VLBI and Archival VLA and WSRT Observations of the GRB 030329 Radio Afterglow

We present VLBI and archival Karl G. Jansky Very Large Array (VLA) and Westerbork Synthesis Radio Telescope (WSRT) observations of the radio afterglow from the gamma-ray burst (GRB) of 2003 March 29 (GRB 030329) taken between 672 and 2032 days after the burst. The EVLA and WSRT data suggest a simple power law decay in the flux at 5 GHz, with no clear signature of any rebrightening from the counter jet. We report an unresolved source at day 2032 of size $1.18\pm0.13$ mas, which we use in conjunction with the expansion rate of the burst to argue for the presence of a uniform, ISM-like circumburst medium. We develop a semi-analytic method to model gamma-ray burst afterglows, and apply it to the 5 GHz light curve to perform burst calorimetry. A limit of $< 0.067$ mas yr$^{-1}$ is placed on the proper motion, supporting the standard afterglow model for gamma-ray bursts.Comment: 24 pages, 5 figure

Gamma-Ray Bursts in Circumstellar Shells: A Possible Explanation for Flares

It is now generally accepted that long-duration gamma ray bursts (GRBs) are due to the collapse of massive rotating stars. The precise collapse process itself, however, is not yet fully understood. Strong winds, outbursts, and intense ionizing UV radiation from single stars or strongly interacting binaries are expected to destroy the molecular cloud cores that give birth to them and create highly complex circumburst environments for the explosion. Such environments might imprint features on GRB light curves that uniquely identify the nature of the progenitor and its collapse. We have performed numerical simulations of realistic environments for a variety of long-duration GRB progenitors with ZEUS-MP, and have developed an analytical method for calculating GRB light curves in these profiles. Though a full, three-dimensional, relativistic magnetohydrodynamical computational model is required to precisely describe the light curve from a GRB in complex environments, our method can provide a qualitative understanding of these phenomena. We find that, in the context of the standard afterglow model, massive shells around GRBs produce strong signatures in their light curves, and that this can distinguish them from those occurring in uniform media or steady winds. These features can constrain the mass of the shell and the properties of the wind before and after the ejection. Moreover, the interaction of the GRB with the circumburst shell is seen to produce features that are consistent with observed X-ray flares that are often attributed to delayed energy injection by the central engine. Our algorithm for computing light curves is also applicable to GRBs in a variety of environments such as those in high-redshift cosmological halos or protogalaxies, both of which will soon be targets of future surveys such as JANUS or Lobster.Comment: 12 pages, 5 figures, Accepted by Ap

Managerial education of naval officers

In the Navy almost all officers, whether junior or senior, hold positions as managers. The economy and efficiency of the Navy's operations, therefore, depends on the ability of it': managers to plan, organize, staff, direct and control the organization. A review is made of what noted authorities on the subject of management have said about the universality of management principles and the need to develop managers through education and training. Also, a review is made of the educational background of officer candidates as to the amount of management development they have received. From these reviews, an attempt is made to show that although naval officers are well educated they are lacking in one important area. This is the area of management development, which is necessary if the Navy is to obtain the maximum performance from its officers. A comparison is also made of the Navy' s manager development program with those of industry and other services. From these are drawn conclusions and recommendations to assist in the managerial development of today's naval officers.http://www.archive.org/details/managerialeducat00leamLieutenant Commander, United States NavyLieutenant Commander, United States NavyApproved for public release; distribution is unlimited