A photon breeding mechanism for the high-energy emission of relativistic jets

We propose a straightforward and efficient mechanism for the high-energy emission of relativistic astrophysical jets associated with an exchange of interacting high-energy photons between the jet and the external environment. Physical processes playing the main role in this mechanism are electron-positron pair production by photons and the inverse Compton scattering. This scenario has been studied analytically as well as with numerical simulations demonstrating that a relativistic jet (with the Lorentz factor larger than 3--4) moving through the sufficiently dense, soft radiation field inevitably undergoes transformation into a luminous state. The process has a supercritical character: the high-energy photons breed exponentially being fed directly by the bulk kinetic energy of the jet. Eventually particles feed back on the fluid dynamics and the jet partially decelerates. As a result, a significant fraction (at least 20 per cent) of the jet kinetic energy is converted into radiation mainly in the MeV -- GeV energy range. The mechanism maybe responsible for the bulk of the emission of relativistic jets in active galactic nuclei, microquasars and gamma-ray bursts.Comment: 10 pages, 9 figures; MNRAS, in pres

The mystery of spectral breaks: Lyman continuum absorption by photon-photon pair production in the Fermi GeV spectra of bright blazars

We reanalyze Fermi/LAT gamma-ray spectra of bright blazars with a higher photon statistics than in previous works and with new Pass 7 data representation. In the spectra of the brightest blazar 3C 454.3 and possibly of 4C +21.35 we detect breaks at 5 GeV (in the rest frame) associated with the photon-photon pair production absorption by He II Lyman continuum (LyC). We also detect confident breaks at 20 GeV associated with hydrogen LyC both in the individual spectra and in the stacked redshift-corrected spectrum of several bright blazars. The detected breaks in the stacked spectra univocally prove that they are associated with atomic ultraviolet emission features of the quasar broad-line region (BLR). The dominance of the absorption by hydrogen Ly complex over He II, rather small detected optical depth, and the break energy consistent with the head-on collisions with LyC photons imply that the gamma-ray emission site is located within the BLR, but most of the BLR emission comes from a flat disk-like structure producing little opacity. Alternatively, the LyC emission region size might be larger than the BLR size measured from reverberation mapping, and/or the gamma-ray emitting region is extended. These solutions would resolve a long-standing issue how the multi-hundred GeV photons can escape from the emission zone without being absorbed by softer photons.Comment: 7 pages, 6 figures; accepted to Ap

An Off-line Scan of the BATSE Daily Records and a Large Uniform Sample of Gamma-Ray Bursts

During a scan of the archival BATSE daily records covering the entire 9.1 years (TJD 8369-11690) of the BATSE operation, 3906 gamma-ray bursts (GRBs) have been detected. 2068 of these GRBs are previously known BATSE triggers while 1838 of them are new non-triggered bursts. It is important that all events were detected in the same type of data and were processed with the same procedure. Therefore these 3906 GRBs constitute a uniform sample. We have created a publically available electronic data base containing this sample. We describe the procedures of the data reduction, the selection of the GRB candidates, and the statistical tests for possible non-GRB contaminations. We also describe a novel test burst method used to measure the scan efficiency and the information obtained using the test bursts. Our scan decreases the BATSE detection threshold to ~0.1 photons/sec/cm2. As a first result, we show that the differential log N - log P distribution corrected for the detection efficiency extends to low brightnesses without any indication of a turn-over. Any reasonable extrapolation of the new log N - log P to lower brightnesses imply a rate of several thousands of GRBs in the Universe per year.Comment: 14 pages; 23 figures; revised version accepted to ApJ; electronic version of Table 2 is available at ftp://ftp.astro.su.se/pub/head/grb/catalogs/etable2.txt The GRB archive is available at http://www.astro.su.se/groups/head/grb_archive.htm

Sythetic Securitization: A Comment on Bell & Dawson

The topic studied in this thesis is the right of public access as a legal institution. In that connection, several questions which are different from each other are raised. The thesis focuses to a great extent on the interaction between questions of a practical-legal nature and those whose character is more connected to legal theory. The point of departure of the discussion in the thesis is that some of the legal norms that are incorporated in the institution of the right of public access are customary law. Thus, the concept customary law is particularly considered, and the question of in what way the customary law can be filled with content raises special interest. A hypothesis is put forward in the thesis, which is that the right of public access constitutes part of those regulations whose purpose is that land should be used appropriately - seen from the societal perspective that land is a limited natural resource which should be used expediently, for the husbanding of resources. What is advocated in this thesis, is that in both the jurisprudential discussion about the right of public access and in the argumentation that is conducted in the practical legal application, the three subjects, the Actual User, the Canalizer and the Actual User in the Collective and their different use of the land, are separated. Further, it is advocated that the discussion as to which activities are allowed by the right of public access should be based on a consciousness that the activities can concern “everyday use” or “recreation” and that, depending on whether the activities are considered to concern the one or the other, different conclusions regarding the permissibility of the activities will be drawn. Furthermore, it is shown in the thesis that in conflicts between different means of using land, the courts seem to presume that all land is covered by the right of public access - a presumption that does not hold if the land is a part of somebody’s zone of home privacy, is needed for certain business or constitute biologically sensitive land.I denna avhandling studeras allemansrätten som rättsinstitut. Därvid aktualiseras flera sinsemellan olikartade frågeställningar. Avhandlingen fokuserar i stor utsträckning på samspelet mellan frågor av praktisk-juridiskt slag och sådana av mer rättsteoretiskt slag. Diskussionen i avhandlingen utgår från att vissa av de i institutet allemansrätten ingående rättsliga normerna är sedvanerätt. Därför diskuteras sedvanerättsbegreppet särskilt, varvid frågan hur sedvanerätt kan fyllas med ett innehåll väcker särskilt intresse. I avhandlingen uppställs en hypotes om att allemansrätten är en del av en reglering syftande till lämplig markanvändning - sett ur den samhälleliga synvinkeln att mark är en begränsad naturresurs som bör nyttjas ändamålsenligt, för hushållning med resurser. I avhandlingen förespråkas att man i såväl den rättsvetenskapliga diskussionen om allemansrätten, som i den argumentation som förs i den praktiska rättstillämpningen, särskiljer de tre subjekten utövaren, kanalisatören och utövaren i kollektivet och deras skilda nyttjande. Vidare förespråkas att diskussionen, om vilka aktiviteter som är allemansrättsligt tillåtna, sker utifrån en medvetenhet om att aktiviteterna kan avse ”vardagsnytta” eller ”rekreation” och att, beroende av om aktiviteterna antas avse det ena eller det andra, olika slutsatser angående aktiviteternas tillåtlighet kommer att dras. Därtill visas i avhandlingen att domstolen, i konflikter mellan olika sätt att nyttja marken, tycks presumera att all mark är allemansrättsligt tillgänglig - en presumtion som bryts om marken ingår i någons hemfridszon, behövs för vissa näringar eller utgör biologiskt känslig mark

Optimization of midcourse velocity corrections

Optimum time to apply single midcourse velocity correction and optimum schedule for corrections in variable time-of-arrival guidance - geometrical mode

Spacecraft high-voltage power supply construction

The design techniques, circuit components, fabrication techniques, and past experience used in successful high-voltage power supplies for spacecraft flight systems are described. A discussion of the basic physics of electrical discharges in gases is included and a design rationale for the prevention of electrical discharges is provided. Also included are typical examples of proven spacecraft high-voltage power supplies with typical specifications for design, fabrication, and testing

Blind search for the real sample: Application to the origin of ultra-high energy cosmic rays

We suggest a method for statistical tests which does not suffer from a posteriori manipulations with tested samples (e.g. cuts optimization) and does not require a somewhat obscure procedure of the penalty estimate. The idea of the method is to hide the real sample (before it has been studied) among a large number of artificial samples, drawn from a random distribution expressing the null hypothesis, and then to search for it as the one demonstrating the strongest hypothesized effect. The statistical significance of the effect in this approach is the inverse of the maximal number of random samples at which the search was successful. We have applied the method to revisit the problem of correlation between the arrival directions of ultra-high energy cosmic rays and BL Lac objects. No significant correlation was found.Comment: 4 pages, 1 figure, accepted to ApJ Letter