VLASS identifies possible radio counterparts to IceCube-201221A, including 4 blazar candidates

ATel #14288; Gregory R. Sivakoff (University of Alberta)
on 23 Dec 2020; 22:13 UT
Credential Certification: Gregory R Sivakoff (sivakoff@ualberta.ca)

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IceCube-201221A is a recently detected (gold-track) astrophysical neutrino (GCN #29102), localized at 90% PSF containment to (J2000):
RA: 261.69 (+2.29/- 2.50)
Dec: 41.81 (+1.29/-1.20)
This source has the lowest False Alarm Probability rate of any AMON ICECUBE_GOLD/BRONZE EVENT; however, it has a relatively large localization.

Here, we present potential counterparts with precursor (2019 May 6) radio emission at 2-4 GHz from the Components table of the Very Large Array Sky Survey Epoch 1 Quick Look catalog (Gordon et al. 2020, RNAAS, 4, 175). We identify 553 components in the above (90% PSF containment) region, excluding components with "Duplicate_flag" >=2 and "Quality" !=0.

We highlight five radio components, including 4 matches to candidate blazars. All radio flux densities below are the peak 2-4 GHz radio flux density, unless otherwise noted. Despite catalog errors of ~0.14 mJy, the likely peak flux density accuracy is about 8%. Even at the brightest flux density below, the sources could easily be unrelated sources in the large IceCube containment region. All positions listed below are J2000.

VLASS1QLCIR J172325.27+420608.0 (FIRST J172325.2+420608) is the brightest VLASS component (106 mJy) and may be a Galactic source given a potential proper motion. It is also the closest of the matches discussed here (within 0.34 times the 90% containment region, compared to 0.87-0.94). This unresolved source has no clear optical counterpart, but it has a catWISE detection with Vega mag of W1=16.93+/-0.03 and W2=16.31+/-0.06 (Eisenhardt et al 2020, ApJS, 247, 69). Although its color is consistent with the peak of the candidate KDE BL Lacs of D'Abrusco et al. 2019 (ApJS, 242, 4), catWISE measures a proper motions of -0.02+/-0.03 in RA and 0.14+/-0.04 in Dec. We adopt the FIRST position, noting that the mean first epoch is 1996.189.
RA: 260.8552083 +/- 0.0000007 deg
Dec: 42.1022333 +/- 0.0000005 deg.

VLASS1QLCIR J171719.22+422659.9 (FIRST J171719.2+422659) is the 2nd brightest VLASS1 component (103 mJy) and is identified in the 5th version of the ROMA BZCAT (2015, Ap&SS, 357, 75) as a BL Lac-galaxy dominated class blazar. The associated galaxy is within 5 arcseconds of the center of the galaxy cluster WHL J171719.2+422655 at z = 0.1792 (Wen and Han 2015, ApJ, 807, 178). This galaxy cluster has a relatively large richness / mass (RL_500*~87; M_500 ~ (5+3/-2)x1e14 M_solar). We adopt the FIRST (J2000) position.
RA: 259.33004583 +/- 0.0000007 deg
Dec: 42.44991944 +/- 0.0000005 deg.

VLASS1QLCIR J171815.21+422818.3 (aka FIRST J171815.2+422818) is the 6th brightest VLASS1 component (58 mJy) and is also a BL Lac-galaxy dominated class blazar in ROMA BZCAT. The associated galaxy is the central galaxy of the cluster WHL J171815.2+422819, also at z = 0.1793 (Wen and Han 2015). This galaxy cluster has a relatively modest richness / mass (RL_500*~26; M_500 ~ (8+5/-3)x1e13 M_solar), and could be associated with WHL J171719.2+422655. We adopt the Gaia DR2 position.
RA: 259.563298578+/-0.000000006 deg
Dec: 42.471765501+/-0.000000004 deg.

VLASS1QLCIR J172552.11+404214.8 (aka FIRST J172552.0+404214) is the 14th brightest VLASS1 component (31 mJy) and is one of two matches to WISE Blazar-like Radio-Loud Sources in the catalog of D'Abrusco et al. 2019 (ApJS, 242, 4). We adopt the Gaia DR2 position.
RA: 261.467057931+/-0.000000006 deg
Dec: 40.704164054+/-0.000000003 deg.

VLASS1QLCIR J171424.81+413401.3 (aka FIRST J171424.6+413402) peaks at 23 mJy/bm and is the slightly extended core of a multi-component radio source that matches to the second WISE Blazar-like Radio-Loud Source. Even at this lower radio flux, the source would still be classified as radio-loud. We adopt the Gaia DR2 position of
RA: 258.6023854530+/-0.0000000010 deg
Dec: 41.5677788744+/-0.0000000008.

We strongly suggest multi-wavelength observations of these sources.

Link to site for CIRADA cutout service and VLASS QL1 catalog