Astroparticle Physics with MILAGRO

University Of California-Irvine, Irvine CA

Investigators

Abstract

This is a proposal to operate the full Milagro air shower telescope,the Milagro pond and the surrounding array of outrigger water tanks,for the next three years and analyze the data to study the generation of TeV gamma rays from extremely energetic cosmic objects, such as nearby Active Galactic Nuclei (Blazars),Gamma Ray Bursts(GRB)and steady emitters in our own Galaxy.Study of TeV gamma rays from sources provides a sensitive tool for understanding the mechanisms for particle acceleration and subsequent gamma ray generation.TeV gamma rays from GRBs of short duration may allow s to test for possible energy dependence of the speed of light as predicted by theories of quantum gravity.The upper end of the gamma ray spectrum is particularly sensitive to the bulk Lorentz factor and magnetic .elds of the source shock.The shape at TeV energies can provide a probe of the extra-galactic IR absorption. Milagro is a water Cherenkov air shower telescope.It consists of a 5000 m 2 central pond and an array of 175 water tanks distributed out to 120 meters from the center of the pond. Its point spread function for gamma rays has a width of 0.8 deg.Its strengths are:all-sky sensitivity,continuous 24 hour operation and ability to study transients on many di .erent time scales.Milagro will be the only contin ously operating TeV gamma ray telescope before GLAST will operate.Milagro is a collaboration of Irvine(UCI),Santa Cruz(UCSC) and Riverside(UCR),LANL,Maryland,New Hampshire,NYU and GMU groups. In the last three year grant,we have operated full Milagro pond detector at a data rate of 1700 Hz.We have developed a new trigger to be able to study GRBs down to a few hundred GeV so that we can be sensitive to GRBs out to a red shift of 0.4.We have completed the array of 175 outrigger tanks to be able to locate shower cores out to about 100 meters which will improve our pointing and angular resolution substantially.We have working algorithms to reject more than 90 percent of cosmic ray triggers while keeping more than 50 percent of gamma ray triggers.We have implemented on-line capability of detecting bursts or transients in real-time,within 5 minutes and sending out alerts for m ltifrequency searches.We have observed the steady Crab at greater than 5 sigma.We have observed Mrk421 during its active phase in 2001.We have observed a 30 sigma de .cit for the shadow of the moon in a year of operation which provides direct energy calibration of Milagro and enables search of anti-proton component of cosmic rays in the TeV energy range.We have begun the study of gamma rays expected from cosmic ray interactions in the galaxy in TeV energy range. Milagro not only makes a signi .cant contribution to high energy astrophysics but also provides an excellent tool for teaching,training and learning for graduate students,under- graduate students and science teachers from K-12.With its location in New Mexico,it provides research and learning experience to Native Americans.At UCI,we have developed educational outreach activities for research experience to undergraduates as a part of on- going UCI REU program,to train high school science teachers through the COSMOS and Quarknet programs of UCI.The UCI Milagro group will continue to provide training to undergraduate and graduate students to work on di .erent aspects of the research and on site work at the Milagro site for gaining real research experience.