Magnetic Field Amplification and Blazar Flares

Recent multiwavelength observations of PKS 0208-512 by SMARTS, Fermi, and Swift revealed that gamma-ray and optical light curves of this flat spectrum radio quasars are highly correlated, but with an exception of one large optical flare having no corresponding gamma-ray activity or even detection. On the other hand, recent advances in SNRs observations and plasma simulations both reveal that magnetic field downstream of astrophysical shocks can be largely amplified beyond simple shock compression. These amplifications, along with their associated particle acceleration, might contribute to blazar flares, including the peculiar flare of PKS 0208-512. Using our time dependent multizone blazar emission code, we evaluate several scenarios that may represent such phenomena. This code combines Monte Carlo method that tracks the radiative processes including inverse Compton scattering, and Fokker-Planck equation that follows the cooling and acceleration of particles. It is a comprehensive time dependent code that fully takes into account the light travel time effects. In this study, both the changes of the magnetic field and acceleration efficiency are explored as the cause of blazar flares. Under these assumption, synchrotron self-Compton and external Compton scenarios produce distinct features that favor the external Compton scenario. The optical flares with/without gamma-ray counterparts can be explained by different allocations of energy between the magnetization and particle acceleration, which in turn can be affected by the relative orientation between the magnetic field and the shock flow. We compare the details of the observations and simulation, and highlight what implications this study has on our understanding of relativistic jets.Comment: 6 pages. To appear in the proceeding of 'The Innermost Regions of Relativistic Jets and Their Magnetic Fields', Granada, Spai

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Magnetic Field Amplification and Flat Spectrum Radio Quasars

We perform time-dependent, spatially-resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts for light-travel-time effects and is applied to flares observed in the flat spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/{\gamma}-ray correlation at some times, but orphan optical flares at other times. Changes in both the magnetic field and the particle acceleration efficiency are explored as causes of flares. Generally, external Compton emission appears to describe the available data better than a synchrotron self-Compton scenario, and in particular orphan optical flares are difficult to produce in the SSC framework. X-ray soft-excesses, {\gamma}-ray spectral hardening, and the detections at very high energies of certain FSRQs during flares find natural explanations in the EC scenario with particle acceleration change. Likewise, optical flares with/without {\gamma}-ray counterparts can be explained by different allocations of energy between the magnetization and particle acceleration, which may be related to the orientation of the magnetic field relative to the jet flow. We also calculate the degree of linear polarization and polarization angle as a function of time for a jet with helical magnetic field. Tightening of the magnetic helix immediately downstream of the jet perturbations, where flares occur, can be sufficient to explain the increases in the degree of polarization and a rotation by >= 180 degree of the observed polarization angle, if light-travel-time effects are properly considered.Comment: 12 pages, 9 figures. Accepted for publication in MNRA

SMARTS OPTICAL AND INFRARED MONITORING OF 12 GAMMA-RAY BRIGHT BLAZARS

We present multiwavelength data for 12 blazars observed from 2008 to 2010 as part of an ongoing optical–infrared photometric monitoring project. Sources were selected to be bright, southern (δ < 20◦) blazars observed by the Fermi Gamma-Ray Space Telescope. Light curves are presented for the 12 blazars in BVRJK at near-daily cadence. We find that optical and infrared fluxes are well correlated in all sources. Gamma-ray bright flat spectrum radio quasars (FSRQs) in our sample have optical/infrared emission correlated with gamma-rays consistent with inverse Compton-scattering models. In FSRQs, variability amplitude increases toward IR wavelengths, consistent with the presence of a thermal accretion disk varying on significantly longer timescales than the jet. In BL Lac objects, variability is mainly constant, or increases toward shorter wavelength. FSRQs have redder optical–infrared colors when they are brighter,whileBLLac objects showno such trend. Several objects showcomplicated color–magnitude behavior: AO 0235+164 appears in two different states depending on its gamma-ray intensity. OJ 287 and 3C 279 show some hysteresis tracks in their color–magnitude diagrams. Individual flares may be achromatic or otherwise depart from the trend, suggesting different jet components becoming important at different times. We present a time-dependent spectral energy distribution of the bright FSRQ 3C 454.3 during its 2009 December flare, which is well fit by an external Compton model in the bright state, although day-to-day changes pose challenges to a simple one-zone model. All data from the SMARTS monitoring program are publicly available on our Web site

Outcomes of Abrupt Switch to Bevacizumab of Patients Undergoing Aflibercept Intravitreal Injections for Neovascular Age-Related Macular Degeneration in a Tertiary Center in Lombardy, Italy: A Real-Life Retrospective Analysis

To assess real-life anatomical and functional outcomes of switch to bevacizumab in patients undergoing aflibercept intravitreal injections for nAMD