30,293 research outputs found
Quiescent NIR and optical counterparts to candidate black hole X-ray binaries
We present near-infrared and optical imaging of fifteen candidate black hole
X-ray binaries. In addition to quiescent observations for all sources, we also
observed two of these sources (IGR J17451-3022 and XTE J1818-245) in outburst.
We detect the quiescent counterpart for twelve out of fifteen sources, and for
the remaining three we report limiting magnitudes. The magnitudes of the
detected counterparts range between = 17.59 and = 22.29 mag. We
provide (limits on) the absolute magnitudes and finding charts of all sources.
Of these twelve detections in quiescence, seven represent the first quiescent
reported values (for MAXI J1543-564, XTE J1726-476, IGR J17451-3022, XTE
J1818-245, MAXI J1828-249, MAXI J1836-194, Swift J1910.2-0546) and two
detections show fainter counterparts to XTE J1752-223 and XTE J2012+381 than
previously reported. We used theoretical arguments and observed trends, for
instance between the outburst and quiescent X-ray luminosity and orbital period
to derive an expected trend between and of
. Comparing this to observations we
find a different behaviour. We discuss possible explanations for this result.Comment: 18 pages, 6 figures. Accepted for publication in MNRA
Characterisation of a candidate dual AGN
We present Chandra and optical observations of a candidate dual AGN
discovered serendipitously while searching for recoiling black holes via a
cross-correlation between the serendipitous XMM source catalog (2XMMi) and
SDSS-DR7 galaxies with a separation no larger than ten times the sum of their
Petrosian radii. The system has a stellar mass ratio M/M. One of the galaxies (Source 1) shows clear evidence for AGN activity in
the form of hard X-ray emission and optical emission-line diagnostics typical
of AGN ionisation. The nucleus of the other galaxy (Source 2) has a soft X-ray
spectrum, bluer colours, and optical emission line ratios dominated by stellar
photoionisation with a "composite" signature, which might indicate the presence
of a weak AGN. When plotted on a diagram with X-ray luminosity vs [OIII]
luminosity both nuclei fall within the locus defined by local Seyfert galaxies.
From the optical spectrum we estimate the electron densities finding n e cm and n e cm. From a 2D
decomposition of the surface brightness distribution we infer that both
galaxies host rotationally supported bulges (Sersic index ). While the
active nature of Source 1 can be established with confidence, whether the
nucleus of Source 2 is active remains a matter of debate. Evidence that a faint
AGN might reside in its nucleus is, however, tantalising.Comment: 16 pages, 9 figures. Accepted for publication on MNRAS. Comments
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Time-resolved spectroscopy of the pulsating CV GW Lib
We present time-resolved optical spectroscopy of the dwarf nova GW Librae during its rare 2007 April superoutburst and compare these with quiescent epochs. The data provide the first opportunity to track the evolution of the principal spectral features. In the early stages of the outburst, the optically thick disc dominates the optical and the line components show clear orbital radial velocity excursions. In the course of several weeks, optically thin regions become more prominent as strong emission lines replace the broad disc absorption.
Post-outburst spectroscopy covering the I band illustrates the advantages of Ca II relative to the commonly used Balmer lines when attempting to constrain binary parameters. Due to the lower ionization energy combined with smaller thermal and shear broadening of these lines, a sharp emission component is seen to be moving in between the accretion disc peaks in the Ca II line. No such component is visible in the Balmer lines. We interpret this as an emission component originating on the hitherto unseen mass donor star. This emission component has a mean velocity of similar to -15 +/- 5 km s(-1) which is associated with the systemic velocity., and a velocity semi-amplitude of K-em = 82.2 +/- 4.9 km s(-1). Doppler tomography reveals an asymmetric accretion disc, with the S-wave mapping to a sharp spot in the tomogram with a velocity consistent to what is obtained with line profile fitting. A centre of symmetry analysis of the disc component suggests a very small value for the WD orbital velocity K-1 as is also inferred from double Gaussian fits to the spectral lines.
While our conservative dynamical limits place a hard upper limit on the binary mass ratio of q < 0.23, we favour a significantly lower value near q similar to 0.06. Pulsation modelling suggests a white dwarf mass similar to 1 M-circle dot. This, paired with a low-mass donor, near the empirical sequence of an evolved cataclysmic variable close to the period bounce, appears to be consistent with all the observational constraints to date
Chandra observations of the millisecond X-ray pulsar IGR J00291+5934 in quiescence
In this Paper we report on our analysis of three Chandra observations of the
accretion-powered millisecond X-ray pulsar IGR J00291+5934 obtained during the
late stages of the 2004 outburst. We also report the serendipitous detection of
the source in quiescence by ROSAT during MJD 48830-48839. The detected 0.3-10
keV source count rates varied significantly between the Chandra observations
from (7.2+-1.2)x10^-3, (6.8+-0.9)x10^-3, and (1.4+-0.1)x10^-2 counts per second
for the 1st, 2nd, and 3rd Chandra observation, on MJD 53371.88, 53383.99, and
53407.57, respectively. The count rate for the 3rd observation is 2.0+-0.4
times as high as that of the average of the first two observations. The
unabsorbed 0.5-10 keV source flux for the best-fit power-law model to the
source spectrum was (7.9+-2.5)x10^-14, (7.3+-2.0)x10^-14, and
(1.17+-0.22)x10^-13 erg cm^-2 s^-1 for the 1st, 2nd, and 3rd Chandra
observation, respectively. We find that this source flux is consistent with
that found by ROSAT [~(5.4+-2.4)x10^-14 erg cm^-2 s^-1]. Under the assumption
that the interstellar extinction, N_H, does not vary between the observations,
we find that the blackbody temperature during the 2nd Chandra observation is
significantly higher than that during the 1st and 3rd observation. Furthermore,
the effective temperature of the neutron star derived from fitting an absorbed
blackbody or neutron star atmosphere model to the data is rather high in
comparison with many other neutron star soft X-ray transients in quiescence,
even during the 1st and 3rd observation. If we assume that the source quiescent
luminosity is similar to that measured for two other accretion powered
millisecond pulsars in quiescence, the distance to IGR J00291+5934 is 2.6-3.6
kpc.Comment: 7 pages, 3 Figures, accepted for publication in MNRA
Three-body hadron systems with strangeness
Recently, many efforts are being put in studying three-hadron systems made of
mesons and baryons and interesting results are being found. In this talk, I
summarize the main features of the formalism used to study such three hadron
systems with strangeness within a framework built on the basis of
unitary chiral theories and solution of the Faddeev equations. In particular, I
present the results obtained for the , and
systems and their respective coupled channels. In the first case, we find four
's and two 's with spin-parity , in the 1500-1800
MeV region, as two meson-one baryon s-wave resonances. In the second case, a
around 1900 MeV is found. For the last one a kaon close to 1420
MeV is formed, which can be identified with K(1460).Comment: Proceeding written for the HYP2012 conferenc
How to generate pentagonal symmetry using Turing systems
We explore numerically the formation of Turing patterns in a confined circular domain with small aspect ratio. Our results show that stable fivefold patterns are formed over a well defined range of disk sizes, offering a possible mechanism for inducing the fivefold symmetry observed in early development of regular echinoids. Using this pattern as a seed, more complex biological structures can be mimicked, such as the pigmentation pattern of sea urchins and the plate arrangements of the calyxes of primitive camerate crinoids
Boson Stars in General Scalar-Tensor Gravitation: Equilibrium Configurations
We study equilibrium configurations of boson stars in the framework of
general scalar-tensor theories of gravitation. We analyse several possible
couplings, with acceptable weak field limit and, when known, nucleosynthesis
bounds, in order to work in the cosmologically more realistic cases of this
kind of theories. We found that for general scalar-tensor gravitation, the
range of masses boson stars might have is comparable with the general
relativistic case. We also analyse the possible formation of boson stars along
different eras of cosmic evolution, allowing for the effective gravitational
constant far out form the star to deviate from its current value. In these
cases, we found that the boson stars masses are sensitive to this kind of
variations, within a typical few percent. We also study cases in which the
coupling is implicitly defined, through the dependence on the radial
coordinate, allowing it to have significant variations in the radius of the
structure.Comment: 19 pages in latex, 3 figures -postscript- may be sent via e-mail upon
reques
Particle Dark Energy
We explore the physics of a gas of particles interacting with a condensate
that spontaneously breaks Lorentz invariance. The equation of state of this gas
varies from 1/3 to less than -1 and can lead to the observed cosmic
acceleration. The particles are always stable. In our particular class of
models these particles are fermions with a chiral coupling to the condensate.
They may behave as relativistic matter at early times, produce a brief period
where they dominate the expansion with w<0 today, and behave as matter at late
time. There are no small parameters in our models, which generically lead to
dark energy clustering and, depending on the choice of parameters, smoothing of
small scale power.Comment: 8 pages, 5 figures; minor update with added refs; version appearing
in Phys. Rev.
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