Discovery of High-Energy and Very High-Energy γ-Ray Emission from the Blazar RBS 0413

: Published: 02 April 2012

RBS 0413 spectral energy distribution. For more details see Figure 3 below.

Reference: E. Aliu et al. (The VERITAS Collaboration), Astrophysical Journal 750: 94, 2012

Contacts: Gunes Senturk, Pascal Fortin, Deirdre Horan

We report on the detection of the blazar RBS 0413 in high-energy (HE; E>100 MeV) and very high-energy (VHE; E>100 GeV) gamma rays with the Fermi Gamma-ray Space Telescope and VERITAS, respectively. RBS 0413 is an active galaxy of the BL Lac class located at a redshift of 0.190. VERITAS, as a ground-based gamma-ray telescope, performs mostly pointed observations, where target selection is crucial. This joint discovery is a case where Fermi provided valuable information for VERITAS observation strategies.

BL Lac objects are natural laboratories where particles in a jet plasma outflowing from a central supermassive black hole are accelerated to ultrarelativistic speeds. Their jet is oriented along the observer’s line of sight, resulting in extreme observational properties such as boosted apparent luminosity and minute-scale variabilities accompanying giant flares that are among nature’s most powerful energy releases. The outstanding question about these objects is which physical mechanisms are responsible for the observed emission. In this work, we analyzed multiwavelength spectral data extending from the optical band to VHE gamma rays and looked for temporal variabilities in HE and VHE bands to investigate this question.

Tar file containing tables from paper and FITS files of results

Figures from paper (click to get full size image):

Figure 1: VERITAS measured photon spectrum of RBS 0413. See text for the parameters of the power-law fit shown.

Figure 2: Top: 30-day light curve for the VERITAS data. A fit with a constant function gives a Χ²/dof value of 14/8, corresponding to a fit probability of 8%, consistent with the hypothesis of a constant flux. The negative flux point corresponding to the upper limit point in the light curve was included in the fit. Bottom: The light curve for the Fermi data using ~6-month wide time bins. The shaded areas represent the time intervals that were excluded to avoid solar contamination. In both graphs, the dashed lines represent the constant fit function.

Figure 3: RBS 0413 spectral energy distribution. Absorption in the VHE region due to the EBL is taken into account in the fits using the model of Finke et al. (2010). The models are described in detail in the text.