EUVE Observations of PKS 2155-304: Variability, Spectra, and a Polarization Measurement Attempt

Details EUVE Observations of PKS 2155-304: Variability, Spectra, and a Polarization Measurement Attempt EUVE Observations of PKS 2155-304: Variability, Spectra, and a Polarization Measurement Attempt

Mar 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...549..938m&link_type=abstract

The Astrophysical Journal, Volume 549, Issue 2, pp. 938-947.

Astronomy and Astrophysics

Astronomy

6

Galaxies: Bl Lacertae Objects: Individual: Alphanumeric: Pks 2155-304, Galaxies: Active, Ultraviolet: Galaxies

Scientific paper

The bright BL Lacertae object PKS 2155-304 was observed with the Extreme Ultraviolet Explorer (EUVE) in 1994 May with the primary objective of attempting to measure the EUV polarization using a novel technique. The light curves and spectra from the observation proved very useful, even though the method failed to produce useful polarimetric information owing to large, poorly understood, systematic instrumental effects. Light curves from this and previous observations showed variations of a factor of 2 over 1 month in 1993 and up to 25% variations on timescales of hours on several occasions (from four separate observations totalling 25 days spanning 3 yr). The soft X-ray spectra of the source were also derived from the EUVE observations and are comparable in shape to previous observations. The spectra do not show significant spectral features and are fitted acceptably with simple power-law spectra with an energy index α=3.0 for an assumed neutral hydrogen column density NH=1.4×1020 cm-2. A flatter index of 2.0 fits the data if the NH is reduced to 1.2×1020 cm-2, within the 2 σ uncertainty on NH as derived from 21 cm observations. Previous models that involve extensive absorption troughs with a flat-index power law (as extended from the X-ray band) are also consistent with the data.

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