VERIFICATION OF THE ASTROMETRIC PERFORMANCE OF THE KOREAN VLBI NETWORK, USING COMPARATIVE SFPR STUDIES WITH THE VLBA AT 14/7 mm

Rioja, María J.; Dodson, Richard; Jung, Taehyun; Sohn, Bong Won; Byun, Doyoung; Agudo, I.; Cho, Se-Hyung; Lee, Sang-Sung; Kim, Jong-Soo; Kim, Kee‐Tae; Oh, Chung Sik; Han, Seog-Tae; Je, Do‐Heung; Chung, Moon Hyun; Wi, Seog-Oh; Kang, Jin Wook; Lee, Jung Won; Chung, Hyunsoo; Kim, Hyo Ryoung; Kim, Hyun‐Goo; Lee, Chang‐Hoon; Roh, Duk-Gyoo; Oh, Se-Jin; Yeom, Jae-Hwan; Song, Mingyu; Kang, Yong-Woo

doi:10.1088/0004-6256/148/5/84

Cited by 37 publications

(47 citation statements)

References 10 publications

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“…The Source Frequency Phase Referencing method, which has been described in detail elsewhere Rioja et al , 2014Rioja et al , 2015Dodson et al 2014), consists of two calibration steps. In a first step, the observations at the higher frequency bands are calibrated using near-simultaneous Rioja et al 2014) or simultaneous (Rioja et al , 2015Dodson et al 2014) observations at a lower frequency band, for each source.…”

Section: Multi-frequency Phase Referencingmentioning

confidence: 99%

“…In a first step, the observations at the higher frequency bands are calibrated using near-simultaneous Rioja et al 2014) or simultaneous (Rioja et al , 2015Dodson et al 2014) observations at a lower frequency band, for each source. This is done for all frequency pairs which have an integer 2 frequency ratio, by which the low frequency calibration phase solutions are scaled.…”

Section: Multi-frequency Phase Referencingmentioning

confidence: 99%

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High-Precision Astrometric Millimeter Very Long Baseline Interferometry Using a New Method for Multi-Frequency Calibration

Dodson

Rioja

Molina

et al. 2017

ApJ

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In this paper we describe a new approach for mm-VLBI calibration that provides bona-fide astrometric alignment of the mm-wavelength images from a single source, for the measurement of frequency dependent effects, such as 'coreshifts' near the black hole of AGN jets. We achieve our astrometric alignment by solving firstly for the ionospheric (dispersive) contributions using wide-band cmwavelength observations. Secondly we solve for the tropospheric (non-dispersive) contributions by using fast frequency-switching at the target mm-wavelengths. These solutions can be scaled and transferred from the low frequency to the high frequency. To complete the calibration chain one additional step was required to remove a residual constant phase offset on each antenna. The result is an astrometric calibration and the measurement of the core-shift between 22 and 43 GHz for the jet in BL Lacertae to be -8±5, 20±6 µas, in RA and Declination, respectively. By comparison to conventional phase referencing at cm-wavelengths we are able to show that this core shift at mm-wavelengths is significantly less than what would be predicted by extrapolating the low frequency result, which closely followed the predictions of the Blandford & Königl conical jet model. As such it would be the first demonstration for the association of the VLBI core with a recollimation shock, normally hidden at low frequencies due to the optical depth, which could be responsible for the γ-ray production in blazar jets.-2 -

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Section: Multi-frequency Phase Referencingmentioning

confidence: 99%

Section: Multi-frequency Phase Referencingmentioning

confidence: 99%

High-Precision Astrometric Millimeter Very Long Baseline Interferometry Using a New Method for Multi-Frequency Calibration

Dodson

Rioja

Molina

et al. 2017

ApJ

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“…This method works well for astrometry at mm wavelengths (e.g. Rioja et al, 2014). We used the Korean VLBI network (KVN) 1 to carry out our SFPR observations towards 3C 66A and 3C 66B.…”

Section: Methods and Observationsmentioning

confidence: 99%

KVN Source-Frequency Phase-Referencing Observation of 3c 66a and 3c 66b

Zhao

Dodson²,

Rioja³

et al. 2015

Publications of The Korean Astronomical Society

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In this proceedings, preliminary results of the KVN Source-Frequency Phase-Referencing (SFPR) observation of 3C 66A and 3C 66B are presented. The motivation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. Two more sources were observed as secondary reference calibrators and each source was observed at 22, 43, and 86 GHz simultaneously. Our preliminary results show that after using the observations at the lower frequency to calibrate those at the higher frequency of the same source, the residual visibility phases for each source at the higher frequencies became more aligned, and the coherence time became much longer; also, the residual phases for different sources, within 10 degrees angular separations, follow similar trends. After reference to the nearby calibrator, the SFPRed maps were obtained as well as the astrometric measurements, i.e. the combined coreshift. The measurements were found to be affected by structural blending effects because of the large beamsize of KVN, but this can be corrected with higher resolution maps (e.g. KAVA maps).

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“…The innovative multi-band receiver [4,5] of KVN is designed to mitigate the atmospheric propagation effects using simultaneous observations at multiple bands. The KVN combined with the Frequency Phase Transfer (FPT) and Source Frequency Phase Referencing (SFPR) data analysis techniques ( [6][7][8][9] see also references therein) allows an effective increase of the coherence time, well beyond that imposed by tropospheric fluctuations, as well as high precision astrometric measurements, respectively, even at the highest frequencies.…”

Section: Introductionmentioning

confidence: 99%

The Power of (Near) Simultaneous Multi-Frequency Observations for mm-VLBI and Astrometry

et al. 2017

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Simultaneous or near-simultaneous observations at multiple frequency bands have the potential to overcome the fundamental limitation imposed by the atmospheric propagation in mm-VLBI observations. The propagation effects place a severe limit in the sensitivity achievable in mm-VLBI, reducing the time over which the signals can be coherently combined, and preventing the use of phase referencing and astrometric measurements. We present two demonstrations of the power of (near) simultaneous multi-frequency observations with the KVN and VLBA, and our recently developed analysis strategies to enable new measurements at mm-VLBI. The first case comprises simultaneous observations at 22, 43, 87 and 130 GHz of a group of five AGNs, the weakest of which is ∼200 mJy at 130 GHz, with angular separations ranging from 3.6 to 11 degrees, using the KVN. We analysed this data using the Frequency Phase Transfer (FPT) and the Source Frequency Phase Referencing (SFPR) techniques, which use the observations at a lower frequency to correct those at a higher frequency. The results of the analysis provide an empirical demonstration of the increase in the coherence times at 130 GHz from a few tens of seconds to about twenty minutes, with FPT, and up to many hours with SFPR. Moreover the astrometric analysis provides high precision relative position measurements between two frequencies, including, for the first time, astrometry at 130 GHz. The second case is a variation of the above, whereby adding dedicated wide-band cm-wavelength observations to measure the ionosphere eliminates the need for a second, calibrator, source. This addresses the scarcity of calibrators at mm-VLBI. We dubbed this technique Multi Frequency Phase Referencing (MFPR). We present bona fide astrometrically aligned VLBA images of BL Lacertae at 22 and 43 GHz using MFPR, which, combined with results from conventional phase referencing at cm-wavelengths, suggests the VLBI core has a recollimation shock that is revealed at mm-wavelengths. These shocks could be responsible for the γ-ray emission in blazar jets.

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VERIFICATION OF THE ASTROMETRIC PERFORMANCE OF THE KOREAN VLBI NETWORK, USING COMPARATIVE SFPR STUDIES WITH THE VLBA AT 14/7 mm

Cited by 37 publications

References 10 publications

High-Precision Astrometric Millimeter Very Long Baseline Interferometry Using a New Method for Multi-Frequency Calibration

High-Precision Astrometric Millimeter Very Long Baseline Interferometry Using a New Method for Multi-Frequency Calibration

KVN Source-Frequency Phase-Referencing Observation of 3c 66a and 3c 66b

The Power of (Near) Simultaneous Multi-Frequency Observations for mm-VLBI and Astrometry

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