Entangled-State Cycles of Atomic Collective-Spin States

We study quantum trajectories of collective atomic spin states of $N$ effective two-level atoms driven with laser and cavity fields. We show that interesting ``entangled-state cycles'' arise probabilistically when the (Raman) transition rates between the two atomic levels are set equal. For odd (even) $N$, there are $(N+1)/2$ ($N/2$) possible cycles. During each cycle the $N$-qubit state switches, with each cavity photon emission, between the states $(|N/2,m>\pm |N/2,-m>)/\sqrt{2}$, where $|N/2,m>$ is a Dicke state in a rotated collective basis. The quantum number $m$ ($>0$), which distinguishes the particular cycle, is determined by the photon counting record and varies randomly from one trajectory to the next. For even $N$ it is also possible, under the same conditions, to prepare probabilistically (but in steady state) the Dicke state $|N/2,0>$, i.e., an $N$-qubit state with $N/2$ excitations, which is of particular interest in the context of multipartite entanglement.Comment: 10 pages, 9 figure

High Energy Gamma-Ray Emission From Blazars: EGRET Observations

We will present a summary of the observations of blazars by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO). EGRET has detected high energy gamma-ray emission at energies greater than 100 MeV from more that 50 blazars. These sources show inferred isotropic luminosities as large as $3\times 10^{49}$ ergs s$^{-1}$. One of the most remarkable characteristics of the EGRET observations is that the gamma-ray luminosity often dominates the bolometric power of the blazar. A few of the blazars are seen to exhibit variability on very short time-scales of one day or less. The combination of high luminosities and time variations seen in the gamma-ray data indicate that gamma-rays are an important component of the relativistic jet thought to characterize blazars. Currently most models for blazars involve a beaming scenario. In leptonic models, where electrons are the primary accelerated particles, gamma-ray emission is believed to be due to inverse Compton scattering of low energy photons, although opinions differ as to the source of the soft photons. Hardronic models involve secondary production or photomeson production followed by pair cascades, and predict associated neutrino production.Comment: 16 pages, 7 figures, style files included. Invited review paper in "Observational Evidence for Black Holes in the Universe," 1999, ed. S. K. Chakrabarti (Dordrecht: Kluwer), 215-23

TEV GAMMA-RAYS FROM PROTON BLAZARS

Proton acceleration in nearby blazars can be diagnosed measuring their intense TeV $\gamma$-ray emission. Flux predictions for 1101+384 (Mrk421) and 1219+285 (ON231), both strong EGRET sources (0.1-10 GeV), are obtained from model spectra of unsaturated synchrotron pair cascades fitted to publicly available multifrequency data. An experimental effort to confirm the predicted emission in the range 1-10 TeV would be of great importance for the problems of the origin of cosmic rays, the era of galaxy formation and the cosmological distance scale.Comment: 10 pages of latex using Kluwer spacekap.sty, to appear in Space Science Review

Gamma-Ray Sources Observed by Cos-B

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Past, Present, and Future X-Ray and Gamma-Ray Missions

X- and -ray astronomy began in the early sixties of the last century with balloons flights, sounding rocket experiment and satellites. Long before space satellite detected X- and -rays emitted by cosmic sources, scientists had known that the Universe should be producing these photons. In this chapter we provided an overview of past and present missions that has made the X- and -ray astronomy an integral part of astronomical research, and prospects of future developments

COMPTEL observations of the Orion complex: evidence for cosmic-ray induces gamma-ray lines

We report the detection of gamma-ray emission from the Orion complex in the 3-7 MeV range by the COMPTEL telescope aboard the Compton Gamma Ray Observatory. This emission can be identified with the 4.44 MeV and 6.13 MeV nuclear de-excitation lines of C-12* and O-16*, respectively, which are predicted to be the strongest gamma-ray lines originating from the interaction of energetic particles with ambient matter. However, the observed flux of (1.0 +/- 0.15) X 10(-4) photon cm-2 s-1 (3-7 MeV) is much larger than anticipated. There is good circumstantial evidence that our findings indicate strongly enhanced abundances of C and O in low-energy cosmic rays (approximately 10 MeV/nucleon), rather than high fluxes of cosmic-ray protons and alpha-particles. The positrons resulting from energetic particle interactions in the Orion region should produce 511 keV annihilation radiation that is detectable by OSSE.</p

A supernova remnant associated with the young gamma-ray pulsar PSR1706-44

THE Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory satellite recently detected1 pulsed -radiation from the radio pulsar PSR1706–44; this is only the fourth radio pulsar to be identified as a -ray source. The other three (Vela, the Crab and PSR1509–58) are all associated with supernova remnants (SNRs), whereas very few—perhaps four—of the remaining 500 or so galactic radio pulsars have convincing associations with SNRs2. We have mapped the field around PSR1706 – 44 at 843 MHz with a resolution of 44 arcsec using the Molonglo Observatory Synthesis Telescope, and have identified a shell-type SNR at a distance of about 3 kpc—consistent with the distance deduced for the pulsar. The pulsar is seen as a slightly variable point source, located in an enhanced knot on the arc of the SNR shell