A FAST FLARE AND DIRECT REDSHIFT CONSTRAINT IN FAR-ULTRAVIOLET SPECTRA OF THE BLAZAR S5 0716+714

The BL Lacertae object S5 0716+714 is one of the most studied blazars on the sky due to its active variability and brightness in many bands, including very-high-energy gamma rays. We present here two serendipitous results from recent far-ultraviolet spectroscopic observations by the Cosmic Origins S...

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Bibliographic Details
Published in:The Astrophysical journal 2013-02, Vol.764 (1), p.1-7
Main Authors: Danforth, Charles W, NALEWAJKO, KRZYSZTOF, France, Kevin, Keeney, Brian A
Format: Article
Language:English
Subjects:
ABSORPTION
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BL LACERTAE OBJECTS
Blazars
BRIGHTNESS
Confidence intervals
FAR ULTRAVIOLET RADIATION
Flares
Flux
GALAXIES
GAMMA RADIATION
Hubble Space Telescope
Onboard
QUASARS
RED SHIFT
SKY
SPECTRA
TELESCOPES
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Summary:The BL Lacertae object S5 0716+714 is one of the most studied blazars on the sky due to its active variability and brightness in many bands, including very-high-energy gamma rays. We present here two serendipitous results from recent far-ultraviolet spectroscopic observations by the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (HST). First, during the course of our 7.3 hr HST observations, the blazar increased in flux rapidly by ~40% (-0.45 mag hr super(-1)) followed by a slower decline (+0.36 mag hr super(-1)) to previous FUV flux levels. We model this flare using asymmetric flare templates and constrain the physical size and energetics of the emitting region. Furthermore, the spectral index of the object softens considerably during the course of the flare from alpha sub(v) approximately -1.0 to alpha sub(v) approximately -1.4. Second, we constrain the source redshift directly using the ~30 intervening absorption systems. A system at z = 0.2315 is detected in Ly alpha , Ly beta , O VI, and N V and defines the lower bound on the source redshift. No absorbers are seen in the remaining spectral coverage (0.2315 < z sub(Ly) alpha [lap] 0.47) and we set a statistical upper bound of z < 0.322 (95% confidence) on the blazar. This is the first direct redshift limit for this object and is consistent with literature estimates of z = 0.31 + or - 0.08 based on the detection of a host galaxy.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/764/1/57