February 2-5, 2021

Oral Presentation

Medium-band Observation of the Neutrino Emitting Blazar, TXS 0506+056

Author(s): Sungyong Hwang (SNU), Myungshin Im (SNU) et al.

Presenter: Sungyong Hwang (Seoul National University)

TXS 0506+056 is a blazar that has been recently identified as the counterpart of the neutrino event IceCube170922A. Understanding the blazar type of TXS 0506+056 is important to constrain the neutrino emission
mechanism, but the blazar nature of TXS 0506+056 is still uncertain. As an attempt to understand the nature of
TXS 0506+056, we report the medium-band observation results of TXS 0506+056, covering the wavelength
range of 0.575–1.025 μm. The use of the medium-band filters allows us to examine if there were any significant
changes in its spectral shapes over the course of one month and give a better constraint on the peak frequency of
synchrotron radiation with quasi-simultaneous data sets. The peak frequency is found to be 10^14.28 Hz, and our
analysis shows that TXS 0506+056 is not an outlier from the blazar sequence. As a way to determine the blazar
type, we also analyzed if TXS 0506+056 is bluer-when-brighter (BL Lac type and some flat spectrum radio
quasars, FSRQs) or redder-when-brighter (found only in some FSRQs). Even though we detect no significant
variability in the spectral shape larger than observational error during our medium-band observation period, the
comparison with a data set taken in 2012 shows a possible redder-when-brighter behavior of FSRQs. Our results
demonstrate that medium-band observations with small to moderate-sized telescopes can be an effective way to
trace the spectral evolution of transients such as TXS 0506+056.

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