The 2-8 kev X-ray number counts determined from Chandra blank field observations

We present the 2-8 keV number counts from the 1 Ms Chandra observation of the Chandra Deep Field-North. We combine these with the number counts from a 78 ks exposure of the Hawaii Survey field SSA22 and with the number counts obtained in independent analyses of the Chandra Deep Field-South and the Hawaii Survey field SSA13 to determine the number counts from 2 x 10(-16) to 10(-13) ergs cm(-2) s(-1). Over this flux range, the contribution to the X-ray background is 1.1 x 10(-11) ergs cm(-2) s(-1) deg(-2). When the contributions above 10(-13) ergs cm(-2) s(-1) from BeppoSAX or ASCA observations are included, the total rises to 1.4 x 10(-11) ergs cm(-2) s(-1) deg(-2). However, there appears to be substantial field-to-field variation in the counts in excess of the statistical uncertainties. When the statistical and flux-calibration uncertainties (in both the background and source measurements) are taken into account, as much as 0.5 x 10(-11) ergs cm(-2) s(-1) deg(-2) could still be present in an unresolved component.