1,849 research outputs found
G. Rowell. Hell and theVictorians. A Study of the nineteenth century theological controversies concerning eternal punishment and the future life
No full textCrépin André. G. Rowell. Hell and theVictorians. A Study of the nineteenth century theological controversies concerning eternal punishment and the future life. In: Revue de l'histoire des religions, tome 190, n°1, 1976. p. 105
Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS2155-304 in July 2006
No full textSimultaneous HESS/CHANDRA/optical observations were performed on the BL Lac object PKS 2155-304 in the night of July 29-30 2006, when the source underwent its second major gamma-ray outburst in Summer 2006. This event took place about 44 hours after the July 28 outburst, known for its ultrafast variability. An unprecedented 6 to 8 hours of uninterrupted coverage was achieved, with spectra and light curves measured down to 7 and 2-minute timescales, respectively. The gamma-ray flux reached a maximum of 11x the Crab flux (>400 GeV), with rise/decay timescales of ~1 hour, plus a few smaller-amplitude flares superimposed on the decaying phase. The emission in the X-ray and VHE bands is strongly correlated, both in flux and spectrum, with no evidence of lags. The VHE spectrum shows a curvature that is variable with time and stronger at higher fluxes. The huge VHE variations (22x) are only accompanied by small-amplitude X-ray and optical variations (factor 2 and 15% respectively). The source has shown for the first time in an HBL a large Compton dominance (L_C/L_S ~10) -- rapidly evolving -- and a cubic relation between VHE and X-ray flux variations, during a decaying phase. These results challenge the common scenarios for the TeV-blazar emission.F. Aharonian...G. Rowell...and A. Zech et al.(HESS Collaboration
G. Rowell. Hell and theVictorians. A Study of the nineteenth century theological controversies concerning eternal punishment and the future life
No full textCrépin André. G. Rowell. Hell and theVictorians. A Study of the nineteenth century theological controversies concerning eternal punishment and the future life. In: Revue de l'histoire des religions, tome 190, n°1, 1976. p. 105
Discovery of VHE gamma-rays from the distant BL Lacertae 1ES 0347-121
No full textAims. Our aim is to study the production mechanism for very-high-energy (VHE; > 100 GeV) γ-rays in distant active galactic nuclei (AGN) and use the observed VHE spectrum to derive limits on the Extragalactic Background Light (EBL). We also want to determine physical quantities through the modeling of the object's broad-band spectral energy distribution (SED). Methods. VHE observations (∼25 h live time) of the BL Lac 1ES 0347-121 (redshift z = 0.188) were conducted with the High Energy Stereoscopic System (HESS) between August and December 2006. Contemporaneous X-ray and UV/optical observations from the SWIFT satellite are used to interpret the SED of the source in terms of a synchrotron self Compton (SSC) model. Results. An excess of 327 events, corresponding to a statistical significance of 10.1 standard deviations, is detected from 1ES 0347-121. Its photon spectrum, ranging from ∼250GeV to ∼3TeV, is well described by a power law with a photon index of Γ = 3.10 ± 0.23stat ± 0.10sys. The integral flux above 250 GeV corresponds to ∼2% of the flux of the Crab Nebula above the same threshold. No VHE flux variability is detected within the data set. Conclusions. Constraints on the EBL density at optical to near-infrared wavelengths derived from the photon spectrum of 1ES 0347-121 are close to the strongest limits derived previously. The strong EBL limits confirm earlier findings, that the EBL density in the near-infrared is close to the lower limits from source counts. This implies that the universe is more transparent to VHE γ-rays than previously believed. An SSC model provides a reasonable description of the contemporaneous SED. © ESO 2007.F. Aharonian...G. Rowell... et al
First deployment and prototype data of HiSCORE
No full textWith the HiSCORE (Hundred*i Square kilometer Cosmic ORigin Explorer) experiment we aim at the exploration of the accelerator sky using indirect air shower observations of cosmic rays from 100 TeV to 1 EeV and gamma rays above 10 TeV to several PeV. In this paper the HiSCORE detector is discribed and the results of the first prototype deployment are shown. Several components are discussed like the photomultiplier tubes, the clip-sum-trigger and the DRS4 based data acquisition. We present data taken with a first prototype station in April 2012 at Tunka.R Nachtigall... G P Rowell... et al
Discovery of VHE gamma-rays from the BL Lacertae object PKS 0548-322
No full textAims. PKS 0548-322 (z = 0.069) is a "high-frequency-peaked" BL Lac object and a candidate very high energy (VHE, E > 100 GeV) γ-ray emitter, due to its high X-ray and radio flux. Observations at the VHE band provide insights into the origin of very energetic particles present in this source and the radiation processes at work. Methods. We report observations made between October 2004 and January 2008 with the HESS array, a four imaging atmospheric-Cherenkov telescopes. Contemporaneous UV and X-ray observations with the Swift satellite in November 2006 are also reported. Results. PKS 0548-322 is detected for the first time in the VHE band with HESS We measure an excess of 216 γ-rays corresponding to a significance of 5.6 standard deviations. The photon spectrum of the source is described by a power-law, with a photon index of Γ = 2.86 ± 0.34stat ± 0.10 sys. The integral flux above 200 GeV is ∼1.3% of the flux of the Crab Nebula, and is consistent with being constant in time. Contemporaneous Swift/XRT observations reveal an X-ray flux between 2 and 10 keV of F 2-10 keV = (2.3±0.2)×10-11 erg cm -2 s-1, an intermediate intensity state with respect to previous observations. The spectral energy distribution can be reproduced using a simple one-zone synchrotron self Compton model, with parameters similar those observed for other sources of this type. © 2010 ESO.F. Aharonian... B. Nicholas... G. Rowell... et al
PKS2005-489 at VHE: four years of monitoring with HESS and simultaneous multi-wavelength observations
No full textVHE observations of PKS 2005-489 were made with HESS from 2004 through 2007, together with three simultaneous multi-wavelength campaigns performed with XMM-Newton and RXTE in 2004 and 2005. A strong VHE signal, ~17sigma total, is detected during the four years of HESS observations (90.3 hrs live time). The integral flux above the average analysis threshold of 400 GeV is ~3% of the Crab and varies weakly on time-scales from days to years. At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (DeltaGamma~0.7) are also observed, which appear to be mirrored in the VHE band. The SED of PKS 2005-489, constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005.F. Acero, B. Nicholas, G. Rowell,...and et al, and H.E.S.S. Collaboration
The sensitivity of the CANGAROO I analyses of the Crab and Vela plerions to image selection cuts
No full textCopyright © 2001 Elsevier Science B.V. All rights reserved.Observations of the Crab nebula from 1996 to 1998 and the Vela synchrotron nebula during 1997, made with the recoated CANGAROO 3.8 m imaging Čerenkov telescope at Woomera, South Australia, have been analysed using the results from new MOCCA simulations (Dazeley and Patterson, paper I). Our analyses do not reproduce the previously published levels of emission from the Vela and Crab plerions, and we discuss the possible reasons, including a sensitivity of the results to the cuts used. The 3σ upper limits derived from these observations are 2.5×10-12 photonscm-2s-1 above ˜2.7 TeV for Vela and 9.3×10-13 photonscm-2s-1 above ˜12 TeV for the Crab. © 2001 Elsevier Science B.V.S. A. Dazeley, J. R. Pattersona, G. P. Rowell and P. G. Edwardshttp://www.elsevier.com/wps/find/journaldescription.cws_home/523319/description#descriptio
A new template background estimate for source searching in TeV gamma-ray astronomy
No full textA new method is described that permits quickly and easily, a 2-dimensional search for TeV -ray sources over large fields of view ( 6 ) with instruments utilising the imaging atmospheric ˇCerenkov technique. It employs as a background estimate, events normally rejected according to a cosmic-ray background rejection criterion based on image shape, but with reconstructed directions overlapping the source of interest. This so-called template background model is demonstrated using example data taken with the stereoscopic HEGRA System of ˇC erenkov Telescopes. Discussion includes comparisons with a conventional background estimate and limitations of the model. The template model is well suited to the search for point-like, moderately extended sources and combinations thereof, and compensates well for localised systematic changes in cosmic-ray background responseG. P. Rowellhttp://www.aanda.org/content/view/98/102/lang,en
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