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Directed search for continuous gravitational waves from the Galactic center
No full textOpen AccessWe present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic center region, performed on two years of data from LIGO’s fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first-order spindown values down to -7.86×10-8Hz/s at the highest frequency. No gravitational waves were detected. The 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic center are ˜3.35×10-25 for frequencies near 150 Hz. These upper limits are the most constraining to date for a large-parameter-space search for continuous gravitational wave signals
Efficient quantum random number generation using quantum indistinguishability
No full textRestricted Access.In this paper, we propose a quantum method for generation of random numbers based on bosonic stimulation. Randomness arises through the path-dependent indeterministic amplification of two competing bosonic modes. We show that the process provides an efficient method for macroscopic extraction of microscopic randomness
Momentum-dependent s-wave and d-wave interactions in atomic Bose-Einstein condensates
No full textOpen AccessWe investigate the role of momentum-dependent interactions to determine the ground-state properties in the Bose-Einstein condensate for large scattering lengths (a) such that ka ≥1, even for small momentum (p) where p=ℏk and k is the wave number. The results for momentum-dependent and momentum-independent interactions differ significantly, even for moderate values of a, and the effect of higher partial-wave interaction increases with the increase in a. We have made an attempt to compare the theoretical column density with experimental results at different magnetic fields [Cornish et al., Phys. Rev. Lett. 85, 1795 (2000)]. Since the initial number of atoms changes while swapping the magnetic field and the actual value of the number of atoms at different magnetic fields is not known, we studied the dependence of column densities on the value of N at different magnetic fields. We present here the results for those values of N for which the theoretical column densities are comparable with the experimental results. It is shown that the column density for 85Rb atoms at 100 nK with momentum-dependent interaction is in fairly good agreement with the experimental values for different values of N at two different values of magnetic fields (B=157.2 and 156.4 G)
Supernovae and AGN driven galactic outflows
No full textRestricted Access. An open-access version is available at arXiv.org. Articles older than 2 years are open to all at the journal siteWe present analytical solutions for winds from galaxies with a Navarro-Frank-White (NFW) dark matter halo. We consider winds driven by energy and mass injection from multiple supernovae (SNe), as well as momentum injection due to radiation from a central black hole. We find that the wind dynamics depends on three velocity scales: (1) describes the effect of starburst activity, with as energy and mass injection rate in a central region of radius R; (2) v • ~ (GM •/2R)1/2 for the effect of a central black hole of mass M • on gas at distance R; and (3) , which is closely related to the circular speed (vc ) for an NFW halo, where rs is the halo scale radius and is a function of the halo concentration parameter. Our generalized formalism, in which we treat both energy and momentum injection from starbursts and radiation from the central active galactic nucleus (AGN), allows us to estimate the wind terminal speed to be (4v 2 sstarf + 6(Γ – 1)v • 2 – 4v 2 s )1/2, where Γ is the ratio of force due to radiation pressure to gravity of the central black hole. Our dynamical model also predicts the following: (1) winds from quiescent star-forming galaxies cannot escape from 1011.5 M ☉ ≤ Mh ≤ 1012.5 M ☉ galaxies; (2) circumgalactic gas at large distances from galaxies should be present for galaxies in this mass range; (3) for an escaping wind, the wind speed in low- to intermediate-mass galaxies is ~400-1000 km s–1, consistent with observed X-ray temperatures; and (4) winds from massive galaxies with AGNs at Eddington limit have speeds gsim 1000 km s–1. We also find that the ratio [2v 2 sstarf – (1 – Γ)v • 2]/v 2 c dictates the amount of gas lost through winds. Used in conjunction with an appropriate relation between M • and Mh and an appropriate opacity of dust grains in infrared (K band), this ratio has the attractive property of being minimum at a certain halo mass scale (Mh ~ 1012-1012.5 M ☉) that signifies the crossover of AGN domination in outflow properties from starburst activity at lower masses. We find that stellar mass for massive galaxies scales as M sstarfvpropM 0.26 h , and for low-mass galaxies, M sstarfvpropM 5/3 h
Testing hadronic models of gamma ray production at the core of Cen A
No full textOpen Access.The Pierre Auger experiment has observed a few cosmic ray events above 55 EeV from the direction of the core of Cen A. These cosmic rays might have originated from the core of Cen A. High-energy gamma ray emission has been observed by HESS from the radio core and inner kpc jets of Cen A. We are testing whether pure hadronic interactions of protons or heavy nuclei with the matter in the core region or photodisintegration of heavy nuclei can explain the cosmic ray and high-energy gamma ray observations from the core of Cen A. The scenario of p-γ interactions followed by photopion decay has been tested earlier by Sahu et al. and found to be consistent with the observational results. In this paper, we have considered some other possibilities: (i) The primary cosmic rays at the core of Cen A are protons, and the high-energy gamma rays are produced in p-p interactions. (ii) The primary cosmic rays are Fe nuclei, and the high-energy gamma rays are produced in Fe-p interactions. (iii) The primary cosmic rays are Fe nuclei, and they are photodisintegrated at the core. The daughter nuclei deexcite, and high-energy gamma rays are produced. The high-energy gamma ray fluxes expected in each of these cases are compared with the flux observed by the HESS experiment to normalize the spectrum of the primary cosmic rays at the core. We have calculated the expected number of cosmic ray nucleon events to be between 55 and 150 EeV in each of these cases to verify the consistencies of the different scenarios with the observations by the Pierre Auger experiment. We find that if the primary cosmic rays are Fe nuclei, then their photodisintegration followed by the deexcitation of daughter nuclei may explain the observed high-energy particle emissions from the core of Cen A. The luminosity of the cosmic ray Fe nuclei required to explain the observational results of HESS and Pierre Auger is higher than the luminosity of the cosmic ray protons in the p-γ interaction model. The required cosmic ray luminosity depends on the density of the low-energy photons at the source, which photodisintegrate the Fe nuclei, and the size of the emitting region
