2012 (IPP)
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Item Systematic study of X-ray Cavities in the brightest galaxy of the Draco Constellation NGC 6338(2012-01-01) Pandge, M. B.; Vagshette, N. D.; David, L. P.; et.alWe present results based on the systematic analysis of currently available Chandra archive data on the brightest galaxy in the Draco constellation NGC 6338, in order to investigate the properties of the X-ray cavities. In the central 6 kpc, at least a two and possibly three, X-ray cavities are evident. All these cavities are roughly of ellipsoidal shapes and show a decrement in the surface brightness of several tens of percent. In addition to these cavities, a set of X-ray bright filaments are also noticed which are spatially coincident with the Hα filaments over an extent of 15 kpc. The Hα emission line filaments are perpendicular to the Xray cavities. Spectroscopic analysis of the hot gas in the filaments and cavities reveal that the X-ray filaments are cooler than the gas contained in the cavities. The emission line ratios and the extended, asymmetric nature of the Hα emission line filaments seen in this system require a harder ionizing source than that produced by star formation and/or young, massive stars. Radio emission maps derived from the analysis of 1.4GHz VLA FIRST survey data failed to show any association of these X-ray cavities with radio jets, however, the cavities are filled by radio emission. The total power of the cavities is 17×1042 erg s−1 and the ratio of the radio luminosity to cavity power is 10−4, implying that most of the jet power is mechanical.Item Active Region Moss: Doppler Shifts from Hinode/EIS Observations(2012-04-04) Tripathi, Durgesh; Mason, Helen E.; Kelimchuk, Jams AStudying the Doppler shifts and the temperature dependence of Doppler shifts in moss regions can help us understand the heating processes in the core of the ac- tive regions. In this paper we have used an active region observation recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) onboard Hinode on 12-Dec- 2007 to measure the Doppler shifts in the moss regions. We have distinguished the moss regions from the rest of the active region by de ning a low density cut-o as derived by Tripathi et al. (2010). We have carried out a very careful analy- sis of the EIS wavelength calibration based on the method described in Young, O'Dwyer and Mason (2012). For spectral lines having maximum sensitivity be- tween log T = 5:85 and log T = 6:25 K, we nd that the velocity distribution peaks at around 0 km s1 with an estimated error of 45 km s1. The width of the distribution decreases with temperature. The mean of the distribution shows a blue shift which increases with increasing temperature and the distribution also shows asymmetries towards blue-shift. Comparing these results with observables predicted from di erent coronal heating models, we nd that these results are consistent with both steady and impulsive heating scenarios. However, the fact that there are a signi cant number of pixels showing velocity amplitudes that exceed the uncertainty of 5 km s1 is suggestive of impulsive heating. Clearly, further observational constraints are needed to distinguish between these two heating scenarios.Item Cosmic Microwave Background Trispectrum and Primordial Magnetic Field Limits(2012-06-08) Trivedi, Pranjal; Seshadri, T. R.; Subramanian, KandaswamyPrimordial magnetic fields will generate non-Gaussian signals in the cosmic microwave background (CMB) as magnetic stresses and the temperature anisotropy they induce depend quadratically on the magnetic field. We compute a new measure of magnetic non-Gaussianity, the CMB trispectrum, on large angular scales, sourced via the Sachs-Wolfe effect. The trispectra induced by magnetic energy density and by magnetic scalar anisotropic stress are found to have typical magnitudes of approximately a few times 10 29 and 10 19, respectively. Observational limits on CMB non-Gaussianity from WMAP data allow us to conservatively set upper limits of a nG, and plausibly sub-nG, on the present value of the primordial cosmic magnetic field. This represents the tightest limit so far on the strength of primordial magnetic fields, on Mpc scales, and is better than limits from the CMB bispectrum and all modes in the CMB power spectrum. Thus, the CMB trispectrum is a new and more sensitive probe of primordial magnetic fields on large scales.Item Spectral and polarization study of the double relics in Abell 3376 using the GMRT and the VLA(2012-06-15) Kale, Ruta; Dwarakanath, K. S; Bagchi, Joydeep; et.alItem A Minimal Model of Neutrino Flavor(2012-07) Luhn, Christoph; Parattu, Krishna Mohan; Wingerter, AkinModels of neutrino mass which attempt to describe the observed lepton mixing pat- tern are typically based on discrete family symmetries with a non-Abelian and one or more Abelian factors. The latter so-called shaping symmetries are imposed in order to yield a realistic phenomenology by forbidding unwanted operators. Here we propose a supersymmetric model of neutrino avor which is based on the group T7 and does not require extra ZN or U(1) factors, which makes it the smallest realistic family symmetry that has been considered so far. At leading order, the model pre- dicts tribimaximal mixing which arises completely accidentally from a combination of the T7 Clebsch-Gordan coe cients and suitable avon alignments. Next-to-leading order (NLO) operators break the simple tribimaximal structure and render the model compatible with the recent results of the Daya Bay and Reno collaborations which have measured a reactor angle of around 9 . Problematic NLO deviations of the other two mixing angles can be controlled in an ultraviolet completion of the model.Item Experimental and theoretical study on the infrared spectroscopy of astrophysically relevant PAH derivatives 2- and 9-vinylanthracene(2012-07-03) Maurya, Anju; Rastogi, Shantanu; Rouill´, Ga¨el; et.alWe propose to evaluate the contribution of polycyclic aromatic hydrocarbon molecules that carry side groups to the mid-infrared emission spectra. Within this framework, the IR absorption spectra of 2- and 9-vinylanthracene were measured in Ar matrices at 12 K and in CsI and polyethylene pellets at room temperature. The laboratory spectra were analyzed with the support of simulations based on the density functional theory. For each PAH molecule, eight IR spectra were computed by combining the B3LYP functional with as many different basis sets, namely 4-31G, 4-31G(d), 6-31G, 6-311G, 6-31G(d), 6-31G(d,p), 6-31+G(d,p), and 6-31++G(d,p). The comparison of the theoretical spectra with the laboratory data allowed us to determine the most suitable combinations for modeling the IR spectra of neutral PAH molecules that carry a vinyl side group. It was concluded from the examples of 2- and 9-VA that the optimum basis set is 6-31G unless a steric interaction has to be taken into account, in which case the optimum basis set is 6-31G(d). Thus, in the presence of such an interaction, the use of d-type polarization functions is recommended. We discuss the possibility for neutral vinyl-substituted PAHs to contribute to the mid-infrared emission spectra and find that their specific features do not match with the mid-infrared aromatic emission bandItem Numerical simulation of time delay interferometry for LISA with the simplification or having only one interferometer(2012-08) Dhurandhar, S.V.; Ni, W.-T.; Wang, G.Item Characterizing Foreground for redshifted 21-cm radiation: 150 MHz GMRT observations(2013-09-05) Ghosh, Abhik; Prasad, Jayanti; Bharadwaj, Somnath; Ali, Saiyad; Chengalur, Jayaram N.Item A New Window into Stochestic Gravitational Wave Background(2013-09-20) Rotti, Aditya; Souradeep, TarunA stochastic gravitational wave background (SGWB) would gravitationally lens the cosmic mi- crowave background (CMB) photons. We correct the results provided in existing literature for modi cations to the CMB polarization power spectra due to lensing by gravitational waves (GW). Weak lensing by gravitational waves (GW) distorts all the four CMB power spectra, however its e ect is most striking in the mixing of power between the E-mode and B-mode of CMB polarization. This suggests the possibility of using measurements of the CMB angular power spectra to constrain the energy density ( GW) of the SGWB. Using current data sets (QUAD, WMAP and ACT), we nd that the most stringent constraints on the present GW come from measurements of the angular power spectra of CMB temperature anisotropies. In near future more stringent bounds on GW can be expected with improved upper limits on the B-modes of CMB polarization. Any detection of B-modes of CMB polarization above the expected signal from large scale structure(LSS) lensing could be a signal for a SGWBItem On the wavy mechanics of particles(IUCAA, 2015-02) Das, SantanuItem WMAP anomaly : Weak lensing in disguise(IUCAA, 2015-02) Rotti, Aditya; Aich, Moumita; Souradeep, TarunItem Machian gravity and the giant galactic forces(IUCAA, 2015-02) Das, SantanuItem Dipole leakage and low CMB multipoles(IUCAA, 2015-02) Das, Santanu; Souradeep, TarunItem Revealing Non-circular beam effect in WMAP-7 CMB maps with BipoSH measures of Statistical Isotropy(IUCAA, 2015-02) Joshi, Nidhi; Das, Santanu; Mitra, SanjitItem Cosmological solution of Machian gravity(IUCAA, 2015-02) Das, Santanu