Will GRB 990123 Perform an Encore?

The recent gamma ray burst, GRB 990123, has an absorption redshift z_s=1.60, implying an apparent energy $E \ge 3 \times 10^{54} erg$, and a peak luminosity $L_{max} \ge 6 \times10^{53}erg/s$, assuming isotropic emission. This energy is ten times larger than hitherto measured and in excess of the rest mass of the sun. Optical observations have revealed an associated galaxy displaced from the line of sight by $\sim 0.6''$. This raises the possibility that the burst is enhanced by gravitational lensing. We argue that existing observations probably only allow magnifications $\mu>400$ if the galaxy is at z_d=1.60 and the burst originates at much higher redshift. It should be possible to exclude this possibility by examining the burst time structure. If, as we anticipate, multiple imaging can be excluded, GRB 990123 remains the most intrinsically luminous event yet observed in its entirety.Comment: Accepted by MNRAS: 4 pages, latex, no figure

Discovery of a Pulsar Candidate Associated with the TeV Gamma-ray Source HESS J1813-178

We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the co-located ASCA source into a compact object surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well-characterized by a power-law with index approx. 1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption, the 2-10 keV X-ray luminosity of the putative pulsar and nebula is L(PSR) = 3.2E33 erg/s and L(PWN) = 1.4E34 erg/s, respectively. Both the flux ratio of L(PWN)/L(PSR) = 4.3 and the total luminosity of this system imply a pulsar spin-down power greater then 1E37 erg/s, on a par with the top ten most energetic young pulsars in the Galaxy. We associate the putative pulsar with the radio remnant and the TeV source and discuss the origin of the gamma-ray emission.Comment: 3 Pages, 3 Figures. Latex, aipproc.cls. To be published in "The Proceedings of the First International GLAST Symposium" (Held Febuary 5-8, 2007, Stanford Univ., USA), AIP, Eds. S. Ritz, P.F. Michelson, and C. Meegan. Updated coordinate

The bird: A pressure-confined explosion in the interstellar medium

The non-thermal radio continuum source G5.3-1.0, mapped at 20 cm with the Very Large Array (VLA) by Becker and Helfand, has an unusual bird-like shape. In order to determine possible interaction of this source with adjacent cold gas, we have mapped this region in the J=1-0 line of CO using the AT and T Bell Laboratories 7m antenna and the FCRAO 14m antenna. The map shown contains 1859 spectra sampled on a 1.5 arcminute grid; each spectrum has an rms noise of 0.2 K in 1 MHz channels. There are several molecular clouds at different velocities along the line of sight. The outer regions of a previously unknown Giant Molecular Cloud (GMC) at l=4.7 deg., b=-0.85 deg., v=200 km s(-1) appears to be interacting with G5.3-10: the molecular cloud has a bird-shaped hole at the position of the continuum source, except that the brightest continuum point (the bird's head) appears to be embedded in the cloud. The velocity of this GMC indicates it is within 2 kpc of the galactic center. The morphology suggests that a supernova or other explosive event occurred near the outside of the GMC, in a region where (n) is approximately 300 cm(-3), and expanded into a region of lower density and pressure. The pressures, densities, and velocity gradients of molecular clouds near the galactic center are on average higher than those of clouds near the Sun. We therefore expect that Type II supernovae near the galactic center would be distorted by their interactions with their parent molecular clouds