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Using the High-Altitude Water Cherenkov (HAWC) observatory, an international team of astronomers has observed a very-high energy gamma-ray source designated TeV J2032+4130. Results of the observational campaign, July 3 on the preprint server arXiv, provide crucial information regarding the nature of this source.

Sources emitting gamma radiation with photon energies between 100 GeV and 100 TeV are called very-high energy (VHE) gamma-ray sources, while those with photon energies above 0.1 PeV are known as ultra-high energy (UHE) gamma-ray sources. The nature of these sources is still not well understood; therefore, astronomers are constantly searching for new objects of this type to characterize them, which could shed more light on their properties in general.

TeV J2032+4130 was identified in 2005 by the High Energy Gamma Ray Astronomy (HEGRA) experiment as the first VHE gamma-ray source in the TeV range with no lower-energy counterpart. Previous observations of TeV J2032+4130 have revealed that it consists of two sources, namely HAWC J2030+409 and HAWC J2031+415, which is coincident with a pulsar wind nebula (PWN).

It was also found that the pulsar PSR J2032+4127 is most likely the power source for this PWN. At a distance of about 4,300 light years, PSR J2032+4127 is a long-period binary (with an orbital period of some 50 years) with a star known as MT91 213, which is about 15 times more massive than the sun. This makes it a rare type of a TeV binary gamma-ray pulsar.

Now, a group of astronomers, led by Ruben Alfaro of the National Autonomous University of Mexico, has employed HAWC to take a closer look at TeV J2032+4130, focusing mainly on the possible PWN HAWC J2031+415.

HAWC observations have shown that HAWC J2031+415 is an extended emission region modeled as a symmetric Gaussian. The region has a spectral shape of a power law with exponential cutoff energy of approximately 19 TeV, indicating that it may be a PWN.

The astronomers concluded that given its close proximity to TeV J2032+4130, HAWC J2031+415 is most probably the high energy extension of this unidentified source. They added that while there is no clear evidence for energy-dependent morphology, the spectral shape matches that of a typical PWN.

Moreover, the observed energy to total energy budget of HAWC J2031+415 was found to be at a level of 1%, which is typical for the known population of PWNe.

Summing up the results, the authors of the paper concluded that the collected data confirm the PWN nature of HAWC J2031+415.

"The leptonic emission result favors emission from HAWC J2031+415, and by extension, TeV J2032+4130 to be produced by a pulsar wind nebula powered by PSR J2032+4127," the scientists wrote.

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