High Energy Gamma Rays from the Galactic Center Ridge
March 2006 Top: TeV gamma rays from the Galactic Center region show two prominent point sources, one located right at the Galactic Center (see also December 2004) and one about a degree away, coincident…
PG 1553+113 – the mystery AGN
February 2006 “Hubble diagram” for host galaxies of BL Lac objects, showing apparent magnitude versus redshift (Sbarufatti et al, 2005). The diagram can be used to estimate unknown redshifts if the brightness of the…
Multiwavelength observations of H2356–309
January 2006 The investigation of very high energy (VHE) gamma ray emission from active galaxies serves multiple goals: on the one hand, one wants to understand the high-energy processes in the jets emitted by…
The Blazar 1ES 1101–232 and the Gamma Ray Horizon
December 2005 The “gamma ray horizon” defined as the distance (measured in redshift z) over which a gamma ray of a given energy will typically propragate before interacting with a photon of the extragalactic…
PKS 2005–489 – the first new AGN discovered by H.E.S.S.
November 2005 The winter months are the main observing season for extragalactic objects for H.E.S.S., hence we will here and in the next SOM’s concentrate on extragalactic sources of TeV gamma rays. PKS 2005-489…
Markarian 421 – a Fresh Look at a Familiar Source
October 2005 Markarian 421 was the first extragalactic source of very high energy gamma rays discovered (Punch et al. 1992). It is an active galaxy with a supermassive black hole at its core, emitting…
HESS J1825–137 – a Crushed Pulsar Wind Nebula?
September 2005 In the H.E.S.S. Galactic Plane Survey (Aharonian et al 2005), a number of new TeV gamma ray sources were discovered in the central region of our Galaxy, among them the source termed…
Very high energy gamma rays from the microquasar LS 5039
August 2005 “Microquasars” are galactic stellar-mass compact objects – neutrons stars or black holes – which accrete matter. Like in quasars – active galactic nuclei with a supermassive black hole – part of the…
HESS J1813–178 – no longer an unidentified TeV source
July 2005 In the survey of the central region of the Milky Way with the H.E.S.S. telescopes (Aharonian et al., 2005), eight previously unknown sources of very high energy gamma rays were discovered. For…
MSH 15-5 2 – a Pulsar Wind Nebula with a Jet
June 2005 The supernova remnant MSH 15-5 2 was first discovered in radio observations, and forms a rather complex object. Radio observations (Caswell et al. 1981) reveal a roughly circular supernova shell 30′ in diameter…
