We have analyzed the deep Chandra observation (∼155 ks) of the Compton thick active galactic nucleus ESO 428-G014, to study in detail the morphology of the diffuse X-ray emission in the inner ∼500 pc ...radius region. Comparing different X-ray energy bands we find localized differences in the absorbing column and in the emission processes. Collisional ionization may be prevalent in the area of most intense optical line emission (H and O iii). There is a good correspondence between optical line, radio continuum, and soft (<3 keV) X-ray features, consistent with simulations of jet-molecular disk interaction. At all energies >3 keV, the extended emission in the central 1 5 (170 pc) radius circumnuclear region amounts to ∼70%-30% of the contribution of a point source in that area (or ∼40%-25% of the total counts in the region). Within a 5″ radius, the contribution from extended emission overcomes that from a nuclear point source in the 3-4 keV band. This extended emission suggests scattering of nuclear photons by dense molecular clouds in the inner galactic disk of ESO 428-G014. Its presence may adversely bias the torus modeling of spectra from X-ray telescopes with inferior angular resolution compared to that of Chandra, such as NuSTAR and XMM-Newton.
We present Chandra and Very Large Array observations of GW170817 at ∼521-743 days post-merger, and a homogeneous analysis of the entire Chandra data set. We find that the late-time nonthermal ...emission follows the expected evolution of an off-axis relativistic jet, with a steep temporal decay F ∝ t − 1.95 0.15 and power-law spectrum F ∝ − 0.575 0.007 . We present a new method to constrain the merger environment density based on diffuse X-ray emission from hot plasma in the host galaxy and find n ≤ 9.6 × 10 − 3 cm − 3 . This measurement is independent from inferences based on jet afterglow modeling and allows us to partially solve for model degeneracies. The updated best-fitting model parameters with this density constraint are a fireball kinetic energy E 0 = 1.5 − 1.1 + 3.6 × 10 49 erg ( E iso = 2.1 − 1.5 + 6.4 × 10 52 erg ) and jet opening angle θ 0 = 5.9 − 0.7 + 1.0 deg with characteristic Lorentz factor Γ j = 163 − 43 + 23 , expanding in a low-density medium with n 0 = 2.5 − 1.9 + 4.1 × 10 − 3 cm − 3 and viewed θ obs = 30.4 − 3.4 + 4.0 deg off-axis. The synchrotron emission originates from a power-law distribution of electrons with index p = 2.15 − 0.02 + 0.01 . The shock microphysics parameters are constrained to ϵ e = 0.18 − 0.13 + 0.30 and ϵ B = 2.3 − 2.2 + 16.0 × 10 − 3 . Furthermore, we investigate the presence of X-ray flares and find no statistically significant evidence of ≥2.5 of temporal variability at any time. Finally, we use our observations to constrain the properties of synchrotron emission from the deceleration of the fastest kilonova ejecta with energy E k KN ∝ ( Γ β ) − into the environment, finding that shallow stratification indexes ≤ 6 are disfavored. Future radio and X-ray observations will refine our inferences on the fastest kilonova ejecta properties.
Abstract
Recent deep Chandra observations of nearby Compton-thick (CT) active galactic nuclei (AGNs) have produced surprising results, uncovering extended emission not only in soft X-rays but also in ...hard emission (>3 keV), challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines are associated with the torus in the standard picture of AGNs. In this work, we present an analysis of our deep (∼261 ks) X-ray Chandra ACIS-S observations of NGC 5728, a nearby (
z
= 0.00932) CT AGN. We find that the diffuse emission is more extended at lower energies, in the bicone direction out to ∼2 kpc radially, but also significantly extended in the direction of the cross-cone, out to ∼1.4 kpc. Our results suggest that the ratio of detected photons in the cross-cone to the bicone region is ∼16%, below 3 keV, decreasing to 5% for energies 3–6 keV. The nuclear spectrum suggests a low-photoionization phase mixed with a more ionized gas component, while the bicone and cross-cone spectra are dominated by a mix of photoionization and shocked gas emission. A mixture of thermal and photoionization models used to fit the spectra indicates the presence of complex gas interactions, consistent with previous observations of other CT AGNs (e.g., ESO 428-G014).
Abstract We present Chandra ACIS-S imaging spectroscopy results of the extended (1.″5–8″, 300–1600 pc) hard X-ray emission of NGC 5728, the host galaxy of a Compton-thick active galactic nucleus. We ...find spectrally and spatially resolved features in the Fe K α complex (5.0–7.5 keV) redward and blueward of the neutral Fe line at 6.4 keV in the extended narrow-line region bicone. A simple phenomenological fit of a power law plus Gaussians gives a significance of 5.4 σ and 3.7 σ for the red and blue wings, respectively. Fits to a suite of physically consistent models confirm a significance of ≥3 σ for the red wing. The significance of the blue wing may be diminished by the presence of rest-frame highly ionized Fe xxv and Fe xxvi lines (1.4 σ –3.7 σ range). A detailed investigation of the Chandra ACIS-S point-spread function and comparison with the observed morphology demonstrates that these red and blue wings are radially extended (∼5″, ∼1 kpc) along the optical bicone axis. If the wing emission is due solely to redshifted and blueshifted high-velocity neutral Fe K α , then the implied line-of-sight velocities are +/− ∼0.1 c , and their fluxes are consistent with being equal. A symmetric high-velocity outflow is then a viable explanation. This outflow has deprojected velocities ∼100 times larger than the outflows detected in optical spectroscopic studies, potentially dominating the kinetic feedback power.
Abstract
We report the analysis of the deep (∼270 ks) X-ray Chandra data of one of the most radio-loud, Seyfert 2 galaxies in the nearby universe (
z
= 0.01135), IC 5063. The alignment of the radio ...structure with the galactic disk and ionized bicone, enables us to study the effects of both radio jet and nuclear irradiation on the interstellar medium (ISM). The nuclear and bicone spectra suggest a low photoionization phase mixed with a more ionized or thermal gas component, while the cross-cone spectrum is dominated by shocked and collisionally ionized gas emission. The clumpy morphology of the soft (<3 keV) X-ray emission along the jet trails, and the large (≃2.4 kpc) filamentary structure perpendicular to the radio jets at softer energies (<1.5 keV), suggest a large contribution of the jet−ISM interaction to the circumnuclear gas emission. The hard X-ray continuum (>3 keV) and the Fe K
α
6.4 keV emission are both extended to kpc size along the bicone direction, suggesting an interaction of nuclear photons with dense clouds in the galaxy disk, as observed in other Compton Thick (CT) active nuclei. The northwest cone spectrum also exhibits an Fe
xxv
emission line, which appears spatially extended and spatially correlated with the most intense radio hot-spot, suggesting jet−ISM interaction.
We present a deep Chandra spectral and spatial study of the kpc-scale diffuse X-ray emission of the Compton-thick (CT) active galactic nucleus (AGN) ESO 428-G014. The entire spectrum is best fit with ...composite photoionization + thermal models. The diffuse emission is more extended at lower energies (<3 keV). The smaller extent of the hard continuum and Fe K profiles implies that the optically thicker clouds responsible for this scattering may be relatively more prevalent closer to the nucleus. These clouds must not prevent soft ionizing X-rays from the AGN escaping to larger radii, in order to have photoionized ISM at larger radii. This suggests that at smaller radii, there may be a larger population of molecular clouds to scatter the hard X-rays, as in the Milky Way. The diffuse emission is also significantly extended in the cross-cone direction, where the AGN emission would be mostly obscured by the torus in the standard AGN model. Our results suggest that the transmission of the obscuring region in the cross-cone direction is ∼10% of that in the cone direction. In the 0.3-1.5 keV band, the ratio of cross-cone to cone photons increases to ∼84%, suggesting an additional soft diffuse emission component disjoint from the AGN. This could be due to hot ISM trapped in the potential of the galaxy. The luminosity of this component, ∼5 × 1038 erg s−1, is roughly consistent with the thermal component suggested by the spectral fits in the 170-900 pc annulus.
Abstract
We present a detailed spectral and imaging analysis of the central 15″ radius (∼7.5 kpc) region of the merger galaxy NGC 6240 that makes use of all the available Chandra-ACIS data (0.3–3 keV ...effective exposure of ∼190 ks). This region shows extended X-ray structures with lower-energy counterparts imaged in CO, O
iii
, and H
α
line emission. We find both photoionized phases of possible nuclear excitation and thermal shock-excited emission in the different large-scale components: the northwest “loop” detected in H
α
, the region surrounding the two nuclei, the large outflow region to the northeast detected in O
iii
, and the southern X-ray extensions. The latter could be the ionization cone of the northern nucleus, with the N counterpart being obscured by the galaxy disk. The radial distribution of the X-ray surface brightness suggests a confined hot interstellar medium at
r
< 2.5 kpc, with a free-flowing wind at larger radii; if the confinement is magnetic, we estimate
B
-field values of ∼100
μ
G, similar to those measured in the halo of M82. The thermal gas of the extended halo at
kT
∼ 1 keV absorbs soft X-rays from the active galactic nucleus, but not the extreme ultraviolet radiation leading to a rapid increase in
F
O
III
/
F
X
beyond ∼3 kpc. The
α
-element to Fe abundance ratios of the thermal components in the different regions of the extended X-ray emission are generally compatible with Type II supernova yields, confirming the importance of active star formation in NGC 6240.
A recent Atacama Large Millimeter/submillimeter Array study of the Seyfert 2 active galactic nucleus (AGN) NGC 2110 by Rosario et al. has reported a remarkable lack of CO 2-1 emission from the ...circumnuclear region, where optical lines and H2 emission are observed, leading to the suggestion of excitation of the molecular clouds by the AGN. As interaction with X-ray photons could be the cause of this excitation, we have searched the archival Chandra data for corroborating evidence. We report the discovery of an extra-nuclear ∼1″ (∼170 pc) feature in the soft (<1.0 keV) Chandra data. This feature is elongated to the north of the nucleus and its shape matches well that of the optical lines and H2 emission in this region, which is devoid of CO 2-1 emission. The Chandra image completes the emerging picture of a multiphase circumnuclear medium excited by the X-rays from the AGN, with dense warm molecular clouds emitting in H2 but depleted of CO 2-1 line emission.
We report a clumpy elongated feature found with deep Chandra Advanced CCD Imaging Spectrometer high-resolution imaging of the Fe K line emission in the nuclear region of the Compton-thick active ...galactic nucleus galaxy NGC 5643. This feature extends for ∼65 pc north to south (N-S). No corresponding feature is seen in the 3.0-6.0 keV continuum. The Fe K feature is spatially consistent with the N-S elongation found in the CO(2-1) high-resolution imaging with the Atacama Large Millimeter/submillimeter Array, but slightly more extended than the rotating molecular disk of diameter 26 pc indicated by the kinematics of the CO(2-1) line. The Chandra detection of a corresponding north to south structure in the neutral Fe K line would argue for both CO and Fe K emission originating from the obscuring torus.
We present an analysis of the optical spectra available in the Sloan Digital Sky Survey data release nine (SDSS DR9) for the blazars listed in the ROMA-BZCAT and for the gamma -ray blazar candidates ...selected according to their IR colors. First, we adopt a statistical approach based on Monte Carlo simulations to find the optical counterparts of the blazars listed in the ROMA-BZCAT catalog. Then, we crossmatched the SDSS spectroscopic catalog with our selected samples of blazars and gamma -ray blazar candidates, searching for those with optical spectra available to classify our blazar-like sources and, whenever possible, to confirm their redshifts. Our main objectives are to determine the classification of uncertain blazars listed in the ROMA-BZCAT and to discover new gamma-ray blazars. For the ROMA-BZCAT sources, we investigated a sample of 84 blazars, confirming the classification for 20 of them and obtaining 18 new redshift estimates. For the gamma -ray blazars, indicated as potential counterparts of unassociated Fermi sources or with uncertain nature, we established the blazar-like nature of 8 out of the 27 sources analyzed and confirmed 14 classifications.
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