Multi-Frequency Observations of the Candidate Neutrino Emitting Blazar BZB J0955+3551

The recent spatial and temporal coincidence of the blazar TXS 0506+056 with the IceCube detected neutrino event IC-170922A has opened up a realm of multi-messenger astronomy with blazar jets as a plausible site of cosmic-ray acceleration. After TXS 0506+056, a second blazar, BZB J0955+3551, has recently been found to be spatially coincident with the IceCube detected neutrino event IC-200107A and undergoing its brightest X-ray flare measured so far. Here, we present the results of our multi-frequency campaign to study this peculiar event that includes observations with the NuSTAR, Swift, NICER, and 10.4 m Gran Telescopio Canarias (GTC). The optical spectroscopic observation from GTC secured its redshift as $z=0.55703^{+0.00033}_{-0.00021}$ and the central black hole mass as 10$^{8.90\pm0.16}~M_{\odot}$. Both NuSTAR and NICER data reveal a rapid flux variability albeit at low-significance ($\lesssim3.5\sigma$). We explore the origin of the target photon field needed for the photo-pion production using analytical calculations and considering the observed optical-to-X-ray flux level. We conclude that seed photons may originate from outside the jet, similar to that reported for TXS 0506+056, although a scenario invoking a co-moving target photon field (e.g., electron-synchrotron) can not be ruled out. The electromagnetic output from the neutrino-producing photo-hadronic processes are likely to make only a sub-dominant contribution to the observed spectral energy distribution suggesting that the X-ray flaring event may not be directly connected with IC-200107A.