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We report on optical-near-infrared photopolarimetric observations of a blazar 3C 454.3 over 200 d. The object experienced an optical outburst in July 2007. This outburst was followed by a short state fainter than $V=15.2$ mag lasting $sim 25$ d. The object, then, entered an active state during which we observed short flares having a timescale of 3-10 d. The object showed two types of features in the color-magnitude relationship. One is a bluer-when-brighter trend in the outburst state, and the other is a redder-when-brighter trend in the faint state. These two types of features suggest a contribution of a thermal emission to the observed flux, as suspected in previous studies. Our polarimetric observation detected two episodes of the rotation of the polarization vector. The first one was a counterclockwise rotation in the $QU$ plane during the outburst state. After this rotation event of the polarization vector, the object entered a rapidly fading stage. The second one was seen in a series of flares during the active state. Each flare had a specific position angle of polarization, and it apparently rotated clockwise from the first to the last flares. Thus, the object exhibited rotations of the polarization vector in opposite directions. We estimated a decay timescale of the short flares during the active state, and then calculated an upper limit of the strength of the magnetic field, $B$=0.2 G, assuming a typical beaming factor of blazars, $delta=20$. This upper limit of $B$ is smaller than those previously estimated from spectral analysis.
We performed an optical spectroscopic monitoring of the blazar 3C 454.3 from September 2003 to July 2008. Sixteen optical spectra were obtained during different runs, which constitute the first spectroscopic monitoring done in the rest-frame UV regio
We report on the second AGILE multiwavelength campaign of the blazar 3C 454.3 during the first half of December 2007. This campaign involved AGILE, Spitzer, Swift,Suzaku,the WEBT consortium,the REM and MITSuME telescopes,offering a broad band coverag
In July 2007, the blazar 3C 454.3 underwent a flare in the optical, reaching R~13 on July 19. Then the optical flux decreased by one magnitude, being R~14 when the source was detected by the gamma-ray satellite AGILE, that observed the source on July
The gamma-ray-detected blazar 3C 454.3 exhibits dramatic flux and polarization variations in the optical and near-infrared bands. In December 2010, the object emitted a very bright outburst. We monitored it for approximately four years (including the
We present the gamma-ray data of the extraordinary flaring activity above 100 MeV from the flat spectrum radio quasar 3C 454.3 detected by AGILE during the month of December 2009. 3C 454.3, that has been among the most active blazars of the FSRQ type