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Session 48 - Gamma Rays & X-ray Instrumentation.
Display session, Thursday, January 08
Exhibit Hall,

[48.08] Gravitational Lensing, Dark Matter, and Gamma-Ray Bursts

G. F. Marani (George Mason U.), R. J. Nemiroff (Michigan Technological U.), J. P. Norris (NASA/GSFC), K. Hurley (UCB/SSL), J. T. Bonnell (NASA/GSFC,USRA)

If gamma-ray bursts (GRBs) lie at cosmological distances, different types of gravitational lensing may affect them. A detection of lensed echoes would provide a definitive evidence of the GRB origin. GRBs could also probe the universe for the existence of dark matter in the form of individual compact objects in different mass scales.

Macrolensing is the gravitational lensing by foreground galaxies or clusters of galaxies. We expect the time-delayed images to be scaled copies of each other in time histories and to have identical spectra at all times during the burst.

Megalensing may be caused by objects in the mass range \sim 10^6 - 10^9 M_ødot which is the Jean's mass at recombination in many early universe scenarios and is, therefore, a popular mass scale for dark matter.

In the microlensing case (M_l \sim 10^-6 - 10^5 M_ødot), macroimages might be slightly altered by microimages caused by stars inside the lensing galaxy.

Picolensing (M_l \sim 10^-12 - 10^-7 M_ødot) may be the only method that low mass objects like planets can be discovered with GRBs. Two well separated GRB detectors in our solar system , like BATSE and Ulysses GRB detectors, can see the same GRB with different amplitudes which may be attributed to lensing by an object in the mentioned mass range.

Interference patterns might be produced by extremely low lens masses in the range \sim 10^-16 - 10^-13 M_ødot, like snowballs, primordial black holes, and comets. This effect is called femtolensing.

We present an update on the search for each type of lensing in BATSE data base and the constraints we are able to impose on the cosmological abundance of compact objects in the above mentioned mass ranges.

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