An observation of the spectrum of Sco X-1 above 50 KeV
Prichard, Howard Milton
Haymes, Robert C.
Master of Science
On November 25, 1970, an observation of the hard X-ray spectrum of the object "Sco X-l" was made by a balloon-borne scintillation detector launched from Parana, Argentina. The information obtained from this flight includes the first data on the shape of the spectrum at energies above 50 KeV. The directional detector consisted of a Nal (Tl) central crystal collimated by a guard crystal of the same material connected in anti-coincidence with the central crystal. An on-board 128 channel analyzer was adjusted to cover the incident photon energy range of 30 to 930 KeV; the analyzed pulses, together with engineering data, were radio-telemetered from the balloon at 128,000 feet to the ground. Alternate tenminute observations of the source and background were made for approximately two hours. Channel-by-channel residuals were obtained by subtracting the time-normalized and averaged count rate of two successive background segments from that of the intervening source segment. After correction for atmospheric and instrumental signal attenuation, and for detector efficiency, these residuals were taken to be a measurement of the flux due to Sco X-l incident at the top of the atmosphere. The resulting spectrum is inconsistent with a single-component thermal bremsstrahlung emission mechanism. In the range 50-350 KeV, a flux distribution more consistent with synchrotron radiation is observed, as a power law of spectral index 1.8 provides a good fit to the data. From 350 to 930 KeV, 2-sigma upper limits are obtained that are well above the expected levels due to the above synchrotron mechanism. No evidence of line emission is seen. Possible implications of this measurement are discussed in the light of previous observations.