A search for high-frequency calibrators within 10 degrees of the Galactic center with the KVN

Despite of enormous efforts to improve density of calibrators, it is not uncommon to hear that there is no good calibrator just in the area where I want to observe. This is especially true if planned observations are at high frequencies or in the difficult area. The Galactic center is one of these difficult areas. Scattering in the interstellar medium broadens a source and we loose long baselines. This makes difficult to judge whether a given source detected at 2–8 GHz will be strong enough to serve as a calibrator at 22/43 GHz. We see no other practical way to determine suitability of a given source for being used as a calibrator as to observe

Goals

The list of candidate sources has two parts: a) known 139 objects detected with VLBI at 2–8 GHz but never observed at 22/43 GHz; b) new 199 sources from VLASS with peak flux density above 30 mJy and the ratio total/peak flux density less than 1.5 that have never been observed with VLBI. We propose to observe both lists with the KVN at 22/43 GHz simultaneously in 2 scans for 3 minutes each. Assuming SEFD 1300 Jy at K-band and 2000 Jy at Q band and doubling sensitivity because we have to observe at 15–30° above the horizon, we expect we will be able to detect sources brighter 30 mJy at K band and Q band recording at 4+4 GBps mode. Counting time for slewing and calibration, we request 75 hours in total in 15 blocks of 5 hours each centered around right ascension 17^h45^m. We will process the KVN data in a similar way as we processed K-band EVN experiment EP066.

Science cases

Use case: astrometry with stellar masers in the Galactic bulge

Use case: detection of excessive scatter in positions due to non-stationarity of the gravitational field

Use case: astrometry of pulsars close to the Galactic Center

Use case: more calibrators for ALMA

Expected outcome

We will evaluate the correlated flux density of detected sources and estimate source positions with accuracies 5–20 mas. The proposed observations will be used for contribution to the next edition of the Radio Fundamental Catalogue and as a separate 24 GHz position catalogue. The images will be publicly available at the Astrogeo VLBI FITS image database. The final results of the proposed observations will be publicly available within 90 days of observations of the last segment at the project web site and then will be published in a referred journal.

Preliminary results on 2020.07.25

Number of segments observed:	14
Number of segments correlated:	14
Number of segments analyzed:	14
Number of target sources observed:	337
Number of target sources analyzed:	337

Statistics of detection

	K-band	Q-band
Detected:	Known: 91	Known: 54
Detected:	New: 24	New: 14

Statistics of non-detection

	K-band	Q-band
Non-detected:	Known: 47	Known: 84
Non-detected:	New: 175	New: 185

Preliminary catalogue

Catalogue 116 sources detected with VLBI at 24 GHz or 43 GHz within 10° of the Galactic center.

Calibrated K-band correlated flux densities of 188 source detected in the campaign, including 116 target sources and 72 amplitude calibrator sources.
Calibrated Q-band correlated flux densities of 141 source detected in the campaign, including 68 target sources and 73 amplitude calibrator sources.

Median K-band correlated flux densities of 188 source detected in the campaign, including 116 target sources and 72 amplitude calibrator sources.
Median Q-band correlated flux densities of 141 source detected in the campaign, including 68 target sources and 73 amplitude calibrator sources.

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This web page was prepared by Leonid Petrov ()
Last update: 2020.07.25_22:07:09