1,436 research outputs found
MAGIC observations of Mkn 421 in 2008, and related optical/X-ray/TeV MWL study
The HBL-type blazar Markarian 421 is one of the brightest TeV gamma-ray
sources of the Northern sky. From December 2007 until June 2008 it was
intensively observed in the VHE (E>100 GeV) band by the MAGIC gamma-ray
telescope. The source showed intense and prolonged activity during the whole
period. In some nights the integral flux rose up to 3.6 Crab units (E>200 GeV).
Intra-night rapid flux variations were observed. We compared the optical (KVA)
and X-ray (RXTE-ASM, Swift-XRT) data with the MAGIC VHE data, investigating the
correlations between different energy bands.Comment: 4 pages,4figures, Contribution to the 31st ICRC, Lodz, Poland, July
200
The Jet and the Supernova in GRB990712
The optical light curve of the afterglow following the gamma-ray burst GRB990712 is re-examined. Recently published polarization measurements of that source require a collimated outflow geometry that in turn predicts a break in the light curve. We show that the V-band light curve is consistent with such a break and that the post-break light curve evolution is dominated by a supernova contribution
A Kpc-scale Radio Polarization Study of PG BL Lacs with the uGMRT
We present here uGMRT band 4 (~650MHz) polarization images of 8 BL~Lac
objects belonging to the Palomar-Green (PG) `blazar' sample. A large fraction
of the sources (~63%) reveal core-halo radio structures with most of the
polarization detected in the inner core-jet regions. PG1101+385 and PG2254+075
exhibit a `spine-sheath structure' in polarization. The core-halo and
`spine-sheath' structures are consistent with the Unified Scheme suggestion
that BL~Lacs are the pole-on beamed counterparts of Fanaroff-Riley (FR) type I
radio galaxies. PG1418+546 and PG0851+203 (OJ287) show the presence of terminal
hotspots similar to FR type II radio galaxies. They were also found to be
low-spectrally peaked BL Lacs, supportive of the `blazar envelope' scenario for
BL~Lacs and quasars. Fractional polarization ranges from 1-13% in the cores and
2-26% in the inner jets/lobes of the sample BL Lacs. Compared to the varied
radio morphology of quasars from the PG `blazar' sample, the BL~Lacs appear to
be less diverse. A comparison of the inferred core magnetic (B-) field
structures on arcsec- (kpc-) scales w.r.t. the Very Long Baseline
Interferometry (VLBI) jet direction does not reveal any preferred orientation,
suggesting that if large-scale ordered B-fields exist, they do so on scales
smaller than probed by the current observations. However, the presence of
polarized emission on arcsec-scales suggests that any mixing of thermal plasma
with the synchrotron emitting plasma is insufficient to fully depolarize the
emission via the internal depolarization process.Comment: 17 pages; 12 figures; MNRAS accepte
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Coupling a single solid-state quantum emitter to an array of resonant plasmonic antennas
Plasmon resonant arrays or meta-surfaces shape both the incoming optical field and the local density of states for emission processes. They provide large regions of enhanced emission from emitters and greater design flexibility than single nanoantennas. This makes them of great interest for engineering optical absorption and emission. Here we study the coupling of a single quantum emitter, a self-assembled semiconductor quantum dot, to a plasmonic meta-surface. We investigate the influence of the spectral properties of the nanoantennas and the position of the emitter in the unit cell of the structure. We observe a resonant enhancement due to emitter-array coupling in the far-field regime and find a clear difference from the interaction of an emitter with a single antenna
Opacity effects and shock-in-jet modelling of low-level activity in Cygnus X-3
We present simultaneous dual-frequency radio observations of Cygnus X-3
during a phase of low-level activity. We constrain the minimum variability
timescale to be 20 minutes at 43 GHz and 30 minutes at 15 GHz, implying source
sizes of 2 to 4 AU. We detect polarized emission at a level of a few per cent
at 43 GHz which varies with the total intensity. The delay of approximately 10
minutes between the peaks of the flares at the two frequencies is seen to
decrease with time, and we find that synchrotron self-absorption and free-free
absorption by entrained thermal material play a larger role in determining the
opacity than absorption in the stellar wind of the companion. A shock-in-jet
model gives a good fit to the lightcurves at all frequencies, demonstrating
that this mechanism, which has previously been used to explain the brighter,
longer-lived giant outbursts in this source, is also applicable to these
low-level flaring events. Assembling the data from outbursts spanning over two
orders of magnitude in flux density shows evidence for a strong correlation
between the peak brightness of an event, and the timescale and frequency at
which this is attained. Brighter flares evolve on longer timescales and peak at
lower frequencies. Analysis of the fitted model parameters suggests that
brighter outbursts are due to shocks forming further downstream in the jet,
with an increased electron normalisation and magnetic field strength both
playing a role in setting the strength of the outburst.Comment: Accepted for publication in MNRAS. 15 pages, 9 figure
Tuning the polarization states of optical spots at the nanoscale on the poincar´e sphere using a plasmonic nanoantenna
It is shown that the polarization states of optical spots at the nanoscale can be manipulated to various points on the Poincar´e sphere using a plasmonic nanoantenna. Linearly, circularly, and elliptically polarized near-field optical spots at the nanoscale are achieved with various polarization states on the Poincar´e sphere using a plasmonic nanoantenna. A novel plasmonic nanoantenna is illuminated with diffraction-limited linearly polarized light. It is demonstrated
that the plasmonic resonances of perpendicular and longitudinal components of the nanoantenna and the angle of incident polarization can be tuned to obtain optical spots beyond the diffraction limit with a desired polarization and handedness
INTEGRAL observations of the blazar Mrk 421 in outburst (Results of a multi-wavelength campaign)
We report the results of a multi-wavelength campaign on the blazar Mrk 421
during outburst. We observed four strong flares at X-ray energies that were not
seen at other wavelengths (partially because of missing data). From the fastest
rise in the X-rays, an upper limit could be derived on the extension of the
emission region. A time lag between high-energy and low-energy X-rays was
observed, which allowed an estimation of the magnetic-field strength. The
spectral analysis of the X-rays revealed a slight spectral hardening of the
low-energy (3 - 43 keV) spectral index. The hardness-ratio analysis of the
Swift-XRT (0.2 - 10 keV) data indicated a small correlation with the intensity;
i. e., a hard-to-soft evolution was observed. At the energies of IBIS/ISGRI (20
- 150 keV), such correlations are less obvious. A multiwavelength spectrum was
composed and the X-ray and bolometric luminosities are calculated.Comment: 15 pages, 18 figures; accepted by Astronomy & Astrophysic
Prognostic performance of computerized tomography scoring systems in civilian penetrating traumatic brain injury : an observational study
Background The prognosis of penetrating traumatic brain injury (pTBI) is poor yet highly variable. Current computerized tomography (CT) severity scores are commonly not used for pTBI prognostication but may provide important clinical information in these cohorts. Methods All consecutive pTBI patients from two large neurotrauma databases (Helsinki 1999-2015, Stockholm 2005-2014) were included. Outcome measures were 6-month mortality and unfavorable outcome (Glasgow Outcome Scale 1-3). Admission head CT scans were assessed according to the following: Marshall CT classification, Rotterdam CT score, Stockholm CT score, and Helsinki CT score. The discrimination (area under the receiver operating curve, AUC) and explanatory variance (pseudo-R-2) of the CT scores were assessed individually and in addition to a base model including age, motor response, and pupil responsiveness. Results Altogether, 75 patients were included. Overall 6-month mortality and unfavorable outcome were 45% and 61% for all patients, and 31% and 51% for actively treated patients. The CT scores' AUCs and pseudo-R(2)s varied between 0.77-0.90 and 0.35-0.60 for mortality prediction and between 0.85-0.89 and 0.50-0.57 for unfavorable outcome prediction. The base model showed excellent performance for mortality (AUC 0.94, pseudo-R-2 0.71) and unfavorable outcome (AUC 0.89, pseudo-R-2 0.53) prediction. None of the CT scores increased the base model's AUC (p > 0.05) yet increased its pseudo-R-2 (0.09-0.15) for unfavorable outcome prediction. Conclusion Existing head CT scores demonstrate good-to-excellent performance in 6-month outcome prediction in pTBI patients. However, they do not add independent information to known outcome predictors, indicating that a unique score capturing the intracranial severity in pTBI may be warranted.Peer reviewe
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Direct iminization of PEEK
Semi-crystalline poly(ether ketone)s are important high-temperature engineering thermoplastics, but are difficult to characterize at the molecular level because of their insolubility in conventional organic solvents. Here we report that polymers of this type, including PEEK, react cleanly at high temperatures with low-volatility aralkyl amines to afford stable, noncrystalline poly(ether-imine)s, which are readily soluble in solvents such as chloroform, THF and DMF and so characterizable by conventional size-exclusion chromatography
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