VLASS identifies possible radio counterparts to IceCube-201115A, including a bright BL Lac candidate

ATel #14177; Gregory Sivakoff (University of Alberta)
on 15 Nov 2020; 16:53 UT
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Credential Certification: Gregory R Sivakoff (sivakoff@ualberta.ca)

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IceCube-201115A is a recently detected (gold-track) astrophysical neutrino (GC #28889), localized at 90% PSF containment to (J2000):
RA: 195.12 (+ 1.27 / - 1.49) deg
Dec: 1.38 (+ 1.30 / - 1.11) deg.
Here, we present potential counterparts with precursor (2019 April 21) radio emission at 2-4 GHz from the catalog of the Very Large Array Sky Survey Epoch 1 Quick Look Components catalog (Gordon et al. 2020, RNAAS, 4, 175). We identify 156 components in the above (90% PSF containment) region, excluding catalog components with "Duplicate_flag" >=2 and "Quality" !=0. We highlight the brightest component in particular, VLASS1QLCIR J125908.35+013606.4 (with a peak radio flux density of 172.3 +/- 0.2 mJy), which may be associated with a BL Lac.

The VLASS detection consists of multiple components. Visual inspection shows a bright source and a ~2.5x fainter source about 6" to the south east. We interpret these as either two radio lobes (or less likely two jet knots) as SDSS J125908.28+013605.2 (aka SDSS J125908.28+013605.3) lies directly between the sources. This optical source has a photo-z of 0.62+/-0.05. While the Initial Gaia Source List (Smart and Nicastro 2013) indicates a 5.2 sigma non-zero proper motion, this catalog states it should be used for care for individual sources. We discount the likelihood that this is a Galactic source, given the two radio detections.

We adopt the Sloan position of the source, specifying positional errors that contain the VLASS radio emission, after accounting for potential 0.5" accuracy issues with VLASS Epoch 1 data in their current processing stage:
RA: 194.78452 +/- 0.00028 deg
Dec: 1.601466 +/- 0.000018 deg.
The VLASS QL position (RA = 194.784795+/- 0.000003, Dec = 1.601785 +/- 0.000002) is 1.5" offset from the SDSS position due to the asymmetry in the radio emission. The radio "source" that typically describes the two VLASS components is PKS 1256+018 (PKS J1259+0136), which is a known radio variable source (Ofek et al. 2011, ApJ, 737, 45). The radio spectral index (-0.59; Vollmer 2010, A&A, 511, 53) is consistent with optically thin synchrotron emission (flux density S_ν proportional to ν^-0.6, where ν is the frequency).

Burbidge & Hewitt (1992, Variability of Blazars, 4) list "1E 1256+018" as a BL Lac and is likely to be the same source as PKS 1256+018. However, the nearest Second Einstein catalog source is 4.7' away, and has a positional error of 0.7'.

Given this potential radio source associated with a BL Lac and an astrophysical neutrino, we strongly suggest multi-wavelength observations of SDSS J125908.28+013605.3.

For completeness, we list the brightest VLASS components (by peak flux density), where the position to 0.5" accuracy is indicated by the name:

 
VLASS1QLCIR J125908.35+013606.4; (172.97+/-0.21) mJy 
VLASS1QLCIR J125834.92+003832.3; (49.32+/-0.17) mJy 
VLASS1QLCIR J125916.11+012536.4; (37.33+/-0.19) mJy 
VLASS1QLCIR J130309.31+012943.0; (36.10+/-0.16) mJy 
VLASS1QLCIR J130040.44+020029.8; (31.97+/-0.15) mJy 
VLASS1QLCIR J125905.80+010554.7; (30.01+/-0.16) mJy 
VLASS1QLCIR J125824.67+020856.6; (21.57+/-0.15) mJy 
VLASS1QLCIR J130141.53+014138.3; (18.95+/-0.15) mJy 
VLASS1QLCIR J125801.19+013432.7; (18.83+/-0.16) mJy 
VLASS1QLCIR J125951.37+015350.5; (16.29+/-0.15) mJy 
VLASS1QLCIR J130059.79+004443.2; (15.49+/-0.16) mJy 
VLASS1QLCIR J125751.93+013713.0; (15.10+/-0.15) mJy 
VLASS1QLCIR J130332.06+014407.7; (15.00+/-0.14) mJy 
VLASS1QLCIR J125844.03+005358.2; (14.57+/-0.15) mJy 
VLASS1QLCIR J125824.80+020841.7; (13.23+/-0.15) mJy 
VLASS1QLCIR J125715.48+012357.4; (12.11+/-0.15) mJy 
VLASS1QLCIR J125734.38+015144.2; (10.81+/-0.14) mJy 
VLASS1QLCIR J125953.32+011249.4; (10.74+/-0.16) mJy 
VLASS1QLCIR J125819.83+020353.5; (10.72+/-0.14) mJy 
VLASS1QLCIR J130416.41+012046.3; (10.65+/-0.15) mJy 
VLASS1QLCIR J125715.25+012355.6; (10.51+/-0.15) mJy 
VLASS1QLCIR J125907.78+015306.1; (10.16+/-0.16) mJy 

Link to site for CIRADA cutout service and VLASS catalog