Astronomy and Astrophysics, volume 319, 459-469 (1997/3-2)
X-ray observations of the Magellanic-type Galaxy NGC 4449.
VOGLER A. and PIETSCH W.
Abstract (from CDS):
X-ray emission (Lx∼2.5x1039erg/s) 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 D25 ellipse of the galaxy. The most luminous source is a supernova remnant detected with an intrinsic luminosity of Lx=4.7x1038erg/s. Another very luminous source (Lx=3.1x1038erg/s) is located between two Hα shells. A source near the southern border of the galaxy (Lx=1.7x1038erg/s) 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 (Lx=1.2x1038erg/s and Lx=0.8x1038erg/s) are positioned at the border of regions that show enhanced blue emission. The center of the galaxy was detected with a luminosity of Lx=7x1037erg/s. 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 (Lx=1.4x1039erg/s), unresolved point sources (Lx=2x1038erg/s), and extended emission possibly arising from a hot (T∼3x106K) gaseous component of the interstellar medium (Lx=1.0x1039erg/s). 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.