Welcome to the homepage of
Asaf Pe'er

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Research Interests

  My main research focuses on high energy astrophysics . Under this title falls transient emission from compact objects, such as Gamma-ray bursts (GRB's), X-ray binaries (microquasars), Active Galactic Nuclei (AGN's) and the recently discovered tidal disruption events (TDE's). Other aspects include the origin of high energy cosmic rays.
  The science I am involved in includes a wide range of physical disciplines, such as nuclear processes, radiative processes, relativistic gas dynamics, particle acceleration, and (relativistic) magneto-hydrodynamics. My research is both theoretical (analytical and numerical), and phenomenological.
  As one of my major scientific achievement, I consider the developement of the theory of thermal emission from relativistically expanding plasmas, which is the relativistic extension of the limb darkening effect.
A few of my research highlights in previous years are listed below; others can be found in my publications list.
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The origin of gamma-ray burst prompt emission

  Gamma-ray bursts are flashes of gamma-rays, that appear at random in the sky. Residing in distant galaxies, these are the most luminous objects in the universe, releasing as much as 10^{52} ergs in few seconds (equivalent to a few % of solar binding energy). We know today... read more...
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Theory of photospheric emission from relativistically expansing plasmas

  Motivated by the need to explain the observed prompt spectra of gamma-ray bursts (GRBs), I study photospheric emission from relativistically expansing plasmas. While naively one may expect a "Planck" function to emerge, due to relativistic abberation of light, the observed spectrum is in fact very different. read more...
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The surprising physics of structured jets

  Relativistic jets are found in a variety of astronomical objects, such as GRBs, AGNs and XRB's. By definition, jets have spatial velocity profile: v=v(r,θ, φ), resulting from different (and, as of yet uncertain) spatial-dependence mass ejection. For example, in the collapsar model of GRBs... read more...
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Implications of identifying thermal component in GRB spectra

  Motivated by the need to understand the origin of GRB prompt emission, it was shown by Ryde that in numerous GRBs, the spectra can be fitted with a Planck function, accompanied by an adidtional power law (non-thermal) component. This idea was further extended by Ryde & Pe'er,... read more...
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Emission models from X-ray binaries: jet contribution

  Observations of the low/hard state of many X-ray binaries reveal a rich broad band spectrum, extending from the radio to the hard X-rays. The radio spectrum observed is typically flat (F_ν ∝ ν^0). At higher frequencies (typically from optical to the soft X-ray), the spectrum is thermal, dominated by the accretion disk and the companion star, while at higher energies (X- and γ-rays), a power law is typically observed. read more...
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Sources of high energy cosmic rays

  Cosmic rays are charged particles that arrive to earth from outer space. They are composed of protons or light nuclei (e.g., iron nuclei), and have been observed up to enormous energies, of 10^20 eV and higher. For comparison, this energy is more than 3 orders of magnitude the maximum energy (in the center of mass) achieved in LHC. read more...
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Relativistic dynamics: expansion and shock waves interactions

  Relativistic outflows are extremely common in many different astronomical objects. Thus, accurate calculation of the dynamics of expanding - and interacting plasmas, including shock waves, is of high interest in studying many objects. One good example is GRBs: the progenitor of read more...

In the media

Paradigm shift in the understanding of GRBs !! Nature News (May 8th, 2012)
Articles about two of my works appeared in popular science magazines ! One appeared in Scientific American and one in Astronomy magazine.