Remo P. J. Tilanus

Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgru2009A*), the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4,000,000 times that of the Sun. A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgru2009A*, where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5u2009mm and 7u2009mm have detected intrinsic structure in Sgru2009A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering. Here we report observations at a wavelength of 1.3u2009mm that set a size of microarcseconds on the intrinsic diameter of Sgru2009A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of Sgru2009A* emission may not be centred on the black hole, but arises in the surrounding accretion flow.

THE 2014 ALMA LONG BASELINE CAMPAIGN: FIRST RESULTS FROM HIGH ANGULAR RESOLUTION OBSERVATIONS TOWARD THE HL TAU REGION

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric

The relational database and calibration software for the Caltech millimeter array

A relational database management system has been implemented on the Caltech millimeter-wave array for both real-time astronomical engineering data and post-processing calibration and analysis. This system provides high storage-efficiency for the data and on-line access to data from multiple observing seasons. The ability to access easily the full database enables more accurate calibration of the raw data and greatly facilitates the calibration process. In this article we describe both the structure of the mm-array database and the implementation of a data analysis program, both of which make extensive use of Sybase, a commercial database management system with application development software. This use of relational database technology in real-time astronomical data storage and calibration may serve as a prototype for similar systems at other observatories.

Jet-launching structure resolved near the supermassive black hole in m87

Black Hole Close-Up M87 is a giant elliptical galaxy about 55 million light-years away. Accretion of matter onto its central massive black hole is thought to power its relativistic jet. To probe structures on scales similar to that of the black holes event horizon, Doeleman et al. (p. 355, published online 27 September) observed the relativistic jet in M87 at a wavelength of 1.3 mm using the Event Horizon Telescope, a special purpose, very-long-baseline interferometry array consisting of four radio telescopes located in Arizona, California, and Hawaii. The analysis suggests that the accretion disk that powers the jet orbits in the same direction as the spin of the black hole. High-resolution observations of the jet in the galaxy M87 probe structures very close to the galaxy’s central black hole. Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by the accretion of matter onto supermassive black holes. Although the measured width profiles of such jets on large scales agree with theories of magnetic collimation, the predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations, at a wavelength of 1.3 millimeters, of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 ± 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.

CO (4-3) and Dust Emission in Two Powerful High-z Radio Galaxies, and CO Lines at High Redshifts

We report the detection of submillimeter emission from dust at 850 μm and of the 12CO J = 4-3 line in the two distant powerful radio galaxies 4C 60.07 (z = 3.79) and 6C 1909+722 (z = 3.53). In 4C 60.07, the dust emission is also detected at 1.25 mm. The estimated molecular gas masses are large, of the order of ~(0.5-1) × 1011 M☉. The large far-infrared (FIR) luminosities (LFIR ~ 1013 L☉) suggest that we are witnessing two major starburst phenomena, while the observed large velocity widths (ΔVFWHM 500 km s-1) are characteristic of mergers. In the case of 4C 60.07, the CO emission extends over ~30 kpc and spans a velocity range of 1000 km s-1. It consists of two distinct features with FWHM of 550 km s-1 and ~150 km s-1, and line centers separated by 700 km s-1. The least massive of these components is probably very gas rich, with potentially 60% of its dynamical mass in the form of molecular gas. The extraordinary morphology of the CO emission in this object suggests that it is not just a scaled-up version of a local ultraluminous infrared galaxy, and it may be a formative stage of the elliptical host of the residing radio-loud active galactic nucleus (AGN). Finally, we briefly explore the effects of the wide range of gas-excitation conditions expected for starburst environments on the luminosity of high-J CO lines and conclude that in unlensed objects, CO (J + 1 → J), J + 1 > 3 lines can be significantly weak with respect to CO J = 1-0, and this can hinder their detection even in the presence of substantial molecular gas masses.

HARP/ACSIS: a submillimetre spectral imaging system on the James Clerk Maxwell Telescope

This paper describes a new Heterodyne Array Receiver Programme (HARP) and AutoCorrelation Spectral Imaging System (ACSIS) that have recently been installed and commissioned on the James Clerk Maxwell Telescope (JCMT). The 16-element focal-plane array receiver, operating in the submillimetre from 325 to 375 GHz, offers high (three-dimensional) mapping speeds, along with significant improvements over single-detector counterparts in calibration and image quality. Receiver temperatures are 120 K across the whole band and system temperatures of 300K are reached routinely under good weather conditions. The system includes a single-sideband filter so these are SSB figures. Used in conjunction with ACSIS, the system can produce large-scale maps rapidly, in one or more frequency settings, at high spatial and spectral resolution. Fully-sampled maps of size 1 square degree can be observed in under 1 hour. The scientific need for array receivers arises from the requirement for programmes to study samples of objects of statistically significant size, in large-scale unbiased surveys of galactic and extra-galactic regions. Along with morphological information, the new spectral imaging system can be used to study the physical and chemical properties of regions of interest. Its three-dimensional imaging capabilities are critical for research into turbulence and dynamics. In addition, HARP/ACSIS will provide highly complementary science programmes to wide-field continuum studies, and produce the essential preparatory work for submillimetre interferometers such as the SMA and ALMA.

1.3 mm WAVELENGTH VLBI OF SAGITTARIUS A*: DETECTION OF TIME-VARIABLE EMISSION ON EVENT HORIZON SCALES

Sagittarius A*, the ~4 × 10^6 M_⊙ black hole candidate at the Galactic center, can be studied on Schwarzschild nradius scales with (sub)millimeter wavelength very long baseline interferometry (VLBI). We report on 1.3 mm nwavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the Arizona Radio nObservatory’s Submillimeter Telescope on Mt. Graham in Arizona, and two telescopes of the CARMA array at nCedar Flat in California. Both Sgr A* and the quasar calibrator 1924−292 were observed over three consecutive nnights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3mmVLBI ninterferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On nthe third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the nfirst two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These nresults suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable nrole in determining the structure of emission near the event horizon of Sgr A*.

The effect of magnetic fields on gamma-ray bursts inferred from multi-wavelength observations of the burst of 23 January 1999

Gamma-ray bursts (GRBs) are thought to arise when an extremely relativistic outflow of particles from a massive explosion (the nature of which is still unclear) interacts with material surrounding the site of the explosion. Observations of the evolving changes in emission at many wavelengths allow us to investigate the origin of the photons, and so potentially determine the nature of the explosion. Here we report the results of γ-ray, optical, infrared, submillimetre, millimetre and radio observations of the burst GRB990123 and its afterglow. Our interpretation of the data indicates that the initial and afterglow emissions are associated with three distinct regions in the fireball. The peak flux of the afterglow, one day after the burst, has a lower frequency than observed for other bursts; this explains the short-lived radio emission. We suggest that the differences between bursts reflect variations in the magnetic-field strength in the afterglow-emitting regions.

Resolved magnetic-field structure and variability near the event horizon of Sagittarius A∗

Magnetic fields near the event horizon Astronomers have long sought to examine a black holes event horizon—the boundary around the black hole within which nothing can escape. Johnson et al. used sophisticated interferometry techniques to combine data from millimeter-wavelength telescopes around the world. They measured polarization just outside the event horizon of Sgr A*, the supermassive black hole at the center of our galaxy, the Milky Way. The polarization is a signature of ordered magnetic fields generated in the accretion disk around the black hole. The results help to explain how black holes accrete gas and launch jets of material into their surroundings. Science, this issue p. 1242 Magnetic fields around the event horizon of a supermassive black hole have been probed. Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizon-scale magnetic-field structure. We report interferometric observations at 1.3-millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered magnetic fields near the event horizon, on scales of ~6 Schwarzschild radii, and we have detected and localized the intrahour variability associated with these fields.

The 2014 ALMA Long Baseline Campaign : Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z = 3.042

We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the