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Piikkiö, Finland

Colin P.,Max Planck Institute for Physics | Eisenacher D.,University of Wurzburg | Hildebrand D.,ETH Zurich | Lombardi S.,National institute for astrophysics | And 17 more authors.
AIP Conference Proceedings | Year: 2012

The Perseus cluster of galaxies is a nearby cool-core cluster with an intra-clustermedium (ICM) characterized by very high central densities. The observation of the Perseus cluster with the MAGIC telescopes, during 85 h from 2009 to 2011, resulted in the discovery of 2 point-like sources at very high energy (>100 GeV, VHE) coinciding with the central radio galaxy NGC1275 and the radio galaxy IC310. The γ-ray properties of these 2 sources are presented, taking into account contemporaneous Fermi-LAT as well as multi-wavelength data. Flux variability and spectral energy distribution shapes indicate that the VHE γ-rays do not originate from large-scale interaction of the radio galaxies with ICM but more likely from the active nuclei of these two galaxies. They could be both misaligned version of BL Lac objects, the most common TeV AGN. Our results provide vital clues to understand emission mechanisms of such misaligned objects, and how they may be related to the beamed emission seen in BL Lacs. No evidence of large-scale VHE γ-ray emission from hadronic cosmic ray (CR) interactions with the ICM has been found. The flux upper limit above 1 TeV reaches the signal expected by some theoretical models, constraining the cluster CR physics. In the framework of the hadronicmodel of the radiomini-halos, this limit implies aminimal magnetic field ranging from 4-9μG for the central cluster region. © 2012 American Institute of Physics. Source

Nevalainen J.,Tartu Observatory | Tempel E.,Tartu Observatory | Liivamagi L.J.,Tartu Observatory | Branchini E.,Third University of Rome | And 10 more authors.
Astronomy and Astrophysics | Year: 2015

We propose a new approach to the problem of the missing baryons. Building on the common assumption that the missing baryons are in the form of the warm hot intergalactic medium (WHIM), we also assume here that the galaxy luminosity density can be used as a tracer of the WHIM. This last assumption is supported by our discovery of a significant correlation between the WHIM density and the galaxy luminosity density in recent hydrodynamical simulations. We also found that the percentage of the gas mass in the WHIM phase is substantially higher (by a factor of ~1.6) within large-scale galactic filaments, i.e. ~70%, compared to the average in the full simulation volume of ~0.1 Gpc3. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with a linear one: δwhim = 0.7 ± 0.1 × δLD 0.9±0.2. We then applied our procedure to the line of sight towards the blazar H2356-309 and found evidence of WHIM that corresponds to the Sculptor Wall (SW) (z ~ 0.03 and log NH = 19.9+ 0.1 -0.3) and Pisces-Cetus (PC) superclusters (z ~ 0.06 and log NH = 19.7+ 0.2 -0.3), in agreement with the redshifts and column densities of the X-ray absorbers identified recently. This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust for estimating WHIM density. The signal that we detected cannot originate in the halos of nearby galaxies because they cannot account for the high WHIM column densities that our method and X-ray analysis consistently find in the SW and PC superclusters. © 2015 ESO. Source

Shi J.C.,Chinese Academy of Sciences | Ma Y.H.,Chinese Academy of Sciences | Zheng J.Q.,Tuorla Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

We presentphotometric investigations of three distant active comets, 228P/LINEAR, C/2006 S3 Lowell Observatory Near-Earth-Object Search (LONEOS) and 29P/Schwassmann-Wachmann 1. The data were obtained with the 1-m optical telescope at Lulin Observatory in Taiwan on 2011 February 5 and 6. These comets were observed at heliocentric distances larger than 3 au, all of them appeared to be active. By cometary morphological and photometric studies, the upper limits of the nuclei radii were derived. Also, the surface brightness profiles, Afρ parameters, mass production rates and the coma colours were measured. Finally, we discussed possible driver of activity in comets. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Bonamente M.,University of Alabama in Huntsville | Bonamente M.,NASA | Nevalainen J.,Tartu Observatory | Tilton E.,University of Colorado at Boulder | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We have analysed Chandra low energy transmission grating and XMM-Newton Reflection Grating Spectrometer (RGS) spectra towards the z = 0.177 quasar PG 1116+215, a sightline that is rendered particularly interesting by the Hubble Space Telescope (HST) detection of several OVI and HI broad Lyman a absorption (BLA) lines that may be associated with the warm-hot intergalactic medium (WHIM). We performed a search for resonance Kα absorption lines from OVII and OVIII at the redshifts of the detected far-ultraviolet lines.We detected an absorption line in the Chandra spectra at the 5.2σ confidence level at wavelengths corresponding to OVIII Kα at z = 0.0911 ± 0.0004 ± 0.0005 (statistical followed by systematic error). This redshift is within 3σ of that of an HI broad Lyman a of b ≃ 130 km s-1 (corresponding to a temperature of log T(K) ≃ 6.1) at z = 0.092 79 ± 0.000 05. We have also analysed the available XMM-Newton RGS data towards PG 1116+215. Unfortunately, the XMM-Newton data are not suitable to investigate this line because of instrumental features at the wavelengths of interest. At the same redshift, the Chandra and XMM-Newton spectra have OVII Kα absorption-line features of significance 1.5σ and 1.8σ, respectively.We also analysed the available Sloan Digital Sky Survey (SDSS) spectroscopic galaxy survey data towards PG 1116+215 in the redshift range of interest. We found evidence for a galaxy filament that intersect the PG 1116+215 sightline and additional galaxy structures that may host WHIM. The HI BLA and the OVIII Kα absorbers are within a few Mpc of the filament (assuming that redshifts track Hubble flow distances) or consistent with gas accreting on to the filament from either direction relative to the sightline with velocities of a few × 100 km s-1. The combination of HST, Chandra, XMM-Newton and SDSS data indicates that we have likely detected a multi-temperature WHIM at z ≃ 0.091-0.093 towards PG 1116+215. The OVIII Ka absorption line indicates gas at high temperature, log T(K) = 6.4, with a total column density of the order of log NH(cm2) = 20 and a baryon overdensity ξb ~ 100-1000 for sightline lengths of L = 1-10 Mpc. This detection highlights the importance of BLA absorption lines as possible signposts of high-temperature WHIM filaments. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Colin P.,Max Planck Institute for Physics | Gonzalez J.B.,Institute of Astrophysics of Canarias | Lindfors E.,Tuorla Observatory | Lombardi S.,University of Padua | Sitarek J.,University of Lodz
Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011 | Year: 2011

The two BL Lac objects 1ES 1215+303 and 1ES 1218+304, separated by 0.8°, were observed with the MAGIC telescopes in 2010 and 2011. The 20 hours of data registered in January 2011 resulted in the first detection at Very High Energy (>100 GeV) of 1ES 1215+303 (also known as ON-325). This observation was triggered by a high optical state of the source reported by the Tuorla blazar monitoring program. Comparison with the 25 hours of data carried out from January to May 2010 suggests that 1ES 1215+303 was flaring also in VHE gamma-rays in 2011. In addition, the Swift ToO observations in X-rays showed that the flux was almost doubled respect to previous observations (December 2009). Instead, 1ES 1218+304 is a well known VHE gamma-ray emitter lying in the same field of view, which was then simultaneously observed with the MAGIC telescopes. The overall observation time of nearly 45 hours has permitted to measure the spectrum of this source with a much higher precision than previously reported by MAGIC. Here, we present the results of the MAGIC and the multi-wavelength observations of these two VHE gamma-ray emitting AGNs. Source

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