Correlation between<i>Fermi</i>/LAT gamma-ray and 37 GHz radio properties of northern AGN averaged over 11 months

Nieppola, E.; Tornikoski, M.; Valtaoja, E.; Hovatta, T.; Lähteenmäki, A.; Tammi, J.

doi:10.1051/0004-6361/201116818

Cited by 29 publications

(32 citation statements)

References 38 publications

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“…Our results have shown that the non-detection of γ-ray is most likely related to lower intrinsic radio core flux, which originated in the jet synchrotron emission. The close realtions of γ-ray to radio emission may support the view of Nieppola et al (2011) that γ-rays are produced cospatially with the arcsecond-scale radio core radiation, indicating that the γ-ray is probably produced mainly through the SSC process in our sample.…”

Section: The Radio Core Flux and γ-Ray Detection Of Bl Lacssupporting

confidence: 81%

“…Typically, the ERC scenario requires that the inverse Compton (IC) radiation, i.e., γ-rays, originate relatively close to center, within the central parsec, while SSC γ-rays come from jets beyond a parsec's distance (Nieppola et al 2011). Our results have shown that the non-detection of γ-ray is most likely related to lower intrinsic radio core flux, which originated in the jet synchrotron emission.…”

Section: The Radio Core Flux and γ-Ray Detection Of Bl Lacsmentioning

confidence: 66%

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Why are some BL Lacertaes detected byFermi, but others not?

Jiang

et al. 2014

A&A

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By cross-correlating an archival sample of 170 BL Lacs with a 2 year Fermi/LAT AGN sample, we have compiled a sample of 100 BL Lacs with Fermi detection (FBLs) and a sample of 70 non-Fermi BL Lacs (NFBLs). We compared various parameters of FBLs with those of NFBLs, including the redshift, the low-frequency radio luminosity at 408 MHz (L 408 MHz ), the absolute magnitude of host galaxies (M host ), the polarization fraction from the NVSS survey (P NVSS ), the observed arcsecond scale radio core flux at 5 GHz (F core ), and the jet Doppler factor. All these parameters are directly measured or derived from available data in the literature. We found that the Doppler factor is on average greater in FBLs than in NFBLs, and the Fermi γ-ray detection rate is higher in sources with higher Doppler factor. In contrast, there are no significant differences in terms of the intrinsic parameters of redshift, L 408 MHz , M host , and P NVSS . FBLs seem to have a higher probability of exhibiting measurable proper motion. These results strongly indicate a stronger beaming effect in FBLs compared to NFBLs. The radio core flux is found to be strongly correlated with γ-ray flux, which remains after excluding the common dependence of the Doppler factor. At the fixed Doppler factor, FBLs have systematically larger radio core flux than NFBLs, implying lower γ-ray emission in NFBLs since the radio and γ-ray flux are significantly correlated. Our results indicate that the Doppler factor is an important parameter of γ-ray detection, that the non-detection of γ-ray emission in NFBLs is probably due to low beaming and/or low intrinsic γ-ray flux, and the γ-rays are very likely produced cospatially with the arcsecond-scale radio core radiation and mainly through the SSC process.

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Section: The Radio Core Flux and γ-Ray Detection Of Bl Lacssupporting

confidence: 81%

Section: The Radio Core Flux and γ-Ray Detection Of Bl Lacsmentioning

confidence: 66%

Why are some BL Lacertaes detected byFermi, but others not?

Jiang

et al. 2014

A&A

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“…The observed radio flare may be a manifestation of it. A delay of the radio flare by four months, with respect to the gamma-ray precursor, is in line with the fact that the radio variability of blazars generally lags the gamma-ray variability by one to eight months (e.g., Lähteenmäki & Valtaoja 2003;Pushkarev et al 2010;Nieppola et al 2011;Leon-Tavares et al 2012). Theoretically, the optical-depth effect should lead to a ν −1 dependence of the time lag, as the core remains optically thick to synchrotron self-absorption up to a distance (from the black hole) r c ∝ ν −1 (Blandford & Königl 1979).…”

Section: Discussionsupporting

confidence: 61%

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

Arlen¹,

Aune²,

Beilicke³

et al. 2012

ApJ

Self Cite

100

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We report on the detection of a very rapid TeV gamma-ray flare from BL Lacertae on 2011 June 28 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The flaring activity was observed during a 34.6 minute exposure, when the integral flux above 200 GeV reached (3.4 ± 0.6) × 10 −6 photons m −2 s −1 , roughly 125% of the Crab Nebula flux measured by VERITAS. The light curve indicates that the observations missed the rising phase of the flare but covered a significant portion of the decaying phase. The exponential decay time was determined to be 13 ± 4 minutes, making it one of the most rapid gamma-ray flares seen from a TeV blazar. The gamma-ray spectrum of BL Lacertae during the flare was soft, with a photon index of 3.6 ± 0.4, which is in agreement with the measurement made previously by MAGIC in a lower flaring state. component from the core around the time of the TeV gamma-ray flare, accompanied by changes in the optical polarization angle. Changes in flux also appear to have occurred at optical, UV, and GeV gamma-ray wavelengths at the time of the flare, although they are difficult to quantify precisely due to sparse coverage. A strong flare was seen at radio wavelengths roughly four months later, which might be related to the gamma-ray flaring activities. We discuss the implications of these multiwavelength results.

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“…A correlation between these two bands has also been found in (e.g. Kovalev et al 2009;Nieppola et al 2011) for larger samples of blazars.…”

Section: Radio Versus Mid-infraredsupporting

confidence: 57%

Empirical multi-wavelength prediction method for Very High Energy Gamma-ray emitting BL Lacs

2016

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Aim:We have collected the most complete multi-wavelength (6.0 − 6.0 × 10 −18 cm) dataset of very high energy (VHE) γ-ray emitting (TeV) BL Lacs, which are the most numerous extragalactic VHE sources. Using significant correlations between different bands, we aim to identify the best TeV BL Lac candidates that can be discovered by the current and next generation of imaging air Cherenkov telescopes. Methods: We formed five datasets from lower energy data, i.e. radio, mid-infrared, optical, X-rays, and GeV γ-ray, and five VHE γ-ray datasets to perform a correlation study between different bands and to construct the prediction method. The low energy datasets were averaged for individual sources, while the VHE γ-ray data were divided into subsets according to the flux state of the source. We then looked for significant correlations and determined their best-fit parameters. Using the best-fit parameters we predicted the level of VHE γ-ray flux for a sample of 182 BL Lacs, which have not been detected at TeV energies. We identified the most promising TeV BL Lac candidates based on the predicted VHE γ-ray flux for each source. Results: We found 14 significant correlations between radio, mid-infrared, optical, γ-ray, and VHE γ-ray bands. The correlation between optical and VHE γ-ray luminosity is established for the first time. We attribute this to the more complete sample and more accurate handling of host galaxy flux in our work. We found nine BL Lac candidates whose predicted VHE γ-ray flux is high enough for detection in less than 25 hours with current imaging air Cherenkov telescopes.

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Correlation betweenFermi/LAT gamma-ray and 37 GHz radio properties of northern AGN averaged over 11 months

Cited by 29 publications

References 38 publications

Why are some BL Lacertaes detected byFermi, but others not?

Why are some BL Lacertaes detected byFermi, but others not?

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

Empirical multi-wavelength prediction method for Very High Energy Gamma-ray emitting BL Lacs

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