Recent observations of nearby Compton thick (CT) active galactic nuclei (AGNs) with Chandra have resolved hard (>3 keV) X-ray emission extending out from the central supermassive black hole to ...kiloparsec scales, challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines originate in the inner ∼parsec due to the excitation of obscuring material. In this paper we present the results of the most recent Chandra ACIS-S observations of NGC 7212, a CT AGN in a compact group of interacting galaxies, with a total effective exposure of ∼150 ks. We find ∼20% of the observed emission is found outside of the central kiloparsec, with ∼17% associated with the soft X-rays, and ∼3% with hard X-ray continuum and Fe K line. This emission is extended both along the ionization cone and in the cross-cone direction up to ∼3.8 kpc scales. The spectrum of NGC 7212 is best represented by a mixture of thermal and photoionization models that indicate the presence of complex gas interactions. These observations are consistent with what is observed in other CT AGN (e.g., ESO 428-G014, NGC 1068), providing further evidence that this may be a common phenomenon. High-resolution observations of extended CT AGN provide an especially valuable environment for understanding how AGN feedback impacts host galaxies on galactic scales.
Abstract
We present the spatial analysis of five Compton thick (CT) active galactic nuclei (AGNs), including MKN 573, NGC 1386, NGC 3393, NGC 5643, and NGC 7212, for which high-resolution Chandra ...observations are available. For each source, we find hard X-ray emission (>3 keV) extending to ∼kiloparsec scales along the ionization cone, and for some sources, in the cross-cone region. This collection represents the first, high-signal sample of CT AGN with extended hard X-ray emission for which we can begin to build a more complete picture of this new population of AGN. We investigate the energy dependence of the extended X-ray emission, including possible dependencies on host galaxy and AGN properties, and find a correlation between the excess emission and obscuration, suggesting a connection between the nuclear obscuring material and the galactic molecular clouds. Furthermore, we find that the soft X-ray emission extends farther than the hard X-rays along the ionization cone, which may be explained by a galactocentric radial dependence on the density of molecular clouds due to the orientation of the ionization cone with respect to the galactic disk. These results are consistent with other CT AGN with observed extended hard X-ray emission (e.g., ESO 428-G014 and the Ma et al. CT AGN sample), further demonstrating the ubiquity of extended hard X-ray emission in CT AGN.
Deep Chandra observations of Pictor A Hardcastle, M. J; Lenc, E; Birkinshaw, M ...
Monthly notices of the Royal Astronomical Society,
02/2016, Letnik:
455, Številka:
4
Journal Article
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We report on deep Chandra observations of the nearby broad-line radio galaxy Pictor A, which we combine with new Australia Telescope Compact Array (ATCA) observations. The new X-ray data have a ...factor of 4 more exposure than observations previously presented and span a 15 yr time baseline, allowing a detailed study of the spatial, temporal and spectral properties of the AGN, jet, hotspot and lobes. We present evidence for further time variation of the jet, though the flare that we reported in previous work remains the most significantly detected time-varying feature. We also confirm previous tentative evidence for a faint counterjet. Based on the radio through X-ray spectrum of the jet and its detailed spatial structure, and on the properties of the counterjet, we argue that inverse-Compton models can be conclusively rejected, and propose that the X-ray emission from the jet is synchrotron emission from particles accelerated in the boundary layer of a relativistic jet. For the first time, we find evidence that the bright western hotspot is also time-varying in X-rays, and we connect this to the small-scale structure in the hotspot seen in high-resolution radio observations. The new data allow us to confirm that the spectrum of the lobes is in good agreement with the predictions of an inverse-Compton model and we show that the data favour models in which the filaments seen in the radio images are predominantly the result of spatial variation of magnetic fields in the presence of a relatively uniform electron distribution.
ABSTRACT
We present the first X-ray observation at sub-arcsecond resolution of the high-redshift (z = 6.18) radio-loud quasar CFHQS J142952 + 544717 (J1429). The ∼100 net-count 0.3–7 keV spectrum ...obtained from ∼30 ks Chandra exposure is best fit by a single power-law model with a photon index Γ = 2.0 ± 0.2 and no indication of an intrinsic absorber, implying a 3.6–72 keV rest-frame luminosity $L_{\rm X}=(2.3^{+0.6}_{-0.5})\times 10^{46}$ erg s−1. We identify a second X-ray source at 30″ distance from J1429 position, with a soft (Γ ≃ 2.8) and absorbed (equivalent hydrogen column density NH < 13.4 × 1020 cm−2) spectrum, which likely contaminated J1429 spectra obtained in lower angular resolution observations. Based on the analysis of the Chandra image, the bulk of the X-ray luminosity is produced within the central ∼3 kpc region, either by the disc/corona system, or by a moderately aligned jet. In this context, we discuss the source properties in comparison with samples of low- and high-redshift quasars. We find indication of a possible excess of counts over the expectations for a point-like source in a 0.5″–1.5″ (∼3−8 kpc) annular region. The corresponding X-ray luminosity at J1429 redshift is 4 × 1045 erg s−1. If confirmed, this emission could be related to either a large-scale X-ray jet, or a separate X-ray source.
ABSTRACT A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a ...luminous radio source at redshift z = 2.5. This is one of only few examples of high-redshift X-ray jets known to date. It has a clear extension of about 12″, corresponding to a projected length of ∼100 kpc, with a possible hot spot located 35″ from the quasar. The archival high resolution Very Large Array maps surprisingly reveal no extended jet emission, except for one knot about 1 4 from the quasar. The high X-ray to radio luminosity ratio for this source appears consistent with the amplification expected from the inverse Compton radiative model. This serendipitous discovery may signal the existence of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a selection bias that must be accounted for when drawing any conclusions about the redshift evolution of jet properties and indeed about the cosmological evolution of supermassive black holes and active galactic nuclei in general.
ABSTRACT We report the γ-ray detection of a young radio galaxy, PKS 1718−649, belonging to the class of compact symmetric objects (CSOs), with the Large Area Telescope (LAT) on board the Fermi ...satellite. The third Fermi Gamma-ray LAT catalog (3FGL) includes an unassociated γ-ray source, 3FGL J1728.0−6446, located close to PKS 1718−649. Using the latest Pass 8 calibration, we confirm that the best-fit 1 position of the γ-ray source is compatible with the radio location of PKS 1718−649. Cross-matching of the γ-ray source position with the positions of blazar sources from several catalogs yields negative results. Thus, we conclude that PKS 1718−649 is the most likely counterpart to the unassociated LAT source. We obtain a detection test statistics TS ∼ 36 (>5 ) with a best-fit photon spectral index Γ = 2.9 0.3 and a 0.1-100 GeV photon flux density F0.1−100 GeV = (11.5 0.3) × 10−9 ph cm−2 s−1. We argue that the linear size (∼2 pc), the kinematic age (∼100 years), and the source distance (z = 0.014) make PKS 1718−649 an ideal candidate for γ-ray detection in the framework of the model proposing that the most compact and the youngest CSOs can efficiently produce GeV radiation via inverse-Compton scattering of the ambient photon fields by the radio lobe non-thermal electrons. Thus, our detection of the source in γ-rays establishes young radio galaxies as a distinct class of extragalactic high-energy emitters and yields a unique insight on the physical conditions in compact radio lobes interacting with the interstellar medium of the host galaxy.
We present the X-ray spectral analysis of the 390 brightest extragalactic sources in the Chandra-Cosmic Evolution Survey catalogue, showing at least 70 net counts in the 0.5-7 keV band. This sample ...has a 100 per cent completeness in optical-infrared identification, with ∼75 per cent of the sample having a spectroscopic redshift and ∼25 per cent a photometric redshift. Our analysis allows us to accurately determine the intrinsic absorption, the broad-band continuum shape (Γ) and intrinsic L
2-10 distributions, with an accuracy better than 30 per cent on the spectral parameters for 95 per cent of the sample. The sample is equally divided in type 1 (49.7 per cent) and type 2 active galactic nuclei (48.7 per cent) plus few passive galaxies at low z. We found a significant difference in the distribution of Γ of type 1 and type 2, with small intrinsic dispersion, a weak correlation of Γ with L
2−10 and a large population (15 per cent of the sample) of high luminosity, highly obscured (QSO2) sources. The distribution of the X-ray/Optical flux ratio (Log(F
X
/F
i
)) for type 1 is narrow (0 < X/O < 1), while type 2 are spread up to X/O = 2. The X/O correlates well with the amount of X-ray obscuration. Finally, a small sample of Compton-thick candidates and peculiar sources is presented. In the appendix, we discuss the comparison between Chandra and XMM-Newton spectra for 280 sources in common. We found a small systematic difference, with XMM-Newton spectra that tend to have softer power laws and lower obscuration.
Abstract
We report the results of high-resolution subpixel imaging of the hard continuum and Fe K
α
line of the Compton-thick (CT) active galactic nucleus (AGN) ESO 428-G014, observed with
Chandra
...ACIS. While the 3–4 keV emission is dominated by an extended component, a single nuclear point source is prominent in the 4–6 keV range. Instead, two peaks of similar intensity, separated by ∼36 pc in projection on the plane of the sky are detected in the Fe K
α
emission. The SE knot could be marginally associated with the heavily obscured hard continuum source. We discuss four possible interpretations of the nuclear morphology. (1) Given the bolometric luminosity and likely black hole mass of ESO 428-G014, we may be imaging two clumps of the CT obscuring torus in the Fe K
α
line. (2) The Fe K
α
knots may be connected with the fluorescent emission from the dusty bicone, or (3) with the light echo of a nuclear outburst. (4) We also explore the less likely possibility that we may be detecting the rare signature of merging nuclei. Considering the large-scale kiloparsec-size extent of the hard continuum and Fe K
α
emission (Papers I and II), we conclude that the AGN in ESO 428-G014 has been active for at least 10
4
yr. Comparison with the models of Czerny et al. suggests high accretion rates during this activity.
Aims. Compact symmetric objects (CSOs) are thought to represent the first step in the evolutionary path of radio galaxies. In the present study, we investigated the X-ray emission of two CSOs ...confirmed to emit at GeV energies: PKS 1718–649 and TXS 1146+596. Unveiling the origin of their observed high-energy emission is crucial to establishing the physical parameters of the radio source and understanding how CSOs interact with the surrounding medium. Methods. We combined archival and new NuSTAR observations of PKS 1718–649 and TXS 1146+596 to have broadband X-ray coverage. For both sources, we modeled the broadband spectral energy distribution (SED) from the radio band up to γ -rays in order to derive their physical parameters. We also discuss the role of the ambient medium in confining the source expansion, which we investigate using X-ray obscuration. Results. For the first time, we report X-ray detections of PKS 1718–649 and 1146+596 with NuSTAR at energies higher than 10 keV. Combining Chandra and NuSTAR observations of TXS 1146+596, we reveal the presence of a multitemperature thermal component dominating the soft X-ray spectrum, and we interpret this finding as indicative of an AGN feedback process in action in this source. In addition, we show that two emitting electron populations are necessary to reproduce the observed broadband SED of TXS 1146+596: in our models, the X-ray emission could either be produced by synchrotron radiation or by a weak X-ray corona, or could be an ADAF-type emission. Interestingly, an additional X-ray component, namely a weak corona, is also required for PKS 1718–649. Moreover, we argue that heavily obscured and possibly frustrated sources tend to show different radio sizes with respect to those that are unobscured and free to expand.
ABSTRACT
We report the discovery of a bright, extended X-ray jet in the quasar RGB J1512+020A (z = 0.22). Chandra observations show the X-ray core and 13 arcsec (∼45 kpc projected) extended emission ...coincident with the radio jet. The jet stands out as one of brightest X-ray jets (LX ∼ 7 × 1043 erg s−1) at low redshift (z < 0.5) discovered so far, with remarkably large X-ray to radio luminosity ratios (LX/Lr up to ∼50). We identified four main components, two unresolved knots and two extended structures, one being the jet brightest feature (JBF). All jet features are also detected in ALMA archival observations. The radio, sub-mm to X-ray spectra of the two knots can be modelled with a single synchrotron component. For the two resolved structures, the ALMA data unveil a turnover of the low-energy continuum at ∼460 GHz. External Comptonization of cosmic microwave background photons can account for the observed X-ray emission if the jet speed remains highly relativistic, with bulk motion Γbulk > 15, up to tens of kiloparsec from the core. However, the comparison with the spectral energy distribution of similar X-ray detected jets shows that the alternative hypothesis of synchrotron emission from an additional population of ultra-high-energy electrons is also possible. We report a tentative (≳2σ) optical detection of the JBF in images of the Dark Energy Camera Legacy Survey. If confirmed, the optical emission should be either the low-energy tail of the radiative component responsible for the X-ray emission or a third, separate component.
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