Multiwavelength Observations of 2HWC J1928+177: Dark Accelerator or New TeV Gamma-Ray Binary?
Abstract
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 $r\sim 4^{\prime} $ . 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2020
- DOI:
- 10.3847/1538-4357/ab9631
- arXiv:
- arXiv:2005.12343
- Bibcode:
- 2020ApJ...897..129M
- Keywords:
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- Gamma-ray sources;
- X-ray astronomy;
- X-ray sources;
- Non-thermal radiation sources;
- Radio pulsars;
- Supernova remnants;
- High mass x-ray binary stars;
- Gamma-ray telescopes;
- Gamma-ray astronomy;
- Interstellar medium;
- 628;
- 1810;
- 634;
- 847;
- 633;
- 1119;
- 1353;
- 733;
- 1822;
- 1667;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- accepted to ApJ, 8 pages, 7 figures