Hard X-ray variability of NGC 4151
- CNR, Istituto di Fisica Cosmica, Milan (Italy) CNR, Istituto di Astrofisica Spaziale, Frascati (Italy)
During a balloon flight on July 15, 1987 of the MIFRASO telescope, a region of the sky containing the Seyfert galaxy NGC 4151 was studied over the photon energy range 15-335 keV. A 13-sigma excess, interpreted as originating from the direction of NGC 4151, was detected in this energy band and the corresponding emission spectrum is represented by a single power law with a photon spectral index of alpha = 1.5 + or {minus} 0.1. With respect to the July 1986 observation of this source with the same telescope, the alpha slope is statistically unchanged, while the X-ray flux in the energy range 27-80 keV shows, at the 95-percent confidence level, an increase of about 40 percent. An observation of the Crab Nebula, that proves the stability of the telescope response through the two measurements of NGC 4151, is also described. 48 refs.
- OSTI ID:
- 5503272
- Journal Information:
- Astrophysical Journal; (United States), Vol. 373; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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