By the end of the decade it is likely that gravitational waves will have been detected by two kinds of experimental efforts: ground based detectors using laser interferometers, and radio pulsar timing experiments. I will discuss what astronomers may hope to learn about the universe during the first years of gravitational-wave observations.
Cosmic rays have been observed up to several 10^20 eV through the showers of secondary particles they induce in the atmosphere. Their existence poses formidable challenges and exciting prospects at the same time: Their origin and sources have not been identified yet, but they already allow to test physics at center of mass energies unattained in the laboratory, albeit in a rather indirect way. We will give an overview over possible sources and acceleration mechanisms, open questions, and future prospects, including the role of secondary gamma-rays and neutrinos produced in interactions of charged primary cosmic rays.
Possible origins of the two tentative extraterrestrial neutrino detections
by IceCube will also briefly be discussed in this context.
The High Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is a wide-field gamma-ray detector under construction at an elevation of 4100 meters above sea level in Mexico. HAWC will be sensitive to gamma rays with energies between 100 GeV and 100 TeV and have sensitivity more than an order-of-magnitude greater than its predecessor Milagro. HAWC consists of 300 large detectors each containing ~200,000 liters of clean water and four photomultiplier tubes. HAWC’s modular design means that even though the detector construction will not be completed until the end of 2014, we are already taking data with HAWC-30 and will begin detector operations in August of this year with HAWC-100. In this talk I will describe HAWC’s design, sensitivity and construction progress. I will also show initial results from HAWC-30.
Measurements of cosmic ray air showers with energies above 10^17.5 eV have yielded significant results. There is some tension between different observations, however, and it is not possible at present to decide between different scenarios for where and how these cosmic rays are accelerated. The history and present status of the observations pose some sharp questions to be addressed by land-based and satellite detectors in the future.