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Hu W.,Yunnan University | Hu W.,Key Laboratory of Astroparticle Physics | Fan Z.-H.,Yunnan University | Fan Z.-H.,Key Laboratory of Astroparticle Physics | And 2 more authors.
Research in Astronomy and Astrophysics | Year: 2015

We have studied the simultaneous spectral energy distributions (SEDs) of the 2009 December flare and those of the quiescent state of blazar 3C 454.3 by constructing a multi-component model. We find that all six SEDs can be explained by a one-zone leptonic model involving synchrotron self-Compton (SSC) plus external Compton emission from an accretion disk (ECD) and that from a broad-line region (ECC). X-ray emission is dominated by the SSC mechanism, and the γ-ray spectrum is well represented by a combination of ECD and ECC processes. Our results indicate that the energy density of the magnetic field and electrons decrease with distance from the central engine, and the Doppler factor increases with the blob moving outward in the development of the 2009 December flare. The increase in the observed flux density is possibly due to the increase in the Doppler factor of the blob. The relation between the Doppler factor δb and the distance from the central black hole suggests the magnetically driven jets span a sub-pc scale, and the relation between the magnetic field B' and the dimension of the emission region R'b is in good agreement with what is required by conservation of magnetic flux. The weak "harder-when-brighter" behavior of the γ-ray spectrum could be a result of the increase in Doppler factor during the outward motion of the blob. The parameters during the quiescent state obviously deviate from those during the flare state. We propose that the flare was likely caused by the ejection of a new blob. The gamma-ray emissions in different states are associated with the evolution of the blob. © 2015 National Astronomical Observatories, Chinese Academy of Sciences and IOP Publishing Ltd.

Dai B.-Z.,Yunnan University | Dai B.-Z.,Key Laboratory of Astroparticle Physics | Zeng W.,Yunnan University | Zeng W.,Key Laboratory of Astroparticle Physics | And 16 more authors.
Astrophysical Journal, Supplement Series | Year: 2015

We present long-term optical multi-band photometric monitoring of blazar S5 0716+714, from 2004 January 11 to 2012 November 4, with high temporal resolution of approximately 15 minutes in the BVRI bands. The source was in an active state during the whole monitoring campaign, showing intraday variability in 11 of 72 days. The average magnitudes in each band were B = 14.398, V = 13.821, R = 13.255, and I = 12.885. The overall variability amplitudes were δB =1m834, δV =2m167, δR =2m148, and δI =1m912. The structure function showed that typical timescales for intraday variability were between approximately 2 and 7.5 hr. The intraday variability amplitudes were from a few percent to approximately 30%. We found typical variation rates of approximately 0.05 mag hr-1 in both the rising and falling phases, with a minimal variability timescale of 130 minutes. A 10 day period short-term variability was observed simultaneously in the BVRI bands. The discrete correlation function suggests that there is significant correlated variability between the B- and I-band light curves. However, no significant time lags were detected. The spectral behaviors in the different variability episodes were studied, and our observations show bluer-when-brighter behavior on long, short, and intraday timescales for the blazar S5 0716+714. The variability and relevant spectral trends can be explained by the shock-in-jet scenario. © 2015. The American Astronomical Society. All rights reserved.

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