A Focused, Hard X-ray Look at Arp 299 with NuSTAR

TL;DR

This study uses NuSTAR and Chandra to resolve and analyze the hard X-ray emission of Arp 299, revealing a dominant Compton-thick AGN in the western nucleus and constraining the properties of other sources.

Contribution

First resolved imaging of Arp 299 up to 45 keV, identifying the primary hard X-ray source and characterizing the obscuration and luminosity of its AGN.

Findings

Arp 299-B hosts a Compton-thick AGN with N_H ~ 4 x 10^{24} cm^{-2}.

Other sources contribute less than 10% to the 10-20 keV emission.

No significant emission above 10 keV from Arp 299-A or X-ray binaries.

Abstract

We report on simultaneous observations of the local starburst system Arp 299 with NuSTAR and Chandra, which provides the first resolved images of this galaxy up to energies of ~ 45 keV. Fitting the 3-40 keV spectrum reveals a column density of $N_{\rm H}$ ~ 4 x10^{24} cm^{-2}, characteristic of a Compton-thick AGN, and a 10-30 keV luminosity of 1.2x 10^{43} ergs s^{-1}. The hard X-rays detected by NuSTAR above 10 keV are centered on the western nucleus, Arp 299-B, which previous X-ray observations have shown to be the primary source of neutral Fe-K emission. Other X-ray sources, including Arp 299-A, the eastern nucleus which is also thought to harbor an AGN, as well as X-ray binaries, contribute $\lesssim 10%$ to the 10-20 keV emission from the Arp 299 system. The lack of significant emission above 10 keV other than that attributed to Arp 299-B suggests that: a) any AGN in Arp 299-A must be heavily obscured ($N_{\rm H}$ > 10^{24} cm^{-2}) or have a much lower luminosity than Arp 299-B and b) the extranuclear X-ray binaries have spectra that cut-off above ~10 keV. Such soft spectra are characteristic of ultraluminous X-ray (ULX) sources observed to date by NuSTAR.