Study of the ultraluminous X-ray sources in NGC 4382 and NGC 1399 with Chandra.

The present work studies the spectral properties of some X-ray point sources in the galaxies NGC 4382 and NGC 1399 as observed by Chandra in different epochs. Five point sources from the galaxy NGC 4382 and twelve point sources from the galaxy NGC 1399 with net source count ≥ 100 were considered for the present work. Spectra of all the seventeen sources were fitted with two empirical models—the absorbed power law and an absorbed disk black body. Most of the sources were found to be equally well explained by both the models except for a few of them which prefers one model over the other. While most of the sources are found to be in the Ultraluminous hard state ( L x ≥ 10 39 erg s - 1 ; powerlaw photon index ( Γ) ∼ 2.0 /kT in > 1.0 keV), for which inverse comptonization of soft photons may be responsible for their emission. Significantly, we found spectral state transitions in two sources - NGC 4382 X-1 & NGC 1399 X-8. Long-term variability in luminosity were also observed in the sources -NGC 4382 X-1, NGC 1399 X-7, NGC 1399 X-8, NGC 1399 X-9 & NGC 1399 X-17. While most of the ULXs here are found to be powered by accretion on to stellar mass black holes, there is one super-soft ULX (NGC 1399 X-9) with k T in ∼ 0.36 keV and bolometric luminosity, L x ∼ 2.69 × 10 39 erg s - 1 , which in one of the epoch, was found to be consistent with harboring Intermediate mass black hole (IMBH) with M BH ∼ 200 - 67 + 62 M ⊙ , accreting at 0.09 times the Eddington limit. However, another two soft ULXs - NGC 1399 X-10 with k T in ∼ 0.66 keV and NGC 1399 X-15 with k T in ∼ 0.53 keV with their corresponding estimated bolometric luminosities were found to be consistent with harboring stellar mass blackholes accreting within their Eddington limit. [ABSTRACT FROM AUTHOR]