Karen E. Williamson
A5015656501- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Neutrino Physics Research
- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Particle physics theoretical and experimental studies
- Astronomical Observations and Instrumentation
- Earthquake Detection and Analysis
- Galaxies: Formation, Evolution, Phenomena
- Particle accelerators and beam dynamics
- Astrophysics and Star Formation Studies
- Geomagnetism and Paleomagnetism Studies
- Stellar, planetary, and galactic studies
- Atomic and Molecular Physics
- Computational Physics and Python Applications
- Cosmology and Gravitation Theories
Boston University
2013-2022
Laboratory for Atmospheric and Space Physics
2010
We analyze the multifrequency behavior of quasar 3C 454.3 during three prominent \gamma-ray outbursts: 2009 Autumn, 2010 Spring, and Autumn. The data reveal a repeating pattern, including triple flare structure, in properties each outburst, which implies similar mechanism(s) location for all events. multi-frequency indicates that lower frequency events are co-spatial with outbursts, although emission varies on shortest timescales. determine variability from UV to IR wavelengths an outburst...
In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing first direct image of center M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole mass approximately 6.5 x 10^9 M_solar. EHTC also partnered several international facilities space on ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents results analysis this campaign, as well...
We present multiwavelength data of the blazar 3C 454.3 obtained during an extremely bright outburst from November 2010 through January 2011. These include flux density measurements with Herschel Space Observatory at five submillimeter-wave and far-infrared bands, Fermi Large Area Telescope gamma-ray energies, Swift X-ray, ultraviolet (UV), optical frequencies, Submillimeter Array 1.3 mm. From this dataset, we form a series 52 spectral energy distributions (SEDs) spanning nearly two months...
Abstract In an effort to locate the sites of emission at different frequencies and physical processes causing variability in blazar jets, we have obtained high time-resolution observations BL Lacertae over a wide wavelength range: with Transiting Exoplanet Survey Satellite (TESS) 6000–10000 Å 2 minute cadence; Neil Gehrels Swift satellite optical, UV, X-ray bands; Nuclear Spectroscopic Telescope Array hard Fermi Large Area γ -ray energies; Whole Earth Blazar for measurement optical flux...
We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright γ-ray outburst detected by Fermi Large Area Telescope in 2012 September–October when source reached flux F>100 MeV = 5.2 ± 0.4 × 10−6 photons cm−2 s−1. At same time, displayed unprecedented optical and near-infrared (near-IR) outburst. evolution parsec-scale jet with ultra-high angular resolution through sequence 80 total polarized intensity Very Long Baseline Array images at 43 GHz,...
We report the results of decade-long (2008-2018) $\gamma$-ray to 1 GHz radio monitoring blazar 3C 279, including GASP/WEBT, $\it{Fermi}$ and $\it{Swift}$ data, as well polarimetric spectroscopic data. The X-ray light curves correlate well, with no delay > 3 hours, implying general co-spatiality emission regions. $\gamma$-ray-optical flux-flux relation changes activity state, ranging from a linear more complex dependence. behaviour Stokes parameters at optical wavelengths, 43 VLBA images,...
We present $\gamma$-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 $\gamma$-ray bright blazars over four years that we have been monitoring since 2008 August with multiple ground-based telescopes the Swift satellite, augmented by data from Fermi Gamma-ray Space Telescope other publicly available Swift. The sample consists 21 flat-spectrum radio quasars (FSRQs) 12 BL Lac objects (BL Lacs). identify quiescent active states sources based on their behavior. derive optical...
Linear polarization is an extremely valuable observational tool for probing the dynamic physical conditions of blazar jets. Some patterns are seen in data, suggestive order that can be explained by shock waves and helical magnetic field components. However, much disorder apparent, which implies turbulence plays a major role as well, especially fluctuations flux polarization, perhaps particle acceleration. Here, we present some actual versus time plus simulations model We analyze output...
We present the results of extensive modeling spectral energy distributions (SEDs) closest blazar (z=0.031) Markarian 421 (Mrk 421) during a giant outburst in February 2010. The source underwent rapid flux variations both X-rays and very high (VHE) gamma-rays as it evolved from low-flux state on 2010 13-15 to high-flux 17. During this period, exhibited significant hardening VHE while exhibiting "harder when brighter" behavior these bands. reproduce broadband SED using time-dependent...
Investigating the magnetic field structure in innermost regions of relativistic jets is fundamental to shed light on crucial physical processes giving rise jet formation, as well its extraordinary radiation output up gamma-ray energies. We study quasar CTA 102 with 3 and 7 mm-VLBI polarimetric observations, reaching an unprecedented resolution (~50 microarcsec). also investigate variability process occurring source during observing period which coincides a very active state till...
Abstract We explore the connection between γ -ray and radio emission in jet of blazar 0716+714 by using 15, 37, 230 GHz 0.1–200 GeV light curves spanning 10.5 yr (2008–2019). find significant positive negative correlations fluxes different time ranges. The delays suggest that observed flares originated from multiple regions upstream core, within a few parsecs central engine. Using time-resolved 43 Very Long Baseline Array maps we identified 14 components moving downstream along jet. Their...
Abstract We report the results of monitoring radio galaxy 3C 120 with Neil Gehrels Swift Observatory , Very Long Baseline Array, and Metsähovi Radio Observatory. The UV-optical continuum spectrum R-band polarization can be explained by a superposition an inverted-spectrum source synchrotron component containing disordered magnetic field. X-ray light curves include dips flares, while several superluminal knots appear in parsec-scale jet. recovery time second dip was longer at wavelengths,...
We present multi-wavelength studies of the radio galaxy 3C 120 and blazar CTA 102 during unprecedented γ-ray flares for both sources. In analysis data has been compared with a series 43 GHz VLBA images from VLBA-BU-BLAZAR program, providing necessary spatial resolution to probe parsec scale jet evolution high energy events. To extend dataset we also used 15 MOJAVE sample. These two objects which represent very different classes AGN, have similar properties The are associated passage new...
Abstract We present multi-epoch optical spectra of the γ -ray bright blazar 1156+295 (4C +29.45, Ton 599) obtained with 4.3 m Lowell Discovery Telescope. During a multiwavelength outburst in late 2017, when flux increased to 2.5 × 10 −6 phot cm −2 s −1 and quasar was first detected at energies ≥100 GeV, Mg ii λ 2798 emission line changed, as did that Fe complex shorter wavelengths. These emission-line fluxes along highly polarized continuum flux, which is presumably synchrotron radiation...
We analyze total and polarized intensity images of the quasar 3C 454.3 obtained monthly with VLBA at 43 GHz within ongoing Boston U. monitoring program gamma-ray blazars started in June 2007. The data are supplemented by observations performed during intense campaigns 2 week duration when was observed 3 times per campaign. find a strong increase activity parsec-scale jet high states December 2009, April 2010, November 2010. detect new superluminal knots, K09 K10, associated autumn 2009 2010...
High- and medium-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph Goddard High Resolution were used to search for weak electric quadrupole transitions of [Mg ii] near 1398.8 Å. This forbidden doublet was detected in eight sight lines. We calculate an empirical f-value (1.29 ± 0.13) × 10−5 all detections discuss prospects using this line future studies translucent interstellar clouds damped Lyα systems.
We have been performing multi-wavelength monitoring of a sample γ -ray blazars since the launch Fermi Gamma-ray Space Telescope in 2008. present and optical light curves for several quasars BL Lac objects from to illustrate different patterns variability. investigate correlations between R-band and, if these are statistically significant, determine delays variations at two wavebands. Such time can reveal relative locations emitting regions AGN jets origin high-energy photons. preliminary...