Recently the BAT gamma-ray detector onboard Swift satellite has discovered very flat hard X-ray sources with photon index ~ 1.5 above 100 keV. The x-ray spectrum obtained with the XRT on Swiftis highly variable on time scales < 90 minutes. This variability and flat continuum spectrum suggests that this source is classified as a blazar. If this association is real, we have a precious chance to obtain spectrum upto several hundred keV in the source frame of the source. This wide range is of particularly importanceto study the blazar spectrum, or the electron distribution.