Filaments in the southern giant lobe of Centaurus A : Constraints on nature and origin from modelling and GMRT observations

Date of acceptance: 22/05/2014We present results from imaging of the radio filaments in the southern giant lobe of CentaurusA using data from Giant Metrewave Radio Telescope observations at 325 and 235 MHz, and outcomes from filament modelling. The observations reveal a rich filamentary structure, largely matching the morphology at 1.4 GHz. We find no clear connection of the filaments to the jet. We seek to constrain the nature and origin of the vertex and vortex filaments associated with the lobe and their role in high-energy particle acceleration. We deduce that these filaments are at most mildly overpressuredwith respect to the global lobe plasma showing no evidence of largescale efficient Fermi I-type particle acceleration, and persist for ~2-3 Myr. We demonstrate that the dwarf galaxy KK 196 (AM 1318-444) cannot account for the features, and that surface plasma instabilities, the internal sausage mode and radiative instabilities are highly unlikely. An internal tearing instability and the kink mode are allowed within the observational and growth time constraints and could develop in parallel on different physical scales. We interpret the origin of the vertex and vortex filaments in terms of weak shocks from transonic magnetohydrodynamical turbulence or from a moderately recent jet activity of the parent AGN, or an interplay of both.Peer reviewe

Ruoppausmassan stabilointi uusiosideaineilla – Hiilijalanjäljen, lujuuden ja kustannusten tarkastelu Matalahden kenttäkokeessa

Maan stabilointi mahdollistaa pehmeiden maiden lujittamisen rakentamiseen soveltuvaksi. Samalla voidaan sitoa haitallisia aineita ja hillitä esimerkiksi haponmuodostusta rikkipitoisissa maa-aineksissa. Tyypillisesti stabilointiin on käytetty sementtiä. Sen valmistamisesta aiheutuu kuitenkin paljon hiilidioksidipäästöjä ja maankäytön muutoksia. Stabilointiin voidaan käyttää teollisuuden sivuvirtoja, myös sellaisia sideaineita, joita päätyy nykyisin kaatopaikoille. Tämä CircVol2-projektin osahankkeen raportti tarkastelee ruoppausmassojen stabilointia käytettyjen sideaineiden ilmastopäästöjen, saavutetun lujuuden ja sideaineiden kustannusten suhteen. Laskennan kohteena oleva stabiloinnin kenttäkoe sekä ruoppaus ja läjitys suoritettiin Naantalin Matalahdella vuonna 2020. Tällöin tehtiin kenttäkokeena stabilointikoeruutuja, joissa testattiin eri sideaineseoksia. Käytettyjä sideaineita olivat sementti, masuunikuona, monipolttolaitoksen tuhka, jätteenpolton pohjakuona, kalkinpolton uunipöly ja kahden yrityksen tekemät seokset. Maata on mahdollista stabiloida riittävän lujaksi käyttämällä teollisuuden jäte- ja sivuvirtoja osana stabilointiseosta ja vähentää samalla huomattavasti ilmastopäästöjä ja säästää kustannuksissa verrattuna stabilointiin pelkällä sementillä. Tämän hankkeen sideaineseoksia käyttämällä raaka-aineiden kustannukset voitiin pudottaa kolmannekseen ja päästöjen määrä kymmenykseen sementtipainotteisiin seoksiin verrattuna. Johtopäätöksenä voidaan sanoa, että maan stabiloinnissa on mahdollista hyödyntää jäte- ja sivuvirtoja. Samalla voidaan vähentää merkittävästi ilmastopäästöjä ja kustannuksia, mutta silti saavuttaa riittäviä lujuuksia. Työn osuus päästöistä ja kustannuksista voi olla merkittävä, kuljetusten harvemmin. Päästöjen ja kustannusten suhteen optimaalinen sideaine tai sideaineseos tulee valita tapauskohtaisesti. Kaupungistumisen jatkuessa ja rakentamisen laajentuessa kohteille, joiden maaperiä pitää stabiloida, on mahdollista löytää kustannustehokkaita ja ilmastoa merkittävästi vähemmän kuormittavia vaihtoehtoja ja samanaikaisesti edistää kiertotaloutta. Stabilization of dredged marine sediments with sustainable binders – Examination of carbon footprint, compressive strength, and costs in Matalahti field test Soil stabilization makes it possible to solidify soft soils for construction. At the same time, harmful substances can be bound and, for example, acid formation in sulphur-containing soils can be controlled. Cement has typically been used for stabilization. However, its production causes a lot of carbon dioxide emissions and involves changes in land use. Industrial waste and side streams can be used for stabilization, including binders that currently end up in landfills. This subproject report of the CircVol2 project examines the stabilization of dredged material in terms of greenhouse gas emissions, achieved strength, and costs of the binders. The stabilization field test, dredging, and disposal, which are the subject of the calculation, were performed in Matalahti, Naantali, in 2020. The field test was performed in different experimental plots, in which different binder mixtures were tested. The binders used were cement, blast furnace slag, ash from a co-fired combined heat and power plant, bottom ash from municipal waste incineration, lime kiln dust, and ready mixtures from two commercial companies. It is possible to stabilize the soil to sufficient strength by using industrial waste and side streams as part of the stabilization mix, while significantly reducing climate emissions and costs compared to stabilization with cement alone. With the binder mixtures of this project, the cost of raw materials could be reduced by a third and the amount of emissions by a tenth compared to cement-based mixtures. In conclusion, it is possible to utilize industrial waste and side streams for soil stabilization. This can significantly reduce greenhouse gas emissions and costs, while still achieving sufficient strength. The labour’s share of emissions and costs can be significant, while transport often plays a minor role. The optimal binder or binder mixture in terms of emissions and costs should be chosen on a case-by-case basis. As urbanization continues and construction expands to sites that need soil stabilization, it will be possible to find cost-effective alternatives with significantly less impact on the climate, while promoting circular economy. Stabilisering av muddringsmassa med hållbara bindemedel – Undersökning av koldioxidavtryck, tryckhållfasthet och kostnad för fälttestet i Matalahti Markstabilisering gör det möjligt att förstärka mjuka jordar som grund för byggande. Samtidigt kan skadliga ämnen bindas och till exempel syrabildning i svavelhaltiga jordar kan kontrolleras. Cement har vanligtvis använts för stabilisering. Dess produktion släpper dock ut mycket koldioxid och orsakar även förändrad markanvändning. Industriella biprodukter kan användas för stabilisering, inklusive material som idag hamnar på deponier. Att använda dessa material som ersättning för cement främjar cirkulär ekonomi och minimerar miljöpåverkan. Denna rapport undersöker CircVol2-projektet som en fallstudie i termer av klimatutsläpp, uppnådd tryckhållfasthet och bindemedelskostnader för bindemedel som används för att stabilisera muddermassor. Fältförsöket med stabilisering, som är föremål för beräkningen, utfördes i Matalahti, Nådendal, år 2020. Fältförsöket hade olika provrutor, i vilka olika bindemedelsrecept undersöktes. Bindemedlen som användes var cement, masugnsslagg, aska från flerbränslekraftverk, bottenaska från avfallsförbränning, kalkugnsdamm samt färdiga blandningar från två kommersiella företag. Det är möjligt att stabilisera marken tillräckligt stark genom att använda industriavfall och biproduktströmmar som en del av stabiliseringsmixen. Samtidigt reduceras klimatutsläppen och kostnadsbesparingar avsevärt jämfört med stabilisering med enbart cement. Med bindemedelsblandningarna i detta projekt skulle kostnaden för råvaror kunna minskas med en tredjedel och mängden utsläpp med en tiondel jämfört med cementvägda blandningar. Undersökningens slutsatser visar att det är möjligt att kunna utnyttja avfalls- och biproduktströmmar för att stabilisera lermassor. Samtidigt som klimatutsläppen och kostnaderna minskar avsevärt, kan man ändå uppnå tillräckliga tryckhållfastheter. Arbetskraftens andel av utsläpp och kostnader kan vara betydande, medan transporterna ofta spelar en mindre roll. Det optimala bindemedlet eller bindemedelsblandningen vad gäller utsläpp och kostnader bör väljas från fall till fall. I takt med att urbaniseringen fortsätter och byggandet utökas på platser som behöver markstabiliseras, är det möjligt att hitta kostnadseffektiva och betydligt mindre klimatförstörande alternativ samtidigt som man främjar en cirkulär ekonomi

Discovery of a Nova-Like Cataclysmic Variable in the Kepler Mission Field

We announce the identification of a new cataclysmic variable star in the field of the Kepler Mission, KIC J192410.81+445934.9. This system was identified during a search for compact pulsators in the Kepler field. High-speed photometry reveals coherent large-amplitude variability with a period of 2.94 h. Rapid, large-amplitude quasi-periodic variations are also detected on time scales of ~1200 s and ~650 s. Time-resolved spectroscopy covering one half photometric period shows shallow, broad Balmer and He I absorption lines with bright emission cores as well as strong He II and Bowen blend emission. Radial velocity variations are also observed in the Balmer and He I emission lines that are consistent with the photometric period. We therefore conclude that KIC J192410.81+445934.9 is a nova-like variable of the UX UMa class in or near the period gap, and it may belong to the rapidly growing subclass of SW Sex systems. Based on 2MASS photometry and companion star models, we place a lower limit on the distance to the system of ~500 pc. Due to limitations of our discovery data, additional observations including spectroscopy and polarimetry are needed to confirm the nature of this object. Such data will help to further understanding of the behavior of nova-like variables in the critical period range of 3-4 h, where standard cataclysmic variable evolutionary theory finds major problems. The presence of this system in the Kepler mission field-of-view also presents a unique opportunity to obtain a continuous photometric data stream of unparalleled length and precision on a cataclysmic variable system.Comment: Accepted for publication in the Astronomical Journal. 8 pages, 7 figures, uses emulateapj

Signatures for a Cosmic Flux of Magnetic Monopoles

Any early universe phase transition occurring after inflation has the potential to populate the universe with relic magnetic monopoles. Observations of galactic magnetic fields, as well as observations matched with models for extragalactic magnetic fields, lead to the conclusion that monopoles of mass \lsim 10^{15} GeV are accelerated in these fields to relativistic velocities. We explore the possible signatures of a cosmic flux of relativistic monopoles impinging on the earth. The electromagnetically-induced signatures of monopoles are reliable. The hadronically-induced signatures are highly model-dependent. Among our findings are (i) the electromagnetic energy losses of monopoles continuously initiate a protracted shower of small intensity; (ii) monopoles may traverse the earth's diameter, making them a probe of the earth's interior structure; (iii) in addition to the direct monopole Cherenkov signal presently employed, a very attractive search strategy for monopoles is detection of their radio-Cherenkov signal produced by the coherent charge-excess in the $e^+-e^-$ shower - in fact, Cherenkov-detectors have the potential to discover a monopole flux (or limit it) several orders of magnitude below the theoretical Parker limit of $10^{-15}/\rm{cm}^2$/s/sr; (iv) it is conceivable (but not compelling) that bound states of colored monopoles may be the primary particles initiating the air showers observed above the GZK cutoff.Comment: 33 pages, 5 figures, revtex, to appear in Astro. Part. Phy

Magnetohydrodynamics of the Early Universe and the Evolution of Primordial Magnetic Fields

We show that the decaying magnetohydrodynamic turbulence leads to a more rapid growth of the correlation length of a primordial magnetic field than that caused by the expansion of the Universe. As an example, we consider the magnetic fields created during the electroweak phase transition. The expansion of the universe alone would yield a correlation length at the present epoch of 1 AU, whereas we find that the correlation length is likely of order 100 AU, and cannot possibly be longer than $10^4$ AU for non-helical fields. If the primordial field is strongly helical, the correlation length can be much larger, but we show that even in this case it cannot exceed 100 pc. All these estimates make it hard to believe that the observed galactic magnetic fields can result from the amplification of seed fields generated at the electroweak phase transition by the standard galactic dynamo.Comment: 15 pages, REVTeX. Added results of numerical simulation, enlarged and revise

A Search for Correlation of Ultra-High Energy Cosmic Rays with IRAS-PSCz and 2MASS-6dF Galaxies

We study the arrival directions of 69 ultra-high energy cosmic rays (UHECRs) observed at the Pierre Auger Observatory (PAO) with energies exceeding 55 EeV. We investigate whether the UHECRs exhibit the anisotropy signal expected if the primary particles are protons that originate in galaxies in the local universe, or in sources correlated with these galaxies. We cross-correlate the UHECR arrival directions with the positions of IRAS-PSCz and 2MASS-6dF galaxies taking into account particle energy losses during propagation. This is the first time that the 6dF survey is used in a search for the sources of UHECRs and the first time that the PSCz survey is used with the full 69 PAO events. The observed cross-correlation signal is larger for the PAO UHECRs than for 94% (98%) of realisations from an isotropic distribution when cross-correlated with the PSCz (6dF). On the other hand the observed cross-correlation signal is lower than that expected from 85% of realisations, had the UHECRs originated in galaxies in either survey. The observed cross-correlation signal does exceed that expected by 50% of the realisations if the UHECRs are randomly deflected by intervening magnetic fields by 5 degrees or more. We propose a new method of analysing the expected anisotropy signal, by dividing the predicted UHECR source distribution into equal predicted flux radial shells, which can help localise and constrain the properties of UHECR sources. We find that the 69 PAO events are consistent with isotropy in the nearest of three shells we define, whereas there is weak evidence for correlation with the predicted source distribution in the two more distant shells in which the galaxy distribution is less anisotropic.Comment: 23 pages, version published in JCA

Cataclysmic Variables from the Sloan Digital Sky Survey. VIII. The Final Year (2007–2008)

This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey (SDSS) I/II. The coordinates, magnitudes, and spectra of 33 CVs are presented. Among the 33 are eight systems known prior to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226, and HS0943+1404), as well as nine objects recently found through various photometric surveys. Among the systems identified since the SDSS are two polar candidates, two intermediate polar candidates, and one candidate for containing a pulsating white dwarf. Our follow-up data have confirmed a polar candidate from Paper VII and determined tentative periods for three of the newly identified CVs. A complete summary table of the 285 CVs with spectra from SDSS I/II is presented as well as a link to an online table of all known CVs from both photometry and spectroscopy that will continue to be updated as future data appear

Clustering in Highest Energy Cosmic Rays: Physics or Statistics?

Directional clustering can be expected in cosmic ray observations due to purely statistical fluctuations for sources distributed randomly in the sky. We develop an analytic approach to estimate the probability of random cluster configurations, and use these results to study the strong potential of the HiRes, Auger, Telescope Array and EUSO/OWL/AirWatch facilities for deciding whether any observed clustering is most likely due to non-random sources.Comment: 19 pages, LaTeX, 3 figure

Relic Neutrino Absorption Spectroscopy

Resonant annihilation of extremely high-energy cosmic neutrinos on big-bang relic anti-neutrinos (and vice versa) into Z-bosons leads to sizable absorption dips in the neutrino flux to be observed at Earth. The high-energy edges of these dips are fixed, via the resonance energies, by the neutrino masses alone. Their depths are determined by the cosmic neutrino background density, by the cosmological parameters determining the expansion rate of the universe, and by the large redshift history of the cosmic neutrino sources. We investigate the possibility of determining the existence of the cosmic neutrino background within the next decade from a measurement of these absorption dips in the neutrino flux. As a by-product, we study the prospects to infer the absolute neutrino mass scale. We find that, with the presently planned neutrino detectors (ANITA, Auger, EUSO, OWL, RICE, and SalSA) operating in the relevant energy regime above 10^{21} eV, relic neutrino absorption spectroscopy becomes a realistic possibility. It requires, however, the existence of extremely powerful neutrino sources, which should be opaque to nucleons and high-energy photons to evade present constraints. Furthermore, the neutrino mass spectrum must be quasi-degenerate to optimize the dip, which implies m_{nu} >~ 0.1 eV for the lightest neutrino. With a second generation of neutrino detectors, these demanding requirements can be relaxed considerably.Comment: 19 pages, 26 figures, REVTeX

Search for Anisotropy of Ultra-High Energy Cosmic Rays with the Telescope Array Experiment

We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E>57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure of the Universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the Universe (the LSS hypothesis), while the event set with E>10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.Comment: 10 pages, 9 figure