Engineering topics

Geballe, T.

Publications and source records attributed to Geballe, T..

3 records

NASA NTRS1998

The X-Ray, Optical and Infrared Counterpart to GRB 980703

We report on our X-ray, optical and infrared follow-up observations of GRB980703. A previously unknown X-ray source in the GRB error box displays a powerlaw decline with index alpha= -1.0,5(exp +0.24 sub -0.29), fairly consistent with the average optical/infrared decay index alpha = -1.61 plus or minus 0.12. We invoke host galaxy extinction to match the observed spectral slope with the slope expected from 'fireball' models. The hypothesis that between 1998 July 4.4 and 8.4 UT no spectral breaks are present in the infrared to X-ray spectral range is in good agreement with the observations. For these two epochs we obtain an extinction of A(sub v) = 1.50 +/- 0.11 (July 4.4) and A(sub v) = 0.85 +/- 0.26 (July 8.4). From the X-ray data we estimate the optical extinction to be A(sub v) = 20.2(+12.3/-7.3), inconsistent with the former value. Optical spectra we took confirm the redshift of z=0.966 found by Djorgovski et al. We compare the afterglow of GRB 980703 with that of GRB 970508 and find that the fraction of the energy in the magnetic field is much lower in the case of GRB 980703.

Vreeswijk, P. M.↗

NASA NTRS1994

Dark matter in the outer solar system

There are now a large number of small bodies in the outer solar system that are known to be covered with dark material. Attempts to identify that material have been thwarted by the absence of discrete absorption features in the reflection spectra of these planetesimals. An absorption at 2.2 micrometers that appeared to be present in several objects has not been confirmed by new observations. Three absorptions in the spectrum of the unusually red planetesimal 5145 Pholus are well-established, but their identity remains a mystery.

Owen, T.↗

NASA NTRS1989

High-excitation lines of molecular hydrogen: A discriminant between shock models

The results of column densities of molecular hydrogen, calculated from nineteen infrared line intensities, are discussed. They were measured at peak 1 of the outflow of the Orion molecular cloud OMC-1. The 1-0 O(7) and 0-0 S(13) lines of H2, at 3.8 microns, are mapped over the source. Their intensity ratio is found to be independent of position in the outflow. These observations are well fitted by a simple cooling-flow model of the line emitting region, but seem to be at variance with predictions of C-shocks current in the literature.

Burton, M.↗