Optical and hubble Space Telescope ultraviolet spectropolarimetry of 3C 273 and PG 1114+445

Paul S. Smith, Gary D. Schmidt, Richard G. Allen

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Ultraviolet polarization measurements of 3C 273 made with the Faint Object Spectrograph of the Hubble Space Telescope are combined with new optical spectropolarimetry and broad-band measurements made during occasions when the linear polarization of the quasar was ≤1%. The HST measurements exhibit very weak UV polarization during the epoch of observation and are consistent with the UV continuum and emission lines being completely unpolarized. However, the optical spectropolarimetry reveals a source of polarized light consistent with a nonthermal component that is diluted by other unpolarized emission sources such as the "big blue bump." The continuum polarized flux has a steep spectral index (α ≈ -2.7) similar to that found in some BL Lac objects and optically violent variable quasars. The fact that the Hα emission line clearly dilutes the continuum polarization, together with the variability of the observed polarization, rules out the possibility that a major fraction of the polarized flux from 3C 273 arises through scattering by dust or electrons exterior to the broad-line region. In addition to our observations of 3C 273, optical spectropolarimetry of the radio-quiet quasar PG 1114+445 are presented. The broad permitted lines of PG 1114+445 as well as narrow [O m] λ5007 are shown to be polarized to the same degree as the continuum, implying that scattering by dust external to the narrow-line region is responsible for the polarization of this QSO. Though both 3C 273 and PG 1114+445 are included in the Palomar-Green survey of optically selected quasars, they offer a striking illustration of the range of polarizing mechanisms which can operate in low-polarization QSOs.

Original languageEnglish (US)
Pages (from-to)604-611
Number of pages8
JournalAstrophysical Journal
Volume409
Issue number2
DOIs
StatePublished - 1993
Externally publishedYes

Keywords

  • Polarization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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