115 research outputs found
Variability and spectral energy distributions of low-luminosity active galactic nuclei: a simultaneous X-ray/UV look with Swift
We have observed four low-luminosity active galactic nuclei classified as
Type 1 LINERs with the X-ray Telescope (XRT) and the UltraViolet-Optical
Telescope (UVOT) onboard Swift, in an attempt to clarify the main powering
mechanism of this class of nearby sources. Among our targets, we detect X-ray
variability in NGC 3998 for the first time. The light curves of this object
reveal variations of up to 30% amplitude in half a day, with no significant
spectral variability on this time scale. We also observe a decrease of ~30%
over 9 days, with significant spectral softening. Moreover, the X-ray flux is
~40% lower than observed in previous years. Variability is detected in M 81 as
well, at levels comparable to those reported previously: a flux increase in the
hard X-rays (1-10 keV) of 30% in ~3 hours and variations by up to a factor of 2
within a few years. This X-ray behaviour is similar to that of
higher-luminosity, Seyfert-type, objects. Using previous
high-angular-resolution imaging data from the Hubble Space Telescope (HST), we
evaluate the diffuse UV emission due to the host galaxy and isolate the nuclear
flux in our UVOT observations. All sources are detected in the UV band, at
levels similar to those of the previous observations with HST. The XRT (0.2-10
keV) spectra are well described by single power-laws and the UV-to-X-ray flux
ratios are again consistent with those of Seyferts and radio-loud AGNs of
higher luminosity. The similarity in X-ray variability and broad-band energy
distributions suggests the presence of similar accretion and radiation
processes in low- and high-luminosity AGNs.Comment: 12 pages, 6 figures, in press in MNRA
The host galaxy/AGN connection in nearby early-type galaxies. A new view of the origin of the radio-quiet/radio-loud dichotomy?
[ABRIDGED] This is the third in a series of three papers exploring the
connection between the multiwavelength properties of AGN in nearby early-type
galaxies and the characteristics of their hosts. We selected 116 AGN candidates
requiring a radio flux of 1 mJy. We classified the objects with HST images into
``core'' and ``power-law'' galaxies, on the basis of the nuclear slope of their
brightness profiles. We used HST and Chandra data to isolate their nuclear
emission to study the multiwavelength behaviour of their nuclei. The properties
of the nuclei hosted by the 29 core galaxies were presented in Paper II. Core
galaxies invariably host a radio-loud nucleus, with a median radio-loudness of
Log R = 3.6 and an X-ray based radio loudness parameter of Log R,X = -1.3. Here
we discuss the properties of the nuclei of the 22 ``power-law'' galaxies. They
show a substantial excess of optical and X-ray emission with respect to core
galaxies at the same level of radio luminosity. Conversely, their
radio-loudness parameters, Log R ~ 1.6 and Log R,X ~ -3.3, are similar to those
measured in Seyfert galaxies. Thus the radio-loudness of AGN hosted by
early-type galaxies appears to be univocally related to the host's brightness
profile: radio-loud AGN are only hosted by core galaxies, while radio-quiet AGN
are found only in power-law galaxies. The brightness profile is determined by
the galaxy's evolution, through its merger history; our results suggest that
the same process sets the AGN flavour.Comment: Accepted for publication in A&
Hacia un enfoque transdisciplinario y de determinantes sociales más amplio para el estudio de la mortalidad infantil
Radio Sources in Low-Luminosity Active Galactic Nuclei.IV. Radio Luminosity Function, Importance of Jet Power, and Radio Properties of the Complete Palomar Sample
We present the completed results of a high resolution radio imaging survey of
all (~200) low-luminosity active galactic nuclei (LLAGNs) and AGNs in the
Palomar Spectroscopic Sample. The high incidences of pc-scale radio nuclei,
with T(brightness) >=10^7 K, and sub-parsec jets argue for accreting black
holes in >=50% of all LINERs and low-luminosity Seyferts; there is no evidence
against all LLAGNs being mini-AGNs. The radio luminosity function (RLF) of
Palomar Sample LLAGNs and AGNs extends three orders of magnitude below, and is
continuous with, that of `classical' AGNs. We find marginal evidence for a
low-power turnover in the RLF; nevertheless LLAGNs are responsible for a
significant fraction of present day mass accretion. Adopting the jet model of
Falcke & Biermann, we show that the accretion energy output in LLAGNs is
dominated by the energy in the observed jets rather than the radiated
bolometric luminosity. The Palomar LLAGNs and AGNs follow the same scaling
between jet power and narrow line region (NLR) luminosity as the pc to kpc jets
in powerful radio galaxies. Eddington ratios of <= 10^{-1} - 10^{-5} are
implied in jet models of the radio emission. We find evidence that, in analogy
to Galactic black hole candidates, LINERs are in a `low/hard' state (gas poor
nuclei, low Eddington ratio, ability to launch collimated jets) while
low-luminosity Seyferts are in a `high' state (gas rich nuclei, higher
Eddington ratio, less likely to launch collimated jets). The jets are
energetically more significant than supernovae in the LLAGN host galaxies, and
are potentially able to deposit sufficient energy into the innermost parsecs to
significantly slow the gas supply to the accretion disk.Comment: Results and content same as pervious submission; language and wording
updated for clarity. To appear in A&
BeppoSAX observations of LINER-2 galaxies
We present BeppoSAX observations of 6 ``type-2'' LINER and ``transition''
galaxies (NGC3379, NGC3627, NGC4125, NGC4374, NGC5195 and NGC5879)from the
Ho et al. (1997) spectroscopic sample of nearby galaxies. All objects are
detected in the 2-10 keV band, having luminosities in the range L(2-10 keV)
~ 1x10^{39}- 1x10^{40} erg s-1. The PDS upper limits above 10 keV place
constraints on the presence of a heavily obscured AGN in the case of NGC3379
and NGC4125. No significant variability is detected in any of the objects.
The spectra are described in most cases by a simple power-law model with a
spectral slope of 1.7-2.5 while there is evidence neither for a significant
absorption above the Galactic nor for an FeK emission line. Therefore, based on
the spectral properties alone, it is difficult to differentiate between a
low-luminosity AGN or a star-forming galaxy scenario.
However, imaging observations of NGC3627 and NGC5195 with
Chandra ACIS-S reveal very weak nuclear sources while most of the X-ray flux
originates either in off-nuclear point sources or in diffuse emission. The
above clearly argue in favour of a star-forming origin for the bulk of the
X-ray emission, at least in the above two sources.Comment: 10 pages, to appear in A&
On Distant Speech Recognition for Home Automation
The official version of this draft is available at Springer via http://dx.doi.org/10.1007/978-3-319-16226-3_7International audienceIn the framework of Ambient Assisted Living, home automation may be a solution for helping elderly people living alone at home. This study is part of the Sweet-Home project which aims at developing a new home automation system based on voice command to improve support and well-being of people in loss of autonomy. The goal of the study is vocal order recognition with a focus on two aspects: distance speech recognition and sentence spotting. Several ASR techniques were evaluated on a realistic corpus acquired in a 4-room flat equipped with microphones set in the ceiling. This distant speech French corpus was recorded with 21 speakers who acted scenarios of activities of daily living. Techniques acting at the decoding stage, such as our novel approach called Driven Decoding Algorithm (DDA), gave better speech recognition results than the baseline and other approaches. This solution which uses the two best SNR channels and a priori knowledge (voice commands and distress sentences) has demonstrated an increase in recognition rate without introducing false alarms
Measuring supermassive black holes with gas kinematics: the active S0 galaxy NGC 3998
We present results from a kinematical study of the gas in the nucleus of the
active S0 galaxy NGC 3998 obtained from archival HST/STIS long-slit spectra. We
analyzed the emission lines profiles and derived the map of the gas velocity
field. The observed velocity curves are consistent with gas in regular rotation
around the galaxy's center. By modeling the surface brightness distribution and
rotation curve of the H_alfa emission line we found that the observed
kinematics of the circumnuclear gas can be accurately reproduced by adding to
the stellar mass component a compact dark mass (black hole) of M_bh =
2.7(-2.0,+2.4) 10**8 M_sun (uncertainties at a 2 sigma level); the radius of
its sphere of influence (R_sph ~ 0".16) is well resolved at the HST resolution.
The BH mass estimate in NGC 3998 is in good agreement with both the M_bh vs.
M_bul (with an upward scatter by a factor of ~2) and M_bh vs. sigma
correlations (with a downward scatter by a factor of ~3-7, depending on the
form adopted for the dependence of M_bh on sigma). Although NGC 3998 cannot be
considered as an outlier, its location with respect to the M_bh-sigma relation
conforms with the trend suggesting the presence of a connection between the
``residuals'' from the M_bh-sigma correlation and the galaxy's effective
radius. In fact, NGC 3998 has one of the smallest values of R_e among the
galaxies with measured M_bh (0.85 kpc) and it shows a negative residual. This
suggests that a combination of both sigma and R_e is necessary to drive the
correlations between M_bh and other bulge properties, an indication for the
presence of a black holes ``fundamental plane''.Comment: Accepted for publication in A&
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