Bulletin of the AAS (BAAS), volume 40, number 1, 2008 (20.06)

The BL Lac object Mrk 421 has been observed in an active state during late 2007 and early 2008 by the VERITAS gamma-ray telescope. Simultaneous X-ray observations have been obtained with Swift-XRT and RXTE. In this contribution we will present the lightcurves and energy spectra obtained in both energy bands and their correlation. Furthermore, we will discuss the implications of these observations in the context of blazar emission models.

Bulletin of the AAS (BAAS), volume 40, number 1, 2008 (20.01I)

With the ground based VERITAS, MAGIC, MILAGRO, and HESS experiments and the space-born GLAST observatory to be launched in mid 2008 we will have access to a powerful suite of observatories to study the gamma-ray emission from extragalactic systems. In this contribution, recent results from ground based gamma-ray observatories and upcoming science opportunities afforded by GLAST will be discussed. The contribution will largely focus on blazars and on possible avenues for using the observational data to constrain the jet properties and the jet formation mechanisms. In addition, the scientific potential of detections of gamma-rays from cosmic rays and dark matter annihilation processes in extragalactic systems will be outlined.

Bulletin of the AAS (BAAS), volume 40, number 1, 2008 (10.12)

The high mass X-ray binary LS I +61 303 has been observed over several months in 2006 and 2007 with the VERITAS array of imaging air-Cherenkov telescopes. A signal of high energy gamma rays with energies above 300 GeV is detected in several orbital cycles of the binary system. The detected flux of gamma rays is strongly variable over the orbital period of 26.5 days, while the maximum flux (corresponding to about 10% of the flux of the Crab Nebula) is always found at approximately apastron. This suggests a strong dependence of particle acceleration and propagation on the relative position of the two objects in the system. In this talk, results from these recent VERITAS observations are discussed in the context of contemporaneous X-ray observations.

Bulletin of the AAS (BAAS), volume 40, number 1, 2008 (12.09)

Observations of the Crab Nebula, the standard candle in TeV astronomy, provide a convenient method to calibrate and to characterize the performance of a Cherenkov telescope. Demonstrating the consistency of these observations with the well established properties of Crab is an important test of a new instrument and builds confidence that the results from other observations with the telescope array are correct. Scientifically, it is interesting to measure the energy spectrum of the Crab Nebula close to the inverse-Compton peak where a deviation from the power law seen at energies above 300 GeV is expected. Additionally, it is important to search for pulsed emission from the Crab Pulsar at energies beyond 10 GeV, the highest energy at which EGRET detected pulsed emission from the Crab. With these motivations, the Crab has been observed extensively during the 2-, 3-, and 4-telescope phases of the comissioning of VERITAS. The energy spectrum of the Crab Nebula between 200 GeV and 7 TeV is constructed from these data sets. A search for pulsed emission from the Crab Pulsar at gamma-ray energies above 100 GeV is also performed. The Crab data set from these observations does not show any significant pulsed excess, so an upper limit on the pulsed emission is obtained.