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Green, P. J.

Publications and source records attributed to Green, P. J..

4 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Surprises from a Deep ASCA Spectrum of the Broad Absorption Line Quasar PHL 5200

We present a deep (approx. 85 ks) ASCA observation of the prototype broad absorption line quasar (BALQSO) PHL 5200. This is the best X-ray spectrum of a BALQSO yet. We find the following: (1) The source is not intrinsically X-ray weak. (2) The line-of-sight absorption is very strong, with N(sub H) = 5 x 10(exp 23)/sq cm. (3) The absorber does not cover the source completely; the covering fraction is approx. 90%. This is consistent with the large optical polarization observed in this source, implying multiple lines of sight. The most surprising result of this observation is that (4) the spectrum of this BALQSO is not exactly similar to other radio-quiet quasars. The hard X-ray spectrum of PHL 5200 is steep, with the power-law spectral index alpha approx. 1.5. This is similar to the steepest hard X-ray slopes observed so far. At low redshifts, such steep slopes are observed in narrow-line Seyfert 1 (NLS1) galaxies, believed to be accreting at a high Eddington rate. This observation strengthens the analogy between BALQSOs and NLS1 galaxies and supports the hypothesis that BALQSOs represent an early evolutionary state of quasars. It is well accepted that the orientation to the line of sight determines the appearance of a quasar: age seems to play a significant role as well.

Mathur, Smita↗
NASA NTRS1997

Using the Tycho catalogue for AXAF: Guiding and aspect reconstruction for half-arcsecond X-ray images

The Advanced X-ray Astrophysics Facility (AXAF) will carry a high resolution mirror, two imaging detectors, and two sets of transmission gratings. The Tycho catalog from the Hipparcos mission will serve as a primary part of the AXAF Guide and Aspect Star Catalog (AGASC). The incorporation of Tycho into AGASC will provide: accurate positions and magnitudes for target acquisition and guidance; the necessary colors for magnitude transformations to the AXAF aspect camera system; high internal astrometric accuracy for half-arcsecond, post-facto image reconstruction; and an external astrometric system.

Green, P. J.↗
NASA NTRS1992

The x ray properties of a large, uniform QSO sample: Einstein observations of the LBQS

Although there are large numbers of Quasi Stellar Objects (QSO's) now observed in X rays, extensive X-ray observations of uniformly selected, 'complete' QSO samples are more rare. The Large Bright QSO Survey (LBQS) consists of about 1000 objects with well understood properties, most brighter than B = 18.8 and thus amenable to X-ray detections in relatively brief exposures. The sample is thought to be highly complete in the range 0.2 less than z less than 3.3, a significantly broader interval than many other surveys. The Einstein IPC observed 150 of these objects, mostly serendipitously, during its lifetime. We report the results of an analysis of these IPC data, considering not only the 20 percent of the objects we find to have positive X-ray detections, but also the ensemble X-ray properties derived by 'image stacking'.

Margon, B.↗