Presentation #410.06 in the session Molecular Clouds, HII Regions, Interstellar Medium I.
X-ray and synchrotron observations of the TeV halo around pulsars exhibit isotropic signatures, seemingly implying that the magnetic field in the pulsars’ ambient region is weak and super-Alfvénic. Previous observations suggest that the magnetic field is unlikely to be greater than 0.8 µG, which is less than the galactic average magnetic field (~6 µG). If this is true, the weak interstellar magnetic field may not be sufficient to explain the scenario of fast cosmic ray diffusion observed in these pulsars.
An alternative scenario is the possibility of a strong mean magnetic field aligning with the line of sight. Recent developments in the “y-parameter” method (Yuen et al., 2023, MNRAS, arXiv:2301.13344; Malik et al., 2023, arXiv:2303.17282) have allowed for a direct diagnosis to retrieve the magnetic field inclination in the interstellar medium (ISM) and identify the dominant turbulence mode. Based on the “y-parameter technique”, we provide direct observational evidence that the TeV halo around a recently observed pulsar has a stronger magnetic field than expected, although it is almost aligned with the line of sight. We estimated the magnetic field strength to have an upper bound estimate of 1.1-2.2 µG. Furthermore, we reveal that the turbulence in this pulsar is compressible-dominant, which favors the fast cosmic ray transport model as suggested by Yan & Lazarian in 2002. Our observations suggest that a strong-field compressible turbulence scenario is plausible for the TeV halo around pulsars. [Based on Malik, Yuen, Yan et al. (in prep), and also Yuen et al., 2023, MNRAS, arXiv:2301.13344; Malik et al., 2023, arXiv:2303.17282]