I did my Ph.D. thesis in theoretical high-energy astrophysics under the supervision of Prof. Robert J. Gould at the University of California, San Diego in 1988. My thesis was titled Thermonuclear Reactions of Light Nuclei in Astrophysical Plasmas, and it consisted of two parts: a) a recalculation of the rate of the fundamental reaction p+pàd+e++ve, which determines not only the production rate of energy in the core of the Sun but also that of neutrinos; b) rates of breakup reactions of light nuclei (protons and alphas on C, N, O, etc.) in various astrophysical environments, particularly in accretion disks around compact objects (black holes and neutron stars), where this is accompanied by gamma-ray line emission.

I then went to NASA’s Goddard Space Flight Center and spent two years as a post-doctoral researcher, under the supervision of the late great Reuven Ramaty, who passed away in 2001 and was posthumously honored with the naming of the HESSI spacecraft after him. With Reuven I got involved in positron annihilation research, a topic on which I have made some of my best contributions. I also worked on a few papers with Demos Kazanas, another bright and eclectic theoretical astrophysicist.

During my time in Algeria, various social and administrative conditions prevented me from carrying on my collaborations with my colleagues in the States. I was only able to make a few-weeks visit to CEA/Saclay, an important research center near Paris, France. When I moved to Kuwait, I resumed my collaboration with Reuven and Demos at NASA/GSFC, spending several weeks each summer between 1995 and 1999, which enabled me to “restart my engine…”

The next big project in gamma-ray astrophysics was going to be INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory), a mostly European spacecraft which was to be launched in October 2002, carrying next-generation (high energy resolution and imaging) instruments. I thus contacted colleagues at the Centre d’Etude Spatiale des Rayonnements in Toulouse, France, a center which was producing one of the two main instruments for Integral; they welcomed my joining their group as a regular collaborator. And indeed, I have now made 8 month-long stays at CESR and co-produced about two dozen papers (half in journals and half in conference proceedings), most notably on the problem of positron-electron annihilation in the milky-way galaxy, a problem which had become one of the main puzzles of contemporary astrophysics, at least in the high-energy domain. The problem is far from having been fully resolved, but we have made substantial progress on it, thanks to the close collaboration between theorists, experimenters/observers, data-analysis experts, and modelers. Finally, I have lately ventured in the gamma-ray burst domain, which in the past decade or more has become one of the most stunning phenomena of the cosmos and has yet to be explained in a satisfactory manner.

I should also note that I have been active in the development of an astrophysical community in the Arab world, especially in the Gulf region; this I report on in the webpage on Education Issues.

Below is a selected list of my notable astrophysics papers.

  • Positron astrophysics and areas of relation to low-energy positron physics”, N. Guessoum, Eur. Phys. J. D, 68: 137 (2014).
  • Revisiting the Amati and Yonetoku correlations with Swift GRBs”, Zitouni, H., Guessoum, N., Azzam, W. J., Astroph. & Sp. Sci., vol. 351, Iss. 1, pp. 267-27 (2014).
  • Time for an Arab astronomy renaissance”, N. Guessoum, Nature, 498, 161
  • Can the Amati Relation be Used as a Discriminator between Short and Long Gamma-ray Bursts?“, H. Hamidani, N. Guessoum, W. J. Azzam, Afr. Sk., Vol. 16, p.68
  • The 511 keV emission from positron annihilation in the Galaxy”, Prantzos, N.; Boehm, C.; Bykov, A. M.; Diehl, R.; Ferrière, K.; Guessoum, N.; Jean, P.; Knoedlseder, J.; Marcowith, A.; Moskalenko, I. V.; Strong, A.; Weidenspointner, G., Reviews of Modern Physics, vol. 83, Iss. 3, pp. 1001-1056 (2011).
  • Positron Annihilation on PAHs in the ISM”, N. Guessoum, W. Gillard, and P. Jean, MNRAS, 402, 1171 (2010).
  • Evolution of the Time-Lag and Variability Luminosity Relations for Long Gamma-Ray Bursts”, W. J. Azzam, M. J. Alothman, N. Guessoum, Adv. Sp. Res., 44, 1354 (2009).
  • Microquasars’ contribution to the galactic positron annihilation radiation”, N. Guessoum, P. Jean, N. Prantzos, Proc. of “The 6th INTEGRAL workshop – The Obscured Universe”, ESA & Space Research Institute, Moscow, Russia, 2007, p. .
  • Ion acceleration and positron production and annihilation in solar flares”,N. Guessoum, Proc. of IAU Symposium 233, vol. 2, eds. V. Bothmer & A. A. Hady, pp. 377-380, 2006.
  • Microquasars as Sources of Positron Annihilation Radiation”, N. Guessoum, P. Jean, and N. Prantzos, Astronomy & Astrophysics, A&A, 457, 753 (2006).
  • First View of the All-Sky Distribution of Positronium Annihilation Continuum Emission with SPI/INTEGRAL”, G. Weidenspointner et al., Astronomy & Astrophysics, 450, 1013 (2006).
  • Ion acceleration and positron production and annihilation in solar flares”, N. Guessoum, Proc. of IAU Symposium 233, vol. 2, eds. V. Bothmer & A. A. Hady, pp. 377-380, 2006.
  • Relevance of slow positron beam research to astrophysical studies of positron interactions and annihilation in the interstellar medium”, N. Guessoum, P. Jean, W. Gillard, ApSS, 252, 3352 (2006).
  • Spectral Analysis of the Galactic e+e- Annihilation Emission”, P. Jean, et al., Astronomy & Astrophysics, 445, 579 (2005).
  • The Lives and Deaths of Positrons in the Interstellar Medium”, N. Guessoum, P. Jean, W. Gillard, Astronomy & Astrophysics, 436, 171 (2005).
  • Detecting 2.223 MeV Line Emission from X-Ray Novae with INTEGRAL”, N. Guessoum & P. Jean, Nuclear Physics B (Proceedings Supplements), 132C, 396-399 (2004).
  • Models of the Positive Latitude e-e+ Annihilation Feature“, P. von Ballmoos, N. Guessoum, P. Jean, and J. Knoedlseder; Astronomy & Astrophysics, 397, 635-643 (2003).
  • Detectability and Characteristics of the 2.223 MeV Line Emission from Nearby X-Ray Binaries”, N. Guessoum & P. Jean, Astronomy & Astrophysics, 396, 157-169 (2002).
  • Neutron-Capture and 2.22 MeV Emission in the Atmosphere of the Secondary of an X-ray Binary”, P. Jean & N. Guessoum, Astronomy & Astrophysics, 378, 509-521 (2001).