Simultaneous View of FRB 180301 with FAST and NICER during a Bursting Phase

FRB180301 is one of the most actively repeating fast radio bursts (FRBs) which has shown polarization angle changes in its burst emission, an indication for their likely origin magnetosphere a highly-magnetized neutron star. We carried out multi-wavelength campaign with FAST telescope and NICER X-ray observatory to investigate any possible emission temporally coincident bright bursts. The observations took place on 2021 March 4, 9 19. detected five FAST, four were strictly simultaneous observations. peak flux-density ranged between $28-105$ mJy, fluence $27-170$ mJy-ms, durations $1.7-12.3$ ms. from FRB~180301 exhibited complex time domain structure, sub-pulses individual bursts, no significant circular polarisation. linear degree polarisation L-band reduced significantly compared 2019 do not detect excess background during 5ms, 10ms, 100ms, 1sec 100sec intervals at/around radio-burst barycenter-corrected arrival times, at $>5\sigma$ confidence level. $5\sigma$ upper limits a) persistent flux $<7.64\times 10^{-12}\, \rm erg\, cm^{-2}\, s^{-1}$ , equivalent $L_{\rm X}<2.50 \times 10^{45} b) 5 ms $<2\times 10^{-11} cm^{-2}$, regions. Using $5$ limit, we can estimate efficiency $\eta_{R/X} \equiv L_{\rm Radio}/L_{\rm X-ray} \gtrsim 10^{-8}$. derived limit $\eta_{R/X}$ consistent both magnetospheric models synchrotron maser involving relativistic shocks.