Frederick K Baganoff | Massachusetts Institute of Technology (MIT) (original) (raw)

Papers by Frederick K Baganoff

BIMA observations of the Orion nebula discovered a giant flare from a young star previously undet... more BIMA observations of the Orion nebula discovered a giant flare from a young star previously undetected at millimeter wavelengths. The star briefly became the brightest compact object in the nebula at 86 GHz. Its flux density increased by more than a factor of 5 on a timescale of hours, to a peak of 160 mJy. This is one of the most luminous stellar radio flares ever observed. Remarkably, the Chandra X-ray observatory was in the midst of a deep integration of the Orion nebula at the time of the BIMA discovery; the source's X-ray flux increased by a factor of 10 approximately 2 days before the radio detection. Follow-up radio observations with the VLA and BIMA showed that the source decayed on a timescale of days, then flared again several times over the next 70 days, although never as brightly as during the discovery. Circular polarization was detected at 15, 22, and 43 GHz, indicating that the emission mechanism was cyclotron. VLBA observations 9 days after the initial flare yiel...

Most galactic nuclei are now believed to harbour supermassive black holes. Studies of stellar mot... more Most galactic nuclei are now believed to harbour supermassive black holes. Studies of stellar motions in the central few light-years of our Milky Way Galaxy indicate the presence of a dark object with a mass of about 2.6 million solar masses. This object is spatially coincident with Sagittarius A* (Sgr A*), the unique compact radio source located at the dynamical centre of our Galaxy. By analogy with distant quasars and nearby active galactic nuclei (AGN), Sgr A* is thought to be powered by the gravitational potential energy released by matter as it accretes onto a supermassive black hole. However, Sgr A* is much fainter than expected in all wavebands, especially in X-rays, casting some doubt on this model. Recently, we reported the first strong evidence of X-ray emission from Sgr A*. Here we report the discovery of rapid X-ray flaring from the direction of Sgr A*. These data provide compelling evidence that the X-ray emission is coming from accretion onto a supermassive black hole ...

We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpa... more We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpart associated with the massive 3-4x10**6 solar mass black hole at the Galactic Center. The main aim is to investigate the physical processes responsible for the variable emission from SgrA*. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory as well as the Submillimeter Array SMA on Mauna Kea, Hawaii, and the Very Large Array in New Mexico. We detected one moderately bright flare event in the X-ray domain and 5 events at infrared wavelengths.

We model thermal X-ray emission from the accreting supermassive black hole Sagittarius A* at the ... more We model thermal X-ray emission from the accreting supermassive black hole Sagittarius A* at the Galactic Center. For the region inside 1.^"5 of the center, we use a generalized radiatively inefficient accretion flow (RIAF) model, and for the region out to 10^" we use published models of the ambient hot gas. We calculate the equivalent widths of Hydrogen-like and Helium-like emission lines of various elements, notably iron. We predict that a strong Helium-like iron line with an equivalent width ∼1 keV should be emitted by both the external medium and the RIAF. The equivalent width in the external medium is sensitive to the metallicity Z of the gas as well as the mean temperature. For reasonable choices of these parameters, the calculated results agree with Chandra's detection of an iron line with an equivalent width of 1.3 keV within 10^". The emission from within 1.^"5 is not sensitive to the external temperature, but is sensitive to the density and, especia...

Despite strong physical reasons that they should exist and decades of search, jets from the Galac... more Despite strong physical reasons that they should exist and decades of search, jets from the Galactic Center Black Hole, Sgr A*, have not yet been convincingly detected. Based on high-resolution Very Large Array images and ultra-deep imaging-spectroscopic data produced by the Chandra X-ray Observatory, we report new evidence for the existence of a parsec-scale jet from Sgr A*, by associating a linear feature G359.944-0.052, previously identified in X-ray images of the Galactic Center, with a radio shock front on the Eastern Arm of the Sgr A West HII region. We show that the shock front can be explained in terms of the impact of a jet having a sharp momentum peak along the Galaxy's rotation axis, whereas G359.944-0.052, a quasi-steady feature with a power-law spectrum, can be understood as synchrotron radiation from shock-induced ultrarelativistic electrons cooling in a finite post-shock region downstream along the jet path. Several interesting implications of the jet properties a...

Stellar dynamics indicate the presence of a super massive 3-4x10^6 Msun solm black hole at the Ga... more Stellar dynamics indicate the presence of a super massive 3-4x10^6 Msun solm black hole at the Galactic Center. It is associated with the variable radio, near-infrared, and X-ray counterpart Sagittarius A* (SgrA*). The goal is the investigation and understanding of the physical processes responsible for the variable emission from SgrA*. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X-ray Observatory (July 2005). We find that for the July 2005 flare the variable and polarized NIR emission of SgrA* occurred synchronous with a moderately bright flare event in the X-ray domain with an excess 2 - 8 keV luminosity of about 8x10^33erg/s. We find no time lag between the flare events in the two wavelength bands with a lower limit of less than 10 minutes. The May 2007 flare shows the highest sub-flare to flare contrast obser...

Sgr A*, the massive black hole at the center of the Galaxy, varies in radio through X-ray emissio... more Sgr A*, the massive black hole at the center of the Galaxy, varies in radio through X-ray emission on hourly time scales. The flare activity is thought to arise from the innermost region of an accretion flow onto Sgr A*. We present simultaneous light curves of Sgr A* in radio, sub-mm and X-rays that show a possible time delay of 110±17 minutes between X-ray and 850 μm suggesting that the sub-mm flare emission is optically thick. At radio wavelengths, we detect time lags of of 20.4±6.8, 30±12 and 20±6 minutes between the flare peaks observed at 13 and 7 mm (22 and 43 GHz) in three different epochs using the VLA. Linear polarization of 1±0.2 0.7±0.1 entire observation on 2006 July 17. A simple model of a bubble of synchrotron emitting electrons cooling via adiabatic expansion can explain the time delay between various wavelengths, the asymmetric shape of the light curves, and the observed polarization of the flare emission at 43 and 22 GHz. The derived physical quantities that charact...

Understanding the origin of the flaring activity from the Galactic center supermassive black hole... more Understanding the origin of the flaring activity from the Galactic center supermassive black hole, Sagittarius A*, is a major scientific goal of the NuSTAR Galactic plane survey campaign. We report on the data obtained between July 2012 and April 2015, including 27 observations on Sgr A* with a total exposure of 1 Ms. We found a total of ten X-ray flares detected in the NuSTAR observation window, with luminosities in the range of L_3-79 keV (0.2-4.0) × 10^35 erg s^-1. With this largest hard X-ray Sgr A* flare dataset to date, we studied the flare spectral properties. Seven flares are detected above 5σ significance, showing a range of photon indices (Γ 2.0-2.8) with typical uncertainties of +/-0.5 (90 no significant spectral hardening for brighter flares as indicated by a smaller sample. The accumulation of all the flare spectra in 1-79 keV can be well fit with an absorbed power-law model with Γ=2.2+/-0.1, and does not require the existence of a spectral break. The lack of variation ...

We present results of our Chandra observation with the ACIS-I instrument centered on the position... more We present results of our Chandra observation with the ACIS-I instrument centered on the position of Sagittarius A* (Sgr A*), the compact nonthermal radio source associated with the massive black hole (MBH) at the dynamical center of the Milky Way Galaxy. We have obtained the first high-spatial-resolution (~1 arcsec), hard X-ray (0.5-7 keV) image of the central 40 pc (17 arcmin) of the Galaxy and have discovered an X-ray source, CXOGC J174540.0-290027, coincident with the radio position of Sgr A* to within 0.35 arcsec, corresponding to a maximum projected distance of 16 light-days for an assumed distance to the center of the Galaxy of 8.0 kpc. We received 222 +/-17 (1 sigma) net counts from the source in 40.3 ks. Due to the low number of counts, the spectrum is well fit either by an absorbed power-law model with photon index Gamma = 2.7 (1.8-4.0) and column density NH = (9.8 [6.8-14.2]) x 10^22 cm^-2 (90% confidence interval) or by an absorbed optically thin thermal plasma model wit...

We report NuSTAR and Chandra observations of two X-ray transients, SWIFT J174540.7-290015 (T15) a... more We report NuSTAR and Chandra observations of two X-ray transients, SWIFT J174540.7-290015 (T15) and SWIFT J174540.2-290037 (T37), which were discovered by the Neil Gehrels Swift Observatory in 2016 within r∼1 pc of Sgr A*. NuSTAR detected bright X-ray outbursts from T15 and T37, likely in the soft and hard states, with 3-79 keV luminosities of 8×10^36 and 3×10^37 erg/s, respectively. No X-ray outbursts have previously been detected from the two transients and our Chandra ACIS analysis puts an upper limit of L_X ≲ 2 ×10^31 erg/s on their quiescent 2-8 keV luminosities. No pulsations, significant QPOs, or type I X-ray bursts were detected in the NuSTAR data. While T15 exhibited no significant red noise, the T37 power density spectra are well characterized by three Lorentzian components. The declining variability of T37 above ν∼ 10 Hz is typical of black hole (BH) transients in the hard state. NuSTAR spectra of both transients exhibit a thermal disk blackbody, X-ray reflection with bro...

The Chandra X-ray Observatory has been used multiple times since the telescope was launched into ... more The Chandra X-ray Observatory has been used multiple times since the telescope was launched into orbit in 1999 to view the central region of our galaxy, the Milky Way. The data from all of these observations have been compounded into a single image of the 40 parsecs (pc) surrounding Sagittarius A*, the compact radio source that is thought to mark the location of the supermassive black hole at the center of our galaxy. In this image, there is a diffuse cloud of background radiation over the entire area, as well as approximately 2400 X-ray point sources. The background radiation is created by non-uniform clouds of hot, ionized gas. Point sources on top of this radiation are more difficult to detect against the background light. We create an image of only the diffuse background emission in this region and simulate a grid of point-sources of known flux to add to the background. By observing how visibility of these sources changes with flux, we determine what fraction of the point source...

http://fermi.gsfc.nasa.gov/science/mtgs/symposia/2012/ Welcome and announcements High Energy Gamm... more http://fermi.gsfc.nasa.gov/science/mtgs/symposia/2012/ Welcome and announcements High Energy Gamma-ray Astrophysics Through the Years Fermi in Context Fermi Mission Overview Break Solar Flare Observations with Fermi Fermi LAT Observation of Impulsive Solar Flares Terrestrial Gamma-ray Flashes: Fermi’s Emerging Role as an Excellent Storm Catcher Multi-component analysis of bright GRB prompt emission spectra observed with Fermi Lunch Pulsars in the Fermi Era Black Widows in the Fermi Pulsar Population Millisecond Pulsar Discovery via Gamma-ray Pulsations Using Radio Polarimetry to Understand the Gamma-ray Emission of Pulsars Particle Acceleration and Gamma-ray Emission from Pulsars Towards the Self-Consistent Theory Break Poster Viewing: Diffuse/Cosmic Ray, Instrumental, PSR, SNR/PWNe, Other Galactic, Solar System 8:20-8:30 8:30-9:00 9:00-9:30 9:30-10:00 10:00-10:30 10:30-11:00 11:00-11:15 11:15-11:45

The Astrophysical Journal

Proceedings of VI Microquasar Workshop: Microquasars and Beyond — PoS(MQW6), Aug 28, 2007

Astronomy & Astrophysics

3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variab... more 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmos...

BIMA observations of the Orion nebula discovered a giant flare from a young star previously undet... more BIMA observations of the Orion nebula discovered a giant flare from a young star previously undetected at millimeter wavelengths. The star briefly became the brightest compact object in the nebula at 86 GHz. Its flux density increased by more than a factor of 5 on a timescale of hours, to a peak of 160 mJy. This is one of the most luminous stellar radio flares ever observed. Remarkably, the Chandra X-ray observatory was in the midst of a deep integration of the Orion nebula at the time of the BIMA discovery; the source's X-ray flux increased by a factor of 10 approximately 2 days before the radio detection. Follow-up radio observations with the VLA and BIMA showed that the source decayed on a timescale of days, then flared again several times over the next 70 days, although never as brightly as during the discovery. Circular polarization was detected at 15, 22, and 43 GHz, indicating that the emission mechanism was cyclotron. VLBA observations 9 days after the initial flare yiel...

Most galactic nuclei are now believed to harbour supermassive black holes. Studies of stellar mot... more Most galactic nuclei are now believed to harbour supermassive black holes. Studies of stellar motions in the central few light-years of our Milky Way Galaxy indicate the presence of a dark object with a mass of about 2.6 million solar masses. This object is spatially coincident with Sagittarius A* (Sgr A*), the unique compact radio source located at the dynamical centre of our Galaxy. By analogy with distant quasars and nearby active galactic nuclei (AGN), Sgr A* is thought to be powered by the gravitational potential energy released by matter as it accretes onto a supermassive black hole. However, Sgr A* is much fainter than expected in all wavebands, especially in X-rays, casting some doubt on this model. Recently, we reported the first strong evidence of X-ray emission from Sgr A*. Here we report the discovery of rapid X-ray flaring from the direction of Sgr A*. These data provide compelling evidence that the X-ray emission is coming from accretion onto a supermassive black hole ...

We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpa... more We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpart associated with the massive 3-4x10**6 solar mass black hole at the Galactic Center. The main aim is to investigate the physical processes responsible for the variable emission from SgrA*. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory as well as the Submillimeter Array SMA on Mauna Kea, Hawaii, and the Very Large Array in New Mexico. We detected one moderately bright flare event in the X-ray domain and 5 events at infrared wavelengths.

We model thermal X-ray emission from the accreting supermassive black hole Sagittarius A* at the ... more We model thermal X-ray emission from the accreting supermassive black hole Sagittarius A* at the Galactic Center. For the region inside 1.^"5 of the center, we use a generalized radiatively inefficient accretion flow (RIAF) model, and for the region out to 10^" we use published models of the ambient hot gas. We calculate the equivalent widths of Hydrogen-like and Helium-like emission lines of various elements, notably iron. We predict that a strong Helium-like iron line with an equivalent width ∼1 keV should be emitted by both the external medium and the RIAF. The equivalent width in the external medium is sensitive to the metallicity Z of the gas as well as the mean temperature. For reasonable choices of these parameters, the calculated results agree with Chandra's detection of an iron line with an equivalent width of 1.3 keV within 10^". The emission from within 1.^"5 is not sensitive to the external temperature, but is sensitive to the density and, especia...

Despite strong physical reasons that they should exist and decades of search, jets from the Galac... more Despite strong physical reasons that they should exist and decades of search, jets from the Galactic Center Black Hole, Sgr A*, have not yet been convincingly detected. Based on high-resolution Very Large Array images and ultra-deep imaging-spectroscopic data produced by the Chandra X-ray Observatory, we report new evidence for the existence of a parsec-scale jet from Sgr A*, by associating a linear feature G359.944-0.052, previously identified in X-ray images of the Galactic Center, with a radio shock front on the Eastern Arm of the Sgr A West HII region. We show that the shock front can be explained in terms of the impact of a jet having a sharp momentum peak along the Galaxy's rotation axis, whereas G359.944-0.052, a quasi-steady feature with a power-law spectrum, can be understood as synchrotron radiation from shock-induced ultrarelativistic electrons cooling in a finite post-shock region downstream along the jet path. Several interesting implications of the jet properties a...

Stellar dynamics indicate the presence of a super massive 3-4x10^6 Msun solm black hole at the Ga... more Stellar dynamics indicate the presence of a super massive 3-4x10^6 Msun solm black hole at the Galactic Center. It is associated with the variable radio, near-infrared, and X-ray counterpart Sagittarius A* (SgrA*). The goal is the investigation and understanding of the physical processes responsible for the variable emission from SgrA*. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X-ray Observatory (July 2005). We find that for the July 2005 flare the variable and polarized NIR emission of SgrA* occurred synchronous with a moderately bright flare event in the X-ray domain with an excess 2 - 8 keV luminosity of about 8x10^33erg/s. We find no time lag between the flare events in the two wavelength bands with a lower limit of less than 10 minutes. The May 2007 flare shows the highest sub-flare to flare contrast obser...

Sgr A*, the massive black hole at the center of the Galaxy, varies in radio through X-ray emissio... more Sgr A*, the massive black hole at the center of the Galaxy, varies in radio through X-ray emission on hourly time scales. The flare activity is thought to arise from the innermost region of an accretion flow onto Sgr A*. We present simultaneous light curves of Sgr A* in radio, sub-mm and X-rays that show a possible time delay of 110±17 minutes between X-ray and 850 μm suggesting that the sub-mm flare emission is optically thick. At radio wavelengths, we detect time lags of of 20.4±6.8, 30±12 and 20±6 minutes between the flare peaks observed at 13 and 7 mm (22 and 43 GHz) in three different epochs using the VLA. Linear polarization of 1±0.2 0.7±0.1 entire observation on 2006 July 17. A simple model of a bubble of synchrotron emitting electrons cooling via adiabatic expansion can explain the time delay between various wavelengths, the asymmetric shape of the light curves, and the observed polarization of the flare emission at 43 and 22 GHz. The derived physical quantities that charact...

Understanding the origin of the flaring activity from the Galactic center supermassive black hole... more Understanding the origin of the flaring activity from the Galactic center supermassive black hole, Sagittarius A*, is a major scientific goal of the NuSTAR Galactic plane survey campaign. We report on the data obtained between July 2012 and April 2015, including 27 observations on Sgr A* with a total exposure of 1 Ms. We found a total of ten X-ray flares detected in the NuSTAR observation window, with luminosities in the range of L_3-79 keV (0.2-4.0) × 10^35 erg s^-1. With this largest hard X-ray Sgr A* flare dataset to date, we studied the flare spectral properties. Seven flares are detected above 5σ significance, showing a range of photon indices (Γ 2.0-2.8) with typical uncertainties of +/-0.5 (90 no significant spectral hardening for brighter flares as indicated by a smaller sample. The accumulation of all the flare spectra in 1-79 keV can be well fit with an absorbed power-law model with Γ=2.2+/-0.1, and does not require the existence of a spectral break. The lack of variation ...

We present results of our Chandra observation with the ACIS-I instrument centered on the position... more We present results of our Chandra observation with the ACIS-I instrument centered on the position of Sagittarius A* (Sgr A*), the compact nonthermal radio source associated with the massive black hole (MBH) at the dynamical center of the Milky Way Galaxy. We have obtained the first high-spatial-resolution (~1 arcsec), hard X-ray (0.5-7 keV) image of the central 40 pc (17 arcmin) of the Galaxy and have discovered an X-ray source, CXOGC J174540.0-290027, coincident with the radio position of Sgr A* to within 0.35 arcsec, corresponding to a maximum projected distance of 16 light-days for an assumed distance to the center of the Galaxy of 8.0 kpc. We received 222 +/-17 (1 sigma) net counts from the source in 40.3 ks. Due to the low number of counts, the spectrum is well fit either by an absorbed power-law model with photon index Gamma = 2.7 (1.8-4.0) and column density NH = (9.8 [6.8-14.2]) x 10^22 cm^-2 (90% confidence interval) or by an absorbed optically thin thermal plasma model wit...

We report NuSTAR and Chandra observations of two X-ray transients, SWIFT J174540.7-290015 (T15) a... more We report NuSTAR and Chandra observations of two X-ray transients, SWIFT J174540.7-290015 (T15) and SWIFT J174540.2-290037 (T37), which were discovered by the Neil Gehrels Swift Observatory in 2016 within r∼1 pc of Sgr A*. NuSTAR detected bright X-ray outbursts from T15 and T37, likely in the soft and hard states, with 3-79 keV luminosities of 8×10^36 and 3×10^37 erg/s, respectively. No X-ray outbursts have previously been detected from the two transients and our Chandra ACIS analysis puts an upper limit of L_X ≲ 2 ×10^31 erg/s on their quiescent 2-8 keV luminosities. No pulsations, significant QPOs, or type I X-ray bursts were detected in the NuSTAR data. While T15 exhibited no significant red noise, the T37 power density spectra are well characterized by three Lorentzian components. The declining variability of T37 above ν∼ 10 Hz is typical of black hole (BH) transients in the hard state. NuSTAR spectra of both transients exhibit a thermal disk blackbody, X-ray reflection with bro...

The Chandra X-ray Observatory has been used multiple times since the telescope was launched into ... more The Chandra X-ray Observatory has been used multiple times since the telescope was launched into orbit in 1999 to view the central region of our galaxy, the Milky Way. The data from all of these observations have been compounded into a single image of the 40 parsecs (pc) surrounding Sagittarius A*, the compact radio source that is thought to mark the location of the supermassive black hole at the center of our galaxy. In this image, there is a diffuse cloud of background radiation over the entire area, as well as approximately 2400 X-ray point sources. The background radiation is created by non-uniform clouds of hot, ionized gas. Point sources on top of this radiation are more difficult to detect against the background light. We create an image of only the diffuse background emission in this region and simulate a grid of point-sources of known flux to add to the background. By observing how visibility of these sources changes with flux, we determine what fraction of the point source...

http://fermi.gsfc.nasa.gov/science/mtgs/symposia/2012/ Welcome and announcements High Energy Gamm... more http://fermi.gsfc.nasa.gov/science/mtgs/symposia/2012/ Welcome and announcements High Energy Gamma-ray Astrophysics Through the Years Fermi in Context Fermi Mission Overview Break Solar Flare Observations with Fermi Fermi LAT Observation of Impulsive Solar Flares Terrestrial Gamma-ray Flashes: Fermi’s Emerging Role as an Excellent Storm Catcher Multi-component analysis of bright GRB prompt emission spectra observed with Fermi Lunch Pulsars in the Fermi Era Black Widows in the Fermi Pulsar Population Millisecond Pulsar Discovery via Gamma-ray Pulsations Using Radio Polarimetry to Understand the Gamma-ray Emission of Pulsars Particle Acceleration and Gamma-ray Emission from Pulsars Towards the Self-Consistent Theory Break Poster Viewing: Diffuse/Cosmic Ray, Instrumental, PSR, SNR/PWNe, Other Galactic, Solar System 8:20-8:30 8:30-9:00 9:00-9:30 9:30-10:00 10:00-10:30 10:30-11:00 11:00-11:15 11:15-11:45

The Astrophysical Journal

Proceedings of VI Microquasar Workshop: Microquasars and Beyond — PoS(MQW6), Aug 28, 2007

Astronomy & Astrophysics

3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variab... more 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmos...