Discovery of VHE gamma-rays from RGB J0152+017

TL;DR

This paper reports the discovery of very high-energy gamma-ray emission from the BL Lac object RGB J0152+017 using H.E.S.S., supported by multi-wavelength observations, and models its spectral energy distribution with a leptonic SSC model.

Contribution

First detection of VHE gamma-rays from RGB J0152+017, confirming its classification as a high-frequency-peaked BL Lac and providing detailed spectral modeling.

Findings

VHE gamma-ray emission detected with 6.6 sigma significance.

The energy spectrum follows a power-law with index ~2.95.

The flux above 300 GeV is about 2% of the Crab nebula flux.

Abstract

The BL Lac object RGB J0152+017 (z = 0.080) was predicted to be a very high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio fluxes. We report recent observations of this source made in late October and November 2007 with the H.E.S.S. array consisting of four imaging atmospheric Cerenkov telescopes. Contemporaneous observations were made in X-rays with the Swift and RXTE satellites, in the optical band with the ATOM telescope, and in the radio band with the Nancay Radio Telescope. As a result, RGB J0152+017 is discovered as a source of VHE gamma-rays by H.E.S.S. A signal of 173 gamma-ray photons corresponding to a statistical significance of 6.6 sigmas was found in the data. The energy spectrum of the source can be described by a powerlaw with a spectral index of = 2.95 +- 0.36stat +- 0.20syst. The integral flux above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source spectral energy distribution (SED) can be described using a two-component (extended jet and blob in jet) non-thermal synchrotron self-Compton (SSC) leptonic model, plus a thermal host galaxy component. The parameters that are found are very close to those found for TeV blazars in similar SSC studies. The location of its synchrotron peak, as derived from the SED in Swift data, allows clear classification as a high-frequency-peaked BL Lac (HBL).