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Title:
Variability of the Galactic center in the hard X-ray range
Authors:
Bazzano, A.; La Padula, C.; Ubertini, P.; Sood, R. K.
Affiliation:
AA(CNR, Istituto di Astrofisica Spaziale, Frascati, Italy), AB(CNR, Istituto di Astrofisica Spaziale, Frascati, Italy), AC(CNR, Istituto di Astrofisica Spaziale, Frascati, Italy), AD(CNR, Istituto di Astrofisica Spaziale, Frascati, Italy)
Publication:
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 385, Jan. 20, 1992, p. L17-L20. (ApJL Homepage)
Publication Date:
01/1992
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Galactic Nuclei, Milky Way Galaxy, X Ray Astronomy, Astronomical Spectroscopy, Black Holes (Astronomy), Proportional Counters
DOI:
10.1086/186267
Bibliographic Code:
1992ApJ...385L..17B

Abstract

Evidence is reported of strong flux variability in the hard X-ray range from IE 1740.7 - 2942 obtained during an observation of the region on May 17, 1989. The measurement was performed with a high-sensitivity array of multiwire proportional counter operative in the energy range 15-180 keV, and with a field of view of 1.9 deg FWHM. The data, when compared with previous data in the same energy range obtained either by a narrow-field of view or imaging instruments, imply a flux variability of a factor of 3 at 40 keV and 2.5 at 100 keV. The spectrum of May 17, 1989, can be described by a single power law with a spectral index of 1.95 and an intensity of 0.000285/sq cm/s keV at 30 keV. The detection of 1E 1740.7 - 2942 in a condition very close to the low state of Cyg X1 confirms the similarity between these two sources, thus supporting the black hole nature of the Galactic center high-energy emitter.

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