We have used the Karl G. Jansky Very Large Array (VLA) to search for 36 GHz and 44 GHz methanol (CH 3 OH) lines in a sample of 21 Galactic supernova remnants (SNRs). Mainly the regions of the SNRs with 1720 MHz OH masers were observed. Despite the limited spatial extent covered in our search, methanol masers were detected in both G1.4−0.1 and W 28. Additional masers were found in Sgr A East. More than 40 masers were found in G1.4−0.1 which we deduce are due to interactions between the SNR and at least two separate molecular clouds. The six masers in W 28 are associated with the molecular cloud that is also associated with the OH maser excitation. We discuss the possibility that the methanol maser may be more numerous in SNRs than the OH maser, but harder to detect due to observational constraints.

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 the Joint Astrophysics Nascent Satellite or Lobster.

We present VLBI and archival Karl G. Jansky Very Large Array (VLA) andWesterbork 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 ± 0.13 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.

Gamma-ray bursts (GRBs) are the ultimate cosmic lighthouses, capable of illuminating the universe at its earliest epochs. Could such events probe the properties of the first stars at z ∼ 20, the end of the cosmic Dark Ages? Previous studies of Population III GRBs only considered explosions in the diffuse relic H II regions of their progenitors, or bursts that are far more more energetic than those observed to date. But the processes that produce GRBs at the highest redshifts likely reset their local environments, creating much more complicated structures than those in which relativistic jets have been modeled so far. These structures can greatly affect the luminosity of the afterglow, and hence the redshift at which it can be detected. We have now simulated Population III GRB afterglows in H II regions, winds, and dense shells ejected by the star during the processes that produce the burst. Our model, which has been used in previous work, has been extended to include contributions from reverse shocks, inverse Compton cooling and the effects of sphericity and beaming in the blast wave, and is valid in a variety of circumjet density profiles. We find that GRBs with E iso,γ = 10 51 -10 53 erg will be visible at z 20 to the next generation of near infrared and radio observatories. In many cases, the environment of the burst, and hence progenitor type, can be inferred from the afterglow light curve. Although some Population III GRBs are visible to Swift and the Very Large Array now, the optimal strategy for their detection will be future missions like EXIST and JANUS, which have large survey areas and onboard X-ray and infrared telescopes that can track their near infrared flux from the moment of the burst, thereby identifying its redshift.

We perform calorimetry on the bright gamma ray burst (GRB) 030329 by fitting simultaneously the broadband radio afterglow and the observed afterglow image size to a semi-analytic magnetohydrodynamical (MHD) and afterglow emission model. Our semi-analytic method is valid in both the relativistic and non-relativistic regimes, and incorporates a model of the interstellar scintillation that substantially effects the broadband afterglow below 10 GHz. The model is fitted to archival measurements of the afterglow flux from 1 day to 8.3 years after the burst. Values for the initial burst parameters are determined and the nature of the circumburst medium is explored. Additionally, direct measurements of the lateral expansion rate of the radio afterglow image size allow us to estimate the initial Lorentz factor of the jet.