42 research outputs found
Fast jet proper motion discovered in a blazar at z = 4.72
High-resolution observations of high-redshift () radio quasars offer a
unique insight into jet kinematics at early cosmological epochs, as well as
constraints on cosmological model parameters. Due to the general weakness of
extremely distant objects and the apparently slow structural changes caused by
cosmological time dilation, only a couple of high-redshift quasars have been
studied with parsec-scale resolutions, and with limited number of observing
epochs. Here we report on very long baseline interferometry (VLBI) observations
of a high-redshift blazar J1430+4204 () in the 8 GHz frequency band at
five different epochs spanning 22 years. The source shows a compact core--jet
structure with two jet components being identified within 3 milli-arcsecond
(mas) scale. The long time span and multiple-epoch data allow for the kinematic
studies of the jet components. That results in a jet proper motion of = 0.0170.002~mas\,yr and =0.1560.015~mas\,yr, respectively. For the fastest-moving
outer jet component J2, the corresponding apparent transverse speed is . The inferred bulk jet Lorentz factor and
viewing angle indicate highly
relativistic beaming. The Lorentz factor and apparent proper motion are the
highest measured to date among the jetted radio sources, while the jet
kinematics is still consistent with the cosmological interpretation of quasar
redshifts.Comment: Science Bulletin, submitte
A method for checking high-redshift identification of radio AGNs
In large-scale optical spectroscopic surveys, there are many objects found to
have multiple redshift measurements due to the weakness of their emission lines
and the different automatic identification algorithms used. These include some
suspicious high-redshift (z >= 5) active galactic nuclei (AGNs). Here we
present a method for inspecting the high-redshift identification of such
sources provided that they are radio-loud and have very long baseline
interferometry (VLBI) imaging observations of their milli-arcsec (mas) scale
jet structure available at multiple epochs. The method is based on the
determination of jet component proper motions, and the fact that the
combination of jet physics (the observed maximal values of the bulk Lorentz
factor) and cosmology (the time dilation of observed phenomena in the early
Universe) constrain the possible values of apparent proper motions. As an
example, we present the case of the quasar J2346+0705 that was reported with
two different redshifts, and , in the
literature. We measured the apparent proper motions () of three components
identified in its radio jet by utilizing VLBI data taken from 2014 to 2018. We
obtained mas yr, mas yr, and mas yr. The
maximal proper motion is converted to an apparent transverse speed of
. if the source is at redshift 5.063. This
value exceeds the blazar jet speeds known to date. This and other arguments
suggest that J2346+0705 is hosted by a low-redshift galaxy. Our method may be
applicable for other high-redshift AGN candidates lacking unambiguous
spectroscopic redshift determination or having photometric redshift estimates
only, but showing prominent radio jets allowing for VLBI measurements of fast
jet proper motions.Comment: accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Jets in AGN at extremely high redshifts
A brief review of VLBI structures in extremely high-redshift AGN
(revised/edited).Comment: To appear in the Proceedings of the IAU Symposium No. 313:
Extragalactic jets from every angle, Galapagos, Ecuador, 15-19 September
2014, F. Massaro, C. C. Cheung, E. Lopez, and A. Siemiginowska (Eds.),
Cambridge University Pres
VLBI observations of a flared optical quasar CGRaBS J0809+5341
A bright optical flare was detected in the high-redshift () quasar
CGRaBS J0809+5341 on 2014 April 13. The absolute magnitude of the object
reached during the flare, making it the brightest one (in flaring
stage) among all known quasars so far. The 15 GHz flux density of CGRaBS
J0809+5341 monitored in the period from 2008 to 2016 also reached its peak at
the same time. To reveal any structural change possibly associated with the
flare in the innermost radio structure of the quasar, we conducted a pilot very
long baseline interferometry (VLBI) observation of CGRaBS J0809+5341 using the
European VLBI Network (EVN) at 5 GHz on 2014 November 18, about seven months
after the prominent optical flare. Three epochs of follow-up KaVA (Korean VLBI
Network and VLBI Exploration of Radio Astrometry Array) observations were
carried out at 22 and 43 GHz frequencies from 2015 February 25 to June 4, with
the intention of exploring a possibly emerging new radio jet component
associated with the optical flare. However, these high-resolution VLBI
observations revealed only the milliarcsecond-scale compact "core" that was
known in the quasar from earlier VLBI images, and showed no sign of any
extended jet structure. Neither the size, nor the flux density of the "core"
changed considerably after the flare according to our VLBI monitoring. The
results suggest that any putative radio ejecta associated with the major
optical and radio flare could not yet be separated from the "core" component,
or the newly-born jet was short-lived.Comment: 4 figures, 2 tables, accepted for publication in PAS
Multiple supermassive black hole systems: SKA's future leading role
Galaxies and supermassive black holes (SMBHs) are believed to evolve through
a process of hierarchical merging and accretion. Through this paradigm,
multiple SMBH systems are expected to be relatively common in the Universe.
However, to date there are poor observational constraints on multiple SMBHs
systems with separations comparable to a SMBH gravitational sphere of influence
(<< 1 kpc). In this chapter, we discuss how deep continuum observations with
the SKA will make leading contributions towards understanding how multiple
black hole systems impact galaxy evolution. In addition, these observations
will provide constraints on and an understanding of stochastic gravitational
wave background detections in the pulsar timing array sensitivity band (nanoHz
-microHz). We also discuss how targets for pointed gravitational wave
experiments (that cannot be resolved by VLBI) could potentially be found using
the large-scale radio-jet morphology, which can be modulated by the presence of
a close-pair binary SMBH system. The combination of direct imaging at high
angular resolution; low-surface brightness radio-jet tracers; and pulsar timing
arrays will allow the SKA to trace black hole binary evolution from separations
of a galaxy virial radius down to the sub-parsec level. This large dynamic
range in binary SMBH separation will ensure that the SKA plays a leading role
in this observational frontier.Comment: 11 pages, 4 figures. To be published in the proceedings of "Advancing
Astrophysics with the Square Kilometre Array", PoS(AASKA14)151, in pres
Thinning of the Motor-Cingulate-Insular Cortices in Siblings Concordant for Tourette Syndrome
Fraternal twin studies on normal subjects have demonstrated low heritability (intra-class correlation coefficient) estimates for frontal brain regions (r=0.43). Here we aimed to investigate the relatedness/similarity estimates of the frontal brain regions in fraternal subjects concordant for Tourette syndrome (TS). We sought to identify regional brain similarities between siblings concordant for TS as an exploratory step towards the identification of potential brain structures involved in the TS phenotype. The identified brain structures may then serve in subsequent molecular genetic and linkage studies. In addition, we regressed cortical thickness and TS clinical severity scores to assess the relation between TS clinical symptoms and cortical structures. Sixteen sibling pairs concordant for TS were scanned using a 1.5T magnetic resonance imaging scanner (age range 10-25, mean 17.19±4.1). Brain morphology was assessed using the fully automated Civet pipeline at the Montreal Neurological Institute. TS was assessed using the Children's Yale-Brown Obsessive Compulsive Scale (CY-BOCS), Yale Global Tic Severity Scale (YGTSS) and the Goetz Tic Scale. We report high relatedness/similarity estimates for fraternal siblings concordant for TS (r=0.86-0.60) in the middle frontal-motor/cingulate/insular cortices. Regression analysis revealed significant negative correlations in the right insula with the YGTSS (r=−0.41, F=6.09, P<0.02) and the left cingulated cortex with the (CY-BOCS) (r=−0.35, F=4.30, P<0.05). Since previous findings have concluded that normal fraternal siblings are less alike in frontal cortices, the present findings may be attributed to TS. We speculate that the high ICC between siblings and the negative correlation between TS symptoms severity and cortical thickness measurements are related to the disturbances in the maturation of the motor-cingulate-insular cortical neural system that mediate self-regulatory processes. Such delayed maturation may consequently contribute to the development of TS by releasing motor and vocal tics from regulatory control. These findings may have important genetic implication
HESS J1943+213: a non-classical high-frequency-peaked BL Lac object
HESS J1943+213 is an unidentified TeV source that is likely a
high-frequency-peaked BL Lac (HBL) object but also compatible with a pulsar
wind nebula (PWN) nature. Each of these enormously different astronomical
interpretations is supported by some of the observed unusual characteristics.
In order to finally classify and understand this object we took a three-pronged
approach, through time-domain, high angular resolution, and multi-frequency
radio studies. First, our deep time-domain observations with the Arecibo
telescope failed to uncover the putative pulsar powering the proposed PWN. We
conclude with ~70% certainty that HESS J1943+213 does not host a pulsar.
Second, long-baseline interferometry of the source with e-MERLIN at 1.5- and 5-
GHz, shows only a core, a point source at ~ 1 - 100 milli-arcsecond resolution.
Its 2013 flux density is about one-third lower than detected in 2011
observations with similar resolution. This radio variability of the core
strengthens the HBL object hypothesis. More evidence against the PWN scenario
comes, third, from the radio spectrum we compiled. The extended structure
follows a power-law behavior with spectral index alpha = -0.54 +- 0.04 while
the core component is flat spectrum (alpha = -0.03 +- 0.03). In contrast, the
radio synchrotron emission of PWNe predicts a single power-law distribution.
Overall we rule out the PWN hypothesis and conclude the source is a BL Lac
object. The consistently high fraction (70%) of the flux density from the
extended structure then leads us to conclude that HESS J1943+213 must be a
non-classical HBL object.Comment: 8 pages, 4 figures, ApJ submitte
Radio Jet Proper-motion Analysis of Nine Distant Quasars above Redshift 3.5
Up to now, jet kinematic studies of radio quasars have barely reached beyond
the redshift range at . This significantly limits our knowledge of
high-redshift jets, which can provide key information for understanding the jet
nature and the growth of the black holes in the early Universe. In this paper,
we selected 9 radio-loud quasars at which display milliarcsec-scale jet
morphology. We provided evidence on the source nature by presenting
high-resolution very long baseline interferometry (VLBI) images of the sample
at 8.4~GHz frequency and making spectral index maps. We also consider Gaia
optical positions that are available for 7 out of the 9 quasars, for a better
identification of the jet components within the radio structures. We find that
6 sources can be classified as core--jet blazars. The remaining 3 objects are
more likely young, jetted radio sources, compact symmetric objects. By
including multi-epoch archival VLBI data, we also obtained jet component proper
motions of the sample and estimated the jet kinematic and geometric parameters
(Doppler factor, Lorentz factor, viewing angle). Our results show that at
, the jet apparent transverse speeds do not exceed 20 times the speed of
light (). This is consistent with earlier high-redshift quasar measurements
in the literature and the tendency derived from low-redshift blazars that fast
jet speeds () only occur at low redshifts. The results from this paper
contribute to the understanding of the cosmological evolution of radio AGN.Comment: 28 pages, 4 figures, 8 tables. To appear in Ap
Confirming the 115.5-day periodicity in the X-ray light curve of ULX NGC 5408 X-1
The Swift/XRT light curve of the ultraluminous X-ray (ULX) source NGC 5408
X-1 was re-analyzed with two new numerical approaches, Weighted Wavelet
-transform (WWZ) and CLEANest, that are different from previous studies.
Both techniques detected a prominent periodicity with a time scale of
days, in excellent agreement with the detection of the same
periodicity first reported by Strohmayer (2009). Monte Carlo simulation was
employed to test the statisiticak confidence of the 115.5-day periodicity,
yielding a statistical significance of (or ). The robust
detection of the 115.5-day quasi-periodic oscillations (QPOs), if it is due to
the orbital motion of the binary, would infer a mass of a few thousand
for the central black hole, implying an intermediate-mass black hole
in NGC 5408 X-1.Comment: 6 pages, 2 figures, submitted to Research in Astronomy and
Astrophysics (RAA