Mark Gurwell
A5071921784- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Planetary Science and Exploration
- Galaxies: Formation, Evolution, Phenomena
- Stellar, planetary, and galactic studies
- Pulsars and Gravitational Waves Research
- Astronomy and Astrophysical Research
- Neutrino Physics Research
- Particle Accelerators and Free-Electron Lasers
- Atmospheric Ozone and Climate
- Solar and Space Plasma Dynamics
- Astronomical Observations and Instrumentation
- Dark Matter and Cosmic Phenomena
- Isotope Analysis in Ecology
- Space Exploration and Technology
- Gyrotron and Vacuum Electronics Research
- Spectroscopy and Laser Applications
- Scientific Research and Discoveries
- Molecular Spectroscopy and Structure
- Geophysics and Gravity Measurements
- Spacecraft and Cryogenic Technologies
Center for Astrophysics Harvard & Smithsonian
2016-2025
Harvard University
2004-2020
Harvard University Press
2008-2018
St Petersburg University
2017
Time Domain (United States)
2017
Boston University
2017
Max Planck Society
2015
Max Planck Institute for Radio Astronomy
2015
CFA Institute
2010-2012
Smithsonian Astrophysical Observatory
1996-2011
When surrounded by a transparent emission region, black holes are expected to reveal dark shadow caused gravitational light bending and photon capture at the event horizon. To image study this phenomenon, we have assembled Event Horizon Telescope, global very long baseline interferometry array observing wavelength of 1.3 mm. This allows us reconstruct event-horizon-scale images supermassive hole candidate in center giant elliptical galaxy M87. We resolved central compact radio source as an...
We present measurements of the properties central radio source in M87 using Event Horizon Telescope data obtained during 2017 campaign. develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) two independent sampling algorithms that consider distinct representations visibility data. show family is statistically preferred over other comparably complex we explore. calibrate model parameters general relativistic magnetohydrodynamic (GRMHD) emission...
We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These show a prominent ring with diameter ~40 micro-as, consistent size and shape lensed photon orbit encircling "shadow" supermassive black hole. The is persistent across four observing nights shows enhanced brightness in south. To assess reliability these results, we implemented two-stage imaging procedure. In stage, teams, each blind to others' work, produced M87 both...
The Event Horizon Telescope (EHT) has mapped the central compact radio source of elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider physical implications asymmetric ring seen in 2017 EHT data. To this end, construct a large library models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by ray tracing. We compare observed visibilities confirm that is consistent earlier predictions strong gravitational...
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\%...
(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...
The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of Earth. At nominal operating wavelength ~1.3 mm, EHT angular resolution (lambda/D) ~25 micro-as, which sufficient resolve nearby supermassive black hole candidates on spatial temporal scales correspond their event horizons. With this capability, scientific goals are probe general...
We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3mm radio wavelength observations supermassive black hole candidate at center galaxy M87 quasar 3C 279, taken during 2017 April 5-11 observing campaign. These global very long baseline interferometric include for first time highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution 25 micro-as, with characteristic sensitivity limits ~1 mJy on baselines to ALMA ~10 other...
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...
We present results from monitoring the multi-waveband flux, linear polarization, and parsec-scale structure of quasar PKS 1510-089, concentrating on eight major gamma-ray flares that occurred during interval 2009.0-2009.5. The peaks were essentially simultaneous with maxima at optical wavelengths, although flux ratio two wavebands varied by an order magnitude. polarization vector rotated 720 degrees a 5-day period encompassing six these flares. This culminated in very bright, roughly 1 day,...
Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by accretion matter onto super massive black holes. While the measured width profiles such jets on large scales agree with theories magnetic collimation, predicted structure disk at jet launch point has not been detected. We report radio interferometry observations 1.3mm wavelength elliptical galaxy M87 that spatially resolve base in this source. The derived size 5.5 +/- 0.4 Schwarzschild radii is...
Gravitational lensing is a powerful astrophysical and cosmological probe particularly valuable at submillimeter wavelengths for the study of statistical individual properties dusty starforming galaxies. However identification gravitational lenses often time-intensive, involving sifting large volumes imaging or spectroscopic data to find few candidates. We used early from Herschel Astrophysical Terahertz Large Area Survey demonstrate that wide-area surveys can simply easily detect strong...
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...
The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to first measurement size a black-hole shadow. This observation offers new and clean gravitational test metric strong-field regime. We show analytically that spacetimes deviate from Kerr but satisfy weak-field tests can lead large deviations predicted shadows are inconsistent with even current EHT measurements. use numerical calculations regular, parametric, non-Kerr metrics identify common...
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...
Magnetic fields near the event horizon Astronomers have long sought to examine a black hole's horizon—the boundary around hole within which nothing can escape. Johnson et al. used sophisticated interferometry techniques combine data from millimeter-wavelength telescopes world. They measured polarization just outside of Sgr A*, supermassive at center our galaxy, Milky Way. The is signature ordered magnetic generated in accretion disk hole. results help explain how holes accrete gas and launch...
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...