Obscuring environment and x-ray variability of compact symmetric objects unveiled with XMM-Newton and NuSTAR

Compact symmetric objects (CSOs) show radio features such as jets, lobes, and hot spots, which are contained within their host galaxies, and likely represent a recent radio activity. A subpopulation of CSOs with high intrinsic X-ray column densities has been inferred from shallow, soft X-ray band exposures, and observed to cluster in the linear radio size versus 5 GHz radio power plane, which suggests that a dense circumnuclear medium may dramatically influence the growth of compact radio structures. Here, we report on the first detection of two CSOs, 2021+614 and J1511+0518, at energies above 10 keV with NuSTAR. We model the NuSTAR data jointly with the new XMM-Newton data of J1511+0518, and with the archival XMM-Newton data of 2021+614. A toroidal reprocessor model fits the data well and allows us to robustly confirm the X-ray properties of the CSO absorbers and continuum. In both sources, we find intrinsic X-ray absorbing column densities in excess of 10$^{23}$ cm$^{-2}$, hard photon indices of the primary emission, $\Gamma$ ∼ 1.4–1.7, Fe K$\alpha$ line emission, and variability of the intrinsic X-ray flux density on the timescale of years. The studied X-ray continua are dominated by the primary power-law emission at energies above 3 keV, and by the scattered component at energies below 3 keV. An additional soft X-ray component, modeled with a hot, collisionally ionized plasma with temperature kT ∼ 1 keV, is required by the XMM-Newton data in J1511+0518, which is corroborated by the tentative evidence for the extension in the archival Chandra image of the source

X-ray Properties of Young Radio Quasars at z > 4.5

We present a comprehensive analysis of Chandra X-ray observations of 15 young radio quasars at redshifts $4.5 < z < 5.0$. All sources are detected in the $0.5-7.0$ keV energy band. Emission spectra are extracted, and the average photon index for the sample is measured to be $1.5\pm0.1$. Unabsorbed rest-frame $2-10$ keV luminosities are found to range between $(0.5-23.2) \times 10^{45}$ erg s$^{-1}$. The optical-X-ray power-law spectral index $\alpha_{ox}$ is calculated for each source using optical/UV data available in the literature. The $\alpha_{ox}$-UV relationship is compared with other quasar surveys, and an anticorrelation is observed that agrees with independent estimates. Rest-frame radio and X-ray luminosities are established for the sample, and a correlation between the luminosities is detected. These multiwavelength results reinforce a lack of spectral evolution for quasars over a broad redshift range. We additionally identify three quasars from our multiwavelength analysis that are statistically significant outliers, with one source being a Compton-thick candidate in the early universe, and discuss each in detail.Comment: Accepted to ApJ, 13 pages, 5 figures, 4 table

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

© 2019 IOP Publishing Ltd. This is an author-created, un-copyedited version of an article accepted for publication in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.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 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 NuSTAR. Our target, OQ+208, is detected up to 30 keV, and thus we establish CSOs as a new class of NuSTAR sources. We analyze the NuSTAR data jointly with our new Chandra and archival XMM-Newton data and find that a young, ~250 years 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 $N_H = 10^{23}$-$10^{24}$ cm$^{-2}$. The primary X-ray emission is characterized by a photon index $\Gamma \sim 1.45$ and intrinsic 0.5-30 keV luminosity $L \sim 10^{43}$ 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 un-obscured/X-ray obscured AGN. 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.Peer reviewedFinal Accepted Versio

The Origin of High-energy Emission in the Young Radio Source PKS 1718–49

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/We present a model for the broadband radio-to-γ-ray spectral energy distribution of the compact radio source PKS 1718 − 649. Because of its young age (≃100 yr) and proximity (z = 0.014), PKS 1718 − 649 offers a unique opportunity to study the nuclear conditions and the jet/host galaxy feedback process at the time of the initial radio jet expansion. PKS 1718 − 649 is one of a handful of young radio jets with γ-ray emission that has been confirmed by the Fermi/LAT detector. We show that in PKS1718−649 this γ-ray emission can be successfully explained by Inverse Compton scattering of the UV photons, presumably from an accretion flow, off nonthermal electrons in the expanding radio lobes. The origin of the X-ray emission in PKS 1718 − 649 is more elusive. While Inverse Compton scattering of the IR photons emitted by a cold gas in the vicinity of the expanding radio lobes contributes significantly to the X-ray luminosity, the data require an additional source of X-rays, e.g., a weak X-ray corona or a radiatively inefficient accretion flow, as expected from a LINER-type nucleus, such as that of PKS 1718 − 649. We find that the jet in PKS 1718 − 649 has low power, L j ≃ 2 × 1042 erg s−1, and expands in an environment with density n 0 ≃ 3–20 cm−3. The inferred mass accretion rate and gas mass reservoir within 50–100 pc of the galactic center are consistent with estimates from the literature obtained by tracing molecular gas in the innermost region of the host galaxy with SINFONI and the Atacama Large Millimeter/submillimeter Array.Peer reviewe

Discovery of Candidate X-ray Jets in High-Redshift Quasars

We present Chandra X-ray observations of 14 radio-loud quasars at redshifts $3 < z < 4$, selected from a well-defined sample. All quasars are detected in the 0.5-7.0 keV energy band, and resolved X-ray features are detected in five of the objects at distances of 1-12" from the quasar core. The X-ray features are spatially coincident with known radio features for four of the five quasars. This indicates that these systems contain X-ray jets. X-ray fluxes and luminosities are measured, and jet-to-core X-ray flux ratios are estimated. The flux ratios are consistent with those observed for nearby jet systems, suggesting that the observed X-ray emission mechanism is independent of redshift. For quasars with undetected jets, an upper limit on the average X-ray jet intensity is estimated using a stacked image analysis. Emission spectra of the quasar cores are extracted and modeled to obtain best-fit photon indices, and an Fe K emission line is detected from one quasar in our sample. We compare X-ray spectral properties with optical and radio emission in the context of both our sample and other quasar surveys.Comment: Accepted to ApJ, 15 pages, 7 figures, 7 table

X-ray properties of the Youngest Radio Sources and their Environments

This is the peer-reviewed version of the following article: A. Siemiginowska, M. Sobolewska, G. Migliori, M. Guainazzi, M. Hardcaste, L. Ostorero and L. Stawarz, ‘X-Ray properties of the youngest radio sources and their environments’, The Astrophysical Journal, Vol 823(1), first published online May 23, 2016, which has been published in final form at doi: http://dx.doi.org/10.3847/0004-637X/823/1/57 © 2016. The American Astronomical Society. All rights reserved.We present the first results from our X-ray study of young radio sources classified as compact symmetric objects (CSOs). Using the Chandra X-ray Observatory we observed six CSOs for the first time in X-rays, and re-observed four CSOs already observed with XMM-Newton or BeppoSAX. We also included six other CSOs with archival data to built a pilot study of a sample of the 16 CSO sources observed in X-rays to date. All the sources are nearby, $z\lt 1$, and the age of their radio structures ($\lt 3000$ yr) has been derived from the expansion velocity of their hot spots. Our results show the heterogeneous nature of the CSOs' X-ray emission, indicating a complex environment associated with young radio sources. The sample covers a range in X-ray luminosity, {L}_{2\mbox{--}10\mathrm{keV}}\sim {10}^{41}–1045 erg s−1, and intrinsic absorbing column density of ${N}_{{\rm{H}}}\simeq {10}^{21}$–1022 cm−2. In particular, we detected extended X-ray emission in 1718−649; a hard photon index of ${\rm{\Gamma }}\simeq 1$ in 2021+614 and 1511+0518 consistent with either a Compton-thick absorber or non-thermal emission from compact radio lobes, and in 0710+439 an ionized iron emission line at ${E}_{\mathrm{rest}}=(6.62\pm 0.04)$ keV and EW $\sim 0.15$–1.4 keV, and a decrease by an order of magnitude in the 2–10 keV flux since the 2008 XMM-Newton observation in 1607+26. We conclude that our pilot study of CSOs provides a variety of exceptional diagnostics and highlights the importance of deep X-ray observations of large samples of young sources. This is necessary in order to constrain theoretical models for the earliest stage of radio source evolution and to study the interactions of young radio sources with the interstellar environment of their host galaxies.Peer reviewedFinal Accepted Versio