VLBI observations of weak sources using fast frequency switching

Abstract

We have developed a new phase referencing technique for high frequency VLBI observations. In conventional phase referencing, one interleaves short scans on a nearby phase calibrator between the target source observations. In fast frequency switching described here, one observes the target source continuously while switching rapidly between the target frequency and a lower reference frequency. We demonstrate that the technique allows phase calibration almost reaching the thermal noise limit and present the first detection of the AGN in the FR I radio galaxy NGC 4261 at 86 GHz. Although point-like, this is the weakest source ever detected with VLBI at this frequency.

arXiv commentAccepted by A&A, 14 pages, 12 figures, needs aa.cls, aas_macros.sty and amsmath.sty, replaced due reformatting

References in corpus (6)

• Sub-milliarcsecond Imaging of Quasars and AGN
• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• General Relativistic Simulations of Jet Formation in a Rapidly Rotating Black Hole Magnetosphere
• VLBA Imaging of NGC 4261: Symmetric Parsec-scale Jets and the Inner Accretion Region
• An Attempt to Probe the Radio Jet Collimation Regions in NGC 4278, NGC 4374 (M84), and NGC 6166
• In the Shadow of the Accretion Disk: Higher Resolution Imaging of the Central Parsec in NGC 4261

Cited by in corpus (23)

• Universal Interferometric Signatures of a Black Hole's Photon Ring
• High Precision Astrometric Millimeter VLBI Using a New Method for Atmospheric Calibration
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• Radio astrometry with chromatic AGN core positions
• Single dish performance of KVN 21-m radio telescopes:Simultaneous observations at 22 and 43 GHz
• Verification of the Effectiveness of VSOP-2 Phase Referencing with a Newly Developed Simulation Tool, ARIS
• Masses of Nearby Supermassive Black Holes with Very-Long Baseline Interferometry
• The Transformational Power of Frequency Phase Transfer Methods for ngEHT
• Interferometric Monitoring of Gamma-ray Bright Active Galactic Nuclei II: Frequency Phase Transfer
• The Impact of Frequency Standards on Coherence in VLBI at the Highest Frequencies
• Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities
• Ejection of Double knots from the radio core of PKS 1510--089 during the strong gamma-ray flares in 2015
• The Power of Simultaneous Multi-frequency Observations for mm-VLBI: Beyond Frequency Phase Transfer
• Spatially Resolved HCN Absorption Features in the Circumnuclear Region of NGC 1052
• VLBI imaging of M81* at 3.4 mm with source-frequency phase-referencing
• The Science Case for Simultaneous mm-Wavelength Receivers in Radio Astronomy
• A broad HCO+ absorption line associated with the circumnuclear torus of NGC 1052
• Absolute kinematics of radio-source components in the complete S5 polar cap sample. IV. Proper motions of the radio cores over a decade and spectral properties
• Kinematics and Collimation of the Two-Sided Jets in NGC 4261: VLBI Study on Sub-parsec Scales
• Dual frequency 230/690 GHz interferometry at the Submillimeter Array
• Demonstration of KVN phase referencing capability
• The Core-shift of Sagittarius A* as a Discriminant between Disk and Jet Emission Models with millimeter-VLBI
• Shared-optical-path VLBI frequency phase transfer from 86 to 258 GHz on an 8600 km baseline: Demonstrated with the APEX and IRAM 30 m telescopes