Context. Blazars are a subset of active galactic nuclei (AGN) with jets that are oriented along our line of sight. Variability and spectral energy distribution (SED) studies are crucial tools for ...understanding the physical processes responsible for observed AGN emission. Aims. We report peculiar behavior in the bright γ-ray blazar PKS 1424−418 and use its strong variability to reveal information about the particle acceleration and interactions in the jet. Methods. Correlation analysis of the extensive optical coverage by the ATOM telescope and nearly continuous γ-ray coverage by the Fermi Large Area Telescope is combined with broadband, time-dependent modeling of the SED incorporating supplemental information from radio and X-ray observations of this blazar. Results. We analyse in detail four bright phases at optical-GeV energies. These flares of PKS 1424−418 show high correlation between these energy ranges, with the exception of one large optical flare that coincides with relatively low γ-ray activity. Although the optical/γ-ray behavior of PKS 1424−418 shows variety, the multiwavelength modeling indicates that these differences can largely be explained by changes in the flux and energy spectrum of the electrons in the jet that are radiating. We find that for all flares the SED is adequately represented by a leptonic model that includes inverse Compton emission from external radiation fields with similar parameters. Conclusions. Detailed studies of individual blazars like PKS 1424−418 during periods of enhanced activity in different wavebands are helping us identify underlying patterns in the physical parameters in this class of AGN.
In a radio search with the Green Bank Telescope of three unidentified low Galactic latitude Fermi Large Area Telescope (LAT) sources, we have discovered the middle-aged pulsar J2030+3641 associated ...with 1FGL J2030.0+3641 (2FGL J2030.0+3640). Following the detection of gamma-ray pulsations using a radio ephemeris, we have obtained a phase-coherent timing solution based on gamma-ray and radio pulse arrival times which spans the entire Fermi mission. With a rotation period of 0.2 s, a spin-down luminosity of 3 x 10 super(34) erg s super(-1), and a characteristic age of 0.5 Myr, PSR J2030+3641 is a middle-aged neutron star with spin parameters similar to those of the exceedingly gamma-ray-bright and radio-undetected Geminga. Its gamma-ray flux is 1% that of Geminga, primarily because of its much larger distance, as suggested by the large integrated column density of free electrons, DM = 246 pc cm super(-3). We fit the gamma-ray light curve, along with limited radio polarimetric constraints, to four geometrical models of magnetospheric emission, and while none of the fits have high significance some are encouraging and suggest that further refinements of these models may be worthwhile. We argue that not many more non-millisecond radio pulsars may be detected along the Galactic plane that are responsible for LAT sources, but that modified methods to search for gamma-ray pulsations should be productive-PSR J2030+3641 would have been found blindly in gamma rays if only > ~0.8 GeV photons had been considered, owing to its relatively flat spectrum and location in a region of high soft background.
Since its launch in late 2004, the Swift satellite triggered or observed an average of one gamma-ray burst (GRB) every 3 days, for a total of 771 GRBs by 2012 January. Here, we report the development ...of a pipeline that semi-automatic ally performs the data-reduction and data-analysis processes for the three instruments on board Swift (BAT, XRT, UVOT). The pipeline is written in Perl, and it uses only HEAsoft tools and can be used to perform the analysis of a majority of the point-like objects (e.g., GRBs, active galactic nuclei, pulsars) observed by Swift. We run the pipeline on the GRBs, and we present a database containing the screened data, the output products, and the results of our ongoing analysis. Furthermore, we created a catalog summarizing some GRB information, collected either by running the pipeline or from the literature. The Perl script, the database, and the catalog are available for downloading and querying at the HEASARC Web site.
Three experiments were conducted with broiler chickens to evaluate the effects of digestible total sulphur amino acid (TSAA) on their performance at three different phases of starter (1–14 d), grower ...(15–28 d) and finisher (29–42 d). The measured traits included: average daily gain (ADG), feed intake, feed conversion ratio (FCR), carcass protein, body lipid (BL), feather weight gain, carcass plus feather protein, carcass TSAA deposition and nitrogen excretion (NE). A dilution technique was used to create seven diets (with eight replicates) increasing the TSAA content from 2.5 to 9.04 g/kg of diet for starter, 2.26 to 8.14 g/kg of diet for grower and 2.08 to 7.5 g/kg of diet for finisher. Data measured were imported to neural networks to predict the measured traits in response to dietary and intake levels of TSAA and find the optimal levels of TSAA that lead to the desired responses. Optimization results showed decreases in optimal dietary TSAA values with increasing age for all traits, while reverse was observed for intake values and requirements were increased as birds aged. The highest TSAA requirement (7.95, 7.2 and 6.6 g/kg and 283, 585 and 1150 mg/bird per d for starter, grower and finisher, respectively) were achieved for minimum BL and lowest (5.8, 5.2 and 4.9 g/kg and 201, 444 and 873 mg/bird per d for starter, grower and finisher, respectively) were suggested for minimum NE. Based on intake models, the optimal TSAA values for minimum FCR in phases 1–3 were 283, 585 and 1150 mg/bird per d while maximum ADGs were achieved with 201, 444 and 873 mg/bird per d of TSAA.
This study focused on the preparation and characterization of films based on biopolymers (hydroxypropylcellulose and low methoxyl pectin) and halloysite nanotubes (HNTs). The morphology is strongly ...dependent on the polymer nature. In particular, we observed a sandwich-like structure composed of two hydroxypropylcellulose layers incorporating the HNTs and a homogeneous distribution of the nanotubes into the low methoxyl pectin matrix. The different mesoscopic properties were invoked to explain the dielectric, thermal, and wettability properties of the corresponding films. Nanocomposites obtained by combining materials from renewable resources and HNTs is a challenging task in view of designing green materials with tunable barrier and delivery properties for specific purposes.
Large scale properties of the Webgraph DONATO, D; LAURA, L; LEONARDI, S ...
The European physical journal. B, Condensed matter physics,
03/2004, Letnik:
38, Številka:
2
Journal Article
We report on Swift observations of four z > 2 radio-loud quasars (0212+735, 0537-286, 0836+710, and 2149-307), classified as blazars. The sources, well-known emitters at soft-to-medium X-rays, were ...detected at >5 sigma with the BAT experiment in 15-150 keV. No flux variability was detected within the XRT and BAT exposures, with the exception of 0836+710, which shows an increase by a factor of 4 in the 15-150 keV flux on a timescale of 1 month. The 0.3-10 keV spectra are well fitted by power-law models, with rather hard continua (photon indices Gamma sub(xrt) similar to 1.3 -1.5); similarly, the 15-150 keV spectra are described by power laws with Gamma sub(BAT) similar to 1.3 -1.8. The XRT data exhibit spectral curvature, which can be modeled in terms of either excess absorption along the line of sight or a downward-curved broken power law. In the former case, if the excess N sub(h) is at the rest frame of the source, columns of unk=(0.3 -6) x 10 super(22) cm super(-2) are measured. Modeling of the SEDs of the four quasars shows that the emission at the higher frequencies, unk10 super(16) Hz, is dominated by the jet, while the steep optlcal-to-UV continua, observed with the UVOT, can be attributed to thermal emission from the accretion disk. The disk luminosity is between 1% and 10% of the jet power, similar to other powerful biazars.
Using public Fermi Large Area Telescope (LAT) and Swift Burst Alert Telescope observations, we constructed the first sample of blazars selected at both hard X-rays and gamma rays. Studying its ...spectral properties, we find a luminosity dependence of the spectral slopes at both energies. Specifically, luminous blazars, generally classified as flat spectrum radio quasars, have hard continua in the medium-hard X-ray range but soft continua in the LAT gamma-ray range (photon indices GAMMA{sub X} {approx}< 2 and GAMMA{sub G} {approx}> 2), while lower luminosity blazars, classified as BL Lacs, have opposite behavior, i.e., soft X-ray and hard gamma-ray continua (GAMMA{sub X} {approx}> 2.4 and GAMMA{sub G} < 2). The trends are confirmed by detailed Monte Carlo simulations explicitly taking into account the observational biases of both instruments. Our results support the so-called blazar sequence which was originally based on radio samples of blazars and radio luminosities. We also argue that the X-ray-to-gamma-ray continua of blazars may provide independent insights into the physical conditions around the jet, complementing/superseding the ambiguities of the traditional classification based on optical properties.
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