The day after the arrival of the IceCube neutrino 200107A 3HSP J095507.9+355101 , an extreme blazar with synchrotron peak frequency \gtrsim 5 \times 10 ^ { 17 } Hz , z = 0.557 , and well within the neutrino event error region , was found to exhibit a very hard X-ray flare .
We report here on its multi-messenger data and classify the source as an unlikely ‘ ‘ masquerading ’ ’ BL Lac , contrary to TXS 0506+056 , the first source so far associated with IceCube neutrinos .
Similarly to TXS 0506+056 , however , 3HSP J095507.9+355101 is also way off the so-called ‘ ‘ blazar sequence ’ ’ .
Finally , we discuss some theoretical implications in terms of neutrino production .
We show that , based on all of the above , 3HSP J095507.9+355101 is a very plausible counterpart to an IceCube neutrino .