PTF 11kx: A Type Ia Supernova with a Symbiotic Nova Progenitor

There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi

The Angular Size and Proper Motion of the Afterglow of GRB 030329

The bright, nearby (z=0.1685) gamma-ray burst of 29 March 2003 has presented us with the first opportunity to directly image the expansion of a GRB. This burst reached flux density levels at centimeter wavelengths more than 50 times brighter than any previously studied event. Here we present the results of a VLBI campaign using the VLBA, VLA, Green Bank, Effelsberg, Arecibo, and Westerbork telescopes that resolves the radio afterglow of GRB 030329 and constrains its rate of expansion. The size of the afterglow is found to be \~0.07 mas (0.2 pc) 25 days after the burst, and 0.17 mas (0.5 pc) 83 days after the burst, indicating an average velocity of 3-5 c. This expansion is consistent with expectations of the standard fireball model. We measure the projected proper motion of GRB 030329 in the sky to <0.3 mas in the 80 days following the burst. In observations taken 52 days after the burst we detect an additional compact component at a distance from the main component of 0.28 +/- 0.05 mas (0.80 pc). The presence of this component is not expected from the standard model.Comment: 12 pages including 2 figures, LaTeX. Accepted to ApJ Letters on May 14, 200

The Rapidly Fading Afterglow from the Gamma-Ray Burst of 1999 May 6

We report on the discovery of the radio afterglow from the gamma-ray burst (GRB) of 1999 May 6 (GRB 990506) using the Very Large Array (VLA). The radio afterglow was detected at early times (1.5 days), but began to fade rapidly sometime between 1 and 5 days after the burst. If we attribute the radio emission to the forward shock from an expanding fireball, then this rapid onset of the decay in the radio predicts that the corresponding optical transient began to decay between 1 and 5 minutes after the burst. This could explain why no optical transient for GRB 990506 was detected in spite of numerous searches. The cause of the unusually rapid onset of the decay for the afterglow is probably the result of an isotropically energetic fireball expanding into a low density circumburst environment. At the location of the radio afterglow we find a faint (R ~ 24 mag) host galaxy with a double morphology.Comment: in press at ApJ Letters, 13 page LaTeX document includes 2 postscript figure

Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study

High quality ZnO thin films were gown using the pulsed laser deposition technique on (0001) Al$_2$O$_3$ substrates in an oxidizing atmosphere, using a Zn metallic target. We varied the growth conditions such as the deposition temperature and the oxygen pressure. First, using a battery of techniques such as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force microscopy, we evaluated the structural quality, the stress and the degree of epitaxy of the films. Second, the relations between the deposition conditions and the structural properties, that are directly related to the nature of the thin films, are discussed qualitatively. Finally, a number of issues on how to get good-quality ZnO films are addressed.Comment: To be published in Jour. Appl. Phys. (15 August 2004

Variability Profiles of Millisecond X-Ray Pulsars: Results of Pseudo-Newtonian 3D MHD Simulations

We model the variability profiles of millisecond period X-ray pulsars. We performed three-dimensional magnetohydrodynamic simulations of disk accretion to millisecond period neutron stars with a misaligned magnetic dipole moment, using the pseudo-Newtonian Paczynski-Wiita potential to model general relativistic effects. We found that the shapes of the resulting funnel streams of accreting matter and the hot spots on the surface of the star are quite similar to those for more slowly rotating stars obtained from earlier simulations using the Newtonian potential. The funnel streams and hot spots rotate approximately with the same angular velocity as the star. The spots are bow-shaped (bar-shaped) for small (large) misalignment angles. We found that the matter falling on the star has a higher Mach number when we use the Paczynski-Wiita potential than in the Newtonian case. Having obtained the surface distribution of the emitted flux, we calculated the variability curves of the star, taking into account general relativistic, Doppler and light-travel-time effects. We found that general relativistic effects decrease the pulse fraction (flatten the light curve), while Doppler and light-travel-time effects increase it and distort the light curve. We also found that the light curves from our hot spots are reproduced reasonably well by spots with a gaussian flux distribution centered at the magnetic poles. We also calculated the observed image of the star in a few cases, and saw that for certain orientations, both the antipodal hot spots are simultaneously visible, as noted by earlier authors.Comment: 9 pages, 10 figures, accepted for publication in ApJ; corrected some typo

Estimation of Heat Loss in a Closed Vessel

Power cartridges are designed and developed for use in military aircraft in association withHigh Energy Materials Research Laboratory, Pune. During development, the cartridge is firedin a closed vessel to generate basic design parameters. When the cartridge is fired, the heat islost to the walls of the vessel due to conduction, convection, radiation, and to some extent, byexpansion of the vessel. An attempt has been made to estimate the heat loss from the vesseland the surrounding. The aim of this study was to lay down the technical results theoreticallyand their validation through experiments

Multiplicity criteria for isothermal reactions involving two species

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Distribution of the second virial coefficients of globular proteins

George and Wilson [Acta. Cryst. D 50, 361 (1994)] looked at the distribution of values of the second virial coefficient of globular proteins, under the conditions at which they crystallise. They found the values to lie within a fairly narrow range. We have defined a simple model of a generic globular protein. We then generate a set of proteins by picking values for the parameters of the model from a probability distribution. At fixed solubility, this set of proteins is found to have values of the second virial coefficient that fall within a fairly narrow range. The shape of the probability distribution of the second virial coefficient is Gaussian because the second virial coefficient is a sum of contributions from different patches on the protein surface.Comment: 5 pages, including 3 figure

Monojet searches for momentum-dependent dark matter interactions

We consider minimal dark matter scenarios featuring momentum-dependent couplings of the dark sector to the Standard Model. We derive constraints from existing LHC searches in the monojet channel, estimate the future LHC sensitivity for an integrated luminosity of 300 fb−1, and compare with models exhibiting conventional momentum-independent interactions with the dark sector. In addition to being well motivated by (composite) pseudo-Goldstone dark matter scenarios, momentum-dependent couplings are interesting as they weaken direct detection constraints. For a specific dark matter mass, the LHC turns out to be sensitive to smaller signal cross-sections in the momentum-dependent case, by virtue of the harder jet transverse-momentum distribution