.org/abs/astro-ph/0006257

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