tokens: power of erg s −1 , very similar to that shown by PSR J1908+0839, but its distance is ∼30 times smaller ( d Geminga = 250 pc). Given the similar spin-down power, the nebula PSR J1908+0839 powers should also have a comparable luminosity with respect to Geminga’s PWN, which would lead to a flux around three orders of magnitude smaller than the flux of Geminga and undetectable by HAWC. Therefore, it is unlikely that 2HWC J1907+084* and PSR J1908+0839 are associated with one another. Finally, the closest pulsar to the source 2HWC J1852+013* is PSR J1851+0118, offset by only 0.10°. This pulsar lies at a distance of 5.6 kpc and has a characteristic age of ∼100 kyr (Yao, Manchester Wang 2017 ). If both objects are related the required pulsar velocity is a reasonable value of ∼100 km s −1 , though this may be as high as ∼245 km s −1 when considering the largest offset given by 0.10° ± 0.10 0.13. However, this pulsar has a relatively low spin-down power, erg s −1 , which along with its high characteristic age make it unlikely to accelerate particles that can emit gamma rays in the TeV regime. To quantitatively test this scenario, we use the Naima software 3 to model the relativistic parent population of the non-thermal gamma-ray emission accounting for different radiative models (see Zabalza 2015 ). To obtain the emissivity of the electron population that gave rise to the gamma-ray emission seen by HAWC, we assume that IC is the dominant radiative process and that the electron spectrum is defined by a simple power law. The target photon field for this process is expected to be a combination of cosmic microwave background (CMB) and infrared (IR) photons. The assumed energy densities in each case are standard Galactic values of u CMB = 0.25 eV cm −3 and u IR = 0.30 eV cm −3 . With such features, the total energy carried by electrons above ∼10 TeV needed to explain HAWC detection would be W e (> 10 TeV) ∼ 6.0 × 10 46 erg. Alternatively, we consider the cooling time of these electrons ( t cool ), which is computed as follows (Aharonian 2004 ): where E e = 10 TeV is the electron energy and u is the total energy density of the medium. In this case, we account for IC and synchrotron losses and hence, assuming a temperature of ∼25 K for the IR photon field (Moderski et al. 2005 ), u can be described as where B is the magnetic field. We use the aforementioned energy densities for the CMB and IR photon fields, and for the magnetic field, we assume the minimum possible value given by the interstellar magnetic field, B = 3 μG, as there is no measured value for the source. Under these assumptions, the cooling time is t cool ∼ 57 kyr. Given the spin-down power of PSR J1851+0118, erg s −1 , the total energy released by the pulsar during the t cool period would be erg. Consequently, even assuming that all the energy released by the pulsar was used to accelerate electrons above 10 TeV, there would not be enough energy to power a PWN with the gamma-ray brightness
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