Pulsars, transients and relativistic astrophysics

The young neutron star X-ray binary, Cir X-1, resides within its natal supernova remnant and experiences ongoing outbursts every 16.5 d, likely due to periastron passage in an eccentric orbit. We present the deepest ever radio image of the field, which reveals relativistic jet-punched bubbles that are aligned with the mean axis of the smaller scale jets observed close to the X-ray binary core. We are able to measure the minimum energy for the bubble, which is around 10^45 erg. The nature and morphological structure of the source were investigated through spectral index mapping and numerical simulations. The spectral index map reveals a large fraction of the nebula’s radio continuum has a steep slope, associated with optically thin synchrotron emission, although there are distinct regions with flatter spectra. Our data are not sensitive enough to measure the spectral index of the protruding bubbles. We used the pluto code to run relativistic hydrodynamic simulations to try and qualitatively reproduce the observations with a combined supernova-plus-jet system. We are able to do so using a simplified model in which the asymmetrical bubbles are best represented by supernova explosion which is closely followed (within 100 yr) by a phase of very powerful jets lasting less than 1000 yr. These are the first observations revealing the initial breakout of neutron star jets from their natal supernova remnant, and further support the scenario in which Cir X-1 is a younger relation of the archetypal jet source SS433.

The recent association of two flaring blazars (TXS 0506+056 and 3HSP J095507.9+355101) with IceCube neutrinos strongly suggests that blazars are at least one source of high-energy neutrinos. A peculiar characteristic of these two blazars is that they both appear to lie above the well-known blazar sequence, and they move further above the blazar sequence during the neutrino emission. Although the reason for this peculiarity is unclear, it may indicate a link between blazar SED properties and neutrino emission. Here, we test whether blazars lying above the blazar sequence are overrepresented in IceCube neutrino error regions. We spatially cross-match IceCube error regions with a sample of γ-ray blazars from the Fermi-LAT 4LAC catalogue, as a function of the blazars' distance in synchrotron peak frequency above the blazar sequence. We do not find a statistically significant excess of counterparts, and thus conclude that the current data cannot confirm that the sources above the blazar sequence are a significant source of IceCube neutrinos. However, we show that the inclusion of more recently detected IceCube events increases the likelihood of an excess of blazars above the blazar sequence, and suggest that this excess may reach statistical significance in the future as the sample of IceCube neutrino detections increases.