Pulsar
At final stage of stellar evolution, massive star may give birth to a neutron star, bequeathing their magnetic and rotational energy to these highly compact object.
The discovery of pulsars will soon celebrate it's 50th birthday and we are far from understanding these fascinating objects whose have been observed in almost every wavelength. Studying pulsars is at the intersection of all the discipline of modern physics: plasma physics, magneto-hydrodynamics, general relativity...).
In one word, pulsars represent a formidable laboratory both for theorists and observers.
Left: Vela pulsar (Credit: Chandra, NASA). Right: Observation of the Vela PSR with H.E.S.S. II in mono mode. [3]
The number of detected pulsars at high energy has known great progress since the launch of the Fermi satellite in 2008, and this number is still growing.
If the mechanisms behind the non-thermal radiation pulsed emission (synchrotron, curvature radiation or inverse Compton) are well known, the details of these processes remain widely debated through several models.
The discovery of pulsed emission from the crab pulsar beyond 40 & 100GeV with the Cherenkov telescopes MAGIC[1] & VERITAS[2], as well as the The detection of pulsed emission from the Vela PSR with H.E.S.S.II in mono mode[3], ask new questions about the origin of VHE pulsed emission and pave the way for a new field of observation for the current and upcoming ground based Cherenkov telescopes.
You would like to know more? Please contact: djannati
in2p3.fr (Arache Djannati-Atai)
Pulsar Wind Nebulae
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 [3]) can be observed via their emission throughout the radio, X-ray and even gammaray 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.
Today, PWNe in various evolutionary states form the most numerous source class in Galactic TeV gammaray astronomy [5]. The H.E.S.S. experiment, in which our group is involved, has achieved the major share of the TeV PWN discoveries[4,5]. 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 [5]). 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.
You would like to know more? Please contact: djannatiin2p3.fr (Arache Djannati-Atai)
References
- E. Aliu et al.,Observation of pulsed γ-Ray above 25 GeV from the Crab Pulsar with MAGIC, Science, 2008,322,1221
- The VERITAS collaboration, Detection of Pulsed Gamma Rays Above 100 GeV from the Crab Pulsar(2011)
- The H.E.S.S. Collaboration, Pulsations from the Vela pulsar down to 20 GeV with H.E.S.S. II,
- 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)