Ultraviolet observations of the gamma-ray blazar 3C 279 following the gamma-ray flare of 1991 june

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Ultraviolet observations of the gamma-ray blazar 3C 279 were carried out in 1991 July with the International Ultraviolet Explorer (IUE) satellite, 28 days after the outburst of intense gamma-ray emission detected from this source with the high-energy EGRET instrument aboard the Compton Gamma-Ray Observatory. IUE observations were conducted over the wavelength range 1200-3200 Å (5-10 eV) and are compared with archival UV measurements spanning the period 1988-1991. This set of observations was analyzed with a uniform, standardized data-reduction procedure. No significant variability in the UV spectrum of 3C 279 is noted over timescales of hours, though variations at the 3 σ level or higher exist on longer timescales of months to years. The UV observations which most closely bracket the γ-ray flare detected by EGRET show ∼3 σ differences in flux and spectral index, consistent with (but not definitive proof of) variations in the UV flux during the period of the γ-ray flare. Statistically marginal evidence for a monotonie correlation is found between UV spectral index and the emission observed from 3C 279, in that a harder spectrum is associated with increased UV flux.

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Astrophysical Journal

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