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Astron. Astrophys. 319, 459-469 (1997)

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X-ray observations of the Magellanic-type Galaxy NGC 4449

A. Vogler and W. Pietsch

Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße, D-85748 Garching, Germany

Received 24 April 1996 / Accepted 30 July 1996


X-ray emission ([FORMULA]  erg s-1) from the nearby, face-on Magellanic-type irregular galaxy NGC 4449 was detected with the ROSAT PSPC and HRI. The HRI resolves seven point sources located within the [FORMULA] ellipse of the galaxy. The most luminous source is a supernova remnant detected with an intrinsic luminosity of [FORMULA]  erg s-1. Another very luminous source ([FORMULA]  erg s-1) is located between two H [FORMULA] shells. A source near the southern border of the galaxy ([FORMULA]  erg s-1) shows flux variations between the HRI and PSPC observations of a factor of two, no counterparts in other wavelengths and most likely is an X-ray binary. Two fainter sources ([FORMULA]  erg s-1   and [FORMULA]  erg s-1) are positioned at the border of regions that show enhanced blue emission. The center of the galaxy was detected with a luminosity of [FORMULA]  erg s-1.

Combining the spatial resolution of the HRI and the spectral capabilities of the PSPC indicates that the total X-ray emission of NGC 4449 is composed of resolved point sources ([FORMULA]  erg s-1), unresolved point sources ([FORMULA]  erg s-1), and extended emission possibly arising from a hot ([FORMULA]  K) gaseous component of the interstellar medium ([FORMULA]  erg s-1). The spectral and spatial findings indicate that most of the thermal emission originates from parts in the outer HI disk and above it. The parameters and implications of a possible gaseous halo component are discussed.

The NGC 4449 X-ray emission components are compared with those of the Magellanic Clouds which can be resolved in the contributing X-ray emission components. The NGC 4449 point source and extended emission components seem to reflect the LMC scaled for the different galaxy masses.

Key words: galaxies: individual: NGC 4449 – galaxies: irregular – X-rays: galaxies

Send offprint requests to: W. Pietsch, (wnp@mpe-garching.mpg.de)

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998