H. D. Aller
A5034924159- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Gamma-ray bursts and supernovae
- Neutrino Physics Research
- Astrophysical Phenomena and Observations
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Astronomical Observations and Instrumentation
- Particle accelerators and beam dynamics
- Astronomy and Astrophysical Research
- Geophysics and Gravity Measurements
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Ionosphere and magnetosphere dynamics
- Stellar, planetary, and galactic studies
- GNSS positioning and interference
- Pulsars and Gravitational Waves Research
- Computational Physics and Python Applications
- Gyrotron and Vacuum Electronics Research
- Superconducting and THz Device Technology
- Calibration and Measurement Techniques
- Superconducting Materials and Applications
- Particle physics theoretical and experimental studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
University of Michigan–Ann Arbor
2014-2023
Michigan United
1997-2022
University of Cologne
2010-2018
Max Planck Institute for Radio Astronomy
2018
Ann Arbor Center for Independent Living
2006-2016
South University
2015
National Radio Astronomy Observatory
1983-2011
Astronomy and Space
1990-2010
Vaisala (Finland)
2009
University of Turku
2009
(Abridged) We have conducted a detailed investigation of the broad-band spectral properties \gamma-ray selected blazars Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated gamma-ray spectra with Swift, radio, infra-red, optical and other hard X-ray/gamma-ray data, collected within three months LBAS data taking period, we were able to assemble high-quality quasi-simultaneous Spectral Energy Distributions (SED) for 48 blazars.The SED these sources is similar that...
ABSTRACT We describe the parsec-scale kinematics of 200 active galactic nucleus (AGN) jets based on 15 GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2011 May 1. present new VLBA images these 59 additional AGNs from MOJAVE 2 cm Survey programs. Nearly all 60 most heavily observed show significant changes in their innermost position angle over a 12–16 yr interval, ranging 10° to 150° sky, corresponding intrinsic variations ∼0. ° 5 ∼2°. The BL Lac smaller than...
We present images from a long term program (MOJAVE: Monitoring of Jets in AGN with VLBA Experiments) to survey the structure and evolution parsec-scale jet phenomena associated bright radio-loud active galaxies northern sky. The observations consist 2424 15 GHz complete flux-density limited sample 135 above declination -20 degrees, spanning period 1994 August 2007 September. These data were acquired as part MOJAVE 2 cm Survey programs, archive. selection criteria are based on multi-epoch...
We present 5321 mas-resolution total intensity and linear polarization maps of 437 active galactic nuclei (AGNs) obtained with the VLBA at 15 GHz as part MOJAVE survey, also from NRAO data archive. The former is a long-term program to study structure evolution powerful parsec-scale outflows associated AGNs. targeted AGNs are drawn several flux-limited radio γ-ray samples, all have correlated flux densities greater than ∼50 mJy GHz. Approximately 80% these sources detected by Fermi LAT...
We present 1625 new 15 GHz (2 cm) VLBA images of 295 jets associated with active galactic nuclei (AGNs) from the MOJAVE and 2 cm surveys, spanning observations between 1994 Aug 31 2013 20. For 274 AGNs at least 5 epochs, we have analyzed kinematics 961 individual bright features in their parsec-scale jets. A total 122 these not been previously by program. In case 451 jet that had 10 also examined for possible accelerations. At half well-sampled non-radial and/or accelerating trajectories,...
We have examined the compact structure in 250 flat-spectrum extragalactic radio sources using interferometric fringe visibilities obtained with Very Long Baseline Array (VLBA) at 15 GHz. With projected baselines out to 440 Mλ, we are able investigate source on typical angular scales as small 0.05 mas. This scale is similar resolution of VLBI Space Observatory Programme data longer a lower frequency and somewhat poorer accuracy. For 171 our sample, more than half total flux density seen by...
view Abstract Citations (412) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectra and linear polarizations of extragalactic variable sources atcentimeter wavelengths. Aller, H. D. ; M. F. Latimer, G. E. Hodge, P. The results multifrequency observations the flux densities 97 obtained with University Michigan 26 m paraboloid through November 1984 are presented. were started at 8.0 GHz in June 1965, 14.5 February 1974, 4.8 September 1977....
view Abstract Citations (237) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The University of Michigan Radio Astronomy Data Base. I. Structure Function Analysis and the Relation between BL Lacertae Objects Quasi-stellar Hughes, P. A. ; Aller, H. D. M. F. We have performed a structure function analysis on well-observed group variable extragalactic sources, monitored in total polarized flux centimeter waveband since 1965. Total functions Lac...
The blazar 3C 279, one of the brightest identified extragalactic objects in γ-ray sky, underwent a large (factor ~10 amplitude) flare γ-rays toward end 3 week pointing by Compton Gamma Ray Observatory (CGRO), 1996 January-February. peak represents highest intensity ever recorded for this object. During high state, extremely rapid variability was seen, including an increase factor 2.6 ~8 hr, which strengthens case relativistic beaming. Coordinated multifrequency observations were carried out...
Eight optical and four radio observatories have been intensively monitoring the BL Lac object 0716+714 in last years: 4854 data points collected UBVRI bands since 1994, while light curves extend back to 1978. Many of these are presented here for first time. The long-term trend shown by seems vary with a characteristic time scale about 3.3 years, longer period 5.5-6 years characterize variations. In general, colour indices only weakly correlated brightness. flux behaviour at different...
view Abstract Citations (252) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarized radio outbursts in BL Lacertae. II. The flux and polarization of a piston-driven shock. Hughes, P. A. ; Aller, H. D. M. F. We present discussion the variable source Lac that occurred during 1982 1983 were seen both total polarized at 4.8, 8.0, 14.5 GHz. These are interpreted terms compressions propagate from an optically thick to thin part beam. Each is...
We have compared the radio emission from a sample of parsec-scale AGN jets as measured by VLBA at 15 GHz, with their associated gamma-ray properties that are reported in Fermi LAT 3-month bright source list. find our radio-selected photon flux correlates well quasi-simultaneously compact density. The LAT-detected complete generally higher densities, and cores brighter (i.e., brightness temperature) than non-detected objects. This suggests preferentially Doppler-boosting factors. In addition,...
We present time-resolved broad-band observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during first two years Fermi Gamma-ray Space Telescope mission. While investigating previously reported gamma-ray/optical flare accompanied by a change in optical polarization, we found that emission appears delayed with respect to gamma-ray about 10 days. X-ray reveal pair `isolated' flares separated ~90 days, only weak counterparts. The spectral structure measured...
We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard gamma-ray bands. Our unique set has allowed us demonstrate that selection method strongly influences results, producing biases cannot be ignored. Almost all BL Lac objects have been detected by Fermi-LAT, whereas ~40% of flat-spectrum radio quasars (FSRQs) radio, X-ray selected are still below detection limit even after integrating 27 months...
We have obtained milliarcsecond-scale spectral index distributions for a sample of 190 extragalactic radio jets through the MOJAVE project. The sources were observed in 2006 at 8.1, 8.4, 12.1, and 15.4 GHz, we study four-frequency spectrum individual jet features. performed detailed simulations to effects image alignment (u,v)-plane coverage on maps verify our results. core indices are average flat, while is general steep with mean -1.04. A simple power-law fit often inadequate regions, as...
We report observations of Faraday rotation measures for a sample 191 extragalactic radio jets observed within the MOJAVE program. Multifrequency Very Long Baseline Array were carried out over 12 epochs in 2006 at four frequencies between 8 and 15 GHz. detect parsec-scale 149 sources find quasars to have larger on average than BL Lac objects. The median core are significantly higher jet components. This is especially true where we significant negative correlation magnitude measure...
We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and γ-ray wavelengths the BL Lacertae object AO 0235+164. analyze timing multi-waveband variations in flux linear polarization, as well changes Very Long Baseline Array images λ = 7 mm with ∼0.15 milliarcsec resolution. The association events different wavebands is confirmed high statistical significance by probability arguments Monte Carlo simulations. A series sharp peaks optical pronounced maximum...
OJ287 is the best candidate active galactic nucleus (AGN) for hosting a supermassive binary black hole (SMBBH) at very close separation.We present 120 Very Long Baseline Array (VLBA) observations (at 15 GHz) covering time between April 1995 and 2017.We find that radio jet precessing on time-scale of ∼22 yr.In addition, our data are consistent with jet-axis rotation yearly time-scale.We model precession (24 ± 2 yr) combined motion rotation.The explains variability total flux-density via...
We examine the coincidence of times high γ-ray flux and ejections superluminal components from core in EGRET blazars based on a Very Long Baseline Array (VLBA) monitoring program at 22 43 GHz 1993 November to 1997 July. In 23 cases flares for which sufficient VLBA data exist, 10 (in eight objects) fall within 1 σ uncertainties extrapolated epoch zero separation radio component. each two sources (0528+134 1730-130), successive were followed by appearance new components. carried out...
The BL Lacertae object AO 0235+16 is well known for its extreme optical and radio variability. New data have been collected in the last four years by a wide international collaboration, which confirm intense activity of this source: on long term, overall variations R band up to factor 18 fluxes were detected, while short-term variability few hours one day was observed band. also include results Whole Earth Blazar Telescope (WEBT) first-light campaign organized November 1997, involving dozen...
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. maximum brightness detected was R = 12.0, which represents the most luminous state thus far observed (M_B ~ -31.4). In order to follow emission behaviour of source detail, a large multiwavelength campaign organized by Whole Earth Blazar Telescope (WEBT). Continuous optical, near-IR monitoring performed several bands. ToO pointings Chandra INTEGRAL satellites provided...
A TeV flare from the BL Lac object Mrk 421 was detected in May of 1994 by Whipple Observatory air Cherenkov experiment during which flux above 250 GeV increased nearly an order magnitude over a 2-day period. Contemporaneous observations ASCA showed X-ray to be very high state. We present these results, combined with first ever simultaneous or at gamma-ray, UV, IR, mm, and radio energies for this nearest object. While gamma-ray slightly, there is little evidence variability comparable that...
view Abstract Citations (176) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Synchrotron Emission from Shocked Relativistic Jets. II. A Model for the Centimeter Wave Band Quiescent and Burst BL Lacertae Hughes, P. A. ; Aller, H. D. M. F. We present a model radio emission Lac based on truncated, conical flow of synchrotron plasma with tangled magnetic field. Outbursts are due to shocks that locally compress field, allowing significant degree...
view Abstract Citations (150) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Synchrotron Emission from Shocked Relativistic Jets. I. The Theory of Radio-Wavelength Variability and Its Relation to Superluminal Motion Hughes, P. A. ; Aller, H. D. M. F. We summarize the theory transfer polarized radiation in a synchrotron plasma arbitrary optical depth, plane shock waves with relativistic flow velocity equation state. then describe construction...