HESS observations and VLT spectroscopy of PG 1553+113

Aharonian, F.; Akhperjanian, A. G.; Almeida, U. Barres de; Bazer‐Bachi, A. R.; Behera, B.; Beilicke, M.; Benbow, W.; Bernlöhr, K.; Boisson, C.; Bolz, O.; Borrel, V.; Braun, I.; Brion, E.; Brown, A. M.; Bühler, R.; Bulik, T.; Büsching, I.; Boutelier, T.; Carrigan, S.; Chadwick, P. M.; Chounet, L.‐M.; Clapson, A. C.; Coignet, G.; Cornils, R.; Costamante, L.; Dalton, M.; Degrange, B.; Dickinson, H. J.; Djannati‐Ataï, A.; Domainko, W.; Drury, L. O’c.; Dubois, F.; Dubus, G.; Dyks, J.; Egberts, K.; Emmanoulopoulos, D.; Espigat, P.; Farnier, C.; Feinstein, F.; Fiaßon, A.; Förster, A.; Fontaine, G.; Funk, S.; Fusling, M.; Gallant, Y. A.; Giebels, B.; Glicenstein, J. F.; Glück, B.; Goret, P.; Hadjichristidis, C.; Hauser, D.; Hauser, M.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hoffmann, A.; Hofmann, W.; Holleran, M.; Hoppe, S.; Horns, D.; Jachołkowska, A.; Jager, O. C. de; Jung, I.; Katarzyński, K.; Kendziorra, E.; Kerschhaggl, M.; Khélifi, B.; Keogh, D.; Komin, Nu.; Kosack, K.; Lamanna, G.; Latham, I. J.; Lemière, A.; Lemoine‐Goumard, M.; Lenain, J.‐P.; Löhse, T.; Martin, Jean‐Michel; Martineau‐Huynh, O.; Marcowith, A.; Masterson, C.; Maurin, D.; Maurin, G.; McComb, T. J. L.; Moderski, R.; Moulin, Emmanuel; Naurois, M. de; Nedbal, D.; Nolan, S. J.; Ohm, S.; Olive, J.-P.; Oña-Wilhelmi, E.; Orford, K. J.; Osborne, J. L.; Ostrowski, M.; Panter, M.; Pedaletti, G.; Pelletier, G.; Petrucci, P.-O.; Pita, S.; Pühlhofer, G.; Punch, M.; Ranchon, S.; Raubenheimer, Britt; Raue, M.; Rayner, S. M.; Renaud, M.; Ripken, J.; Rob, L.; Rolland, L.; Rosier‐Lees, S.; Rowell, G.; Rudak, B.; Ruppel, J.; Sahakian, V.; Santangelo, A.; Schlickeiser, R.; Schöck, F. M.; Schröder, R.; Schwanke, U.; Schwarzburg, S.; Schwemmer, S.; Shalchi, A.; Sol, H.; Spangler, D.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Superina, G.; Tam, P. H. T.; Tavernet, J.‐P.; Terrier, R.; Eldik, C. van; Vasileiadis, G.; Venter, C.; Vialle, J. P.; Vincent, P.; Vivier, M.; Völk, H. J.; Volpe, F.; Wagner, S. J.; Ward, M. J.; Zdziarski, A. A.; Zech, A.

doi:10.1051/0004-6361:20078603

Cited by 47 publications

(54 citation statements)

References 27 publications

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“…The imaging atmospheric Cherenkov telescope array, VERITAS, is capable of detecting PG 1553+113 above 100 GeV with a significance of 5σ after ∼43 minutes of observations, given its average flux. Previous measurements of PG 1553+113, made by H.E.S.S., yielded a time-averaged VHE spectral index Γ (refers to photon spectrum dN/dE ∝ E −Γ ) of 4.46 ± 0.34 between 225 GeV and 1.3 TeV (Aharonian et al 2008), consistent with measurements by MAGIC (Albert et al 2007). The Fermi-LAT 2 Year Catalog reports the spectral index between 100 MeV and 100 GeV to be 1.67 ± 0.02 (Nolan et al 2012).…”

Section: Introductionsupporting

confidence: 77%

Veritas Observations of the Bl Lac Object Pg 1553+113

Aliu

Archer

Aune

et al. 2015

ApJ

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We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560 GeV, is well described by a power law with a spectral index of 4.33 ± 0.09. The time-averaged integral flux above 200 GeV measured for this period was (1.69 ± 0.06) × 10 −11 photons cm −2 s −1 , corresponding to 6.9% of the Crab Nebula flux. We also present the combined γ -ray spectrum from the Fermi Large Area Telescope and VERITAS covering an energy range from 100 MeV to 560 GeV. The data are well fit by a power law with an exponential cutoff at 101.9 ± 3.2 GeV. The origin of the cutoff could be intrinsic to PG 1553+113 or be due to the γ -ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of z > 0.395 based on optical/UV observations of PG 1553+113, the cutoff would be dominated by EBL absorption. Conversely, the small statistical uncertainties of the VERITAS energy spectrum have allowed us to provide a robust upper limit on the redshift of PG 1553+113 of z 0.62. A strongly elevated mean flux of (2.50±0.14)×10−11 photons cm −2 s −1 (10.3% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as (4.44±0.71)×10−11 photons cm −2 s −1(18.3% of the Crab Nebula flux) on MJD 56048. The light curve measured during the 2012 observing season is marginally inconsistent with a steady flux, giving a χ 2 probability for a steady flux of 0.03%.

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Section: Introductionsupporting

confidence: 77%

Veritas Observations of the Bl Lac Object Pg 1553+113

Aliu

Archer

Aune

et al. 2015

ApJ

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“…II mono spectral results are in reasonable agreement with the earlier measurements by H.E.S.S. (Aharonian et al 2008;Abramowski et al 2015) (at E > 200 GeV), MAGIC (Albert et al 2007;Aleksić et al 2010Aleksić et al , 2012b and VERITAS (Aliu et al 2015), as well as with the Fermi-LAT catalogue spectra (at E < 200 GeV). These comparisons with previous measurements indicate that PG 1553+113 was indeed in a low state during the H.E.S.S.…”

Section: Variabilitysupporting

confidence: 89%

“…The H.E.S.S. I measurements (Aharonian et al 2008) yielded a photon index Γ = 4.5 ± 0.3 stat ± 0.1 syst above 225 GeV. At high energies Send offprint requests to: H.E.S.S.…”

Section: Introductionmentioning

confidence: 99%

Gamma-ray blazar spectra with H.E.S.S. II mono analysis: The case of PKS 2155−304 and PG 1553+113

Abdalla

Abramowski

Aharonian

et al. 2017

A&A

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Context. The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity to lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies below 100 GeV for small zenith angle observations. Such an extension of the instrument's energy range is particularly beneficial for studies of Active Galactic Nuclei (AGNs) with soft spectra, as expected for those at a redshift ≥ 0.5. The high-frequency peaked BL Lac objects PKS 2155−304 (z = 0.116) and PG 1553+113 (0.43 < z < 0.58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E > 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL). Aims. This work is directed toward a twofold aim: to demonstrate the monoscopic analysis of CT5 data with a low energy threshold, and to obtain accurate measurements of the spectral energy distributions (SED) of PKS 2155−304 and PG 1553+113 near their SED peaks at energies ≈ 100 GeV. Methods. Multiple observational campaigns of PKS 2155−304 and PG 1553+113 were conducted during 2013 and 2014 using the full H.E.S.S. II instrument (CT1-5). A monoscopic analysis of the data taken with the new CT5 telescope was developed along with an investigation into the systematic uncertainties on the spectral parameters which are derived from this analysis. Results. Using the data from CT5, the energy spectra of PKS 2155−304 and PG 1553+113 were reconstructed down to conservative threshold energies of 80 GeV for PKS 2155−304, which transits near zenith, and 110 GeV for the more northern PG 1553+113. The measured spectra, well fitted in both cases by a log-parabola spectral model (with a 5.0 σ statistical preference for non-zero curvature for PKS 2155−304 and 4.5 σ for PG 1553+113), were found consistent with spectra derived from contemporaneous Fermi-LAT data, indicating a sharp break in the observed spectra of both sources at E ≈ 100 GeV. When corrected for EBL absorption, the intrinsic H.E.S.S. II mono and Fermi-LAT spectrum of PKS 2155−304 was found to show significant curvature. For PG 1553+113, however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties.

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“…In fact, no significant spectral variability is observed in VHE bands. For example, PG 1553+113 has many VHE observations (Aharonian et al 2006b(Aharonian et al , 2008Albert et al 2007f, 2009, and its photon index is very similar as observed by HESS and MAGIC (Abdo et al 2010a). For PKS 2155-304, no significant spectral variability appears despite flux variation with a factor of two (Aharonian et al 2009).…”

Section: Resultsmentioning

confidence: 70%

Constraining extragalactic background light from TeV blazars

Yang

Wang

2010

A&A

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Aims. Our goal is to research the upper limits to the extragalactic background light (EBL). Methods. The upper limits to the extragalactic background light (EBL) are presented, using the Fermi and very high energy (VHE) spectra recently observed in TeV blazars. We use an assumption that the VHE intrinsic photon index cannot be harder than the Fermi index measured by the Fermi-LAT. Results. These upper limits are compatible with ones given by most EBL models; however, the models of high EBL density are contradicted by TeV blazars.

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HESS observations and VLT spectroscopy of PG 1553+113

Cited by 47 publications

References 27 publications

Veritas Observations of the Bl Lac Object Pg 1553+113

Veritas Observations of the Bl Lac Object Pg 1553+113

Gamma-ray blazar spectra with H.E.S.S. II mono analysis: The case of PKS 2155−304 and PG 1553+113

Constraining extragalactic background light from TeV blazars

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