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Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes at the center of galaxies violently disrupt stars that pass too close. TDEs provide a new window to study accretion onto supermassive black holes; in some cases, this accretion leads to launching of a relativistic jet, but the necessary conditions are not fully understood. Here, we report the optical discovery of AT2022cmc, a rapidly fading source located at redshift z=1.19325. Observations of a bright counterpart at other wavelengths, including X-rays, sub-millimeter, and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ``afterglow.'' Using 4 years of Zwicky Transient Facility survey data, we calculated a rate of 0.02 ^{+ 0.04 }_{- 0.01 } Gpc^{-3} yr^{-1} for jetted TDEs based on the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X--ray and radio observations (Brown et al., 2015), confirming that ~1% of TDEs have on-axis jets. Forthcoming observations of AT2022cmc could resolve the jet through high-resolution imaging, while optical surveys have the potential to unveil a population of cosmological flares of the AT2022cmc class.

Neutron star (NS) masses and radii can be estimated from observations of photospheric radius-expansion X-ray bursts, provided the chemical composition of the photosphere, the spectral colour-correction factors in the observed luminosity range, and the emission area during the bursts are known. By analysing 246 X-ray bursts observed by the Rossi X-ray Timing Explorer from 11 low-mass X-ray binaries, we find a dependence between the persistent spectral properties and the time evolution of the black body normalisation during the bursts. All NS atmosphere models predict that the colour-correction factor decreases in the early cooling phase when the luminosity first drops below the limiting Eddington value, leading to a characteristic pattern of variability in the measured blackbody normalisation. However, the model predictions agree with the observations for most bursts occurring in hard, low-luminosity, 'island' spectral states, but rarely during soft, high-luminosity, 'banana' states. The observed behaviour may be attributed to the accretion flow, which influences cooling of the NS preferentially during the soft state bursts. This result implies that only the bursts occurring in the hard, low-luminosity spectral states can be reliably used for NS mass and radius determination., Comment: 18 pages, 4 figures, accepted to MNRAS