Hope Boyce
A5039015823- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Radio Astronomy Observations and Technology
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- High-pressure geophysics and materials
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Particle Accelerators and Free-Electron Lasers
- Adaptive optics and wavefront sensing
- Magnetic confinement fusion research
- Stellar, planetary, and galactic studies
- Mechanics and Biomechanics Studies
- Optical measurement and interference techniques
- Black Holes and Theoretical Physics
- Ionosphere and magnetosphere dynamics
- High-Energy Particle Collisions Research
- Advanced Vision and Imaging
- Superconducting Materials and Applications
- Astronomical Observations and Instrumentation
- Digital Holography and Microscopy
- Particle Detector Development and Performance
- Advanced X-ray Imaging Techniques
McGill University
2017-2024
Space Telescope Science Institute
2017
Canadian Institute for Theoretical Astrophysics
2014
We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A$^*$), Galactic center source associated with a supermassive black hole. These were conducted in 2017 using global interferometric array eight telescopes operating at wavelength $\lambda=1.3\,{\rm mm}$. The EHT data resolve compact emission region intrahour variability. A variety imaging and modeling analyses all support an image that is dominated by bright, thick ring diameter $51.8 \pm 2.3$\,\uas (68\%...
Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This synchrotron radiation probes structure of magnetic fields and plasma properties near hole. Here we compare resolved polarization observed by EHT, along with simultaneous unresolved Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear image suggests that is scrambled scales...
Astrophysical black holes are expected to be described by the Kerr metric. This is only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein's equations and does not have pathologies outside of event horizon. We present new constraints on potential deviations from prediction based 2017 EHT observations Sagittarius A* (Sgr A*). calibrate relationship between geometrically defined hole shadow observed size ring-like images using a library includes...
Abstract In this paper we provide a first physical interpretation for the Event Horizon Telescope's (EHT) 2017 observations of Sgr A*. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT from radio X-ray wavelengths predictions library models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, stellar-wind-fed simulations; radiative transfer performed assuming both thermal nonthermal electron distribution...
Abstract In 2017 April, the Event Horizon Telescope (EHT) observed near-horizon region around supermassive black hole at core of M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in immediate vicinity hole. Here we present corresponding linear-polarimetric EHT images center M87. We find that only part ring is significantly polarized. The...
Abstract We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with Event Horizon Telescope in 2017 April at a wavelength 1.3 mm. Imaging has been conducted through surveys over wide range imaging assumptions using classical CLEAN algorithm, regularized maximum likelihood methods, Bayesian posterior sampling method. Different prescriptions have used to account for scattering effects by interstellar medium toward Galactic center. Mitigation rapid intraday...
We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at position supermassive black hole Sagittarius A* (Sgr A*), collected during 2017 April 5--11 campaign. The observations were carried out with eight facilities six locations across globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. majority emission arises from horizon scales, where intrinsic structural variability is detected on timescales minutes hours. effects...
In this paper we quantify the temporal variability and image morphology of horizon-scale emission from Sgr A*, as observed by EHT in 2017 April at a wavelength 1.3 mm. We find that A* data exhibit exceeds what can be explained uncertainties or effects interstellar scattering. The magnitude substantial fraction correlated flux density, reaching $\sim$100\% on some baselines. Through an exploration simple geometric source models, demonstrate ring-like morphologies provide better fits to than...
Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by Event Horizon Telescope (EHT). We use here M87* shadow size infer constraints on physical charges a large variety nonrotating or rotating black holes. For example, we show that quality is already sufficient rule out highly charged dilaton hole. Similarly, when considering holes with two and independent charges, are able exclude considerable regions space parameters...
The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in Galactic Center on 2017 April 5-11 1.3 millimeter wavelength band. At same time, interferometric array data from Atacama Large Millimeter/submillimeter Array and Submillimeter were collected, providing Sgr light curves simultaneous with EHT observations. These sets, complementing very-long-baseline interferometry, are characterized by a cadence signal-to-noise ratio previously unattainable for at...
Abstract Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at center M87 galaxy. EHT images in linear polarization further identified coherent spiral pattern hole, produced from ordered magnetic fields threading emitting plasma. Here we present first analysis circular using data, acquired 2017, which can potentially provide additional insights into and plasma composition near hole. Interferometric closure quantities...
Abstract The Event Horizon Telescope observed the horizon-scale synchrotron emission region around Galactic center supermassive black hole, Sagittarius A* (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with diameter of 51.8 ± 2.3 μ as and modest azimuthal brightness asymmetry, consistent expected appearance hole mass M ≈ 4 × 10 6 ⊙ . From these observations, we present first resolved linear circular polarimetric images Sgr A*. polarization demonstrate that is...
Abstract In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using Event Horizon Telescope, global very long baseline interferometric array operating at wavelength 1.3 mm. Here interpret this both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large linear polarization fraction (24%–28%, peaking ∼40%) is most stringent constraint parameter space, disfavoring...
In April 2019, the Event Horizon Telescope (EHT) Collaboration reported first-ever event-horizon-scale images of a black hole, resolving central compact radio source in giant elliptical galaxy M 87. These reveal ring with southerly brightness distribution and diameter ∼42 μas, consistent predicted size shape shadow produced by gravitationally lensed emission around supermassive hole. results were obtained as part 2017 EHT observation campaign, using global very long baseline interferometric...
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...
Abstract Synchrotron radiation from hot gas near a black hole results in polarized image. The image polarization is determined by effects including the orientation of magnetic field emitting region, relativistic motion gas, strong gravitational lensing hole, and parallel transport curved spacetime. We explore these using simple model an axisymmetric, equatorial accretion disk around Schwarzschild hole. By approximate expression for null geodesics derived Beloborodov conservation...
3C84 is a nearby radio source with complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates use VLBI above hitherto available maximum frequency 86GHz. Using ultrahigh resolution observations at highest 228GHz, we aim to directly detect compact structures understand physical conditions in 3C84. We used EHT 228GHz and, given limited (u,v)-coverage, applied geometric model fitting data. also employed...
We report the time-resolved spectral analysis of a bright near-infrared and moderate X-ray flare Sgr A*. obtained light curves in $M$-, $K$-, $H$-bands mid- $2-8~\mathrm{keV}$ $2-70~\mathrm{keV}$ bands X-ray. The observed slope band is $\nu L_\nu\propto \nu^{0.5\pm0.2}$; L_\nu \propto \nu^{-0.7\pm0.5}$. tested synchrotron self-Compton (SSC) scenarios. brightness faintness, together with slopes, pose challenges for all models explored. rule out scenario which emission SSC. A one-zone model...
ABSTRACT Sgr A* exhibits regular variability in its multiwavelength emission, including daily X-ray flares and roughly continuous near-infrared (NIR) flickering. The origin of this is still ambiguous since both inverse Compton synchrotron emission are possible radiative mechanisms. underlying particle distributions also not well constrained, particularly the non-thermal contribution. In work, we employ GPU-accelerated general relativistic magnetohydrodynamics code H-AMR to perform a study...
The blazar J1924-2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic Center's black hole Sagittarius A*. Here we present first total and linearly polarized intensity images of this source obtained with unprecedented 20 $\mu$as resolution EHT. very compact flat-spectrum radio strong optical variability polarization. In April 2017 was observed quasi-simultaneously EHT (April 5-11), Global Millimeter VLBI Array 3), Very Long Baseline 28), giving novel view at four...
Abstract We present a framework for characterizing the spatiotemporal power spectrum of variability expected from horizon-scale emission structure around supermassive black holes, and we apply this to library general relativistic magnetohydrodynamic (GRMHD) simulations associated ray-traced images relevant Event Horizon Telescope (EHT) observations Sgr A*. find that is generically red-noise process in both temporal spatial dimensions, with peak occurring on longest timescales largest scales....
Abstract The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto astrophysical phenomena unfolding on horizon scales in two known black holes, M87 * and Sgr A*. However, with this leap come new set of practical complications. A* exhibits intraday variability that violates assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales data sets very sparse ( u , v ) coverage. We present...
Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon Telescope (EHT) to resolve innermost accretion flows of largest supermassive black holes on sky. The sparse nature EHT's $(u, v)$-coverage presents a challenge when attempting highly time-variable sources. We demonstrate that changing (u, v)-coverage EHT can contain regions time over course single observation facilitate dynamical imaging. These optimal typically projected distributions...
We report on the observations of quasar NRAO 530 with Event Horizon Telescope (EHT) 2017 April 5-7, when was used as a calibrator for EHT Sagittarius A*. At z=0.902 this is most distant object imaged by so far. reconstruct first images source at 230 GHz, an unprecedented angular resolution $\sim$ 20 $\mu$as, both in total intensity and linear polarization. do not detect variability, allowing us to represent whole data set static images. The reveal bright feature located southern end jet,...
We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star - black hole (NS-BH) merger GW190814/S190814bv. This compact binary was detected through gravitational waves by LIGO/Virgo interferometers, with masses suggestive of NS-BH merger. imaged localization region using MegaCam instrument on Canada-France-Hawaii Telescope. describe our hybrid observing strategy both tiling and galaxy-targeted observations, as well image differencing transient...