The 0.3-30 keV Spectra of Powerful Starburst Galaxies: NuSTAR and Chandra Observations of NGC 3256 and NGC 3310

摘要: We present nearly simultaneous Chandra and NuSTAR observations of two actively star-forming galaxies within 50 Mpc: NGC 3256 3310. Both are significantly detected by both NuSTAR, which together provide the first-ever spectra these spanning 0.3–30 keV. The X-ray emission from is spatially resolved Chandra; we find that hot gas dominates E 1–3 galaxy-wide follow steep power-law distributions with Γ ≈ 2.6 at > 5–7 Using new archival data, search for signatures heavily obscured or low luminosity active galactic nuclei (AGNs). 3310 have sources coincident nuclear regions; however, restricts to be either AGNs (L_(2−10 keV)/L_(Edd) 10^(−5)) non-AGNs in nature (e.g., ULXs crowded reach L_(2−10 keV) ~ 10^(40) erg s^(−1) cannot ruled out). Combining our constraints on keV equivalent measurements nearby M83 253, analyze star formation rate (SFR) normalized starburst galaxies. all four show sharply declining slopes energies above 3–6 primarily due ULX populations. Our therefore constrain average spectral shape populations luminous accreting binaries (i.e., ULXs). Interestingly, despite a completely different galaxy sample selection, emphasizing here range SFRs stellar masses, properties similar those super-Eddington been studied individually targeted program. also exhibits factor ≈3–10 elevation over other corresponding overabundance ULXs. argue excess most likely explained relatively metallicity young population this galaxy, property expected produce an given SFR.