On the sensitivity of the HAWC observatory to gamma-ray bursts

We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn could help to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles

Capturing photons with transformation optics

Metallic objects in close contact and illuminated by light show spectacular enhancements of electromagnetic fields, due to excitation of surface plasmons, which have potential for exploitation in ultra sensitive spectroscopy and in nonlinear phenomena. They also play a role in Van der Waals forces, heat transfer, and non contact friction. The extremes of length scales, varying from the micron to the sub nano, challenge direct computational attack. Here we show that the new technique of transformation optics enables an analytic approach which offers both physical insight and easy access to quantitative analysis. For two metal spheres at various separations we present details of the new technique, discuss the optical absorption spectrum, spatial distribution of the modes, and the Van der Waals forces.Accepted versio