Several types of galactic sources are under study in the groupe:
Supernova remnants are the fraction of the interstellar medium resulting from supernova explosions. When such explosions occur, a supersonic blast wave expands, and a shock with a relatively high magnetic field is created. Is in this shock where a large amount of particles are accelerated.
In our group, where are interested in detecting gamma-ray emitting supernova remnants. By doing so we can assess the efficiency by which supernova remnants accelerate particles, and also have some insight on what are the highest energies those particles may reach. These are two crucial observations that may allow to proof or disproof the most common ideas on the origin of cosmic rays.
You would like to know more? Please contact Ignasi Reichardt
Young and energetic pulsars can drive powerful particle winds believed to consist mainly of electrons and positrons. Upon interaction with the surrounding medium, these winds form nebulae consisting of a magnetized pair plasma. These so-called pulsar wind nebulae (PWNe, see ) can be observed via their emission throughout the radio, X-ray and even gamma-ray bands. The prime example is the famous Crab Nebula, a young object less than 1000 years old, which was the first astrophysical source to be detected at TeV gamma rays almost 25 years ago.
|Young and energetic pulsars can drive powerful particle winds believed to consist mainly of electrons and positrons. Upon interaction with the surrounding medium, these winds form nebulae consisting of a magnetized pair plasma. These so-called pulsar wind nebulae (PWNe, see ) can be observed via their emission throughout the radio, X-ray and even gamma-ray bands. The prime example is the famous Crab Nebula, a young object less than 1000 years old, which was the first astrophysical source to be detected at TeV gamma rays almost 25 years ago.||
The Crab Nebula (image credit: NASA).
Today, PWNe in various evolutionary states form the most numerous source class in Galactic TeV gamma-ray astronomy . The H.E.S.S. experiment, in which our group is involved, has achieved the major share of the TeV PWN discoveries [2,3]. Future observations with the upcoming CTA observatory will allow even more detailed studies of these fascinating objects.
Our group's interest regarding PWNe mainly lies with the study of spectral and morphological properties of their very-high-energy gamma-ray emission, in order to learn about the particles and magnetic fields at the origin of the emission and to investigate the connection with the characteristics of the pulsar (see ). There are many open questions, e.g. regarding the underlying acceleration mechanisms, and concerning the potential role of pulsars and their wind nebulae as the main sources of Galactic cosmic-ray electrons and positrons.
PWNe currently detected in
You would like to know more? Please contact Kathrin Valerius
B. M. Gaensler & P. O. Slane: The Evolution and Structure of Pulsar Wind Nebulae, Annual Review of Astronomy and Astrophysics (2006), vol. 44, pp. 17-47 (arXiv link).
S. Wakely and D. Horan: The online catalog for TeV Astronomy (TeVCat website).
O. C. de Jager & A. Djannati-Atai: Implications of HESS Observations of Pulsar Wind Nebulae,
in: Neutron Stars and Pulsars, Astrophysics and Space Science Library, Volume 357 (2009), p. 451 (ADS link)
The center of our Galaxy hosts a Super-Massive Black Hole (SMBH).This SMBH has an estimated mass of 4×106 Msol and is extremely faint nowadays with a bolometric luminosity 8 order of magnitude below its Eddington luminosity. Since it has been argued that the SMBH can accelerate particles up to very high energies, its current and past activity must contribute to the population of Galactic cosmic-rays (CRs), the
energetic particles that pervade the Galaxy.
Recently the HESS experiment has reported a bright TeV point-like source at a position compatible with that of the SMBH. After subtraction of this point source, a diffuse emission stretching over few degrees along the Galactic longitude was revealed. Its relative correlation with the local gas density suggesting the emission is due to the collision of multi-TeV protons and ions with the dense clouds of interstellar gas and its hard spectrum, revealed an over-abundance of freshly injected CRs. The origin of this excess is unclear.
The APC team work currently on the HESSI data to determine the location, density, nature, propagation as well as the origin of the CR excess and test its possible connection to the past activity of the SMBH. To study the correlation between the gamma-ray emission and the high density molecular structures we currently use public ISM data (lien vers MWL page). We also look for possible local accelerators in the region by searching for associated X-ray signatures (lien vers MWL page) in order to determine their nature. The study of the diffuse emission with HESS II above 50 GeV that will start this year, will allow to characterize the CR distribution over the whole central 200 pc as well as in the vicinity of the SMBH or possibly in the halo.
You would like to know more? Please contact Anne Lemière