Abstract
Abstract Using archival Chandra ACIS-S data, $0.5 \hbox{--} 8.0 \,\mathrm{keV}$ X-ray spectra of two luminous X-ray sources in the nearby dwarf irregular galaxy NGC 4449 were studied. One, with an extremely high luminosity of $1.3 \times 10^{39} \;\mathrm{erg} \,\mathrm{s}^{-1}$ in the $0.5 \hbox{--} 8.0 \;\mathrm{keV}$ band, shows a spectrum that is well described with a power-law model of photon index $\sim 2$. Its properties are consistent with those of ultraluminous compact X-ray sources observed in nearby galaxies. The spectrum of the other, with a luminosity of $2.7 \times 10^{38} \,\mathrm{erg} \,\mathrm{s}^{-1}$ in the same band, is successfully represented with a so-called multi-color disk blackbody emission model with an inner-most disk temperature of $\sim 0.59 \,\mathrm{keV}$. Its spectral parameters are typical of ordinary black hole binaries observed in our Galaxy and the Large Magellanic Cloud. These young population objects, together with a bright supernova remnant and diffuse hot gas already reported, suggest that the X-ray emission from irregular galaxies is generally enhanced by their recent star-forming activities.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
