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A Suzaku view of IGR J16393-4643
No full textOpen Access.The pulsar IGR J16393–4643 belongs to a class of highly absorbed supergiant high-mass X-ray binaries (HMXBs), characterized by a very high column density of absorbing matter. We present the results of simultaneous broad-band pulsation and spectrum analysis from a 44-ks Suzaku observation of the source. The orbital intensity profile created with the Swift Burst Alert Telescope (Swift–BAT) light curve shows an indication of IGR J16393–4643 being an eclipsing system with a short eclipse semi-angle θE ∼ 17°. For a supergiant companion star with a 20-R⊙ radius, this implies an inclination of the orbital plane in the range 39°–57°, whereas for a main-sequence B star as the companion with a 10-R⊙ radius, the inclination of the orbital plane is in the range 60°–77°. Pulse profiles created for different energy bands have complex morphology, which shows some energy dependence and increases in pulse fraction with energy. We have also investigated broad-band spectral characteristics, phase-averaged spectra and resolving the pulse phase into peak and trough phases. The phase-averaged spectrum has a very high NH(∼ 3 × 1023 cm−2) and is described by a power law (Γ ∼ 0.9) with a high-energy cut-off above 20 keV. We find a change in the spectral index in the peak and trough phases, implying an underlying change in the source spectrum
Dynamic light scattering study and DLVO analysis of physicochemical interactions in colloidal suspensions of charged disks
No full textRestricted Access.The interparticle interactions in colloidal suspensions of charged disks of Laponite clay in water were investigated using dynamic light scattering (DLS) and Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. We studied the effects of clay concentration (CL), the concentration of externally added salt (CS), and temperature (T) on the microscopic dynamics of the clay suspensions. The fast (τ1) and mean slow relaxation times (⟨τww⟩) of Laponite suspensions were extracted from intensity autocorrelation functions measured at different waiting times (tw) after sample preparation. Comprehensive Laponite concentration–salt concentration–temperature–time superpositions of both the microscopic diffusive time scales and the stretching exponent corresponding to the slow relaxation process highlight the self-similar nature of the energy landscapes of the Laponite suspensions. The evolution of the sodium ion concentration in the aging suspension with tw, measured for several values of CL, CS, and T, was used in a DLVO analysis of the free energy of the suspension for two charged disks parallely approaching one another. This analysis confirms that, in addition to repulsive interparticle interactions, attractive interactions also play a pivotal role in the microscopic dynamics of spontaneously evolving Laponite suspension
The low-frequency environment of the Murchison widefield array: radio-frequency interference analysis and mitigation
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolutio
Late time X-ray, IR and radio observations of the tidal disruption event galaxy NGC 5905
No full textRestricted Access.NGC 5905 is one of the few galaxies with no prior evidence for an active galactic nucleus (AGN) in which an X-ray flare was detected by the ROSAT All Sky Survey (RASS) in 1990–1991. Follow-up studies showed that the X-ray flare was due to the tidal disruption of a star by the massive black hole in the center of the galaxy. In this study we present analysis of late-time follow-up observations of NGC 5905 using Chandra archival data, Spitzer archival data, GMRT 1.28 GHz radio observations and VLA 3 GHz and 8 GHz archival data. The X-ray image shows no compact source that could be associated with an AGN. Instead, the emission is extended—likely due to nuclear star formation. The total measured X-ray luminosity from this extended emission region is comparable to the X-ray luminosity determined from the 2002 Chandra observations and is a factor of 200 less than the peak of the X-ray flare observed in 1990. Diffuse X-ray emission was detected close to the circum-nuclear star forming ring. The Spitzer 2006 mid-infrared spectrum also shows strong evidence of nuclear star formation but no clear AGN signatures. The semi-analytical models of Tommasin et al. (Astrophys. J. 709:1257, 2010) together with the measured [OIV]/[NeII] line ratio suggest that at most only 5.6 % of the total IR Flux at 19 μm is being contributed by the AGN. The GMRT 1.28 GHz observations reveal a nuclear source. In the much higher resolution VLA 3 GHz map, the emission has a double lobed structure of size 2.7′′ due to the circumnuclear star forming ring. The GMRT 1.28 GHz peak emission coincides with the center of the circumnuclear ring.
We did not detect any emission in the VLA 8 GHz (1996) archival data. Instead we give upper limits to the radio afterglow of the tidal disruption event (TDE) using 3 σ upper limits where σ is the map noise. The 3 σ limits at 1.28 GHz, 3 GHz and 8 GHz are 0.17 mJy, 0.09 mJy and 0.09 mJy, respectively. Our studies thus show that (i) NGC 5905 has a declining X-ray flux consistent with a TDE, (ii) the IR flux is dominated by nuclear star formation, (iii) the nuclear radio emission observed from the galaxy is due to circumnuclear star formation, (iv) no compact radio emission associated with a radio afterglow from the TDE is detected
Effect of lateral substituent and chain length on mesomorphic properties of novel alkoxy benzyloxy benzoates of cyanophenyl rod-shaped compounds
No full textRestricted Access.Three novel homologous series of rod-shaped cyanophenyl alkoxy benzoate liquid crystalline compounds with lateral polar fluorine and chlorine substituent were prepared, and chemical structures of novel materials have been characterized by standard spectral technique and elemental analysis. The mesophase characterization was carried out using the combination of polarized optical microscopy and differential scanning calorimetry. All the compounds exhibit wide thermal range of enantiotropic SmA phase
SARAS measurement of the radio background at long wavelengths
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)SARAS is a correlation spectrometer connected to a frequency independent antenna that is purpose-designed for precision measurements of the radio background at long wavelengths. The design, calibration, and observing strategies admit solutions for the internal additive contributions to the radiometer response, and hence a separation of these contaminants from the antenna temperature. We present here a wideband measurement of the radio sky spectrum by SARAS that provides an accurate measurement of the absolute brightness and spectral index between 110 and 175 MHz. Accuracy in the measurement of absolute sky brightness is limited by systematic errors of magnitude 1.2%; errors in calibration and in the joint estimation of sky and system model parameters are relatively smaller. We use this wide-angle measurement of the sky brightness using the precision wide-band dipole antenna to provide an improved absolute calibration for the 150 MHz all-sky map of Landecker and Wielebinski: subtracting an offset of 21.4 K and scaling by a factor of 1.05 will reduce the overall offset error to 8 K (from 50 K) and scale error to 0.8% (from 5%). The SARAS measurement of the temperature spectral index is in the range −2.3 to −2.45 in the 110–175 MHz band and indicates that the region toward the Galactic bulge has a relatively flatter index
Tagged particle diffusion in one-dimensional gas with Hamiltonian dynamics-II
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We study various temporal correlation functions of a tagged particle in one-dimensional systems of interacting point particles evolving with Hamiltonian dynamics. Initial conditions of the particles are chosen from the canonical thermal distribution. The correlation functions are studied in finite systems, and their forms examined at short and long times. Various one-dimensional systems are studied. Results of numerical simulations for the Fermi–Pasta–Ulam chain are qualitatively similar to results for the harmonic chain, and agree unexpectedly well with a simple description in terms of linearized equations for damped fluctuating sound waves. Simulation results for the alternate mass hard particle gas reveal that—in contradiction to our earlier results (Roy et al. in J Stat Phys 150(5):851–866, 2013) with smaller system sizes—the diffusion constant slowly converges to a constant value, in a manner consistent with mode coupling theories. Our simulations also show that the behaviour of the Lennard–Jones gas depends on its density. At low densities, it behaves like a hard-particle gas, and at high densities like an anharmonic chain. In all the systems studied, the tagged particle was found to show normal diffusion asymptotically, with convergence times depending on the system under study. Finite size effects show up at time scales larger than sound traversal times, their nature being system-specific
Morphology parameters: substructure identification in X-ray galaxy clusters
No full textOpen AccessContext. In recent years multi-wavelength observations have shown the presence of substructures related to merging events in a large proportion of galaxy clusters. Clusters can be roughly grouped into two categories – relaxed and non-relaxed – and a proper characterisation of the dynamical state of these systems is crucial for both astrophysical and cosmological studies.
Aims. In this paper we investigate the use of a number of morphological parameters (Gini, M20, concentration, asymmetry, smoothness, ellipticity, and Gini of the second-order moment, GM) introduced to automatically classify clusters as relaxed or dynamically disturbed systems.
Methods. We apply our method to a sample of clusters at different redshifts extracted from the Chandra archive and investigate possible correlations between morphological parameters and other X-ray gas properties.
Results. We conclude that a combination of the adopted parameters is a very useful tool for properly characterising the X-ray cluster morphology. According to our results, three parameters – Gini, M20, and concentration – are very promising for identifying cluster mergers. The Gini coefficient is a particularly powerful tool, especially at high redshift, because it is independent of the choice of the position of the cluster centre. We find that high Gini (>0.65), high concentration (>1.55), and low M20 (<–2.0) values are associated with relaxed clusters, while low Gini (<0.4), low concentration (<1.0), and high M20 (>–1.4) characterise dynamically perturbed systems. We also estimate the X-ray cluster morphological parameters in the case of radio loud clusters. Since they are in excellent agreement with previous analyses we confirm that diffuse intracluster radio sources are associated with major mergers