Astronomy Seminar
| Date/Time: | Friday, 24 Apr 2015 at 4:10 pm |
|---|---|
| Location: | 38 Physics |
| Contact: | Steve Kawaler, Physics and Astronomy |
| Phone: | 515-294-5440 |
| Channel: | College of Liberal Arts and Sciences |
| Categories: | Lectures |
| Actions: | Download iCal/vCal | Email Reminder |
As gamma rays with energies of 10s of GeV to 10s of TeV propagate over extragalactic distances, their cross-section with diffuse photons from the Extragalactic Background Light (EBL) can result in electron-positron pairs that are effectively deflected by intergalactic magnetic fields. This loss of primary photons from cosmological gamma-ray sources has long been perceived as an impediment to extragalactic TeV gamma-ray astronomy. However, the opacity associated with this mechanism is less than previously thought, and now provides a more extensive reach for constraining and measuring the EBL indirectly as a function of redshift.
Observations with current generation satellite and ground-based gamma-ray telescopes have revealed a surprisingly low gamma-ray opacity of the universe. The Energy spectra of samples of blazars now provide strong constraints to the EBL in the UV/optical light, the near-IR and the mid-IR. However, a completely self-consistent picture where direct measurements of the EBL and lower limits from galaxy counts converge with indirect measurements of gamma rays have converged is yet to be confirmed by observations.
Recent results from gamma-ray observations, their interpretation and caveats will be discussed.