The flattening of the X-ray spectrum of Sco X-1 at energies beyond 40 keV

Abstract

The measurements of the hard X-ray spectrum of Sco X-1 in the energy interval 20-150 keV in three balloon flights from Hyderabad, India are reported. These results show conclusively that the spectrum of Sco X-1 is very flat in the energy interval 40-150 keV and the measured fluxes beyond 60 keV are several orders of magnitude higher than those expected on the basis of an extrapolation of bremsstrahlung spectrum from a thin hot plasma at a temperature corresponding to kT=5 keV, which is applicable for Sco X-1 for energies < 40 keV. The results are compared with those of other investigators of hard X-rays from Sco X-1, and the implication of the results is briefly discussed.