| 1. |
- Abdo, A. A., et al.
(författare)
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Multiwavelength Monitoring of the Enigmatic Narrow-Line Seyfert 1 PMN J0948+0022 in 2009 March-July
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 707:1, s. 727-737
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Tidskriftsartikel (refereegranskat)abstract
- Following the recent discovery of γ rays from the radio-loud narrow-line Seyfert 1 galaxy PMN J0948+0022 (z = 0.5846), we started a multiwavelength campaign from radio to γ rays, which was carried out between the end of 2009 March and the beginning of July. The source displayed activity at all the observed wavelengths: a general decreasing trend from optical to γ-ray frequencies was followed by an increase of radio emission after less than two months from the peak of the γ-ray emission. The largest flux change, about a factor of about 4, occurred in the X-ray band. The smallest was at ultraviolet and near-infrared frequencies, where the rate of the detected photons dropped by a factor 1.6-1.9. At optical wavelengths, where the sampling rate was the highest, it was possible to observe day scale variability, with flux variations up to a factor of about 3. The behavior of PMN J0948+0022 observed in this campaign and the calculated power carried out by its jet in the form of protons, electrons, radiation, and magnetic field are quite similar to that of blazars, specifically of flat-spectrum radio quasars. These results confirm the idea that radio-loud narrow-line Seyfert 1 galaxies host relativistic jets with power similar to that of average blazars.
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| 2. |
- Keimpema, A., et al.
(författare)
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The SFXC software correlator for very long baseline interferometry: algorithms and implementation
- 2015
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 39:2, s. 259-279
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a description is given of the SFXC software correlator, developed and maintained at the Joint Institute for VLBI in Europe (JIVE). The software is designed to run on generic Linux-based computing clusters. The correlation algorithm is explained in detail, as are some of the novel modes that software correlation has enabled, such as wide-field VLBI imaging through the use of multiple phase centres and pulsar gating and binning. This is followed by an overview of the software architecture. Finally, the performance of the correlator as a function of number of CPU cores, telescopes and spectral channels is shown.
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| 3. |
- Alef, Walter, et al.
(författare)
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Geodetic data analysis of VGOS experiments
- 2021
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Ingår i: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021.
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Konferensbidrag (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth's orientation variations. The technical upgrade of the VLBI method known as the VLBI Global Observing System (VGOS) includes a critical re-design of the observed frequencies from the dual band mode (S and X band, i.e. 2 GHz and 8 GHz) to observations in a broadband (2-14 GHz). Since 2019 the first VGOS experiments are available for the geodetic analysis in free access at the International VLBI service for Geodesy and Astrometry (IVS). Also regional-only subnetworks such as European VLBI stations have succeeded already in VGOS mode. Based on these brand-new observations we review the current geodetic data analysis workflow to build a bridge between geodetic observed delays derived from different bands.
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| 4. |
- Lindqvist, Michael, 1960, et al.
(författare)
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Present status and technical directions of the EVN
- 2014
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- The European VLBI Network has evolved significantly during recent years. This has been made possible by the addition of new antennas, the introduction of the Mark 5 recording system and the emergence of high bandwidth optical fibre networks, the SFXC software correlator, and most recently, by the upgrade to digital backends at the stations. Here we describe the present status of the array and outline some of the planned future technical directions. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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| 5. |
- Szomoru, A, et al.
(författare)
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From tape reel to intercontinental lightpaths: Technical developments in the EVN
- 2013
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Ingår i: IEEE AFRICON Conference. - 2153-0025 .- 2153-0033. - 9781467359405 ; , s. Article no. 6757823-
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Konferensbidrag (refereegranskat)abstract
- This paper describes the recent developments in European Very Long Baseline Interferometry (VLBI), centered around the three themes of real-time e-VLBI, correlation and VLBI space science. © 2013 IEEE.
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