Speaker Name:
Okkie de Jager
Speaker Affiliation:
North-West University & H.E.S.S. Collaboration
Talk Subject:
Opening a new spectral window on the Universe: Very High Energy Gamma Rays
Date:
05/21/2008 - 13:00
Venue:
Postgraduate Seminar Room, Otto Beit Building
With the High Energy Stereoscopic System (H.E.S.S.) of gamma-ray telescopes (located in Namibia)
we were able for the first time to reveal a population of mostly resolved sources, dotted in
a narrow band (|b|< 1 degree) around the midplane of the Milky Way. They consist mostly
of pulsar wind nebulae (such as the Crab Nebula), supernova remnants (SNR) and diffuse emission from
molecular clouds, activated by recent supernova explosions. One example of a gamma-ray bright SNR is Vela Junior,
which exploded most likely in the year 1460 AD relatively close to us, as seen from Berillium 10
ice core data from both the Antarctic and Arctic regions. The ice core date should also allow us to
narrow a search for the historical event in archives such as those in Timbuktu, Mali.
The Active Galactic Nuclei seen by HESS and other similar telescopes enable us
to constrain the extragalactic background light (EBL). The EBL limits allow us to constrain early epochs of star formation,
since we employ high energy and very high energy gamma rays from AGN as mulitwavelength messengers, which have "probed" and "measured" the EBL density on cosmological time scales along their respective paths to Earth.