First Hard X-Ray Observation of a Compact Symmetric Object: A Broadband X-Ray Study of a Radio Galaxy OQ+208 with NuSTAR and Chandra

Abstract

Compact symmetric objects (CSOs) have been observed with Chandra and XMM - Newton  to gain insights into the initial stages of a radio source evolution and to probe the black hole activity at the time of relativistic outflow formation. However, there have been no CSO observations to date at the hard X-ray energies (>10 keV), impeding our ability to robustly constrain the properties of the intrinsic X-ray emission and of the medium surrounding the young expanding jets. We present the first hard X-ray observation of a CSO performed with the Nuclear Spectroscopic Telescope Array ( NuSTAR ). Our target, OQ +208, is detected up to 30 keV, and thus we establish CSOs as a new class of the NuSTAR sources. We analyze the NuSTAR data jointly with our new Chandra  and archival XMM - Newton data and find that a young (∼250 yr old) radio jet spanning the length of 10 pc coexists with cold obscuring matter, consistent with a dusty torus, with an equivalent hydrogen column density of N H  = 10 23 –10 24 cm −2 . The primary X-ray emission is characterized by a photon index of Γ ∼ 1.45 and an intrinsic 0.5–30 keV luminosity of L ≃ 10 43 erg s −1 . The results of our spectral modeling and broad-line optical classification of the source suggest a porous structure of the obscuring torus. Alternatively, the source may belong to the class of optically unobscured/X-ray-obscured active galactic nucleus. The observed X-ray emission is too weak compared to that predicted by the expanding radio lobes model, leaving an accretion disk corona or jets as the possible origins of the X-ray emission from this young radio galaxy.