177 research outputs found
Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity
We present results from monitoring the multi-waveband flux, linear
polarization, and parsec-scale structure of the quasar PKS 1510-089,
concentrating on eight major gamma-ray flares that occurred during the interval
2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at
optical wavelengths, although the flux ratio of the two wavebands varied by an
order of magnitude. The optical polarization vector rotated by 720 degrees
during a 5-day period encompassing six of these flares. This culminated in a
very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of
emission passed through the highest-intensity, stationary feature (the "core")
seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate
down the jet at an apparent speed of 22c and emit strongly at gamma-ray
energies as a months-long X-ray/radio outburst intensified. We interpret these
events as the result of the knot following a spiral path through a mainly
toroidal magnetic field pattern in the acceleration and collimation zone of the
jet, after which it passes through a standing shock in the 43 GHz core and then
continues downstream. In this picture, the rapid gamma-ray flares result from
scattering of infrared seed photons from a relatively slow sheath of the jet as
well as from optical synchrotron radiation in the faster spine. The 2006-2009.7
radio and X-ray flux variations are correlated at very high significance; we
conclude that the X-rays are mainly from inverse Compton scattering of infrared
seed photons by 20-40 MeV electrons.Comment: 10 pages of text + 5 figures, to be published in Astrophysical
Journal Letters in 201
On the Location of the Gamma-ray Emission in the 2008 Outburst in the BL Lacertae Object AO 0235+164 through Observations across the Electromagnetic Spectrum
We present observations of a major outburst at centimeter, millimeter,
optical, X-ray, and gamma-ray wavelengths of the BL Lacertae object AO
0235+164. We analyze the timing of multi-waveband variations in the flux and
linear polarization, as well as changes in Very Long Baseline Array (VLBA)
images at 7mm with 0.15 milliarcsecond resolution. The association of the
events at different wavebands is confirmed at high statistical significance by
probability arguments and Monte-Carlo simulations. A series of sharp peaks in
optical linear polarization, as well as a pronounced maximum in the 7 mm
polarization of a superluminal jet knot, indicate rapid fluctuations in the
degree of ordering of the magnetic field. These results lead us to conclude
that the outburst occurred in the jet both in the quasi-stationary "core" and
in the superluminal knot, both parsecs downstream of the supermassive black
hole. We interpret the outburst as a consequence of the propagation of a
disturbance, elongated along the line of sight by light-travel time delays,
that passes through a standing recollimation shock in the core and propagates
down the jet to create the superluminal knot. The multi-wavelength light curves
vary together on long time-scales (months/years), but the correspondence is
poorer on shorter time-scales. This, as well as the variability of the
polarization and the dual location of the outburst, agrees with the
expectations of a multi-zone emission model in which turbulence plays a major
role in modulating the synchrotron and inverse Compton fluxes.Comment: Accepted for Publication in the Astrophysical Journal Letters. 7
pages (including 5 figures). Minor corrections with regard to previous
version, as proposed by the refere
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 July 2007-January 2009. We show the results of
the AGILE campaigns which took place on May-June 2008, July-August 2008, and
October 2008-January 2009. During the May 2008-January 2009 period, the source
average flux was highly variable, from an average gamma-ray flux F(E>100MeV) >
200E-8 ph/cm2/s in May-June 2008, to F(E>100MeV)~80E-8 ph/cm2/s in October
2008-January 2009. The average gamma-ray spectrum between 100 MeV and 1 GeV can
be fit by a simple power law (Gamma_GRID ~ 2.0 to 2.2). Only 3-sigma upper
limits can be derived in the 20-60 keV energy band with Super-AGILE. During
July-August 2007 and May-June 2008, RXTE measured a flux of F(3-20 keV)=
8.4E-11 erg/cm2/s, and F(3-20 keV)=4.5E-11 erg/cm2/s, respectively and a
constant photon index Gamma_PCA=1.65. Swift/XRT observations were carried out
during all AGILE campaigns, obtaining a F(2-10 keV)=(0.9-7.5)E-11 erg/cm2/s and
a photon index Gamma_XRT=1.33-2.04. BAT measured an average flux of ~5 mCrab.
GASP-WEBT monitored 3C 454.3 during the whole 2007-2008 period from the radio
to the optical. A correlation analysis between the optical and the gamma-ray
fluxes shows a time lag of tau=-0.4 days. An analysis of 15 GHz and 43 GHz VLBI
core radio flux observations shows an increasing trend of the core radio flux,
anti- correlated with the higher frequency data. The modeling SEDs, 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.Comment: Accepted for publication in ApJ. Adapted Abstract. 17 pages, 19
Figures, 5 Table
AGILE detection of extreme gamma-ray activity from the blazar PKS 1510-089 during March 2009. Multifrequency analysis
We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089
observed by AGILE in March 2009. In the same period a radio-to-optical
monitoring of the source was provided by the GASP-WEBT and REM. Moreover,
several Swift ToO observations were triggered, adding important information on
the source behaviour from optical/UV to hard X-rays. We paid particular
attention to the calibration of the Swift/UVOT data to make it suitable to the
blazars spectra. Simultaneous observations from radio to gamma rays allowed us
to study in detail the correlation among the emission variability at different
frequencies and to investigate the mechanisms at work. In the period 9-30 March
2009, AGILE detected an average gamma-ray flux of (311+/-21)x10^-8 ph cm^-2
s^-1 for E>100 MeV, and a peak level of (702+/-131)x10^-8 ph cm^-2 s^-1 on
daily integration. The gamma-ray activity occurred during a period of
increasing activity from near-IR to UV, with a flaring episode detected on
26-27 March 2009, suggesting that a single mechanism is responsible for the
flux enhancement observed from near-IR to UV. By contrast, Swift/XRT
observations seem to show no clear correlation of the X-ray fluxes with the
optical and gamma-ray ones. However, the X-ray observations show a harder
photon index (1.3-1.6) with respect to most FSRQs and a hint of
harder-when-brighter behaviour, indicating the possible presence of a second
emission component at soft X-ray energies. Moreover, the broad band spectrum
from radio-to-UV confirmed the evidence of thermal features in the optical/UV
spectrum of PKS 1510-089 also during high gamma-ray state. On the other hand,
during 25-26 March 2009 a flat spectrum in the optical/UV energy band was
observed, suggesting an important contribution of the synchrotron emission in
this part of the spectrum during the brightest gamma-ray flare, therefore a
significant shift of the synchrotron peak.Comment: 13 pages, 7 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysic
A supernova origin for dust in a high-redshift quasar
Interstellar dust plays a crucial role in the evolution of the Universe by
assisting the formation of molecules, by triggering the formation of the first
low-mass stars, and by absorbing stellar ultraviolet-optical light and
subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought
to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass
stars. This picture has, however, recently been brought into question by the
discovery of large masses of dust in the host galaxies of quasars at redshift
z>6, when the age of the Universe was less than 1 Gyr. Theoretical studies,
corroborated by observations of nearby supernova remnants, have suggested that
supernovae provide a fast and efficient dust formation environment in the early
Universe. Here we report infrared observations of a quasar at redshift 6.2,
which are used to obtain directly its dust extinction curve. We then show that
such a curve is in excellent agreement with supernova dust models. This result
demonstrates a supernova origin for dust in this high-redshift quasar, from
which we infer that most of the dust at high redshifts has probably the same
origin.Comment: To Appear in Nature, September 30, 200
CSF glial markers are elevated in a subset of patients with genetic frontotemporal dementia
Neuroinflammation has been shown to be an important pathophysiological disease mechanism in frontotemporal dementia (FTD). This includes activation of microglia, a process that can be measured in life through assaying different glia-derived biomarkers in cerebrospinal fluid. However, only a few studies so far have taken place in FTD, and even fewer focusing on the genetic forms of FTD.We investigated the cerebrospinal fluid concentrations of TREM2, YKL-40 and chitotriosidase using immunoassays in 183 participants from the Genetic FTD Initiative (GENFI) study: 49 C9orf72 (36 presymptomatic, 13 symptomatic), 49 GRN (37 presymptomatic, 12 symptomatic) and 23 MAPT (16 presymptomatic, 7 symptomatic) mutation carriers and 62 mutation-negative controls. Concentrations were compared between groups using a linear regression model adjusting for age and sex, with 95% bias-corrected bootstrapped confidence intervals. Concentrations in each group were correlated with the Mini-Mental State Examination (MMSE) score using non-parametric partial correlations adjusting for age. Age-adjusted z-scores were also created for the concentration of markers in each participant, investigating how many had a value above the 95th percentile of controls.Only chitotriosidase in symptomatic GRN mutation carriers had a concentration significantly higher than controls. No group had higher TREM2 or YKL-40 concentrations than controls after adjusting for age and sex. There was a significant negative correlation of chitotriosidase concentration with MMSE in presymptomatic GRN mutation carriers. In the symptomatic groups, for TREM2 31% of C9orf72, 25% of GRN, and 14% of MAPT mutation carriers had a concentration above the 95th percentile of controls. For YKL-40 this was 8% C9orf72, 8% GRN and 0% MAPT mutation carriers, whilst for chitotriosidase it was 23% C9orf72, 50% GRN, and 29% MAPT mutation carriers.Although chitotriosidase concentrations in GRN mutation carriers were the only significantly raised glia-derived biomarker as a group, a subset of mutation carriers in all three groups, particularly for chitotriosidase and TREM2, had elevated concentrations. Further work is required to understand the variability in concentrations and the extent of neuroinflammation across the genetic forms of FTD. However, the current findings suggest limited utility of these measures in forthcoming trials.© 2022 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association
CSF glial markers are elevated in a subset of patients with genetic frontotemporal dementia
Background: Neuroinflammation has been shown to be an important pathophysiological disease mechanism in frontotemporal dementia (FTD). This includes activation of microglia, a process that can be measured in life through assaying different glia-derived biomarkers in cerebrospinal fluid. However, only a few studies so far have taken place in FTD, and even fewer focusing on the genetic forms of FTD. Methods: We investigated the cerebrospinal fluid concentrations of TREM2, YKL-40 and chitotriosidase using immunoassays in 183 participants from the Genetic FTD Initiative (GENFI) study: 49 C9orf72 (36 presymptomatic, 13 symptomatic), 49 GRN (37 presymptomatic, 12 symptomatic) and 23 MAPT (16 presymptomatic, 7 symptomatic) mutation carriers and 62 mutation-negative controls. Concentrations were compared between groups using a linear regression model adjusting for age and sex, with 95% bias-corrected bootstrapped confidence intervals. Concentrations in each group were correlated with the Mini-Mental State Examination (MMSE) score using non-parametric partial correlations adjusting for age. Age-adjusted z-scores were also created for the concentration of markers in each participant, investigating how many had a value above the 95th percentile of controls. Results: Only chitotriosidase in symptomatic GRN mutation carriers had a concentration significantly higher than controls. No group had higher TREM2 or YKL-40 concentrations than controls after adjusting for age and sex. There was a significant negative correlation of chitotriosidase concentration with MMSE in presymptomatic GRN mutation carriers. In the symptomatic groups, for TREM2 31% of C9orf72, 25% of GRN, and 14% of MAPT mutation carriers had a concentration above the 95th percentile of controls. For YKL-40 this was 8% C9orf72, 8% GRN and 0% MAPT mutation carriers, whilst for chitotriosidase it was 23% C9orf72, 50% GRN, and 29% MAPT mutation carriers. Conclusions: Although chitotriosidase concentrations in GRN mutation carriers were the only significantly raised glia-derived biomarker as a group, a subset of mutation carriers in all three groups, particularly for chitotriosidase and TREM2, had elevated concentrations. Further work is required to understand the variability in concentrations and the extent of neuroinflammation across the genetic forms of FTD. However, the current findings suggest limited utility of these measures in forthcoming trials
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