A NuSTAR and Chandra Investigation of the Enigmatic Pulsar Filament of the Lighthouse Nebula

The parsec-scale elongated structures recently discovered in X-rays in the vicinity of several fast-moving pulsars are defying the standard hydrodynamic picture in which the pulsar wind is expected to be confined within the pulsar’s bow shock. These structures, known as misaligned outflows or pulsar filaments, are attributed to ultra-relativistic particles escaping the bow shock and emitting synchrotron radiation in the ISM magnetic field. The properties of these outflows shed light on the particle acceleration mechanisms, the propagation of ultra-relativistic particles in the ISM, and the properties of the ISM itself (e.g., magnetic field structure on parsec scales). The most prominent misaligned outflow is associated with the Lighthouse Nebula, powered by the young and energetic pulsar J1101-6101, which belongs to the rare type of radio- and gamma-ray-quiet pulsars that are bright in hard X-rays. We report on NuSTAR observations of PSR J1101-6101 and its misaligned outflow — the first observation of such a structure above 10 keV. We confidently detect the outflow up to 25 keV in the NuSTAR images. By jointly analyzing NuSTAR and archival Chandra data, we investigate the spectral changes within the outflow with distance from the pulsar and place constraints on particle energies and magnetic field in the outflow. We also discuss the remarkable fine structure of the outflow resolved by Chandra down to sub-arcsecond scales. We detect pulsations from PSR J1101-6101 up to 20 keV, obtain energy-resolved pulse profiles, confirm previous period derivative measurements, and perform phase-resolved spectroscopy.