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Nonlinear absorption and photoluminescence next emission in nanocomposite films of Fuchsine Basic dye-polymer system
No full textRestricted Access.Fuchsine Basic dye-polyvinyl alcohol composite films were fabricated and their structure, nonlinear absorption as well as linear absorption and photoluminescence properties were investigated. Switchover from saturable absorption to two-photon assisted excited state absorption with increase in intensity was observed in the open aperture Z-scan study (Nd:YAG, 532 nm, 7 ns). The effective two-photon absorption coefficient beta was found to be several orders higher than that reported for rhodamine B. The dye-polymer films were characterized as nanocomposites with dye microdomains encapsulated between molecules of the amorphous polymer and having average surface roughness as low as approximate to 0.46 nm. The samples also exhibited intense photoluminescence emission when excited with 534 nm radiation
The Australia telescope 20GHz (AT20G) Survey: analysis of the extragalactic source sample
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The Australia Telescope 20 GHz (AT20G) survey is a blind survey of the whole Southern sky at 20 GHz with follow-up observations at 4.8, 8.6 and 20 GHz carried out with the Australia Telescope Compact Array (ATCA) from 2004 to 2008. In this paper we present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| < <file name="mnr_17917_mu1.gif" type="gif"/>).
The sample has a flux density limit of 40 mJy. Completeness has been measured as a function of scan region and flux density. Averaging over the whole survey area the follow-up survey is 78 per cent complete above 50 mJy and 93 per cent complete above 100 mJy. 3332 sources with declination delta < -15 degrees have good quality almost simultaneous observations at 4.8, 8.6 and 20 GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources, with 69 per cent having spectral index alpha 20(8.6) > - 0.5 (S proportional to nu alpha). The fraction of flat-spectrum sources decreases from 81 per cent for S(20 GHz) > 500 mJy to 60 per cent for S(20 GHz) < 100 mJy. There is also a clear spectral steepening at higher frequencies with the median alpha decreasing from -0.16 between 4.8 and 8.6 GHz to -0.28 between 8.6 and 20 GHz.
Simultaneous observations in polarization are available for all the sources at all the frequencies. 768 sources have a good-quality detection of polarized flux density at 20 GHz; 467 of them were also detected in polarization at 4.8 and/or at 8.6 GHz so that it has been possible to compare the spectral behaviour in total intensity and polarization. We have found that the polarized fraction increases slightly with frequency and decreases with flux density. The spectral indices in total intensity and in polarization are, on average, close to each other, but we also found several sources for which the spectral shape of the polarized emission is substantially different from the spectral shape in total intensity. The correlation between the spectral indices in total intensity and in polarization is weaker for flat-spectrum sources.
Cross-matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and gamma-ray bands. Redshift estimates are available for 825 sources
X-ray spectroscopy of the high-mass x-ray binary pulsar centaurus x-3 over its binary orbit
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present a comprehensive spectral analysis of the high-mass X-ray binary (HMXB) pulsar Centaurus X-3with the Suzaku observatory covering nearly one orbital period. The light curve shows the presence of extended dips which are rarely seen in HMXBs. These dips are seen up to as high as ∼40 keV. The pulsar spectra during the eclipse, out-of-eclipse, and dips are found to be well described by a partial covering power-law model with high-energy cutoff and three Gaussian functions for 6.4 keV, 6.7 keV, and 6.97 keV iron emission lines. The dips in the light curve can be explained by the presence of an additional absorption component with high column density and covering fraction, the values of which are not significant during the rest of the orbital phases. The iron line parameters during the dips and eclipse are significantly different compared to those during the rest of the observation. During the dips, the iron line intensities are found to be lesser by a factor of 2–3 with a significant increase in the line equivalent
widths. However, the continuum flux at the corresponding orbital phase is estimated to be lesser by more than
an order of magnitude. Similarities in the changes in the iron line flux and equivalent widths during the dips and eclipse segments suggest that the dipping activity in Cen X-3 is caused by an obscuration of the neutron star by dense matter, probably structures in the outer region of the accretion disk, as in the case of dipping low-mass X-ray
binaries
Dust in the IGM: pro and contra
No full textRestricted Access.Observations of dust grains in the intergalactic medium (IGM) allow us to study an important aspect in the evolution of galaxies. Although it existence had been previously speculated upon, direct evidence of the presence of dust in the intergalactic space has only been available recently.
We discuss various issues regarding the presence of dust in the IGM—its sources, transport mechanisms from galaxies into the IGM, its effect on reddening and on cosmological studies
Theory of the asymmetric ripple phase in achiral lipid membranes
No full textOpen Access.We present a phenomenological theory of phase transitions in achiral lipid membranes
in terms of two coupled order parameters—a scalar order parameter describing lipid chain melting, and a vector order parameter describing the tilt of the hydrocarbon chains below the chain-melting
transition. Existing theoretical models fail to account for all the observed features of the phase diagram, in particular the detailed microstructure of the asymmetric ripple phase lying between the fluid and the tilted gel phase. In contrast, our two-component theory reproduces all the salient structural features of the ripple phase, providing a unified description of the phase diagram and microstructure
Pulse profile stability of the crab pulsar
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present an X-ray timing analysis of the Crab pulsar, PSR B0531+21, using archival RXTE data. We have investigated the stability of the Crab pulse profile, in soft (2-20 keV) and hard (30-100 keV) X-ray energies, over the last decade of RXTE operation. The analysis includes measurement of the separation between the two pulse peaks and the intensity and widths of the two peaks. We did not find any significant time dependency in the pulse shape. The two peaks have been stable in phase, intensity and width for the last ten years. The first pulse is relatively stronger at soft X-rays. The first pulse peak is narrower than the second peak in both soft and hard X-ray energies. Both the peaks show a slow rise and a steeper fall. The ratio of the pulsed photons in the two peaks is also constant in time
Zoo of radio relics: cluster cores to filaments
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Radio relics in galaxy clusters can be electrons accelerated at cluster merger shocks or adiabatically compressed fossil radio cocoons or dying radio galaxies. The spectral evolution of radio relics is affected by the surrounding thermal plasma. We present a low frequency study of three radio relics representing environments of dense cluster core (A4038), cluster outskirts (A1664) and filaments (A786). The properties of the relics are found to be consistent with the effect of confinement by external medium if the effects of projection are ignored
Thomson X-ray polarimeter for a small satellite mission
No full textOpen AccessX-ray polarimetry is an unexplored area in high energy astrophysics. We describe a Thomson X-ray polarimeter developed for a small satellite mission. The instrument works in the 5-30 keV energy band and will be suitable for X-ray polarization measurement in about 50 hard X-ray sources. Currently, a laboratory model has been made and tested successfully and the design and fabrication of an engineering model is in progress. Different aspects related to mission specifications, instrument design, test results, and sensitivity for polarization measurement are discussed
Radio-Optical imaging of ATLBS survey
No full textOpen AccessWe present the radio-optical imaging of ATLBS, a sensitive radio survey (Subrahmanyan et al. 2010). The primary aim of the ATLBS survey is to image low-power radio sources which form the bulk of the radio source population to moderately high red-shifts (z ∼ 1.0). The accompanying multiband optical and near infra-red observations provide information about the hosts and environments of the radio sources. We give here details of the imaging of the radio data and optical data for the ATLBS survey
The Australia telescope 20 GHz survey: hardware, observing strategy, and scanning survey catalog
No full textRestricted AccessThe Australia Telescope 20 GHz (AT20G) survey is a large area (2 π sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog