IUCAA Preprints
Permanent URI for this communityhttp://localhost:4000/handle/11007/149
Browse
39 results
Search Results
Item OVRO CMB anisotropy measurement constraints on flat - ^ and open CDM cosmogonies(2012-03-13) Mukherjee, Pia; Souradeep, Tarun; Ratra, Bharat; et al.We use Owens Valley Radio Observatory (OVRO) cosmic microwave backgroun (CMB) anisotropy data to constrain cosmological parameters. We account for th OVRO beamwidth and calibration uncertainties, as well as the uncertainty induced b the removal of non-CMB foreground contamination. We consider open and spatially flat-Λ cold dark matter cosmogonies, with nonrelativistic-mass density parameter Ω0 the range 0.1–1, baryonic-mass density parameter ΩB in the range (0.005–0.029)h− and age of the universe t0 in the range (10–20) Gyr. Marginalizing over all paramete but Ω0, the OVRO data favors an open (spatially-flat-Λ) model with Ω0 ≃ 0.33 (0.1 At the 2 σ confidence level model normalizations deduced from the OVRO data a mostly consistent with those deduced from the DMR, UCSB South Pole 1994, Pytho I-III, ARGO, MAX 4 and 5, White Dish, and SuZIE data sets.Item Collimated flow driven by radiative pressure from the nucleus of quasar Q 1511 + 091(2011-07-06) Srianand, R.; Petitjean, Patrick; Ledoux, C.; et al.High velocity outflows from quasars are revealed by the absorption signatures they produce in the spectrum of the quasar. Clues on the nature and origin of these flows are important for our understanding of the dynamics of gas in the central regions of the Active Galactic Nucleus (AGNs) but also of the metal enrichment of the intergalactic space. Line radiation pressure has often been suggested to be an important process in driving these outflows, however no convincing evidence has been given so far. Here we report observation of a highly structured flow, toward Q 1511+091, where the velocity separations between distinct components are similar to O vi, N v and C iv doublet splittings with some of the profiles matching perfectly. This strongly favors the idea that the absorbing clumps originate at similar physical location and are driven by radiative acceleration due to resonance lines. The complex absorption can be understood if the flow is highly collimated so that the different optically thick clouds are aligned and cover the same region of the background source. One component shows saturated H i Lyman series lines together with absorptions from excited levels from C ii and Si ii but covers only 40% of the source of continuum. The fact that clouds cover only part of the small continuum source implies that the flow is located very close to it.Item CMB Anisotropy Constraints on Flat-Lambda and Open CDM Cosmogonies from DMR, UCSB South Pole, Python, ARGO, MAX, White Dish, OVRO, and SuZIE Data(2011-07-06) Mukherjee, Pia; Ken, Ganga; Ratra, Bharat; et al.We use joint likelihood analyses of combinations of fifteen cosmic microwave back- ground (CMB) anisotropy data sets from the DMR, UCSB South Pole 1994, Python I–III, ARGO, MAX 4 and 5, White Dish, OVRO, and SuZIE experiments to constrain cosmogonies. We consider open and spatially-flat-Λ cold dark matter cosmogonies, with nonrelativistic-mass density parameter Ω0 in the range 0.1–1, baryonic-mass den- sity parameter ΩB in the range (0.005–0.029)h−2 , and age of the universe t0 in the range (10–20) Gyr. Marginalizing over all parameters but Ω0, the data favor Ω0 ≃ 0.9–1 (0.4–0.6) flat- Λ (open) models. The range in deduced Ω0 values is partially a consequence of the different combinations of smaller-angular-scale CMB anisotropy data sets used in the analyses, but more significantly a consequence of whether the DMR quadrupole moment is accounted for or ignored in the analysis. While the open model is difficult to reconcile with the results of less exact analyses of more recent CMB anisotropy data, the lower values of Ω0 found in this case are more easily reconciled with dynamical estimates of this parameter. For both flat-Λ and open models, after marginalizing over all other parameters, a lower ΩBh2 ≃ 0.005–0.009 is favored. This is also marginally at odds with estimates from more recent CMB anisotropy data and some estimates from standard nucleosynthesis theory and observed light element abundances. For both sets of models a younger universe with t0 ≃ 12–15 Gyr is favored, consistent with other recent non- CMB indicators. We emphasize that since we consider only a small number of data sets, these results are tentative. More importantly, the analyses here do not rule out the currently favored flat-Λ model with Ω0 ∼ 0.3, nor the larger ΩBh2 values favored by some other data.Item Time delay interferometry and LISA optimal sensitivity(2011-07-05) Pai, A.; Nayak, K. R.; Dhurandhar, Sanjeev; et al.The sensitivity of LISA depends on the suppression of several noise sources; dominant one is laser frequency noise. It has been shown that the six Doppler data streams obtained from three space-crafts can be appropriately time delayed and optimally combined to cancel this laser frequency noise. We show that the optimal data combinations when operated in a network mode improves the sensitivity over Michelson ranging from 40% to 100%. In this article, we summarize these results. We further show that the residual laser noise in the optimal data combination due to typical arm-length inaccuracy of 200 m is much below the level of optical path and the proof mass noises.Item Possible evidence of surface vibration of realistic strange stars from stellar observations(2011-07-05) Ray, Subharthi; Dey, Jishnu; Dey, Mira; et al.Emission lines in the eV and keV range by certain stellar candidates from their recent analysis invoke the question of their possible origin. These stars under consideration, are the 4U 0614+091 (0.65, 0.86, and 1.31 keV ), 2S 0918−549 (0.8 keV with width 55 eV ), 4U 1543−624 (0.7 keV ), 4U 1850 −087 (0.7 keV ) and 4U 1820−30 (0.6 and 0.9 keV ) and also the 0.6 keV excess emission in RX J170930.2−263927. Recently, it has been suggested that the resonance absorption at ∼ in 0.7, 1.4, 2.1 and 2.8 keV 1E1207−5209 and 0.35, 0.7 and 1.4 keV RX J1856.5−3754 are due to harmonic surface vibrations in strange stars. We propose that these harmonic vibrations may also responsible for emission lines in the above mentioned compact stellar candidates.Item Outflowing material in the Zem=4.92 BAL QSO SDSS J160501.21 - 011220.0(2011-07-05) Gupta, Neeraj; Srianand, R.; Petitjean, Patrick; et al.We present the analysis of broad absorption lines (BALs) seen in the spectrum of the zem ≃4.92 QSO SDSS J160501.21-011220.0. Our high spectral resolution UVES spectrum shows two well detached absorption line systems at zabs= 4.685 and 4.855. The system at zabs= 4.855 covers the background source completely suggesting that the gas is located outside the broad emission line region. On the contrary the system at zabs= 4.685, which covers only on the continuum source, has a covering factor of the order of 0.9. Physical conditions are investigated in the BAL system at zabs= 4.855 using detailed photoionization models. The observed H i absorption line together with the limits on C ii and Si ii absorptions suggest that 16 < log N(H i) (cm−2 ) < 17 in this system. Comparison with models show that the observed column densities of N v , Si iv and C iv in this system require that nitrogen is underabundant by more than a factor 3 compared to silicon if the ionizing radiation is similar to a typical QSO spectrum. This is contrary to what is usually derived for the emission line gas in QSOs. We show that the relative suppression in the N v column density can be explained for Solar abundance ratios or abundance ratios typical of Starburst abundances if an ionizing spectrum devoid of X-rays is used instead. Thus, if the composition of BAL is like that of the emission line regions it is most likely that the cloud sees a spectrum devoid of X-rays similar to what we observe from this QSO. This is consistent with the fact that none of our models have high Compton optical depth to remove X-rays from the QSO. Similar arguments lead to the conclusion that the system at zabs= 4.685 as well is not Compton thick. Using simple Eddington arguments we show that the mass of the central black hole is ∼ 8 × 108 M⊙. This suggests that the accretion onto a seed black hole must have started as early as z = 11.Item Origin and interpretation of kilohertz QPOs from strange stars in X-ray Binary system: Theoretical hydrodynamical description(2011-07-05) Mukhopadhyay, B.; Ray, Subharthi; Dey, Jishnu; et al.We model and interpret the Kilohertz QPOs from the hydrodynamical description of accretion disk around a rapidly rotating compact strange star. The higher QPO frequency is described by the viscous effects of accretion disk leading to shocks, while the lower one is taken to be the Keplerian motion of the accreting matter. Comparing our results with the observations for two of the fastest rotating compact stellar candidates namely, 4U 1636−53 and KS 1731−260, we find that they match to a very good approximation, thus interpreting them as strange stars.Item Giant meterwave radio telescope observations of an M2.8 flare: insights into the initiation of a flare-coronal mass ejection event(2011-07-05) Subramanian, Prasad; Ananthakrishnan, S.; Janardhan, P.; et al.We present the first observations of a solar flare with the GMRT. An M2.8 flare observed at 1060 MHz with the GMRT on Nov 17 2001 was associated with a prominence eruption observed at 17 GHz by the Nobeyama radioheliograph and the initiation of a fast partial halo CME observed with the LASCO C2 corono- graph. Towards the start of the eruption, we find evidence for reconnection above the prominence. Subsequently, we find evidence for rapid growth of a vertical current sheet below the erupting arcade, which is accompanied by the flare and prominence eruption.Item Exploring the expanding universe and dark energy using the statefinder diagnostic(2011-07-05) Ujjaini, Alam; Sahni, Varun; Saini, Tarun Deep; et al.The coming few years are likely to witness a dramatic increase in high quality Sn data as current surveys add more high redshift supernovae to their inventory and as newer and deeper supernova experiments become operational. Given the current variety in dark energy models and the expected improvement in observational data, an accurate and versatile diagnostic of dark energy is the need of the hour. This paper examines the Statefinder diagnostic in the light of the proposed SNAP satellite which is expected to observe about 2000 supernovae per year. We show that the Statefinder is versatile enough to differentiate between dark energy models as varied as the cosmological constant on the one hand, and quintessence, the Chaplygin gas and braneworld models, on the other. Using SNAP data, the Statefinder can distinguish a cosmological constant (w = −1) from quintessence models with w > −0.9 and Chaplygin gas models with κ 6 15 at the 3σ level if the value of Ωm is known exactly. The Statefinder gives reasonable results even when the value of Ωm is known to only ∼ 20% accuracy. In this case, marginalizing over Ωm and assuming a fiducial LCDM model allows us to rule out quintessence with w > −0.85 and the Chaplygin gas with κ 6 7 (both at 3σ). These constraints can be made even tighter if we use the Statefinders in conjunction with the deceleration parameter. The Statefinder is very sensitive to the total pressure exerted by all forms of matter and radiation in the universe. It can therefore differentiate between dark energy models at moderately high redshifts of z < 10.Item Magnetic quenching of alpha and diffusity tensors in helical turbulence(2011-07-06) Brandenburg, Axel; Biman, B.; Subramanian, Kandaswamy; et al.We study the implications of primordial magnetic fields for the thermal and ionization history of the post-recombination era. In particular we compute the effects of dissipation of primordial magnetic fields owing to ambipolar diffusion and decaying turbulence in the intergalactic medium (IGM) and the collapsing halos and compute the effects of the altered thermal and ionization history on the formation of molecular hydrogen.We show that, for magnetic field strengths in the range 2×10−10 G < ∼ B0 < ∼ 2× 10−9 G, the molecular hydrogen fraction in IGM and collapsing halo can increase by a factor 5 to 1000 over the case with no magnetic fields. We discuss the implication of the increased molecular hydrogen fraction on the radiative transfer of UV photons and the formation of first structures in the universe