ROSAT X-ray observations of the interacting pair of galaxie NGC 4410: evidence for a central starburst

Abstract

We present X-ray observations of the interacting pair of galaxies NGC 4410a/b with the ROSAT HRI and PSPC. The ROSAT HRI images reveal a point-like source corresponding to NGC 4410a and an X-ray halo, extending 10&#34; from the nucleus toward the southeast. The halo emission accounts for ~1/3 (L_X=1.3x10^{41} erg s^{-1} in the 0.1 - 2.4 keV ROSAT band) of the total X-ray emission detected from NGC 4410a. The spectrum of the total X-ray emission from NGC 4410a can be fitted at best with a two-component emission model, combining a Raymond-Smith spectrum with T = 10^7 K and a power-law spectrum (Gamma = 2.2). The fraction of the thermal component to the total flux within this model is 35%, supporting the results of the HRI observation. The total unresolved X-ray luminosity detected with the PSPC amounts to 4x10^{41} erg s^{-1} in the ROSAT PSPC band (for D = 97 Mpc). A preferable explanation might be the interaction between the two galaxies causing a circumnuclear starburst around the active nucleus in the peculiar late type Sab galaxy NGC 4410a. As a cumulative effect of exploding stars a superbubble forms a bipolar outflow from the galactic disk with an expansion time of ~8 Myr. The central source injects mechanical energy at a constant rate of a few times 10^{42} erg s^{-1} into the superbubble. A HST WFPC2 image decovers that NGC 4410a is seen almost face-on so that only the approaching outflow is visible. The HRI contours reveal an elongation of this outflow indicative for a faint X-ray ridge below the detection limit (L_X <= 1.4x10^{39} erg s^{-1}) toward the neighbouring galaxy NGC 4410b caused by its tidal interaction. NGC 4410b houses only a faint X-ray source (L_X <= 3.8x10{39} erg s^{-1}).