Discovery of a remarkable subpulse drift pattern in PSR B0818-41

We report the discovery of a remarkable subpulse drift pattern in the relatively less studied wide profile pulsar, B0818-41, using high sensitivity GMRT observations. We find simultaneous occurrence of three drift regions with two different drift rates: an inner region with steeper apparent drift rate flanked on each side by a region of slower apparent drift rate. Furthermore, these closely spaced drift bands always maintain a constant phase relationship. Though these drift regions have significantly different values for the measured P2, the measured P3 value is the same and equal to 18.3 P1. We interpret the unique drift pattern of this pulsar as being created by the intersection of our line of sight (LOS) with two conal rings on the polar cap of a fairly aligned rotator (inclination angle alpha ~ 11 deg), with an ``inner'' LOS geometry (impact angle beta ~ -5.4 deg). We argue that both the rings have the same values for the carousel rotation periodicity P4 and the number of sparks Nsp. We find that Nsp is 19-21 and show that it is very likely that, P4 is the same as the measured P3, making it a truly unique pulsar. We present results from simulations of the radiation pattern using the inferred parameters, that support our interpretations and reproduce the average profile as well as the observed features in the drift pattern quite well.Comment: 5 pages and 7 figures, Accepted for publication in MNRAS Letter

Probing the anisotropy of the Milky Way gaseous halo: Sight-lines toward Mrk 421 and PKS2155-304

(Abridged) We recently found that the halo of the Milky Way contains a large reservoir of warm-hot gas that contains a large fraction of the missing baryons from the Galaxy. The average physical properties of this circumgalactic medium (CGM) are determined by combining average absorption and emission measurements along several extragalactic sightlines. However, there is a wide distribution of both, the halo emission measure and the \ovii column density, suggesting that the Galactic warm-hot gaseous halo is anisotropic. We present {\it Suzaku} observations of fields close to two sightlines along which we have precise \ovii absorption measurements with \chandran. The column densities along these two sightlines are similar within errors, but we find that the emission measures are different. Therefore the densities and pathlengths in the two directions must be different, providing a suggestive evidence that the warm-hot gas in the CGM of the Milky Way is not distributed uniformly. However, the formal errors on derived parameters are too large to make such a claim. The average density and pathlength of the two sightlines are similar to the global averages, so the halo mass is still huge, over 10 billion solar masses. With more such studies, we will be able to better characterize the CGM anisotropy and measure its mass more accurately. We also show that the Galactic disk makes insignificant contribution to the observed \ovii absorption; a similar conclusion was also reached independently about the emission measure. We further argue that any density inhomogeneity in the warm-hot gas, be it from clumping, from the disk, or from a non-constant density gradient, would strengthen our result in that the Galactic halo path-length and the mass would become larger than what we estimate here. As such, our results are conservative and robust.Comment: 27 pages, 5 figures, submitted to Ap

Understanding the effects of geometry and rotation on pulsar intensity profiles

We have developed a method to compute the possible distribution of radio emission regions in a typical pulsar magnetosphere, taking into account the viewing geometry and rotational effects of the neutron star. Our method can estimate the emission altitude and the radius of curvature of particle trajectory as a function of rotation phase for a given inclination angle, impact angle, spin-period, Lorentz factor, field line constant and the observation frequency. Further, using curvature radiation as the basic emission mechanism, we simulate the radio intensity profiles that would be observed from a given distribution of emission regions, for different values of radio frequency and Lorentz factor. We show clearly that rotation effects can introduce significant asymmetries into the observed radio profiles. We investigate the dependency of profile features on various pulsar parameters. We find that the radiation from a given ring of field lines can be seen over a large range of pulse longitudes, originating at different altitudes, with varying spectral intensity. Preferred heights of emission along discrete sets of field lines are required to reproduce realistic pulsar profiles, and we illustrate this for a known pulsar. Finally, we show how our model provides feasible explanations for the origin of core emission, and also for one-sided cones which have been observed in some pulsars.Comment: 21 pages, 11 figures, accepted for publication in MNRA

Donor complex formation due to a high-dose Ge implant into Si

To investigate boron deactivation and/or donor complex formation due to a high‐dose Ge and C implantation and the subsequent solid phase epitaxy, SiGe and SiGeC layers were fabricated and characterized. Cross‐sectional transmission electron microscopy indicated that the SiGe layer with a peak Ge concentration of 5 at. % was strained; whereas, for higher concentrations, stacking faults were observed from the surface to the projected range of the Ge as a result of strain relaxation. Photoluminescence (PL) results were found to be consistent with dopant deactivation due to Ge implantation and the subsequent solid phase epitaxial growth of the amorphous layer. Furthermore, for unstrained SiGe layers (Ge peak concentration ≥7 at. %), the PL results support our previously proposed donor complex formation. These findings were confirmed by spreading resistance profiling. A model for donor complex formation is proposed

A huge reservoir of ionized gas around the Milky Way: Accounting for the Missing Mass?

Most of the baryons from galaxies have been "missing" and several studies have attempted to map the circumgalactic medium (CGM) of galaxies in their quest. Recent studies with the Hubble Space Telescope have shown that many galaxies contain a large reservoir of ionized gas with temperatures of about 10^5 K. Here we report on X-ray observations made with the Chandra X-ray Observatory probing an even hotter phase of the CGM of our Milky Way at about 10^6 K. We show that this phase of the CGM is massive, extending over a large region around the Milky Way, with a radius of over 100 kpc. The mass content of this phase is over ten billion solar masses, many times more than that in cooler gas phases and comparable to the total baryonic mass in the disk of the Galaxy. The missing mass of the Galaxy appears to be in this warm-hot gas phase.Comment: 15 pages, 3 figures; http://stacks.iop.org/2041-8205/756/L

Chiral Phase Transition in Lattice QCD with Wilson Quarks

The nature of the chiral phase transition in lattice QCD is studied for the cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice with the temporal direction extension $N_t=4$. We find that the chiral phase transition is continuous for the case of 2 flavors, while it is of first order for 3 and 6 flavors.Comment: uuencoded compressed tar file, LaTeX, 14 pages, 7 figure

On the implications of a dilaton in gauge theory

Some recent work on the implications of a dilaton in 4d gauge theories are revisited. In part I of this paper we see how an effective dilaton coupling to gauge kinetic term provides a simple attractive mechanism to generate confinement. In particular, we put emphasis on the derivation of confining analytical solutions and look into the problem how dilaton degrees of freedom modify Coulom potential and when a confining phase occurs. In part II, we solve the semi-relativistic wave equation, for Dick interquark potential using the Shifted l-expansion technique (SLET) in the heavy quarkonium sector. The results of this phenomenological analysis proves that these effective theories can be relevant to model quark confinement and may shed some light on confinement mechanism.Comment: 8 pages. Talk given at CTP Symposium on Supersymmetry at LHC: Theoretical and Experimental Prospectives, Cairo, Egypt, 11-14 Mar 200

Where we stand on structure dependence of ISGMR in the Zr-Mo region: Implications on K_\infty

Isoscalar giant resonances, being the archetypal forms of collective nuclear behavior, have been studied extensively for decades with the goal of constraining bulk nuclear properties of the equation of state, as well as for modeling dynamical behaviors within stellar environments. An important such mode is the isoscalar electric giant monopole resonance (ISGMR) that can be understood as a radially symmetric density vibration within the saturated nuclear volume. The field has a few key open questions, which have been proposed and remain unresolved. One of the more provocative questions is the extra high-energy strength in the $A\approx 90$ region, which manifested in large percentages of the $E0$ sum rule in $^{92}$Zr and $^{92}$Mo above the main ISGMR peak. The purpose of this article is to introduce these questions within the context of experimental investigations into the phenomena in the zirconium and molybdenum isotopic chains, and to address, via a discussion of previously published and preliminary results, the implications of recent experimental efforts on extraction of the nuclear incompressibility from this data.Comment: 9 pages, 7 figures, invited to be submitted to a special issue of EPJA honoring Prof. P. F. Bortigno

Surfactant induced smooth and symmetric interfaces in Cu/Co multilayers

In this work we studied Ag surfactant induced growth of Cu/Co multilayers. The Cu/Co multilayers were deposited using Ag surfactant by ion beam sputtering technique. It was found that Ag surfactant balances the asymmetry between the surface free energy of Cu and Co. As a result, the Co-on-Cu and Cu-on-Co interfaces become sharp and symmetric and thereby improve the thermal stability of the multilayer. On the basis of obtained results, a mechanism leading to symmetric and stable interfaces in Cu/Co multilayers is discussed.Comment: 7 Pages, 7 Figure

Flux-density spectral analysis for several pulsars and two newly-identified gigahertz-peaked spectra

In this paper we present results from flux density measurements for 21 pulsars over a wide frequency range, using the Giant Metrewave Radio Telescope (GMRT) and the Effelsberg telescope. Our sample was a set of mostly newly discovered pulsars from the selection of candidates for gigahertz-peaked spectra (GPS) pulsars. Using the results of our observations along with previously published data, we identify two new GPS pulsars. One of them, PSR J1740+1000, with dispersion measure of 24 pc cm$^{-3}$, is the first GPS pulsar with such a low DM value.We also selected several strong candidates for objects with high frequency turnover in their spectra which require further investigation.We also revisit our source selection criteria for future searches for GPS pulsars.Comment: 10 pages, 2 tables, 9 figures, accepted for publication in MNRA