Broadband spectral energy distribution of 1ES 0806+524. The Swift data are taken on two separate nights (gray and black points). The solid and dashed curves are SSC fits to the Swift data. For more details, see Figure 4 below.

1ES0806+524 - Discovery of a new VHE Blazar

Reference:  V. A. Acciari et al. (The VERITAS Collaboration), The Astrophysical Journal, 690: L126, 2009

Full text version

ArXiv version: ArXiV:0812.0978

Contact person: Peter Cogan

1ES 0806+524 is a blazar located at a redshift of 0.138. This blazar was identified as a candidate source of very-high energy gamma-ray emission based on the presence of both high-energy electrons and sufficient seed photons. Theoretical studies predict a flux of 1.36×10^-11 cm^-2 s^-1 above 0.3 TeV (but it was detected by VERITAS at the significantly lower flux of 4.4×10^-12 cm^-2 s^-1). 1ES 0806+524 was observed by VERITAS while the array was being constructed in the 2006/2007 observing season (and thus used fewer than four telescopes) and after it was complete during the 2007/2008 observing season. The blazar was observed for a total of 65 hours (after quality cuts for weather and detector performance). The peak source location of the gamma-ray excess is RA=8h9m59s and DEC=52^o19'2" which is statistically consistent with the known blazar position.

Using only the higher-quality four-telescope data, the energy spectrum is fit to the form dN/dE=F×(E/400GeV)^-Γ where F=6.8±1.7 (stat)±1.3 (sys) 10^-12 cm^-2 s^-1 and Γ=3.6±1(stat)±0.3(sys). Absorption on the infrared component of the extragalactic background light softens the spectral index. The spectrum can be deabsorbed giving an
intrinsic spectral index of 2.8±0.5 (stat). No variability is found on monthly timescales.

Following the announcement  by VERITAS of the detection of very-high energy gamma-ray emission from 1ES 0806+524, observations of the blazar were performed using the Swift telescope in the ultraviolet to optical and X-ray energy bands. These data are combined with an archival (non-contemporaneous) data point from the Tuorla observatory to create a broad-band spectral energy distribution. This is modeled using a one-zone jet radiation transfer code. The synchrotron peak is located at 8.3×10¹⁵ Hz and the inverse-Compton peak is located at 3.5×10²⁴ Hz.

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

Figure 1: Distribution of the parameter theta-squared, the squared angular distance between the reconstructed shower direction and the location of 1ES 0806+524. The vertical line, located at theta-squared = (0.013 degrees)^2 indicates the size of the integration region. The simulated line indicates the expected shape of the theta-squared distribution for a point source of this strength.

Figure 2: Differential photon spectrum of 1ES 0806+524. The spectrum is well fit by a power law with index 3.6±1.0 (stat) ±0.3 (sys). The deabsorbed spectrum is calculated by applying the extragalactic absorption model according to Franceschini et al. (2008).

Figure 3: Month-by-month integral flux above 300 GeV from observations of 1ES 0806+524. The chi-square probability of the straight line fit is 0.24.

Figure 4: Broadband spectral energy distribution of 1ES 0806+524. The Swift data are taken on two separate nights, with a lower flux on 2008 March 8 (gray points) and a higher flux on 2008 March 12 (black points). The solid and dashed curves are SSC fits to the 2008 March 8 and 2008 March 12 Swift data, respectively.