Open AccessA survey of hard spectrum ROSAT sources – I. X‐ray source catalogue
Author(s) -
Page M. J.,
Mittaz J. P. D.,
Carrera F. J.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03735.x
Subject(s) - rosat , physics , astrophysics , flux (metallurgy) , population , monte carlo method , spectral line , source counts , astronomy , galaxy , statistics , redshift , demography , metallurgy , materials science , mathematics , sociology
We present a catalogue of 147 serendipitous X‐ray sources selected to have hard spectra ( α <0.5) from a survey of 188 ROSAT fields. Such sources must be the dominant contributors to the X‐ray background at faint fluxes. We have used Monte Carlo simulations to verify that our technique is very efficient at selecting hard sources: the survey has 10 times as much effective area for hard sources as it has for soft sources above a 0.5–2 keV flux level of 10 −14 erg cm −2 s −1 . The distribution of best‐fitting spectral slopes of the hard sources suggests that a typical ROSAT hard source in our survey has a spectral slope α ∼0. The hard sources have a steep number flux relation (d N /d S ∝ S − γ with a best‐fitting value of γ =2.72±0.12) and make up about 15 per cent of all 0.5–2 keV sources with S >10 −14 erg cm −2 s −1 . If their N ( S ) continues to fainter fluxes, the hard sources will comprise ∼40 per cent of sources with 5×10 −15 < S <10 −14 erg cm −2 s −1 . The population of hard sources can therefore account for the harder average spectra of ROSAT sources with S <10 −14 erg cm −2 s −1 . They probably make a strong contribution to the X‐ray background at faint fluxes and could be the solution to the X‐ray background spectral paradox.