Follow-up Observations for IceCube-170922A: Detection of Rapid Near-Infrared Variability and Intensive Monitoring of TXS 0506+056

TL;DR

This study reports rapid near-infrared variability and intensive multi-wavelength monitoring of the blazar TXS 0506+056 following its potential association with the IceCube-170922A neutrino event, revealing significant flux changes and polarization characteristics.

Contribution

The paper provides the first detailed multi-wavelength follow-up observations of TXS 0506+056 after a neutrino detection, highlighting its variability and polarization properties.

Findings

TXS 0506+056 showed a ~1.0 mag flux variability over days.

No significant short-term variability within a day was observed.

The blazar exhibited a bluer-when-brighter trend in optical and near-infrared wavelengths.

Abstract

We present our follow-up observations to search for an electromagnetic counterpart of the IceCube high-energy neutrino, IceCube-170922A. Monitoring observations of a likely counterpart, TXS 0506+056, are also described. First, we quickly took optical and near-infrared images of 7 flat-spectrum radio sources within the IceCube error region right after the neutrino detection and found a rapid flux decline of TXS 0506+056 in Kanata/HONIR J-band data. Motivated by this discovery, intensive follow-up observations of TXS 0506+056 are continuously done, including our monitoring imaging observations, spectroscopic observations, and polarimetric observations in optical and near-infrared wavelengths. TXS 0506+056 shows a large amplitude (~1.0 mag) variability in a time scale of several days or longer, although no significant variability is detected in a time scale of a day or shorter. TXS 0506+056 also shows a bluer-when-brighter trend in optical and near-infrared wavelengths. Structure functions of variabilities are examined and indicate that TXS 0506+056 is not a special blazar in terms of optical variability. Polarization measurement results of TXS 0506+056 are also discussed.