29 research outputs found
Multiwavelength observations of 3C 454.3. III. Eighteen months of agile monitoring of the "crazy diamond"
We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (Crazy Diamond) carried out in the period 2007 July-2009 January. In particular, we show the results of the AGILE campaigns which took place on 2008 May-June, 2008 July-August, and 2008 October-2009 January. During the 2008 May-2009 January period, the source average flux was highly variable, with a clear fading trend toward the end of the period, from an average Îł-ray flux F E>100 MeV âł 200 Ă 10-8photonscm -2s-1 in 2008 May-June, to F E>100 MeV 80 Ă 10-8photonscm-2s-1 in 2008 October-2009 January. The average Îł-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law, showing a moderate softening (from ÎGRID ⌠2.0 to ÎGRID ⌠2.2) toward the end of the observing campaign. Only 3Ï upper limits can be derived in the 20-60 keV energy band with Super-AGILE, because the source was considerably off-axis during the whole time period. In 2007 July-August and 2008 May-June, 3C 454.3 was monitored by Rossi X-ray Timing Explorer (RXTE). The RXTE/Proportional Counter Array (PCA) light curve in the 3-20 keV energy band shows variability correlated with the Îł-ray one. The RXTE/PCA average flux during the two time periods is F 3-20 keV = 8.4 Ă 10-11ergcm-2s -1, and F 3-20 keV = 4.5 Ă 10 -11ergcm-2s-1, respectively, while the spectrum (a power law with photon index ÎPCA = 1.65 0.02) does not show any significant variability. Consistent results are obtained with the analysis of the RXTE/High-Energy X-Ray Timing Experiment quasi-simultaneous data. We also carried out simultaneous Swift observations during all AGILE campaigns. Swift/XRT detected 3C 454.3 with an observed flux in the 2-10 keV energy band in the range (0.9-7.5) Ă 10-11ergcm-2s-1 and a photon index in the range ÎXRT = 1.33-2.04. In the 15-150 keV energy band, when detected, the source has an average flux of about 5mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007-2008 period in the radio, millimeter, near-IR, and optical bands. The observations show an extremely variable behavior at all frequencies, with flux peaks almost simultaneous with those at higher energies. A correlation analysis between the optical and the Îł-ray fluxes shows that the Îł-optical correlation occurs with a time lag of Ï = -0.4+0.6-0.8 days, consistent with previous findings for this source. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations in the period 2007 July-2009 February shows an increasing trend of the core radio flux, anti-correlated with the higher frequency data, allowing us to derive the value of the source magnetic field. Finally, the modeling of the broadband spectral energy distributions for the still unpublished data, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year. © 2010. The American Astronomical Society. All rights reserved
Sequential Linear Stapling Technique for Perineal Resection of Intractable Pediatric Rectal Prolapse
SCOR WG149 Handbook to support the SCOR Best Practice Guide for âMultiple Driversâ Marine Research
Drinking outcome expectancies and normative perceptions of students engaged in university sport in England
This study examined whether students engaged in university sport have different drinking outcome expectancies and normative beliefs than students who are not engaged in university sport. A cross-sectional survey of university students in England in 2008â2009 was undertaken. A questionnaire battery, including the Drinking Expectancies Questionnaire (DEQ) and a measure of normative beliefs, was completed by 770 students from seven universities across England. Responses from 638 students who were not abstaining from alcohol were analyzed. Students engaged in university sport have significantly higher drinking expectancies of assertion compared with students not engaged in university sport. Moreover, students engaged in university sport consistently report higher personal alcohol consumption and higher perceptions of consumption in those around them than students not engaged in university sport. Both assertion and the perception that students around them drink heavily provide only a partial explanation for why students engaged in university sport drink more than those not engaged in university sport. Further research is required to identify the reasons for heavy drinking among students involved in university sport in England