P. D. Smith

Prospects for GRB Science with the Fermi Large Area Telescope

The Large Area Telescope (LAT) instrument on the Fermi mission will reveal the rich spectral and temporal gamma-ray burst (GRB) phenomena in the >100 MeV band. The synergy with Fermis Gamma-ray Burst Monitor detectors will link these observations to those in the well explored 10-1000 keV range; the addition of the >100 MeV band observations will resolve theoretical uncertainties about burst emission in both the prompt and afterglow phases. Trigger algorithms will be applied to the LAT data both onboard the spacecraft and on the ground. The sensitivity of these triggers will differ because of the available computing resources onboard and on the ground. Here we present the LATs burst detection methodologies and the instruments GRB capabilities.

PARSEC-SCALE JET BEHAVIOR OF THE QUASAR 3C273 DURING A HIGH GAMMA-RAY STATE IN 2009–2010

We compare the γ-ray light curves of the blazars, constructed with data provided by the Fermi Large Area Telescope, with flux and polarization variations in the VLBI core and bright superluminal knots obtained via monthly monitoring with the Very Long Baseline Array at 43 GHz. For all blazars in the sample that exhibit a high γ-ray state on time scales from several weeks to several months, an increase of the total flux in the mm-wave core is contemporaneous with the γ-ray activity (more than a third of the sample). Here we present the results for quasars with the most extreme γ-ray behavior (3C 454.3, 3C 273, 3C 279, 1222+216, and 1633+382). The sources show that in addition to the total flux intensity behavior, a maximum in the degree of polarization in the core or bright superluminal knot nearest to the core coincides with the time of a γ-ray peak to within the accuracy of the sampling of the radio data. These argue in favor of location of many of γ-ray outbursts in blazars outside of the broad line region, either in the vicinity or downstream of the mm-wave VLBI core.We analyze total and polarized intensity images of the quasar 3C273 obtained at 43 GHz monthly during 2008-2010 with the VLBA. We find a strong increase of activity in the parsec-scale jet during a high γ-ray state lasting from 2009 June to 2010 May featuring an increase of the total and polarized flux in the mm-wave core and the appearance of superluminal knots in the jets. Although the optical variability is low, owing to strong contamination by the big blue bump, we observe an increase in optical polarization by a factor of 3 during a gamma-ray flare in 2010 April. We discuss the locations in the jet where high gamma-ray fluxes occur. These include stationary features in the jet flow that we identify with standing shocks.

Exploring the Connection between Parsec-scale Jet Activity and Broadband Outbursts in 3C 279

We use a combination of high-resolution very long baseline interferometry (VLBI) radio and multi-wavelength flux density and polarization observations to constrain the physics of the dissipation mechanism powering the broadband flares in 3C 279 during an episode of extreme flaring activity in 2013-2014. Six bright flares superimposed on a long-term outburst are detected at

Polarimetric Observations of 15 AGNs at High Frequencies

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Ground-based observations of PKS 2155-304 in November 1991.

-ray energies. Four of the flares have optical and radio counterparts. The two modes of flaring activity (faster flares sitting on top of a long term outburst) present at radio, optical,