Sandra Bustamante
A5015140450- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Radio Astronomy Observations and Technology
- Particle Accelerators and Free-Electron Lasers
- Laser-Plasma Interactions and Diagnostics
- Gamma-ray bursts and supernovae
- Magnetic confinement fusion research
- Mechanics and Biomechanics Studies
- Laser-Matter Interactions and Applications
- High-pressure geophysics and materials
- Atomic and Molecular Physics
- Galaxies: Formation, Evolution, Phenomena
- Radiation Detection and Scintillator Technologies
- Dark Matter and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Particle Detector Development and Performance
- GNSS positioning and interference
- Ionosphere and magnetosphere dynamics
Amherst College
2024-2025
University of Massachusetts Amherst
2022-2024
European Organization for Nuclear Research
2017-2019
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\%...
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 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...
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...
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 give direct experimental evidence for the observation of full transverse self-modulation a long, relativistic proton bunch propagating through dense plasma. The exits plasma with periodic density modulation resulting from radial wakefield effects. show that is seeded by ionization front created using an intense laser pulse copropagating bunch. extends over length following seed point. By varying one order magnitude, we frequency scales expected dependence on density, i.e., it equal to...
The seeded self-modulation of a relativistic, charged particle bunch in plasma is shown to grow both along the and plasma, resulting transverse wakefield amplitudes that far exceed initial seed values.
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....
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,...
AWAKE is a proton-driven plasma wakefield acceleration experiment. % We show that the experimental setup briefly described here ready for systematic study of seeded self-modulation 400\,GeV proton bunch in 10\,m-long rubidium with density adjustable from 1 to 10$\times10^{14}$\,cm$^{-3}$. short laser pulse used ionization vapor propagates all way along column, suggesting full vapor. occurs bunch, at time and follows affects bunch.
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...
The first very long baseline interferometry (VLBI) detections at 870$\mu$m wavelength (345$\,$GHz frequency) are reported, achieving the highest diffraction-limited angular resolution yet obtained from surface of Earth, and highest-frequency example VLBI technique to date. These include strong for multiple sources observed on inter-continental baselines between telescopes in Chile, Hawaii, Spain, during observations October 2018. longest-baseline approach 11$\,$G$\lambda$ corresponding an...
The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered first very long baseline interferometry (VLBI) images at frequency 230 GHz, leading to a number unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed: main science targets, Sgr A* M87 along with various calibrators. We investigated morphology sixteen AGN in EHT data set, focusing properties VLBI cores: size, flux density, brightness temperature....
The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered first very long baseline interferometry (VLBI) images at frequency 230,GHz, leading to a number unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed, including main science targets, Sgr,A* M,87, various calibrators. Sixteen AGN. We investigated morphology sixteen AGN in EHT data set, focusing properties VLBI cores: size, flux density,...
The Event Horizon Telescope (EHT) observation of M87 ∗ in 2018 has revealed a ring with diameter that is consistent the 2017 observation. brightest part shifted to southwest from southeast. In this paper, we provide theoretical interpretations for multi-epoch EHT observations by comparing new general relativistic magnetohydrodynamics model image library both and 2018. images include aligned tilted accretion parameterized thermal nonthermal synchrotron emission properties. again shows spin...
Interpretation of resolved polarized images black holes by the Event Horizon Telescope (EHT) requires predictions emission observable an Earth-based instrument for a particular model hole accretion system. Such are generated general relativistic radiative transfer (GRRT) codes, which integrate equations in curved spacetime. A selection ray-tracing GRRT codes used within EHT collaboration is evaluated accuracy and consistency producing test images, demonstrating that various methods...
Context. The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by Event Horizon Telescope (EHT). In 2018, more than dozen multi-wavelength (MWL) facilities (from radio to γ -ray energies) took part in second EHT campaign. Aims. goal this extensive MWL campaign was better understand physics accreting hole M87*, relationship between inflow and inner jets, high-energy particle acceleration. Understanding...