Multiwavelength Observations of 2HWC J1928+177: Dark Accelerator or New TeV Gamma-Ray Binary?

• Published in: The Astrophysical journal 2020-07, Vol.897 (2), p.129
• Main Authors: Mori, Kaya, An, Hongjun, Feng, Qi, Malone, Kelly, Prado, Raul R., Schutt, Yve E., Dingus, Brenda L., Gotthelf, E. V., Hailey, Charles J., Hare, Jeremy, Kargaltsev, Oleg, Mukherjee, Reshmi
• Format: Article
• Language: English
• Subjects: ASTRONOMY AND ASTROPHYSICS; Astrophysics; Binary stars; Elastic scattering; Emission; Energy bands; Gamma ray sources; Gamma rays; Gamma-ray astronomy; Gamma-ray telescopes; High altitude; High energy astronomy; High mass x-ray binary stars; Interstellar medium; Molecular clouds; Nebulae; Non-thermal radiation sources; O stars; Point sources; Pulsar winds; Pulsars; Radio pulsars; Stellar winds; Stereoscopy; Supernova; Supernova remnants; X ray sources; X ray spectra; X-ray astronomy; X-ray emissions; X-ray fluxes
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/ab9631

2HWC J1928+177 is a Galactic TeV gamma-ray source detected by the High Altitude Water Cherenkov (HAWC) Observatory up to ∼56 TeV. The HAWC source, later confirmed by the High Energy Stereoscopic System, still remains unidentified as a dark accelerator since there is no apparent supernova remnant or pulsar wind nebula detected in the lower-energy bands. The radio pulsar PSR J1928+1746, coinciding with the HAWC source position, has no X-ray counterpart. Our SED modeling shows that inverse Compton scattering in the putative pulsar wind nebula can account for the TeV emission only if the unseen nebula is extended beyond . Alternatively, TeV gamma-rays may be produced by hadronic interactions between relativistic protons from an undetected supernova remnant associated with the radio pulsar and a nearby molecular cloud G52.9+0.1. NuSTAR and Chandra observations detected a variable X-ray point source within the HAWC error circle, potentially associated with a bright infrared (IR) source. The X-ray spectra can be fitted with an absorbed power-law model with NH = (9 3) × 1022 cm−2 and ΓX = 1.6 0.3 and exhibit long-term X-ray flux variability over the last decade. If the X-ray source, possibly associated with the IR source (likely an O star), is the counterpart of the HAWC source, it may be a new TeV gamma-ray binary powered by collisions between the pulsar wind and stellar wind. Follow-up X-ray observations are warranted to search for diffuse X-ray emission and determine the nature of the HAWC source.