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Excitations in {sup 192}Po have been studied via in-beam {gamma}-ray spectroscopy following the {sup 164}Er + 164 MeV {sup 32}S reaction. The experiment was performed at the ATLAS facility using ten Compton-suppressed Ge detectors and the Fragment Mass Analyzer. The {alpha} decay of {sup 192}Po has been used to identify prompt {gamma}-ray transitions by means of the recoil decay tagging technique. The first three excited states of {sup 192}Po were established. The particle-core model has been successfully used to model these excitations and the quasiparticle random phase approximation has been applied to extract microscopic wave functions of the 2{sub 1}{sup +} states. {copyright} {ital 1997} {ital The American Physical Society}

We adopt the scenario of radio pulsar evolution proposed by Ruderman and his coworkers, in which pulsars evolving in different phases radiate characteristic gamma-ray spectra. The neutron star spins down until the outer magnetosphere e ± -pair production and current flow are quenched and the magnetic dipole radiation torque aligns the dipole with the spin axis. Such aligned dead pulsars can be reignited by transient thermal X-ray emission from the stellar surface; thermal energy released, say, during glitches. The resultant gamma-ray spectra are used to fit several observed hard gamma-ray burst spectra, and provide a consistent fit. The amount of e ± -pairs produced during the process is calculated, and is large enough to cause the annihilation-line features observed in some of the bursts

We assume that the centers of some active galactic nuclei consists of a supermassive non‐rotating black hole surrounded by a magnetized, cool Keplerian disk and a magnetosphere which is resembling that found surrounding a magnetic neutron star in an accreting binary system. Flux tubes passing through two differential rotation regions could result in a large potential drop along the B‐field lines. Electrons are expected to accelerate and radiate curvature photons. These curvature photons are energetic enough to produce secondary e± pairs in collisions with the ambient infrared photons. These secondary pairs will radiate synchrotron photons in a wide energy range but only those photons with energies in the range of 10 GeV and below can escape from the ambient UV and soft X‐ray photon field. The γ‐ray spectral index is luminosity dependent, but the X‐ray spectral index is very insensitive to the luminosity. We use 3C279 and 3C273 to illustrate our model.

We adopt the scenario of the evolution of radio pulsars proposed by Ruderman and his co‐workers, in which the model pulsars evolve in different phases radiate a characteristic γ‐ray spectrum. The neutron star will spin down to some extent that the outer magnetosphere e± pair production and current flow are quenched, the star’s magnetic dipole radiation torque will align its dipole with the spinning axis. Such aligned dead pulsars can be reignited by a transient thermal x‐ray emission from the stellar surface. The resulting γ‐ray spectra are used to fit several observed hard γ‐ray spectra and provide a consistent fit. The amount of e± pairs produced during the process is calculated and is large enough to cause the annihilation line features of some of the bursts. It is concluded that re‐ignition of nearby dead pulsars can be one of the possible sources of producing γ‐ray bursts.

Prompt, in-beam γ rays in coincidence with evaporation residues were measured in the 164,166Er + 164 MeV 32S reactions. A level scheme built on the 13/2+ isomer has been deduced from four transitions assigned to 191Pb. The states in 191Pb are interpreted in terms of a weak coupling of the odd i13/2 neutron-hole to the spherical states in the even-mass 192Pb core.

The production mechanisms of medium-energy γ-rays from accreting X-ray pulsars are studied. The models concern electrons accelerated in strongly shielded accelerators above the inner part of the accretion disk whose energies are limited by curvature radiation reaction. The curvature photons are sufficiently energetic to produce secondary e ± pairs in collisions with the hard X-rays from the accretion shock front above the neutron star surface outside the acceleration regions, which are shielded from X-rays