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Register a new userA Three-Year Multi-Wavelength Study of the Very High Energy Gamma-ray Blazar 1ES 0229+200
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The high-frequency-peaked BL Lacertae object 1ES 0229+200 is a relatively distant (z = 0.1396), hard-spectrum (Gamma ~ 2.5), very-high-energy-emitting (E > 100 GeV) gamma-ray blazar. Very-high-energy measurements of this active galactic nucleus have been used to place constraints on the intensity of the extragalactic background light and the intergalactic magnetic field. A multi-wavelength study of this object centered around very-high-energy observations by VERITAS is presented. This study obtained, over a period of three years, an 11.7 standard deviation detection and an average integral flux F(E>300 GeV) = (23.3 +- 2.8_stat +- 5.8_sys) x 10^-9 photons m^-2 s^-1, or 1.7% of the Crab Nebulas flux (assuming the Crab Nebula spectrum measured by H.E.S.S). Supporting observations from Swift and RXTE are analyzed. The Swift observations are combined with previously published Fermi observations and the very-high-energy measurements to produce an overall spectral energy distribution which is then modeled assuming one-zone synchrotron-self-Compton emission. The chi^2 probability of the TeV flux being constant is 1.6%. This, when considered in combination with measured variability in the X-ray band, and the demonstrated variability of many TeV blazars, suggests that the use of blazars such as 1ES 0229+200 for intergalactic magnetic field studies may not be straightforward and challenges models that attribute hard TeV spectra to secondary gamma-ray production along the line of sight.
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The blazar 1ES 0229+200 is a high frequency peaked BL Lac object with a hard TeV spectrum extending to 10 TeV. Its unusual spectral characteristics make it a frequently used probe for intergalactic radiation and magnetic fields. With new, simultaneous observations in the optical, ultraviolet (UV) and X-rays, the synchrotron emission is probed in great detail. The X-ray emission varies by a factor of ~2 in 2009, while being rather stable in 2010. The X-ray spectrum is very hard (Gamma ~ 1.8) and it shows an indication of excess absorption above the Galactic value. The X-ray emission is detected up to ~100 keV without any significant cut-off, thus 1ES 0229+200 belongs to the class of extreme blazars. The simultaneous measured, host galaxy- and extinction-corrected optical and UV fluxes illustrate that the cut-off of the low energy part of the synchrotron emission is located in the UV regime. The minimum energy of the electron distribution has to be rather high to account for this cut-off. This implies that there is a narrow-band energy distribution function of radiating electrons, which is responsible for the unusually hard TeV spectrum. Other extreme blazars have similar synchrotron peak frequencies but much softer TeV spectra, hence 1ES 0229+200 has one of the highest inverse Compton (IC) peak frequency and the narrowest electron distribution among the extreme blazars known to date.
A hotspot at a position compatible with the BL Lac object 1ES 2322-409 was serendipitously detected with H.E.S.S. during observations performed in 2004 and 2006 on the blazar PKS 2316-423. Additional data on 1ES 2322-409 were taken in 2011 and 2012, leading to a total live-time of 22.3h. Point-like very-high-energy (VHE; E>100GeV) $gamma$-ray emission is detected from a source centred on the 1ES 2322-409 position, with an excess of 116.7 events at a significance of 6.0$sigma$. The average VHE $gamma$-ray spectrum is well described with a power law with a photon index $Gamma=3.40pm0.66_{text{stat}}pm0.20_{text{sys}}$ and an integral flux $Phi(E>200GeV) = (3.11pm0.71_{rm stat}pm0.62_{rm sys})times10^{-12} cm^{-2} s^{-1}$, which corresponds to 1.1$%$ of the Crab nebula flux above 200 GeV. Multi-wavelength data obtained with Fermi LAT, Swift XRT and UVOT, RXTE PCA, ATOM, and additional data from WISE, GROND and Catalina, are also used to characterise the broad-band non-thermal emission of 1ES 2322-409. The multi-wavelength behaviour indicates day-scale variability. Swift UVOT and XRT data show strong variability at longer scales. A spectral energy distribution (SED) is built from contemporaneous observations obtained around a high state identified in Swift data. A modelling of the SED is performed with a stationary homogeneous one-zone synchrotron-self-Compton (SSC) leptonic model. The redshift of the source being unknown, two plausible values were tested for the modelling. A systematic scan of the model parameters space is performed, resulting in a well-constrained combination of values providing a good description of the broad-band behaviour of 1ES 2322-409.
We present very-high-energy $gamma$-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above background of $20.8sigma$ in $47.2$ hours (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations the temporal properties of 1ES 2344+514 are studied on short and long times scales. We fit a constant flux model to nightly- and seasonally-binned light curves and apply a fractional variability test, to determine the stability of the source on different timescales. We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly-binned light curves and for the long-term seasonally-binned light curve at the $> 3sigma$ level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (${chi^2/NDF = 7.89/6}$) by a power-law function with index $Gamma = 2.46 pm 0.06_{stat} pm 0.20_{sys} $ and extends to at least 8 TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit (${chi^2/NDF = 6.73/6}$) by a power-law function with index $Gamma = 2.15 pm 0.06_{stat} pm 0.20_{sys} $ while an F-test indicates that the power-law with exponential cutoff function provides a marginally-better fit ($chi^2/NDF $ = $2.56 / 5 $) at the 2.1$sigma$ level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source.
We present the first detection of the nearby (z=0.084) low-luminosity BL Lac object 1ES 1741+196 in the very high energy (VHE: E$>$100 GeV) band. This object lies in a triplet of interacting galaxies. Early predictions had suggested 1ES 1741+196 to be, along with several other high-frequency BL Lac sources, within the reach of MAGIC detectability. Its detection by MAGIC, later confirmed by VERITAS, helps to expand the small population of known TeV BL Lacs. The source was observed with the MAGIC telescopes between 2010 April and 2011 May, collecting 46 h of good quality data. These observations led to the detection of the source at 6.0 $sigma$ confidence level, with a steady flux $mathrm{F}(> 100 {rm GeV}) = (6.4 pm 1.7_{mathrm{stat}}pm 2.6_{mathrm{syst}}) cdot 10^{-12}$ ph cm$^{-2}$ s$^{-1}$ and a differential spectral photon index $Gamma = 2.4 pm 0.2_{mathrm{stat}} pm 0.2_{mathrm{syst}}$ in the range of $sim$80 GeV - 3 TeV. To study the broad-band spectral energy distribution (SED) simultaneous with MAGIC observations, we use KVA, Swift/UVOT and XRT, and Fermi/LAT data. One-zone synchrotron-self-Compton (SSC) modeling of the SED of 1ES 1741+196 suggests values for the SSC parameters that are quite common among known TeV BL Lacs except for a relatively low Doppler factor and slope of electron energy distribution. A thermal feature seen in the SED is well matched by a giant ellipticals template. This appears to be the signature of thermal emission from the host galaxy, which is clearly resolved in optical observations.
Motivated by the Costamante & Ghisellini (2002) predictions we investigated if the blazar 1ES 1727+502 (z=0.055) is emitting very high energy (VHE, E>100 GeV) gamma rays. We observed the BL Lac object 1ES 1727+502 in stereoscopic mode with the two MAGIC telescopes during 14 nights between May 6th and June 10th 2011, for a total effective observing time of 12.6 hours. For the study of the multiwavelength spectral energy distribution (SED) we use simultaneous optical R-band data from the KVA telescope, archival UV/optical and X-ray observations by instruments UVOT and XRT on board of the Swift satellite and high energy (HE, 0.1 GeV - 100 GeV) gamma-ray data from the Fermi-LAT instrument. We detect, for the first time, VHE gamma-ray emission from 1ES 1727+502 at a statistical significance of 5.5 sigma. The integral flux above 150 GeV is estimated to be (2.1pm0.4)% of the Crab Nebula flux and the de-absorbed VHE spectrum has a photon index of (2.7pm0.5). No significant short-term variability was found in any of the wavebands presented here. We model the SED using a one-zone synchrotron self-Compton model obtaining parameters typical for this class of sources.
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