Abstract
The third iteration of the International Celestial Reference Frame (ICRF3) is made up of 4536 quasars observed at
S/X
bands using very-long-baseline interferometry. These sources are ...high-redshift quasars, typically between 1 <
z
< 2, that are believed to host active galactic nuclei at their centers. The position of compact radio sources can be determined better than sources with large amounts of extended radio structure. Here we report information on a series of 20 observations from 2017 January through December 2017 that were designed for precise astrometry and to monitor the structure of sources included in the ICRF3. We targeted 3627 sources over the one year campaign and found the median flux density of 2697 detected sources at
S
band is 0.13 Jy, and the median flux density of 3209 sources detected at
X
band is 0.09 Jy. We find that 70% of detected sources in our campaign are considered compact at
X
band and ideal for use in the ICRF and 89% of the 2615 sources detected at both frequencies have a flat spectral index,
α
> 0.5
Abstract
We present results from the Very Long Baseline Array multifrequency (1.6, 4.4, 8.6, and 22 GHz), high-sensitivity (∼25
μ
Jy beam
−1
), subparsec-scale (<1 pc) observations and spectral ...energy distributions for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard-X-ray (14–195 keV) luminosities above 10
42
erg s
−1
, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the
C
(4.4 GHz) and
X
(8.6 GHz) bands, 75% in the
L
band (1.6 GHz), and 50% in the
K
band (22 GHz). Most sources showed compact, resolved/slightly resolved, central subparsec-scale radio morphology, except for a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with the nearby interstellar medium. The spectral slopes are mostly gigahertz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that at the subparsec scale, the gigahertz-peaked spectra belong to the low-accreting, radio-loud AGNs, with a tendency to produce strong outflows, possibly small-scale jets, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from the central regions of highly accreting AGNs, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.
We present the first results from the Fundamental Reference active galactic nucleus (AGN) Monitoring Experiment, an observational campaign dedicated to understanding the physical processes that ...affect the apparent positions and morphologies of AGNs. In this work, we obtained simultaneous Swift X-ray Telescope and Very Long Baseline Array (VLBA) radio observations for a snapshot campaign of 25 local AGNs that form a volume-complete sample with hard X-ray (14-195 keV) luminosities above 1042 erg s−1, out to a distance of 40 Mpc. Despite achieving an observation depth of ∼20 Jy, we find that 16 of 25 AGNs in our sample are not detected with the VLBA on milliarcsecond (subparsec) scales, and the corresponding core radio luminosity upper limits are systematically below predictions from the Fundamental Plane of black hole activity. Using archival Jansky Very Large Array (VLA) radio measurements, our sample jumps back onto the Fundamental Plane, suggesting that extended radio emission is responsible for the apparent correlation between radio emission, X-ray emission, and black hole mass. We suggest that this discrepancy is likely due to extranuclear radio emission produced via interactions between the AGN and host environment. We compare VLBA observations of AGNs to VLA observations of nearby Galactic black holes, and we find a mass-independent correlation between radio and X-ray luminosities of black holes of / ∼10−6, in line with predictions for coronal emission, but allowing for the possibility of truly radio-silent AGNs.
Abstract
Using simultaneous Very Long Baseline Array and Neil Gehrels Swift Observatory X-ray Telescope observations of the active galactic nucleus (AGN) in NGC 2992 over a six-month observing ...campaign, we observed a large drop in core 5 cm radio luminosity, by a factor of >3, in tandem with a factor of >5 increase in 2–10 keV X-ray luminosity. While NGC 2992 has long been an important object for studies of X-ray variability, our study is the first simultaneous X-ray and radio variability campaign for this object. We observe that the X-ray spectral index does not change over the course of the flare, consistent with a change in the bulk amount of Comptonizing plasma, potentially due to a magnetic reconnection event in the accretion disk. The drop in apparent radio luminosity can be explained by a change in free–free absorption, which we calculate to correspond to an ionized region with a physical extent and electron density consistent with the broad-line region (BLR). Our results are consistent with magnetic reconnection events in the dynamic accretion disk creating outbursts of ionizing material, increasing Compton up-scattering of UV accretion disk photons and feeding material into the BLR. These findings present an important physical picture for the dynamical relationship between X-ray and radio emission in AGNs.
II ZWICKY 23 AND FAMILY: A GROUP IN INTERACTION Wehner, Elizabeth M. H.; Gallagher III, John S.; Cigan, Phillip J. ...
The Astronomical journal,
09/2016, Volume:
152, Issue:
3
Journal Article
Peer reviewed
Open access
ABSTRACT II Zw 23 (UGC 3179) is a luminous (MB ∼ −21) nearby compact narrow emission line starburst galaxy with blue optical colors and strong emission lines. We present a photometric and ...morphological study of II Zw 23 and its interacting companion, KPG103a, using data obtained with the WIYN 3.5 m telescope in combination with a WFPC2 image from the Hubble Space Telescope archives. II Zw 23 has a highly disturbed outer structure with long trails of debris that may be contributing material toward the production of tidal dwarfs. Its central regions appear disky, a structure that is consistent with the overall rotation pattern observed in the H velocity field measured from Densepak observations obtained with WIYN. We find additional evidence for interaction in this system, including the discovery of a new tidal loop extending from an associated dwarf galaxy, which appears to be in the process of disrupting along its orbit. We also present H equivalent widths and discuss the relative star formation rates across this interacting system.
We present results from the Very Long Baseline Array (VLBA) multi-frequency (1.6, 4.4, 8.6, 22 GHz), high-sensitivity (~25 microJy beam^-1), sub-parsec scale (<1 pc) observations and Spectral Energy ...Distributions (SEDs) for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard X-ray (14-195 keV) luminosities above 10^42 erg s^-1, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6 GHz) bands, 75% in the L band(1.6 GHz), and 50% in the K band (22 GHz). Most sources showed compact, resolved/slightly resolved, central sub-parsec scale radio morphology, except a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with nearby ISM. The spectral slopes are mostly GHz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that in the sub-parsec scale, the GHz-peaked spectra belong to the low-accreting, radio-loud AGNs with a tendency to produce strong outflows, possibly small-scale jet, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from highly-accreting AGNs' central region, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.
The third iteration of the International Celestial Reference Frame (ICRF3) is made up of 4536 quasars observed at S/X bands using Very Long baseline Interferometry (VLBI). These sources are high ...redshift quasars, typically between \(1<z<2\), that are believed to host active galactic nuclei (AGN) at their centers. The position of compact radio sources can be determined better than sources with large amounts of extended radio structure. Here we report information on a series of 20 observations from January 2017 through December 2017 which were designed for precise astrometry and to monitor the structure of sources included in the ICRF3. We targeted 3627 sources over the one year campaign and found the median flux density of 2697 detected sources at S-band is 0.13 Jy, and the flux density of 3209 sources detected at X-band is 0.09 Jy. We find that \(70\%\) of detected sources in our campaign are considered compact at X-band and ideal for use in the ICRF and \(89\%\) of the 2615 sources detected at both frequencies have a flat spectral index, \(\alpha>0.5\)
We present follow-up results from the first Fundamental Reference AGN Monitoring Experiment (FRAMEx) X-ray/radio snapshot program of a volume-complete sample of local hard X-ray-selected active ...galactic nuclei (AGNs). Here, we added 9 new sources to our previous volume-complete snapshot campaign, two of which are detected in the 6 cm Very Long Baseline Array (VLBA) observations. We also obtained deeper VLBA observations for a sample of 9 AGNs not detected by our previous snapshot campaign. We recovered 3 sources with approximately twice the observing sensitivity. In contrast with lower angular resolution Very Large Array (VLA) studies, the majority of our sources continue to be undetected with the VLBA. The sub-parsec radio (6 cm) and X-ray (2-10 keV) emission show no significant correlation, with L_R/L_X ranging from 10^-8 to 10^-4, and the majority of our sample lies well below the fiducial 10^-5 relationship for coronal synchrotron emission. Additionally, our sources are not aligned with any of the proposed "fundamental" planes of black hole activity, which purport to unify black hole accretion in the M_BH-L_X-L_R parameter space. The new detections in our deeper observations suggest that the radio emission may be produced by the synchrotron radiation of particles accelerated in low luminosity outflows. Non-detections may be a result of synchrotron self-absorption at 6 cm in the radio core, similar to what has been observed in X-ray binaries (XRBs) transitioning from the radiatively inefficient state to a radiatively efficient state.
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