On the Origin and Survival of UHE Cosmic-Ray Nuclei in GRBs and Hypernovae

The chemical composition of the ultra-high-energy (UHE) cosmic rays serves as an important clue for their origin. Recent measurements of the elongation rates by the Pierre Auger Observatory hint at the possible presence of heavy or intermediate mass nuclei in the UHE cosmic rays. Gamma-ray bursts (GRBs) and hypernovae have been suggested as possible sources of the UHE cosmic rays. Here we derive the constraints on the physical conditions under which UHE heavy nuclei, if they are accelerated in these sources, can survive in their intense photon fields. We find that in the GRB external shock and in the hypernova scenarios, UHE nuclei can easily survive photo-disintegration. In the GRB internal shock scenario, UHE nuclei can also survive, provided the dissipation radius and/or the bulk Lorentz factor of the relativistic outflow are relatively large, or if the low-energy self-absorption break in the photon spectrum of the prompt emission occurs above several KeV. In internal shocks and in the other scenarios, intermediate-mass UHE nuclei have a higher probability of survival against photo-disintegration than UHE heavy nuclei such as Fe.Comment: accepted by ApJ, references added, 12 pages, 4 figures, emulateapj styl

A Giant Bipolar Shell around the WO star in the Galaxy IC 1613: Structure and Kinematics

Observations of the nebula associated with the WO star in the galaxy IC 1613 are presented. The observations were carried out with a scanning Interferometer Fabry-Perot in H_alpha at the 6m Special Astrophysical Observatory telescope; narrow-band H_alpha and [OIII] images were obtained with the 4-m KPNO telescope. The monochromatic H_alpha image clearly reveals a giant bipolar shell structure outside the bright nebula S3. The sizes of the southeastern and northwestern shells are 112x77 pc and (186-192)x(214-224) pc, respectively. We have studied the object's kinematics for the first time and found evidence for expansion of both shells. The expansion velocities of the southeastern and northwestern shells exceed 50 and 70 km/s, respectively. We revealed a filamentary structure of the shells and several compact features in the S3 core. A scenario is proposed for the formation of the giant bipolar structure by the stellar wind from the central WO star located at the boundary of a dense ``supercavity'' in the galaxy's H I distribution.Comment: 10 pages with 4 PS figure