99 research outputs found
Unveiling the nature of the highly obscured AGN in NGC5643 with XMM-Newton
We present results from an XMM-Newton observation of the nearby Seyfert 2
galaxy NGC5643. The nucleus exhibits a very flat X-ray continuum above 2 keV,
together with a prominent K-alpha fluorescent iron line. This indicates heavy
obscuration. We measure an absorbing column density N_H in the range 6-10 x
10^{23} atoms/cm/cm, either directly covering the nuclear emission, or covering
its Compton-reflection. In the latter case, we might be observing a rather
unusual geometry for the absorber, whereby reflection from the inner far side
of a torus is in turn obscured by its near side outer atmosphere. The nuclear
emission might be then either covered by a Compton-thick absorber, or
undergoing a transient state of low activity. A second source (christened "X-1"
in this paper) at the outskirts of NGC5643 optical surface outshines the
nucleus in X-rays. If belonging to NGC5643, it is the third brightest (L_X ~ 4
x 10^{40} erg/s) known Ultra Luminous X-ray source. Comparison with past large
aperture spectra of NGC 5643 unveils dramatic X-ray spectral changes above 1
keV. We interpret them as due to variability of the active nucleus and of
source X-1 intrinsic X-ray powers by a factor >10 and 5, respectively.Comment: 11 LATEX pages, 12 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
Chandra and XMM-Newton observations of Tololo 0109-383
We present and discuss Chandra and XMM-Newton observations of the Seyfert 2
galaxy and Compton-thick absorbed source, Tololo~0109-383. The hard X-ray
emission (i.e. above 2 keV), is dominated by a spatially unresolved
reflection component, as already discovered by previous ASCA and BeppoSAX
observ ations. The soft X-ray emission is partly (15%) extended over
about 1 kpc. Below 2 keV, the spectrum is very steep and two emission lines,
probably due to recombination to He-like ions of oxygen and neon, are clearly
present. Combining X-rays and optical information taken from the literature, we
propose an overall scenario for the nuclear regions of this source.Comment: 6 pages, 6 figures, A&A 399, 51
Colchicine Does Not Reduce Abdominal Aortic Aneurysm Growth in a Mouse Model
Background and Aims. The nacht domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome is upregulated in human abdominal aortic aneurysm (AAA), but its pathogenic role is unclear. The aims of this study were firstly to examine whether the inflammasome was upregulated in a mouse model of AAA and secondly to test whether the inflammasome inhibitor colchicine limited AAA growth. Methods. AAA was induced in eight-week-old male C57BL6/J mice with topical application of elastase to the infrarenal aorta and oral 3-aminopropionitrile (E-BAPN). For aim one, inflammasome activation, abdominal aortic diameter, and rupture were compared between mice with AAA and sham controls. For aim two, 3 weeks after AAA induction, mice were randomly allocated to receive colchicine (n=28, 0.2 mg/kg/d) or vehicle control (n=29). The primary outcome was the rate of maximum aortic diameter increase measured by ultrasound over 13 weeks. Results. There was upregulation of NLRP3 markers interleukin- (IL-) 1 beta (median, IQR; 15.67, 7.11-22.60 pg/mg protein versus 6.87, 4.54-11.60 pg/mg protein, p=.048) and caspase-1 (109, 83-155 relative luminosity units (RLU) versus 45, 38-65 RLU, p <.001) in AAA samples compared to controls. Aortic diameter increase over 80 days (mean difference, MD, 4.3 mm, 95% CI 3.3, 5.3, p <.001) was significantly greater in mice in which aneurysms were induced compared to sham controls. Colchicine did not significantly limit aortic diameter increase over 80 days (MD -0.1 mm, 95% CI -1.1, 0.86, p=.922). Conclusions. The inflammasome was activated in this mouse model of AAA; however, daily oral administration of colchicine did not limit AAA growth
Discovery of Water Maser Emission in Five AGN and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities
We report the discovery of water maser emission in five active galactic
nuclei (AGN) with the 100-m Green Bank Telescope (GBT). The positions of the
newly discovered masers, measured with the VLA, are consistent with the optical
positions of the host nuclei to within 1 sigma (0.3 arcsec radio and 1.3 arcsec
optical) and most likely mark the locations of the embedded central engines.
The spectra of three sources, 2MASX J08362280+3327383, NGC 6264, and UGC 09618
NED02, display the characteristic spectral signature of emission from an
edge-on accretion disk with maximum orbital velocity of ~700, ~800, and ~1300
km s^-1, respectively. We also present a GBT spectrum of a previously known
source MRK 0034 and interpret the narrow Doppler components reported here as
indirect evidence that the emission originates in an edge-on accretion disk
with orbital velocity of ~500 km s^-1. We obtained a detection rate of 12
percent (5 out of 41) among Seyfert 2 and LINER systems with 10000 km s^-1 <
v_sys < 15000 km s^-1. For the 30 nuclear water masers with available hard
X-ray data, we report a possible relationship between unabsorbed X-ray
luminosity (2-10 keV) and total isotropic water maser luminosity, L_{2-10}
proportional to L_{H2O}^{0.5+-0.1}, consistent with the model proposed by
Neufeld and Maloney in which X-ray irradiation and heating of molecular
accretion disk gas by the central engine excites the maser emission.Comment: 16 pages, 5 tables, 3 figures, to appear in the November 10, 2006,
v651n2 issue of the Astrophysical Journa
Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the 22 GHz water vapor line towards galaxies
with nuclear activity, large nuclear column densities or high infrared
luminosities, we present H_2O spectra for NGC2273, UGC5101 and NGC3393 with
isotropic luminosities of 7, 1500, and 400 L_sun. The H_2O maser in UGC5101 is
by far the most luminous yet found in an ultraluminous infrared galaxy. NGC3393
reveals the classic spectrum of a `disk maser', represented by three distinct
groups of Doppler components. As in all other known cases except NGC4258, the
rotation velocity of the putative masing disk is well below 1000 km/s. Based on
the literature and archive data, X-ray absorbing column densities are compiled
for the 64 galaxies with reported maser sources beyond the Magellanic Clouds.
For NGC2782 and NGC5728, we present Chandra archive data that indicate the
presence of an active galactic nucleus in both galaxies. The correlation
between absorbing column and H_2O emission is analyzed. There is a striking
difference between kilo- and megamasers with megamasers being associated with
higher column densities. All kilomasers (L_H_2O < 10 L_sun) except NGC2273 and
NGC5194 are Compton-thin, i.e. their absorbing columns are < 10^24 cm^-2. Among
the H_2O megamasers, 50% arise from Compton-thick and 85% from heavily obscured
(> 10^23 cm^-2) active galactic nuclei. These values are not larger but
consistent with those from samples of Seyfert 2 galaxies not selected on the
basis of maser emission. The similarity in column densities can be explained by
small deviations in position between maser spots and nuclear X-ray source and a
high degree of clumpiness in the circumnuclear interstellar medium.Comment: 16 pages, 7 figures, 5 tables. Accepted for publication in A&
X-ray Spectral Survey with XMM--Newton of a Complete Sample of Nearby Seyfert Galaxies
Results obtained from an X-ray spectral survey of nearby Seyfert galaxies
using XMM--Newton are reported. The sample was optically selected, well
defined, complete in B mag, and distance limited: it consists of the nearest
(D<22 Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et
al. (1997) sample. This is one of the largest atlases of hard X-ray spectra of
low-L active galaxies ever assembled. All nuclear sources except two Sey 2s are
detected between 2-10 keV, half for the first time ever, and average spectra
are obtained for all of them. Nuclear luminosities reach values down to 10**38
erg/s. The shape of the distribution of X-ray parameters is affected by the
presence of Compton-thick objects (> 30% among type 2s). The latter have been
identified either directly from their intense FeK line and flat X-ray spectra,
or indirectly with flux diagnostic diagrams which use isotropic indicators.
After taking into account these highly absorbed sources, we find that (i) the
intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities
above 2 keV) are consistent between type 1 and type 2 Sey, as expected from
``unified models'', (ii) Sey galaxies as a whole are distributed fairly
continuously over the entire range of Nh, between 10**20 and 10**25 cm**-2, and
(iii) while Sey 1s tend to have lower Nh and Sey 2s tend to have the highest,
we find 30% and 10% exceptions, respectively. Overall the sample well
represents the average intrinsic X-ray spectral properties of nearby AGN,
including a proper estimate of the distribution of their absorbing columns.
Finally, we conclude that, with the exception of a few cases, the present study
agrees with predictions of unified models of Sey galaxies, and extends their
validity down to very low luminosities.Comment: 23 pages, 4 tables, 4 figures, 2 Appendices with 27 source spectra
and notes, to be published in the Astronomy & Astrophysics Journa
Resolving the extragalactic hard X-ray background
The origin of the hard (2-10 keV) X-ray background has remained mysterious
for over 35 years. Most of the soft (0.5-2 keV) X-ray background has been
resolved into discrete sources, which are primarily quasars; however, these
sources do not have the flat spectral shape required to match the X-ray
background spectrum. Here we report the results of an X-ray survey 30 times
more sensitive than previous studies in the hard band and four times more
sensitive in the soft band. The sources detected in our survey account for at
least 75 per cent of the hard X-ray background. The mean X-ray spectrum of
these sources is in good agreement with that of the background. The X-ray
emission from the majority of the detected sources is unambiguously associated
with either the nuclei of otherwise normal bright galaxies or optically faint
sources, which could either be active nuclei of dust enshrouded galaxies or the
first quasars at very high redshifts.Comment: Nature article in pres
The complex radio and X-ray structure in the nuclear regions of the active galaxy NGC1365
We present a multiwavelength analysis of the prominent active galaxy NGC1365,
in particular looking at the radio and X-ray properties of the central regions
of the galaxy.
We analyse ROSAT observations of NGC1365, and discuss recent ASCA results. In
addition to a number of point sources in the vicinity of NGC1365, we find a
region of X-ray emission extending along the central bar of the galaxy,
combined with an emission peak near the centre of the galaxy. This X-ray
emission is centred on the optical/radio nucleus, but is spatially extended.
The X-ray spectrum can be well fitted by a thermal plasma model, with
kT=0.6-0.8keV and a low local absorbing column. The thermal spectrum is
suggestive of starburst emission rather than emission from a central
black-hole.
The ATCA radio observations show a number of hotspots, located in a ring
around a weak radio nucleus. Synchrotron emission from electrons accelerated by
supernovae and supernova remnants (SNRs) is the likely origin of these
hotspots. The radio nucleus has a steep spectrum, indicative perhaps of an AGN
or SNRs. The evidence for a jet emanating from the nucleus is at best marginal.
The extent of the radio ring is comparable to the extended central X-ray
source.Comment: 13 pages, 5 figures, to be published in MNRA
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