28 research outputs found
High-Sensitivity 86GHz (3.5mm) VLBI Observations of M87: Deep Imaging of the Jet Base at a 10 Schwarzschild-Radius Resolution
We report on results from new high-sensitivity, high-resolution 86GHz (3.5
millimeter) observations of the jet base in the nearby radio galaxy M87,
obtained by the Very Long Baseline Array in conjunction with the Green Bank
Telescope. The resulting image has a dynamic range exceeding 1500 to 1, the
highest ever achieved for this jet at this frequency, resolving and imaging a
detailed jet formation/collimation structure down to ~10 Schwarzschild radii
(Rs). The obtained 86GHz image clearly confirms some important jet features
known at lower frequencies, i.e., a wide-opening angle jet base, a
limb-brightened intensity profile, a parabola-shape collimation profile and a
counter jet. The limb-brightened structure is already well developed at <
0.2mas (< 28Rs, projected) from the core, where the corresponding apparent
opening angle becomes as wide as ~100 degrees. The subsequent jet collimation
near the black hole evolves in a complicated manner; there is a "constricted"
structure at tens Rs from the core, where the jet cross section is locally
shrinking. We suggest that an external pressure support from the inner part of
radiatively-inefficient accretion flow may be dynamically important in
shaping/confining the footprint of the magnetized jet. We also present the
first VLBI 86GHz polarimetric experiment for this source, where a highly
polarized (~20%) feature is detected near the jet base, indicating the presence
of a well-ordered magnetic field. As a by-product, we additionally report a
43/86 GHz polarimetric result for our calibrator 3C 273 suggesting an extreme
rotation measure near the core.Comment: Accepted for publication in ApJ. 39 pages, 11 figures, 3 table
Pilot KaVA monitoring on the M87 jet: confirming the inner jet structure and superluminal motions at sub-pc scales
We report the initial results of our high-cadence monitoring program on the
radio jet in the active galaxy M87, obtained by the KVN and VERA Array (KaVA)
at 22 GHz. This is a pilot study that preceded a larger KaVA-M87 monitoring
program, which is currently ongoing. The pilot monitoring was mostly performed
every two to three weeks from December 2013 to June 2014, at a recording rate
of 1 Gbps, obtaining the data for a total of 10 epochs. We successfully
obtained a sequence of good quality radio maps that revealed the rich structure
of this jet from <~1 mas to 20 mas, corresponding to physical scales
(projected) of ~0.1-2 pc (or ~140-2800 Schwarzschild radii). We detected
superluminal motions at these scales, together with a trend of gradual
acceleration. The first evidence for such fast motions and acceleration near
the jet base were obtained from recent VLBA studies at 43 GHz, and the fact
that very similar kinematics are seen at a different frequency and time with a
different instrument suggests these properties are fundamental characteristics
of this jet. This pilot program demonstrates that KaVA is a powerful VLBI array
for studying the detailed structural evolution of the M87 jet and also other
relativistic jets.Comment: 10 pages, 9 figures, accepted for publication in PAS
Precessing jet nozzle connecting to a spinning black hole in M87
The nearby radio galaxy M87 offers a unique opportunity to explore the
connections between the central supermassive black hole and relativistic jets.
Previous studies of the inner region of M87 revealed a wide opening angle for
the jet originating near the black hole. The Event Horizon Telescope resolved
the central radio source and found an asymmetric ring structure consistent with
expectations from General Relativity. With a baseline of 17 years of
observations, there was a shift in the jet's transverse position, possibly
arising from an eight to ten-year quasi-periodicity. However, the origin of
this sideways shift remains unclear. Here we report an analysis of radio
observations over 22 years that suggests a period of about 11 years in the
position angle variation of the jet. We infer that we are seeing a spinning
black hole that induces the Lense-Thirring precession of a misaligned accretion
disk. Similar jet precession may commonly occur in other active galactic nuclei
but has been challenging to detect owing to the small magnitude and long period
of the variation.Comment: 41 pages, 7 figures, 7 table
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