5941 research outputs found
Sort by
pγ interactions in Galactic jets as a plausible origin of the positron excess
No full textOpen Access.The positron flux measured near Earth shows a rise with energy beyond 30 GeV. We show that this rise might be compatible with the production of positrons in pγ interactions in the jets of microquasars
Astrosat Mission
No full textRestricted Access.ASTROSAT is India’s first astronomy satellite that will carry an array of instruments capable of simultaneous observations in a broad range of wavelengths: from the visible, near ultraviolet (NUV), far-UV (FUV), soft X-rays to hard X-rays. There will be five principal scientific payloads aboard the satellite: (i) a Soft X-ray Telescope (SXT), (ii) three Large Area Xenon Proportional Counters (LAXPCs), (iii) a Cadmium-Zinc-Telluride Imager (CZTI), (iv) two Ultra-Violet Imaging Telescopes (UVITs) one for visible and near-UV channels and another for far-UV, and (v) three Scanning Sky Monitors (SSMs). It will also carry a charged particle monitor (CPM). Almost all the instruments have qualified and their flight models are currently in different stages of integration into the satellite structure in ISRO Satellite Centre. ASTROSAT is due to be launched by India’s Polar Satellite Launch Vehicle (PSLV) in the first half of 2015 in a circular 600 km orbit with inclination of ~6 degrees, from Sriharikota launching station on the east coast of India. A brief description of the design, construction, capabilities and scientific objectives of all the main scientific payloads is presented here. A few examples of the simulated observations with ASTROSAT and plans to utilize the satellite nationally and internationally are also presented
Optical and saturation behavior of thermally surface plasmon-tuned cu nanorod composite glasses
No full textRestricted Access.In this work, the optical and nonlinear optical properties of copper (Cu) nanocomposite glasses have been reported. Cu nanocomposite glasses are prepared through ion exchange process, further thermal annealing yields the shape variations. Optical absorption studies reveal the dual bands in the vicinity of surface plasmon absorption; this is attributed to the shape changes after thermal annealing and theoretical predictions, using Gans theory for nonspherical metal nanoparticles, about absorption maxima is well agreed with the optical absorption data. The investigations of fluorescence signify the possibility of Cu+ ions in the glass matrix along with Cu nanoparticles. Nonlinear optical studies show saturation behavior, which is due to plasmon band bleach
Classical light sources with tunable temporal coherence and tailored photon number distributions
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We demonstrate a method of obtaining, from coherent light, tunable classical light where the temporal characteristics and photon number distribution can be controlled electronically. The tunability of the temporal coherence is shown through second-order correlation (G 2(τ)) measurements, both in the continuous intensity measurement as well as in the photon counting regime. The generation of desired classical photon number distributions is illustrated by creating two light sources —one emitting a thermal state and the other a specific classical non-Gaussian state. Such tailored light sources with emission characteristics quite different from those of existing natural light sources are likely to be useful in quantum information processing, for example, in conjunction with photon addition, to generate tailored non-classical states of light with desired photon number distributions. As a particular application in this direction we also outline how a tailored classical non-Gaussian state generated by our technique may be mixed with a non-classical Gaussian state at a beamsplitter, to generate novel forms of non-Gaussian entanglement
Search for gravitational radiation from intermediate mass black hole binaries in data from the second LIGO-Virgo joint science run
No full textOpen AccessThis paper reports on an unmodeled, all-sky search for gravitational waves from merging intermediate mass black hole binaries (IMBHB). The search was performed on data from the second joint science run of the LIGO and Virgo detectors (July 2009–October 2010) and was sensitive to IMBHBs with a range up to ∼200 Mpc, averaged over the possible sky positions and inclinations of the binaries with respect to the line of sight. No significant candidate was found. Upper limits on the coalescence-rate density of nonspinning IMBHBs with total masses between 100 and 450 M⊙ and mass ratios between 0.25 and 1 were placed by combining this analysis with an analogous search performed on data from the first LIGO-Virgo joint science run (November 2005–October 2007). The most stringent limit was set for systems consisting of two 88 M⊙ black holes and is equal to 0.12 Mpc−3 Myr−1 at the 90% confidence level. This paper also presents the first estimate, for the case of an unmodeled analysis, of the impact on the search range of IMBHB spin configurations: the visible volume for IMBHBs with nonspinning components is roughly doubled for a population of IMBHBs with spins aligned with the binary’s orbital angular momentum and uniformly distributed in the dimensionless spin parameter up to 0.8, whereas an analogous population with antialigned spins decreases the visible volume by ∼20%
Gravitational waves from known pulsars: results from the initial detector era
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper
Constraints on cosmic strings from the LIGO-Virgo gravitational-wave detectors
No full textOpen AccessCosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension Gμ below 10−8 in some regions of the cosmic string parameter space
Choosing Raman's successor for Raman Research Institute.
No full textOpen AccessRaman Research Institute, Bangalore, is an internationally recognized scientific research centre. How, soon after the founder C. V. Raman’s death, it was transformed from a private work place into a state-funded national facility is a fascinating chapter in the institutional history of modern science in independent India. This transformation is discussed here in the light of primary source material not consulted before and oral history recorded expressly for the purpose
Catch the Raman effect
No full textNews item on Exhibition " Celebrating the life of a Rare Gem" organised by IISc Archives and Publication cell