1,853 research outputs found
Mrk 1014: An AGN Dominated ULIRG at X-rays
In this paper we report on an XMM-Newton observation of the ultraluminous
infrared QSO Mrk 1014. The X-ray observation reveals a power-law dominated
(photon index of about 2.2) spectrum with a slight excess in the soft energy
range. AGN and starburst emission models fit the soft excess emission equally
well, however, the most plausible explanation is an AGN component as the
starburst model parameter, temperature and luminosity, appear physically
unrealistic. The mean luminosity of Mrk 1014 is about 2 times 10^44 erg s^-1.
We have also observed excess emission at energies greater than 5 keV. This
feature could be attributed to a broadened and redshifted iron complex, but
deeper observations are required to constrain its origin. The light curve shows
small scale variability over the 11 ks observation. There is no evidence of
intrinsic absorption in Mrk 1014. The X-ray observations support the notion of
an AGN dominated central engine. We establish the need for a longer observation
to constrain more precisely the nature of the X-ray components.Comment: 5 pages incl. 3 figures, MNRAS in pres
XMM-Newton spectral properties of the Ultraluminous IRAS Galaxy Mrk 273
We present a 23 ks XMM-Newton observation of the ULIRG Mrk 273. The hard
X-ray spectrum can be modeled by a highly absorbed power law plus an Fe Kalpha
emission line. The iron line is broad, suggesting possible superposition of a
neutral iron line at 6.4 keV, and a blend of ionized iron lines from Fe XXV and
Fe XXVI. Given the relatively short exposure, the three line components can not
be singularly resolved with high statistical significance: the neutral
component is detected at ~2.5sigma and the Fe XXV line at ~2sigma c.l., while
for the Fe XXVI line we can only estimate an upper limit. The broad band
spectrum requires, in addition to a highly absorbed power law, at least three
collisionally ionized plasma components, which may be associated with
star-forming regions. The temperatures of the three plasmas are about 0.3, 0.8
and 6 keV, where the highest of the three is sufficient to produce ionized iron
emission lines. An alternative interpretation for the origin of the soft
emission might also be given in terms of reflection off some photoionized gas,
as has been observed in a number of nearby Compton-thick Seyfert 2 galaxies. A
hot gas, photoionized by the primary, continuum can also produce ionized iron
lines. Unfortunately, given the limited statistics and the lack of high
resolution spectroscopy, it is not possible to distinguish between the two
models investigated. We further compare the XMM-Newton findings with the
Chandra data obtaining consistent spectral results. The absorption corrected
hard X-ray (2-10 keV) luminosity of Mrk 273 corresponds to ~0.2% of the far-IR
luminosity, similar to typical values found in pure starbursts. The thermal
contribution to the soft X-ray luminosity is ~0.2-0.7x10^42 erg s^-1,
comparable to those found in NGC 6240 and other starburst dominated ULIRGs.Comment: 10 pages, 10 figures, 4 tables, accepted for publication in Astronomy
and Astrophysi
Curie-Weiss model of the quantum measurement process
A hamiltonian model is solved, which satisfies all requirements for a
realistic ideal quantum measurement. The system S is a spin-\half, whose
-component is measured through coupling with an apparatus A=M+B, consisting
of a magnet \RM formed by a set of spins with quartic infinite-range
Ising interactions, and a phonon bath \RB at temperature . Initially A is
in a metastable paramagnetic phase. The process involves several time-scales.
Without being much affected, A first acts on S, whose state collapses in a very
brief time. The mechanism differs from the usual decoherence. Soon after its
irreversibility is achieved. Finally the field induced by S on M, which may
take two opposite values with probabilities given by Born's rule, drives A into
its up or down ferromagnetic phase. The overall final state involves the
expected correlations between the result registered in M and the state of S.
The measurement is thus accounted for by standard quantum statistical mechanics
and its specific features arise from the macroscopic size of the apparatus.Comment: 5 pages Revte
Unveiling the central parsec region of an AGN: the Circinus nucleus in the near infrared with the VLT
VLT J- to M\p-band adaptive optics observations of the Circinus Galaxy on
parsec scales resolve a central bright Ks-band source with a FWHM size of 1.9
0.6 pc. This source is only visible at wavelengths longward of 1.6 m
and coincides in position with the peak of the [Si VII]~2.48 m coronal
line emission. With respect to the peak of the central optical emission, the
source is shifted by 0.15\arcsec (2.8 pc) to the south-east. Indeed, it
defines the vertex of a fairly collimated beam which extends for 10 pc,
and which is seen in both continuum light shortward of 1.6 m and in
H line emission. The source also lies at the center of a 19 pc
size [Si VII] ionization {\it bicone}.
Identifying this source as the nucleus of Circinus, its size is compatible
with a putative parsec-scale torus. Its spectral energy distribution,
characterized by a prominent narrow peak, is compatible with a dust temperature
of 300 K. Hotter dust within a 1 pc radius of the center is not detected. The
AGN luminosity required to heat this dust is in the range of X-ray luminosities
that have been measured toward the central source. This in turn supports the
existence of highly obscuring material, with column densities of
cm, that must be located within 1 pc of the core.Comment: 15 pages, 4 figures; To appear in The Astrophysical Journa
ISO-SWS spectroscopy of NGC 1068
We present ISO-SWS spectroscopy of NGC 1068 for the wavelength range 2.4 to
45um, detecting a total of 36 emission lines. Most of the observed transitions
are fine structure and recombination lines originating in the narrow line
region. We compare the line profiles of optical lines and reddening-insensitive
infrared lines to constrain the dynamical structure and extinction properties
of the NLR. The considerable differences found are most likely explained by two
effects. (1) The spatial structure of the NLR is a combination of a highly
ionized outflow cone and lower excitation extended emission. (2) Parts of the
NLR, mainly in the receding part at velocities above systemic, are subject to
extinction that is significantly suppressing optical emission. Line asymmetries
and net blueshifts remain, however, even for infrared fine structure lines
suffering very little obscuration. This may be either due to an intrinsic
asymmetry of the NLR, or due to a very high column density obscuring component
which is hiding part of the NLR even from infrared view. Mid-infrared emission
of molecular hydrogen in NGC 1068 arises in a dense molecular medium at
temperatures of a few hundred Kelvin that is most likely closely related to the
warm and dense components seen in the near-infrared H2 transitions, and in
millimeter wave tracers of molecular gas. Any emission of the putative pc-scale
molecular torus is likely overwhelmed by this larger scale emission.Comment: aastex (V4), 9 eps figures. Accepted by Ap
Infrared spectroscopy of NGC 1068: Probing the obscured ionizing AGN continuum
The ISO-SWS 2.5-45 um infrared spectroscopic observations of the nucleus of
the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a
compilation of UV to IR narrow emission line data to determine the spectral
energy distribution (SED) of the obscured extreme-UV continuum that
photoionizes the narrow line emitting gas in the active galactic nucleus. We
search a large grid of gas cloud models and SEDs for the combination that best
reproduces the observed line fluxes and NLR geometry. Our best fit model
reproduces the observed line fluxes to better than a factor of 2 on average and
is in general agreement with the observed NLR geometry. It has two gas
components that are consistent with a clumpy distribution of dense outflowing
gas in the center and a more extended distribution of less dense and more
clumpy gas farther out that has no net outflow. The best fit SED has a deep
trough at ~4 Ryd, which is consistent with an intrinsic Big Blue Bump that is
partially absorbed by ~6x10^19 cm^-2 of neutral hydrogen interior to the NLR.Comment: 15 pp, 4 figures, ApJ accepte
Solar-Type Post-T Tauri Stars in the Nearest OB Subgroups
I discuss results from the recent spectroscopic survey for solar-type pre-MS
stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) OB
subgroups by Mamajek, Meyer, & Liebert (2002, AJ, 124, 1670). LCC and UCL are
subgroups of the Sco-Cen OB association, and the two nearest OB subgroups to
the Sun. In the entire survey of 110 pre-main sequence stars, there exists only
one Classical T Tauri star (PDS 66), implying that only ~1% of ~1 Msun stars
are still accreting at age 137 (1) Myr. Accounting for
observational errors, the HRD placement of the pre-MS stars is consistent with
the bulk of star-formation taking place within 5-10 Myr. In this contribution,
I estimate conservative upper limits to the intrinsic velocity dispersions of
the post-T Tauri stars in the LCC and UCL subgroups (<1.6 km/s and <2.2 km/s,
respectively; 95% CL) using Monte-Carlo simulations of Tycho-2 proper motions
for candidate subgroup members. I also demonstrate that a new OB subgroup
recently proposed to exist in Chamaeleon probably does not.Comment: 8 pages, 2 figures, to appear in proceedings for "Open Issues in
Local Star Formation and Early Stellar Evolution", eds. J. Gregorio-Hetem &
J. Lepine. Minor edits (5/30/03
Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory and the (1405) and (1670) Resonances
The wave meson-baryon scattering is analyzed for the strangeness
and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism
incorporating Chiral Symmetry. Four channels have been considered: , , and . The required input to solve
the Bethe-Salpeter equation is taken from lowest order Chiral Perturbation
Theory in a relativistic formalism. There appear undetermined low energy
constants, as a consequence of the renormalization of the amplitudes, which are
obtained from fits to the mass-spectrum, to the elastic
and --matrices and to the
cross section data. The position and residues of the
complex poles in the second Riemann Sheet of the scattering amplitude determine
masses, widths and branching ratios of the (1405) and
(1670) resonances, in reasonable agreement with experiment. A good
overall description of data, from threshold up to 1.75 GeV, is
achieved despite the fact that three-body channels have not been explicitly
included.Comment: 23 pages, Latex, 10 Figures. In this revised version a new subsection
3.6 on Heavy Baryon Expansion and new references have been adde
The MRN complex is transcriptionally regulated by MYCN during neural cell proliferation to control replication stress
The MRE11/RAD50/NBS1 (MRN) complex is a major sensor of DNA double strand breaks, whose role in controlling faithful DNA replication and preventing replication stress is also emerging. Inactivation of the MRN complex invariably leads to developmental and/or degenerative neuronal defects, the pathogenesis of which still remains poorly understood. In particular, NBS1 gene mutations are associated with microcephaly and strongly impaired cerebellar development, both in humans and in the mouse model. These phenotypes strikingly overlap those induced by inactivation of MYCN, an essential promoter of the expansion of neuronal stem and progenitor cells, suggesting that MYCN and the MRN complex might be connected on a unique pathway essential for the safe expansion of neuronal cells. Here, we show that MYCN transcriptionally controls the expression of each component of the MRN complex. By genetic and pharmacological inhibition of the MRN complex in a MYCN overexpression model and in the more physiological context of the Hedgehog-dependent expansion of primary cerebellar granule progenitor cells, we also show that the MRN complex is required for MYCN-dependent proliferation. Indeed, its inhibition resulted in DNA damage, activation of a DNA damage response, and cell death in a MYCN- and replication-dependent manner. Our data indicate the MRN complex is essential to restrain MYCN-induced replication stress during neural cell proliferation and support the hypothesis that replication-born DNA damage is responsible for the neuronal defects associated with MRN dysfunctions.Cell Death and Differentiation advance online publication, 12 June 2015; doi:10.1038/cdd.2015.81
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