Finding Candidate TeV Halos among Very-High Energy Sources

We search for possible pulsar TeV halos among the very-high-energy (VHE) sources reported in different VHE surveys, among which in particular we use the results from the first Large High Altitude Air Shower Observatory (LHAASO) catalog of γ-ray sources. Six candidates are found. They share the properties of containing a middle-aged, gamma-ray--bright pulsar in their positional error circles (the respective pulsars are J0248+6021, J0359+5414, J0622+3749, J0633+0632, J2006+3102, and J2238+5903), being in a rather clean field without any common Galactic VHE-emitting supernova remnants or (bright) pulsar wind nebulae (PWNe), and showing the absence of any gamma-ray emissions in 0.1--500\,GeV after removing the pulsars' emissions. Combining with several (candidate) TeV halos reported, we find nearly the same relations as previously ones between their luminosities at 50\,TeV, L50TeV, and the corresponding pulsars' spin-down luminosities, Ė, which are L50TeV~ Ė0.9 and L50TeV/Ė~ 6.4× 10⁻⁴. We probe possible connections between the extension sizes of the VHE sources and the pulsars' ages, and find a weak trend of being older and smaller. By comparing to the VHE detection results for PWNe, it is clear to see that the (candidate) TeV halos have hard emissions by having their power-law indices smaller than 2 in 1--25\,TeV or only being detected in 25--100\,TeV. In addition, we also consider other seven VHE sources as possible TeV halos because of different study results for them, but they do not cleanly fit in the properties listed above, indicating their potential complex nature.