Soebur Razzaque

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A cornerstone of Einstein's special relativity is Lorentz invariance-the postulate that all observers measure exactly the same speed of light in vacuum, independent of photon-energy. While special relativity assumes that there is no fundamental length-scale associated with such invariance, there is a fundamental scale (the Planck scale, l(Planck)(More)
Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB(More)
M. Ackermann, M. Ajello, A. Albert,* A. Allafort, L. Baldini, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, E. Bissaldi, E. D. Bloom, E. Bonamente, E. Bottacini, T. J. Brandt, J. Bregeon, M. Brigida, P. Bruel, R. Buehler, S. Buson, G.A. Caliandro, R. A. Cameron, P. A. Caraveo, J.M. Casandjian, C. Cecchi, E. Charles, R. C. G. Chaves, A. Chekhtman,(More)
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton(More)
We estimate the high energy neutrino flux from the giant flare of SGR 180620 on December 27, 2004, which irradiated Earth with a gamma-ray flux ∼ 10 times larger than the most luminous gamma-ray bursts (GRBs) ever detected. The Antarctic Cherenkov neutrino detector AMANDA was on-line during the flare, and may either have detected high energy neutrinos for(More)
Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray(More)
Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in(More)
A fraction of core-collapse supernovae of type Ib/c are associated with gamma-ray bursts, which are thought to produce highly relativistic jets. Recently, it has been hypothesized that a larger fraction of core-collapse supernovae produce slower jets, which may contribute to the disruption and ejection of the supernova envelope, and explain the unusually(More)
We have calculated the opacities and secondary production mechanisms of high-energy photons arising in gamma-ray burst internal shocks, using exact cross sections for the relevant processes. We find that for reasonable choices of parameters, photons in the range of tens to hundreds of GeV may be emitted in the prompt phase. Photons above this range are(More)
I. Kravchenko, D. Seckel, J. Adams, A. Baird, S. Churchwell, P. Harris, S. Seunarine, A. Bean, D. Besson, K. Byleen-Higley, S. Chambers, J. Drees, S. Graham, D. McKay, J. Meyers, L. Perry, J. Ralston, J. Snow, S. Razzaque (1) M.I.T. Lab. for Nuclear Science, Cambridge, MA 02139 (2) Bartol Research Institute, U. of Delaware, Newark DE 19716 (3) Department of(More)