Associated HI absorption in the z=3.4 radio galaxy B2 0902+343 observed with the GMRT

We have made observations of the associated HI absorption of a high redshift radio galaxy 0902+34 at z=3.395 with the Giant Meterwave Radio Telescope in the $323\pm1$ MHz band. We find a narrow absorption line with a flux density of 11.5 mJy at a redshift of 3.397 consistent with that observed by Uson et al. (1991), Briggs et al. (1993) and de Bruyn (1996).A weak broad absorption feature reported by de Bruyn (1996) has not been detected in our observations. We also place an upper limit of 4 mJy (2 $\sigma$) on emission line strength at the position where Uson et al. (1991) claimed to have found a narrow emission line.Comment: To appear in Journal of Astronomy and Astrophysic

A Luminous Companion to SGR 1806-20

We have obtained infrared spectra of the star suggested to be the counterpart of the soft gamma-ray repeater (SGR) 1806-20. We found strong emission lines similar to those seen in the spectra of the rare Luminous Blue Variables and B[e] stars. A He I absorption line is also seen, from which we infer a spectral type O9--B2. This classification, in combination with the minimum distance of \simgt6 kpc inferred from its extinction, makes the star one of the most luminous in the Galaxy. We infer that it is a companion to SGR 1806-20, and suggest that the presence of a companion is somehow related to the SGR phenomenon.Comment: 5 pages, AASTEX text+table and 2 PostScript figures (needs LaTeX style files aaspptwo.sty, epsf.sty and rotate.sty). In case of problems, contact [email protected]. Postscript file of complete article available on request. (Replaced because first version had one wrong reference in it

Formation of rectifier with gold nanoclusters

Gold nanoclusters encapsulated with organic molecules are of great interest for its possible applications in the fields of molecular electronics, catalysis and medical science. Here we demonstrate that monolayer and bilayer films of thiol-capped gold nanoclusters can exhibit diode-like properties provided controlled spatial asymmetry exist between two tunnel junctions used to connect a thiol capped gold nanoclusters. Current-voltage characteristics of this rectifier were obtained from conducting probe atomic force microscopy measurements and also from conventional two probe resistance measurements. Systematic x-ray reflectivity and atomic force microscopy measurements were carried out to characterize the spatial asymmetry introduced by a monolayer of fatty acid salt gadolinium stearate used to deposit thiol-capped gold nanocluster molecules on hydrophilic SiO2-Si(001) substrate by Langmuir Blodgett technique. This information was used to explain prominent rectification observed in these nano-structured films.Comment: 13 pages, 3 figure

On associating Fast Radio Bursts with afterglows

A radio source that faded over six days, with a redshift of $z\approx0.5$ host, has been identified by Keane et al. (2016) as the transient afterglow to a fast radio burst (FRB 150418). We report follow-up radio and optical observations of the afterglow candidate and find a source that is consistent with an active galactic nucleus. If the afterglow candidate is nonetheless a prototypical FRB afterglow, existing slow-transient surveys limit the fraction of FRBs that produce afterglows to 0.25 for afterglows with fractional variation, $m=2|S_1-S_2|/(S_1+S_2)\geq0.7$, and 0.07 for $m\geq1$, at 95% confidence. In anticipation of a barrage of bursts expected from future FRB surveys, we provide a simple framework for statistical association of FRBs with afterglows. Our framework properly accounts for statistical uncertainties, and ensures consistency with limits set by slow-transient surveys.Comment: Accepted version (ApJL

Inhomogeneous vortex-state-driven enhancement of superconductivity in nanoengineered ferromagnet-superconductor heterostructures

Thin film heterostructures provide a powerful means to study the antagonism between superconductivity (SC) and ferromagnetism (FM). One interesting issue in FM-SC hybrids which defies the notion of antagonistic orders is the observation of magnetic field induced superconductivity (FIS). Here we show that in systems where the FM domains/islands produce spatial inhomogeneities of the SC order parameter, the FIS can derive significant contribution from different mobilities of the magnetic flux identified by two distinct critical states in the inhomogeneous superconductor. Our experiments on nanoengineered bilayers of ferromagnetic CoPt and superconducting NbN where CoPt/NbN islands are separated by a granular NbN, lend support to this alternative explanation of FIS in certain class of FM-SC hybrids.Comment: 5 figure

A model of the Algol type close binary TT Hydrae

UBV photometric observations and elements of TT Hydrae obtained by Kulkarni and Abhyankar (1980) are combined with the radial velocity curve of Popper (1979, personal communication) to derive the absolute dimensions and a model of this important Algol system. While the photometric ratios of radii in V and B are in agreement giving k = 0.3812 for a limb darkening coefficient of x = 0.6, application of Irwin's (1947) method gives x = 0.4 for U. The primary is found to be a main sequence A1 V star of mass 2.61M⊙ and radius 2.01 R⊙, and the secondary is classified as a K1 III star of mass 0.70 M⊙ and radius 5.33 R⊙. The observed Fourier coefficients for the light outside the eclipse agree with those calculated from theory for the reflection and ellipticity effects. The system shows an ultraviolet excess of 0.5 to 0.6 magnitudes during primary eclipse, which is attributed to an asymmetric circumstellar distribution of matter around the primary. The evolutionary status of the secondary, which does not appear to fill its Roche lobe completely, is discussed

Absolute dimensions of TT hydrae

The photometric elements of the Algol type binary TT Hydrae derived by the authors from their UBV observations during 1973-77 have been combined with the spectroscopic elements given by Sanford (1937) and Sahade and Cesco (1946) to obtain the absolute dimensions of the system. It is found that the spectroscopic orbital elements given by Sanford represent the evolutionary status of the secondary component better than those of Sahade and Cesco. The primary appears to be an Al v main sequence star of mass ~ 3 to 4m⊙ and radius ~2.3R⊙. The secondary fills its Roche lobe; it can be represented by a K0III star of mass ~0.8m⊙ and radius ~6.0Rm⊙. Better spectroscopic data are needed for confirmation of these results

Cu K-absorption edge study of cuprate superconductors

Cu K-absorption edges of YBa2Cu3O6.9, Tl2CaBa2Cu2O8 and Bi2CaSr2Cu2O8 show similar features. Copper is mainly in the 2+ state in these cuprates suggesting the likely presence of oxygen holes