RT Journal Article T1 Multifrequency observations of the candidate neutrino-emitting blazar BZB J0955+3551 A1 Paliya, Vaidehi S. A1 Böttcher, M. A1 Olmo García, A. A1 Domínguez, A. A1 Gil de Paz, Armando A1 Franckowiak, A. A1 Garrappa, S. A1 Stein, R. AB 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 multimessenger astronomy with blazar jets as a plausible site of cosmic-ray acceleration. After TXS 0506+056, a second blazar, BZB J0955+3551, was recently 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 multifrequency campaign to study this peculiar event that includes observations with the NuSTAR, Swift, Neutron star Interior Composition Explorer (NICER), and 10.4 m Gran Telescopio Canarias (GTC). The optical spectroscopic observation from GTC secured its redshift as z = 0.55703_(-0.00021) ^(+0.00033) and the central black hole mass as 10^(8.90 0.16) Mꙩ. Both NuSTAR and NICER data reveal a rapid flux variability, albeit at low significance (