[vsnet-grb-info 26790] VLASS identifies possible radio counterparts to IceCube-201115A, including a bright BL Lac candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28893
SUBJECT: VLASS identifies possible radio counterparts to IceCube-201115A, including a bright BL Lac candidate
DATE:    20/11/15 17:05:18 GMT
FROM:    Gregory R Sivakoff at U of Alberta  <sivakoff at ualberta.ca>

The following is an abbreviated form of Astronomers Telegram #14177. Here
we fix the link to the original IceCube GCN for the source (we originally
missed the N, which prevents auto linking in ATels).

IceCube-201115A is a recently detected (gold-track) astrophysical neutrino
(GCN #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 highlight the brightest component in particular, VLASS1QLCIR
J125908.35+013606.4 (with a peak radio flux density of 172.3 +/- 0.2 mJy,
and an association to SDSS J125908.28+013605.3). This source may be
associated with a BL Lac type object.

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.