HUT Observations of the Far-Ultraviolet Spectrum of MKN 421

Details HUT Observations of the Far-Ultraviolet Spectrum of MKN 421 HUT Observations of the Far-Ultraviolet Spectrum of MKN 421

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...186.2002k&link_type=abstract

American Astronomical Society, 186th AAS Meeting, #20.02; Bulletin of the American Astronomical Society, Vol. 27, p.834

Astronomy and Astrophysics

Astronomy

Scientific paper

We observed the BL-Lac object Markarian 421 with the Hopkins Ultraviolet Telescope on two occasions during the Astro-2 space shuttle mission in March 1995. The spectra cover the range from the Galactic Lyman edge at 912 Angstroms to 1850 Angstroms, with a resolution of 2-4 Angstroms. The individual spectra have typical signal-to-noise ratios of 10-18 per Angstroms, and the combined spectrum has a S/N of 14-25 per Angstroms. There was no sign of changes in incident flux during either observation, but the measured flux increased by 10% over the 61 hours separating the two pointings. The mean flux was 1.0 times 10(-13) ergs cm(-2) s(-1) Angstroms(-1) at 1400 Angstroms. This is nearly double the historical average flux for MKN 421, and only 30% below the highest flux recorded. The spectrum itself is well-represented by a single power law over our entire wavelength range, plus absorption by gas in the galactic ISM. The spectral index observed was alpha ~ 1.1 (for f_nu ~ nu (-alpha ) ), and was the same for both pointings. This is somewhat larger than the average value for alpha , and differs from past behavior in that values of alpha larger than 0.9 - 1.0 have tended to be correlated with lower than average flux. This research is supported by NASA contract NAS 5-27000 to the Johns Hopkins University.

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