837 research outputs found
A candidate supermassive binary black hole system in the brightest cluster galaxy of RBS 797
The radio source at the center of the cool core galaxy cluster RBS 797
(z=0.35) is known to exhibit a misalignment of its radio jets and lobes
observed at different VLA-scale, with the innermost kpc-scale jets being almost
orthogonal to the radio emission which extends for tens of kpc filling the
X-ray cavities. Gitti et al. suggested that this peculiar radio morphology may
indicate a recurrent activity of the central radio source, where the jet
orientation is changing between the different outbursts due to the effects of
supermassive binary black holes (SMBBHs). We aim at unveiling the nuclear radio
properties of the brightest cluster galaxy (BCG) in RBS 797 and at
investigating the presence of a SMBBH system in its center. We have performed
new high-resolution observations at 5 GHz with the European VLBI Network (EVN),
reaching an angular resolution of 9x5 mas^2 and a sensitivity of 36
microJy/beam. We report the EVN detection of two compact components in the BCG
of RBS 797, with a projected separation of ~77 pc. We can envisage two possible
scenarios: the two components are two different nuclei in a close binary
system, or they are the core and a knot of its jet. Both interpretations are
consistent with the presence of SMBBHs. Our re-analysis of VLA archival data
seems to favor the first scenario, as we detect two pairs of radio jets
misaligned by ~90 degrees on the same kpc scale emanating from the central
radio core. If the two outbursts are almost contemporaneous, this is clear
evidence of the presence of two active SMBHs, whose radio nuclei are unresolved
at VLA resolution. The nature of the double source detected by our EVN
observations in the BCG of RBS 797 can be established only by future sensitive,
multi-frequency VLBI observations. If confirmed, RBS 797 would be the first
SMBBH system observed at medium-high redshift at VLBI resolution. (abridged)Comment: 4 pages, 2 figures, A&A Letter in pres
A Chandra Snapshot Survey for 3C Radio Galaxies with redshifts between 0.3 and 0.5
This paper contains an analysis of short Chandra observations of 19 3C
sources with redshifts between 0.3 and 0.5 not previously observed in the
X-rays. This sample is part of a project to obtain Chandra data for all of the
extragalactic sources in the 3C catalogue. Nuclear X-ray intensities as well as
any X-ray emission associated with radio jet knots, hotspots or lobes have been
measured in 3 energy bands: soft, medium and hard. Standard X-ray spectral
analysis for the 4 brightest nuclei has been also performed. X-ray emission was
detected for all the nuclei of the radio sources in the current sample with the
exception of 3C 435A. There is one compact steep spectrum (CSS) source while
all the others are FRII radio galaxies. X-ray emission from two galaxy clusters
(3C 19 and 3C 320); from 6 hotspots in 4 radio galaxies (3C 16, 3C 19, 3C
268.2, 3C 313); and extended X-ray emission on kpc scales in 3C 187 and 3C 313,
has been detected.Comment: 33 pages, 22 figures, 7 tables, accepted for publication on the ApJ
Supplement Series. arXiv admin note: text overlap with arXiv:1210.602
A BMA Analysis to Assess the Urbanization and Climate Change Impact on Urban Watershed Runoff
Abstract A reliable planning of urban drainage systems aimed at the mitigation of flooding, should take into account the possible change over time of impervious cover in the urban watershed and of the climate features. The present study proposes a methodology to analyze the changing in runoff response for a urban watershed accounting several plausible future states of new urbanization and climate. To this aim, several models simulating the evolution scenario of impervious watershed area and of climate change were adopted. However, it is known that an evolution scenario represents only one of all possible occurrence and it is not necessary the true future state, therefore it is needed to find the plausible forecast of the future state by taking into account and combining several possible evolution models. According to this aim, in the present study the Bayesian Model Averaging (BMA) approach was applied to several evolution models for climate variables. The Bayesian Model Averaging is a statistic multi-model method that computes a weighted average of the series of available competing models forecast overcoming the problem of arbitrary selecting of single best model and, consequently, the relative requirements of uncertainty analysis. The weighted average is the probability density function (pdf) of the quantity to be forecasted, while the weights correspond to the comparative performance of the models over training period of observation. After the application of BMA, for a given probability, the impervious area extension and the design rainfall event were identified and used as input data for a numerical model based on the SWMM software which was adopted to simulate the behavior of the urban drainage-system adopted as case study. Particularly, the proposed procedure was applied with reference to the Sicilian climate regions (southern Italy)
Exploring the bulk of the BL Lac object population:1. parsec-scale radio structures
Context. The advent of Fermi is changing our understanding on the radio and
gamma-ray emission in Active Galactic Nuclei. Contrary to pre-Fermi ideas, BL
Lac objects are found to be the most abundant emitters in the gamma-ray band.
However, since they are relatively weak radio sources, most of their
parsec-scale structure and their multi-frequency properties are poorly
understood and/or have not been investigated in a systematically fashion. Aims.
Our main goal is to analyze the radio and gamma-ray emission properties of a
sample of 42 BL Lacs selected, for the first time in the literature, with no
constraint on their radio and gamma-ray flux densities/emission. Methods.
Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the
whole sample, we present here fundamental parameters such as radio flux
densities, spectral index information, and parsec-scale structure. Moreover, we
search for gamma-ray counterparts using data reported in the Second Catalog of
Fermi Gamma-ray sources. Results. Parsec-scale radio emission is observed in
the majority of the sources at both frequencies. Gamma-ray counterparts are
found for 14/42 sources. Conclusions. The comparison between our results in
radio and gamma-ray bands points out the presence of a large number of faint BL
Lacs showing "non classical" properties such as low source compactness, core
dominance, no gamma-ray emission and steep radio spectral indexes. A deeper
multiwavelength analysis will be needed.Comment: 19 pages, 6 figures, 6 tables, accepted for publication in A&
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