Swift detection of all previously undetected blazars in a micro-wave flux-limited sample of WMAP foreground sources

¹ ASI Science Data Center, ASDC c/o ESRIN, via G. Galilei 00044 Frascati, Italy e-mail: paolo.giommi@asi.it
² Agenzia Spaziale Italiana, Unitá Osservazione dell'Universo, via le Liegi, 26 00198 Roma, Italy
³ INAF - Osservatorio Astronomico di Roma via Frascati 33, 00040 Monteporzio, Italy
⁴ Department of Astronomy and Astrophysics, Pennsylvania State University, USA
⁵ Universitá di Roma “La Sapienza” Dipartimento di Fisica P.le A. Moro, 2 00185, Roma, Italy
⁶ INAF - Osservatorio Astronomico di Brera via Bianchi 46, 23807 Merate, Italy
⁷ Dipartimento di Fisica, Universitá di Perugia, via A. Pascoli, Perugia, Italy
⁸ UCL, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁹ University of Southampton, Highfield, S017 1BJ Southampton, UK
¹⁰ NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
¹¹ Department of Physics, University of Nevada, Las Vegas, NV 89154-4002, USA

Received: 6 September 2006
Accepted: 25 January 2007

Abstract

Almost the totality of the bright foreground sources in the WMAP Cosmic Microwave Background (CMB) maps are blazars, a class of sources that show usually also X-ray emission. However, 23 objects in a flux-limited sample of 140 blazars of the WMAP catalog (first year) were never reported before as X-ray sources. We present here the results of 41 Swift observations which led to the detection of all these 23 blazars in the 0.3–10 keV band. We conclude that all micro-wave selected blazars are X-ray emitters and that the distribution of the micro-wave to X-ray spectral slope () of LBL blazars is very narrow, confirming that the X-ray flux of most blazars is a very good estimator of their micro-wave emission. The X-ray spectral shape of all the objects that were observed long enough to allow spectral analysis is flat and consistent with inverse Compton emission within the commonly accepted view where the radiation from blazars is emitted in a Sychrotron-Inverse-Compton scenario. We predict that all blazars and most radio galaxies above the sensitivity limit of the WMAP and of the Planck CMB missions are X-ray sources detectable by the present generation of X-ray satellites. An hypothetical all-sky soft X-ray survey with sensitivity of approximately 10^-15 erg cm^-2 s^-1 would be crucial to locate and remove over 100 000 blazars from CMB temperature and polarization maps and therefore accurately clean the primordial CMB signal from the largest population of extragalactic foreground contaminants.