Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that, in some cases, can harbor powerful relativistic jets. One of them, PKS 2004-447, shows γ -ray emission, and ...underwent its first recorded multifrequency flare in 2019. However, past studies revealed that in radio this source can be classified as a compact steep-spectrum source (CSS), suggesting that, unlike other γ -ray sources, the relativistic jets of PKS 2004-447 have a large inclination with respect to the line of sight. We present here a set of spectroscopic observations of this object, aimed at carefully measuring its black hole mass and Eddington ratio, determining the properties of its emission lines, and characterizing its long term variability. We find that the black hole mass is (1.5 ± 0.2)×10 7 M ⊙ , and the Eddington ratio is 0.08. Both values are within the typical range of NLS1s. The spectra also suggest that the 2019 flare was caused mainly by the relativistic jet, while the accretion disk played a minor role during the event. In conclusion, we confirm that PKS 2004-447 is one of the rare examples of γ -ray emitting CSS/NLS1s hybrid, and that these two classes of objects are likely connected in the framework of AGN evolution.
Abstract
We study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area ...Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. Nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at X-rays and very-high-energy (VHE)
γ
-rays. A significant correlation (>3
σ
) between X-rays and VHE
γ
-rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. This is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the Swift X-Ray Telescope and Fermi-LAT. We additionally find correlations between high-energy
γ
-rays and radio, with the radio lagging by more than 100 days, placing the
γ
-ray emission zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501 showed a historically low activity in X-rays and VHE
γ
-rays from mid-2017 to mid-2019 with a stable VHE flux (>0.2 TeV) of 5% the emission of the Crab Nebula. The broadband spectral energy distribution (SED) of this 2 yr long low state, the potential baseline emission of Mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from IceCube. We explore the time evolution of the SED toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock.
ABSTRACT
We report multiwavelength observations of the gravitationally lensed blazar QSO B0218+357 in 2016–2020. Optical, X-ray, and GeV flares were detected. The contemporaneous MAGIC observations ...do not show significant very high energy (VHE; ≳100 GeV) gamma-ray emission. The lack of enhancement in radio emission measured by The Owens Valley Radio Observatory indicates the multizone nature of the emission from this object. We constrain the VHE duty cycle of the source to be <16 2014-like flares per year (95 per cent confidence). For the first time for this source, a broad-band low-state spectral energy distribution is constructed with a deep exposure up to the VHE range. A flux upper limit on the low-state VHE gamma-ray emission of an order of magnitude below that of the 2014 flare is determined. The X-ray data are used to fit the column density of (8.10 ± 0.93stat) × 1021 cm−2 of the dust in the lensing galaxy. VLBI observations show a clear radio core and jet components in both lensed images, yet no significant movement of the components is seen. The radio measurements are used to model the source-lens-observer geometry and determine the magnifications and time delays for both components. The quiescent emission is modelled with the high-energy bump explained as a combination of synchrotron-self-Compton and external Compton emission from a region located outside of the broad-line region. The bulk of the low-energy emission is explained as originating from a tens-of-parsecs scale jet.
The market comes to education in Sweden Bjorklund, Anders; Clark, Melissa A; Edin, Per-Anders ...
Russell Sage Foundation,
2005, 20060109, 2006, 2006-01-00
eBook, Book
A large central government providing numerous public services has long been a hallmark of Swedish society, which is also well-known for its pursuit of equality. Yet in the 1990s, Sweden moved away ...from this tradition in education, introducing market-oriented reforms that decentralized authority over public schools and encouraged competition between private and public schools. Many wondered if this approach would improve educational quality, or if it might expand inequality that Sweden has fought so hard to hold down. In The Market Comes to Education in Sweden, economists Anders Björklund, Melissa Clark, Per-Anders Edin, Peter Fredriksson, and Alan Krueger measure the impact of Sweden's bold experiment in governing and help answer the questions that societies across the globe have been debating as they try to improve their children's education. The Market Comes to Education in Sweden injects some much-needed objectivity into the heavily politicized debate about the effectiveness of educational reform. While advocates for reform herald the effectiveness of competition in improving outcomes, others suggest that the reforms will grossly increase educational inequality for young people. The authors find that increased competition did help improve students' math and language skills, but only slightly, and with no effect on the performance of foreign-born students and those with low-educated parents. They also find some signs of increasing school segregation and wider inequality in student performance, but nothing near the doomsday scenarios many feared. In fact, the authors note that the relationship between family background and school performance has hardly budged since before the reforms were enacted. The authors conclude by providing valuable recommendations for school reform, such as strengthening school evaluation criteria, which are essential for parents, students, and governments to make competent decisions regarding education. Whether or not the market-oriented reforms to Sweden's educational system succeed will have far reaching implications for other countries considering the same course of action. The Market Comes to Education in Sweden offers firm empirical answers to the questions raised by school reform and brings crucial facts to the debate over the future of schooling in countries across the world.
Abstract
The author discusses and questions the settled approach relating to responsibility under international law for mixed agreements, i.e. agreements to which both the EC and all or some of its ...member states are parties. He concludes that the rosy picture prevailing in much of the literature may not be justified, and stresses the difficulties involved for third parties.
Minkowski’s First Theorem and Dirichlet’s Approximation Theorem provide upper bounds on certain minima taken over lattice points contained in domains of Euclidean spaces. We study the distribution of ...such minima and show, under some technical conditions, that they exhibit Weibull asymptotics with respect to different natural measures on the space of unimodular lattices in \mathbb {R}^d. This follows from very general Poisson approximation results for shrinking targets which should be of independent interest. Furthermore, we show in the appendix that the logarithm laws of Kleinbock-Margulis Invent. Math. 138 (1999), pp. 451–494, Khinchin and Gallagher J. London Math. Soc. 37 (1962), pp. 387–390 can be deduced from our distributional results.
Structural design of pressure pipes Bjorklund, I
Water Science & Technology: Water Supply,
01/2001, Volume:
1, Issue:
3
Journal Article, Conference Proceeding
Peer reviewed
There exist various methods for structural design of buried pressure pipes. However, it must be remembered that sophisticated design methods needs a significant supervision of the construction work ...to be reliable. The need for detailed calculations varies for different materials. Ductile iron (DCI) pipes have high strength properties and for most DCI pipe installations a design check against EN 545 is fully sufficient as regards the structural design. Glass fibre reinforced polyester (GRP) pipes have a limited strainability and are thus highly dependent on the quality of the installation work. It is recommendable to check that the combined strain of the load cases which the pipe shall be designed for does not exceed the allowable strain for the pipe material. Polyethylene (PE) and Polyvinylchloride (PVC) pipes are flexible pipes with a high strainability. The allowable working pressure for these pipes will normally be determined by the PN class and the operating temperature and the need for structural design calculations is limited. It is interesting to note that PE pipes which have the lowest strength properties of all of the above mentioned materials have the lowest failure rate. The latter shows that it is not just the tensile strength, but other factors such as strainability and corrosion resistance which affect the structural performance of buried pipelines.
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