William Junor

Flaring X-Ray Emission from HST-1, a Knot in the M87 Jet

We present Chandra X-ray monitoring of the M87 jet in 2002, which shows that the intensity of HST-1, an optical knot 08 from the core, increased by a factor of 2 in 116 days and a factor of 4 in 2 yr. There was also a significant flux decrease over 2 months, with suggestive evidence for a softening of the spectrum. From this variability behavior, we argue that the bulk of the X-ray emission of HST-1 comes from synchrotron emission. None of the other conceivable emission processes can match the range of observed characteristics. By estimating synchrotron model parameters for various bulk relativistic velocities, we demonstrate that a model with a Doppler factor δ in the range 2-5 fits our preliminary estimates of light-travel time and synchrotron loss timescales.

A VLBA movie of the jet launch region in M87

M87 has one of the largest angular size black holes known. It also has a bright jet that is well resolved across the jet near the core using high frequency VLBI. As such it is the best object to observe to study the launch region of jets where the physical sizes of structures of interest scale with the gravitational radius. Modern numerical simulations suggest that the jet formation extends over 100-1000 Rs. M87 has been observed with a resolution of about 60 Rs at 43 GHz with the VLBA every 3 weeks through 2007, and every 5 days between January and April 2008. A preliminary movie, made from the first 11 observations in 2007, shows fast (~2c) and complex motions in an edge brightened structure with a wide opening angle at the base.

Observations of the Structure and Dynamics of the Inner M87 Jet

M87 is the best source in which to study a jet at high resolution in gravitational units because it has a very high mass black hole and is nearby. The angular size of the black hole is second only to Sgr A*, which does not have a strong jet. The jet structure is edge brightened with a wide opening angle base and a weak counterjet. We have roughly annual observations for 17 years plus intensive monitoring at three week intervals for a year and five day intervals for 2.5 months made with the Very Long Baseline Array (VLBA) at 43 GHz. The inner jet shows very complex dynamics, with apparent motions both along and across the jet. Speeds from zero to over 2c are seen, with acceleration observed over the first 3 milli-arcseconds. The counterjet decreases in brightness much more rapidly than the main jet, as is expected from relativistic beaming in an accelerating jet oriented near the line-of-sight. Details of the structure and dynamics are discussed. The roughly annual observations show side-to-side motion of the whole jet with a characteristic time scale of about 9 years.

The Structure and Dynamics of the Subparsec Jet in M87 Based on 50 VLBA Observations over 17 Years at 43 GHz

The central radio source in M87 provides the best opportunity to study jet formation because it has a large angular size for the gravitational radius of the black hole and has a bright jet that is well resolved by VLBI observations. We present intensive monitoring observations from 2007 and 2008, plus roughly annual observations that span 17 years, all made with the the Very Long Baseline Array at 43 GHz with a resolution of about 30 by 60 Rs. Our high-dynamic-range images clearly show the wide-opening-angle structure and the counter-jet. The jet and counter-jet are nearly symmetric in the inner 1.5 milli-arcseconds (mas; 0.12 pc in projection) with both being edge brightened. Both show deviations from parabolic shape in the form of an initial rapid expansion and subsequent contraction followed by further rapid expansion and, beyond the visible counter-jet, subsequent collimation. Proper motions and counter-jet/jet intensity ratios both indicate acceleration from apparent speeds of

Passive interferometric millimeter-wave imaging: achieving big results with a constellation of small satellites

\lesssim 0.5c

The Outburst of HST-1 in the M87 Jet

to

High-Frequency VLBI Imaging of the Jet Base of M87

\gtrsim 2c

From Clark Lake to the Long Wavelength Array: Bill Erickson's Radio Science

in the inner about 2 mas and suggest a helical flow. The jet displays a sideways shift with an approximately 8 to 10 year quasi-periodicity. The shift propagates outwards non-ballistically and significantly more slowly than the flow speed revealed by the fastest moving components. Polarization data show a systematic structure with magnetic field vectors that suggest a toroidal field close to the core.

Imaging a Jet Base - Prospects with M87

Los Alamos National Laboratory (LANL) and AeroAstro have recently investigated the feasibility of space-based passive interferometric millimeter wave imaging (PIMI). The goal of this study is to explore a new capability that can offer day/night, all-weather, passive imaging with a 1-meter resolution, by means of millimetric interferometry via a small constellation of microsatellites. According to our preliminary study, a system with four LEO satellites operating at multiple frequency channels within 95-150 GHz is capable of providing an imagery of 1-m spatial resolution. The corresponding temperature sensitivity is estimated to be ~20°K, enough to distinguish most artifacts from a variety of backgrounds. To achieve the stated resolution and sensitivity with only four satellites, we make use of ten frequency channels to synthesize ten effective baselines between any pair of satellites. In addition, the satellites will “stare” at a common target area off the track direction for about 2 minutes while they pass over the area. This type of observation will introduce much improved spatial frequency coverage due to the relative rotation of the baseline vectors. It also improves the imagery SNR with a longer viewing time, as compared to a downward looking system. To the target, the side-looking observation also has the advantage of near constant incident (zenith) angle. The satellites are required to perform a formation flight but a rigid formation is not necessary. Simultaneous interferometric measurement of GPS signals, together with inter-satellites ranging will allow us to monitor the baseline length and direction to an adequate accuracy. A tradeoff study has also been conducted between the system performance and the technology availability, i.e., the current state-of-the-art technologies for space-borne antenna, millimeter-wave receiver, high-speed digitizer, inter-satellites data communication, and so forth.