Discovery of strong X-ray variability in an H II type galaxy

Details Discovery of strong X-ray variability in an H II type galaxy Discovery of strong X-ray variability in an H II type galaxy

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..403b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 2, p. 403-410

Astronomy and Astrophysics

Astronomy

14

Active Galactic Nuclei, Active Galaxies, Emission Spectra, H Ii Regions, Interstellar Gas, Starburst Galaxies, Variability, X Ray Spectra, Balmer Series, Color-Color Diagram, Ionized Gases, Rosat Mission, Sky Surveys (Astronomy), X Ray Astronomy

Scientific paper

We present the first detection of X-ray variability in an H II type galaxy. The standard line radio diagnostics of the galaxy, IRAS 15564+6359, all point to the H II nature of the source. On the other hand, in terms of X-ray flux and spectral variability, the source is very similar to very active active galactic nuclei (AGN). The shortest doubling time scale found in the ROSAT (0.1-2.4keV) energy band is only about 1500 seconds. Amplitude variations of a factor of 10 are detected on a time scale of about half a day. The small size of the emitting region, less than 2 x 10-5 pc, deduced from the rapid variations can be taken as the strongest proof for the presence of an active nucleus in the H II type galaxy IRAS 15564+6359. Our analysis of the X-ray spectra indicate that the flux variations are connected with strong spectral changes. We detected a significant hardening of the ROSAT spectrum with increasing source intensity. Spectral simulations show that the ROSAT spectrum can be represented by a combination of a steep thermal starburst component and a flatter power law AGN contribution. On the basis of this model we can disentangle the (0.1-2.4keV) luminosity emitted in the starburst from the luminosity emerging from the AGN component as a function of varying source intensity.

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