Energy Spectrum and Time Variations of Hard X-Rays from Cyg X-1

Details Energy Spectrum and Time Variations of Hard X-Rays from Cyg X-1 Energy Spectrum and Time Variations of Hard X-Rays from Cyg X-1

Oct 1972

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1972ap%26ss..18..408a&link_type=abstract

Astrophysics and Space Science, Volume 18, Issue 2, pp.408-424

Astronomy and Astrophysics

Astrophysics

15

Scientific paper

Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22 154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E -(1.92±0.10) photons cm-2s-1 keV-1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25 151 keV band and given by dN/dE=(3.54±2.44)E -(1.89±0.22) photons cm-2s-1 keV-1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of ˜E -2, while below 20 keV the spectrum varies fromE -1.7 toE -5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.

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