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Astron. Astrophys. 362, L57-L61 (2000)

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Letter to the Editor

Extragalactic 2-10 keV source counts from a fluctuation analysis of deep BeppoSAX MECS images

M. Perri 1,2 and P. Giommi 1

1 Beppo SAX Science Data Center, ASI, Via Corcolle, 19, 00131 Roma, Italy
2 Università di Roma "Tor Vergata", Dipartimento di Fisica, Via della Ricerca Scientifica, 1, 00133 Roma, Italy

Received 15 May 2000 / Accepted 8 June 2000


We present an analysis of the spatial fluctuations of the 2-10 keV Cosmic X-ray Background (CXB) as measured from 22 high galactic latitude ([FORMULA]) fields observed with the MECS instrument on-board Beppo SAX. This technique allowed us to probe extragalactic source counts a factor 3-4 fainter than is possible with direct measurements of pointlike sources in MECS deep fields. The slope of the 2-10 keV logN-logS relationship is found to be still close to the "Euclidean" one ([FORMULA]) down to our flux limit of [FORMULA] [FORMULA], where the contribution of discrete sources to the 2-10 keV CXB amounts to [FORMULA]. Source counts derived from the analysis presented in this letter are in very good agreement both with those directly measured with ASCA and Beppo SAX deep surveys at bright fluxes and with a first estimation of the 2-10 keV Chandra logN-logS at fainter fluxes.

Key words: methods: statistical – galaxies: active – cosmology: diffuse radiation – X-rays: general

Send offprint requests to: M. Perri

© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000