7,919 research outputs found
A Multiwavelength Investigation of the Relationship Between 2CG135+1 and LSI+61o 303
We present the results of a multiwavelength monitoring campaign targeting the
gamma-ray source 2CG 135+1 in an attempt to confirm the association of this
object with the radio/Be/X-ray binary system LSI +61o 303. The campaign
included simultaneous radio, optical, infrared, and hard x-ray/gamma-ray
observations carried out with a variety of instruments, covering (not
continously) almost three binary cycles of LSI +61o 303 during the period
April-July 1994. Three separate OSSE observations of the gamma-ray source were
carried out, covering different phases of the radio lightcurve. Hard
X-ray/gamma-ray emission was detected from the direction of 2CG 135+1 during
the first of these OSSE observations. The signal to noise ratio of the OSSE
observations was insufficient to establish a spectral or intensity correlation
of the high-energy emission with simultaneous radio, optical and infrared
emission of LSI +61o 303. We briefly discuss the theoretical implications of
our observations.Comment: 17 pages, 9 figures, 6 tables to be published in Astrophysical
Journal, 10 April 199
Magnetic behavior of lamellar mnps3 and cdps3 composites with a paramagnetic manganese(iii) macrocyclic guest
Indexación: ScieloSix new composites derived from the intercalation of the MPS3 phases (M = MnII, CdIII) with the macrocyclic manganese(III) complex [MnL(H2O)2].NO3(H2O) (LH2 = Schiff base macrocyclic ligand derived from the condensation of 2-hydroxy-5-methy1-1,3-benzene-dicarbaldehyde and 1,2-diamine-benzene) were obtained by two different synthetic procedures: a conventional and a microwave assisted method. The composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1), and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (2) were obtained by the conventional method, after stirring a suspension of the corresponding potassium precursor and the macrocyclic complex for two weeks, while [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3) and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (4) after stirring for four weeks at room temperature. Using a microwave assisted reaction permitted to obtain in a shorter period of time as compared with the conventional method, composites [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5) and [MnL]0.15K0.15Cd 0. 80PS3(H2O)~0.5 (6). All the M = MnII, MnIII composites show a bulk antiferromagnetic behavior. However, the spontaneous magnetization present at low temperature in the potassium precursor K0.40Mn0.80 PS3(H2O)~1.0 is observable in composite [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5), while it is completely absent in composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1) and [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3).
Keywords: Intercalation; MPS3 phases; MnIII macrocyclic complex; microwave assisted synthesis; magnetic properties
Long Term X-ray Monitoring Of The TeV Binary LS I +61 303 with RXTE
We report on the results of a long term X-ray monitoring campaign of the
galactic binary LS I +61 303 performed by the Rossi X-ray Timing Explorer. This
dataset consists of 1 ks pointings taken every other day between 2007 August 28
until 2008 February 2. The observations covered six full cycles of the 26.496
day binary period and constitute the largest continuous X-ray monitoring
dataset on LS I +61 303 to date with this sensitivity. There is no
statistically strong detection of modulation of flux or photon index with
orbital phase; however, we do find a strong correlation between flux and photon
index, with the spectrum becoming harder at higher fluxes. The dataset contains
three large flaring episodes, the largest of these reaching a flux level of 7.2
(+0.1,-0.2)*10^-11 erg cm^-2 s^-1 in the 3-10 keV band, which is a factor of
three times larger than flux levels typically seen in the system. Analysis of
these flares shows the X-ray emission from LS I +61 303 changing by up to a
factor of six over timescales of several hundred seconds as well as doubling
times as fast as 2 seconds. This is the fastest variability ever observed from
LS I +61 303 at this wavelength and places constraints on the size of the X-ray
emitting region.Comment: 24 pages, 7 figures, 2 tables. Accepted for publication in Ap
Leptonic secondary emission in a hadronic microquasar model
Context: It has been proposed that the origin of the very high-energy photons
emitted from high-mass X-ray binaries with jet-like features, so-called
microquasars (MQs), is related to hadronic interactions between relativistic
protons in the jet and cold protons of the stellar wind. Leptonic secondary
emission should be calculated in a complete hadronic model that include the
effects of pairs from charged pion decays inside the jets and the emission from
pairs generated by gamma-ray absorption in the photosphere of the system. Aims:
We aim at predicting the broadband spectrum from a general hadronic microquasar
model, taking into account the emission from secondaries created by charged
pion decay inside the jet. Methods: The particle energy distribution for
secondary leptons injected along the jets is consistently derived taking the
energy losses into account. We also compute the spectral energy distribution
resulting from these leptons is calculated after assuming different values of
the magnetic field inside the jets. The spectrum of the gamma-rays produced by
neutral pion-decay and processed by electromagnetic cascades under the stellar
photon field. Results: We show that the secondary emission can dominate the
spectral energy distribution at low energies (~1 MeV). At high energies, the
production spectrum can be significantly distorted by the effect of
electromagnetic cascades. These effects are phase-dependent, and some
variability modulated by the orbital period is predicted.Comment: 8 pages, 5 figures. Accepted for publication in Astronomy &
Astrophysic
Three-dimensional Ising model confined in low-porosity aerogels: a Monte Carlo study
The influence of correlated impurities on the critical behaviour of the 3D
Ising model is studied using Monte Carlo simulations. Spins are confined into
the pores of simulated aerogels (diffusion limited cluster-cluster aggregation)
in order to study the effect of quenched disorder on the critical behaviour of
this magnetic system. Finite size scaling is used to estimate critical
couplings and exponents. Long-range correlated disorder does not affect
critical behavior. Asymptotic exponents differ from those of the pure 3D Ising
model (3DIS), but it is impossible, with our precision, to distinguish them
from the randomly diluted Ising model (RDIS).Comment: 10 pages, 10 figures. Submitted to Physical Review
Chandra Observations of the Gamma-ray Binary LSI+61303: Extended X-ray Structure?
We present a 50 ks observation of the gamma-ray binary LSI+61303 carried out
with the ACIS-I array aboard the Chandra X-ray Observatory. This is the highest
resolution X-ray observation of the source conducted so far. Possible evidence
of an extended structure at a distance between 5 and 12 arcsec towards the
North of LSI+61303 have been found at a significance level of 3.2 sigma. The
asymmetry of the extended emission excludes an interpretation in the context of
a dust-scattered halo, suggesting an intrinsic nature. On the other hand, while
the obtained source flux, of F_{0.3-10 keV}=7.1^{+1.8}_{-1.4} x 10^{-12}
ergs/cm^2/s, and hydrogen column density, N_{H}=0.70+/-0.06 x 10^{22} cm^{-2},
are compatible with previous results, the photon index Gamma=1.25+/-0.09 is the
hardest ever found. In light of these new results, we briefly discuss the
physics behind the X-ray emission, the location of the emitter, and the
possible origin of the extended emission ~0.1 pc away from LSI+61303.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter
Joint constraints on galaxy bias and through the N-pdf of the galaxy number density
We present a full description of the N-probability density function of the
galaxy number density fluctuations. This N-pdf is given in terms, on the one
hand, of the cold dark matter correlations and, on the other hand, of the
galaxy bias parameter. The method relies on the assumption commonly adopted
that the dark matter density fluctuations follow a local non-linear
transformation of the initial energy density perturbations. The N-pdf of the
galaxy number density fluctuations allows for an optimal estimation of the bias
parameter (e.g., via maximum-likelihood estimation, or Bayesian inference if
there exists any a priori information on the bias parameter), and of those
parameters defining the dark matter correlations, in particular its amplitude
(). It also provides the proper framework to perform model selection
between two competitive hypotheses. The parameters estimation capabilities of
the N-pdf are proved by SDSS-like simulations (both ideal log-normal
simulations and mocks obtained from Las Damas simulations), showing that our
estimator is unbiased. We apply our formalism to the 7th release of the SDSS
main sample (for a volume-limited subset with absolute magnitudes ). We obtain and , for galaxy number density fluctuations in cells of a size of
Mpc. Different model selection criteria show that galaxy biasing is
clearly favoured.Comment: 25 pages, 9 figures, 2 tables. v2: Substantial revision, adding the
joint constraints with \sigma_8 and testing with Las Damas mocks. Matches
version accepted for publication in JCA
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