Two Candidate Pulsar TeV Halos Identified from Property-similarity Studies

Abstract

Teraelectronvolt halos have been suggested to be a common phenomenon associated with middle-aged pulsars. Based on our recent work on the middle-aged pulsar J0631+1036, which is the only known source positionally coincident with a hard teraelectronvolt γ-ray source and likely powers the latter as a teraelectronvolt halo, we select three candidate teraelectronvolt halos from the first Large High Altitude Air Shower Observatory (LHAASO) catalog of γ-ray sources. The corresponding pulsars, given by the positional coincidences and property similarities, are PSR J1958+2846, PSR J2028+3332, and PSR J1849-0001. We analyze the gigaelectronvolt γ-ray data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope for the first two pulsars, as the last is γ-ray quiet. We remove the pulsed emissions of the pulsars from the source regions from timing analysis, and determine that there are no residual gigaelectronvolt emissions in the regions as any possible counterparts to the teraelectronvolt sources. Considering the previous observational results for the source regions and comparing the two pulsars to Geminga (and Monogem), the LHAASO-detected teraelectronvolt sources are likely the pulsars’ respective teraelectronvolt halos. We find that the candidate and identified teraelectronvolt halos, including that of PSR J1849-0001, have luminosities at 50 TeV (estimated from the differential fluxes) approximately proportional to the spin-down energy E ̇ of the pulsars, and the ratios of the former to the latter are ∼6 × 10−4.

Finding Candidate TeV Halos among Very-high-energy Sources

“…The pulsars' properties, including information for their X-ray emissions, are summarized in Table 1. As discussed in Zheng & Wang (2023), there may be a relationship between the TeV halos' luminosity at 50 TeV, L 50TeV , and the corresponding pulsars' spin-down energy E  . This relationship helps indicate the fraction of the total energy spent on powering the TeV halos.…”

“…Following our previous work on identifying candidate pulsar TeV halos (Zheng et al 2023a;Zheng & Wang 2023) by mainly analyzing the off-pulse GeV data of γ-ray pulsars in the fields of VHE sources, from which any residual emissions may help reveal their nature as possibly being primary Galactic sources, such as SNRs or PWNe, we further found six candidates because of the nondetection of any significant residual emissions. The pulsars' properties, including information for their X-ray emissions, are summarized in Table 1.…”

“…The L 50TeV values are provided in Table 1. Fitting the data points that include four sources in Zheng & Wang (2023)  with reduced χ 2 ; 0.6 for dof = 8. Both results are also very similar to those previously obtained in Zheng & Wang (2023).…”

“…The nondetections, combined with the pulsars' many similarities to Geminga and the fact that no primary Galactic VHE-emitting sources (e.g., H. E.S.S. Collaboration et al 2018a), such as supernova remnants (SNRs) or pulsar wind nebulae (PWNe), are known in the fields, led to our identification of the three VHE sources as being TeV halos powered by their respective pulsars (Zheng et al 2023a;Zheng & Wang 2023).…”

“…The wide energy-range coverage allows us to select sources with spectra harder than those of PWNe (H.E.S.S. Collaboration et al 2018b), which is a possible feature that may be used to differentiate the TeV halos from the PWNe (see Zheng et al 2023a;Zheng & Wang 2023). In addition, the Third Fermi/LAT Catalog of Gamma-ray Pulsars (3PC) has very recently been released (Smith et al 2023).…”