88 research outputs found
Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique
The third Fermi-LAT catalog (3FGL) presented the data of the first four years
of observations from the Fermi Gamma-ray Space Telescope mission. There are
3034 sources, 1010 of which still remain unidentified. Identifying and
classifying gamma-ray emitters is of high significance with regard to studying
high-energy astrophysics. We demonstrate that optical polarimetry can be an
advantageous and practical tool in the hunt for counterparts of the
unidentified gamma-ray sources (UGSs). Using data from the RoboPol project, we
validated that a significant fraction of active galactic nuclei (AGN)
associated with 3FGL sources can be identified due to their high optical
polarization exceeding that of the field stars. We performed an optical
polarimetric survey within uncertainties of four unidentified 3FGL
sources. We discovered a previously unknown extragalactic object within the
positional uncertainty of 3FGL J0221.2+2518. We obtained its spectrum and
measured a redshift of . Using these measurements and
archival data we demonstrate that this source is a candidate counterpart for
3FGL J0221.2+2518 and most probably is a composite object: a star-forming
galaxy accompanied by AGN. We conclude that polarimetry can be a powerful asset
in the search for AGN candidate counterparts for unidentified Fermi sources.
Future extensive polarimetric surveys at high galactic latitudes (e.g.,
PASIPHAE) will allow the association of a significant fraction of currently
unidentified gamma-ray sources.Comment: accepted to A&
RoboPol: Connection between optical polarization plane rotations and gamma-ray flares in blazars
We use results of our 3 year polarimetric monitoring program to investigate
the previously suggested connection between rotations of the polarization plane
in the optical emission of blazars and their gamma-ray flares in the GeV band.
The homogeneous set of 40 rotation events in 24 sources detected by {\em
RoboPol} is analysed together with the gamma-ray data provided by {\em
Fermi}-LAT. We confirm that polarization plane rotations are indeed related to
the closest gamma-ray flares in blazars and the time lags between these events
are consistent with zero. Amplitudes of the rotations are anticorrelated with
amplitudes of the gamma-ray flares. This is presumably caused by higher
relativistic boosting (higher Doppler factors) in blazars that exhibit smaller
amplitude polarization plane rotations. Moreover, the time scales of rotations
and flares are marginally correlated.Comment: 12 pages, 16 figures, accepted to MNRA
Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry Demonstration of the technique
Context. The third Fermi-LAT catalog (3FGL) presented the data of the first four years of observations from the Fermi Gamma-ray Space Telescope mission. There are 3034 sources, 1010 of which still remain unidentified. Identifying and classifying gamma-ray emitters is of high significance with regard to studying high-energy astrophysics.Aims. We demonstrate that optical polarimetry can be an advantageous and practical tool in the hunt for counterparts of the unidentified gamma-ray sources (UGSs).Methods. Using data from the RoboPol project, we validated that a significant fraction of active galactic nuclei (AGN) associated with 3FGL sources can be identified due to their high optical polarization exceeding that of the field stars. We performed an optical polarimetric survey within 3 sigma uncertainties of four unidentified 3FGL sources.Results. We discovered a previously unknown extragalactic object within the positional uncertainty of 3FGL J0221.2 + 2518. We obtained its spectrum and measured a redshift of z = 0.0609 +/- 0.0004. Using these measurements and archival data we demonstrate that this source is a candidate counterpart for 3FGL J0221.2 + 2518 and most probably is a composite object: a star-forming galaxy accompanied by AGN.Conclusions. We conclude that polarimetry can be a powerful asset in the search for AGN candidate counterparts for unidentified Fermi sources. Future extensive polarimetric surveys at high Galactic latitudes (e.g., PASIPHAE) will allow the association of a significant fraction of currently unidentified gamma-ray sources
Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique
Context. The third Fermi-LAT catalog (3FGL) presented the data of the first four years of observations from the Fermi Gamma-ray Space Telescope mission. There are 3034 sources, 1010 of which still remain unidentified. Identifying and classifying Îł-ray emitters is of high significance with regard to studying high-energy astrophysics.
Aims. We demonstrate that optical polarimetry can be an advantageous and practical tool in the hunt for counterparts of the unidentified Îł-ray sources (UGSs).
Methods. Using data from the RoboPol project, we validated that a significant fraction of active galactic nuclei (AGN) associated with 3FGL sources can be identified due to their high optical polarization exceeding that of the field stars. We performed an optical polarimetric survey within 3Ï uncertainties of four unidentified 3FGL sources.
Results. We discovered a previously unknown extragalactic object within the positional uncertainty of 3FGL J0221.2+2518. We obtained its spectrum and measured a redshift of zâ=â0.0609â
屉
0.0004. Using these measurements and archival data we demonstrate that this source is a candidate counterpart for 3FGL J0221.2+2518 and most probably is a composite object: a star-forming galaxy accompanied by AGN.
Conclusions. We conclude that polarimetry can be a powerful asset in the search for AGN candidate counterparts for unidentified Fermi sources. Future extensive polarimetric surveys at high Galactic latitudes (e.g., PASIPHAE) will allow the association of a significant fraction of currently unidentified Îł-ray sources
RoboPol: the optical polarization of gamma-ray-loud and gamma-ray-quiet blazars
We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gamma-ray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3Ï level. We have not found any evidence that this discrepancy is related to differences in the redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high-synchrotron-peaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low-synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high-synchrotron-peaked sources, it tends to concentrate around preferred directions while for low-synchrotron-peaked sources, it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock
CSF from Parkinson disease Patients Differentially Affects Cultured Microglia and Astrocytes
<p>Abstract</p> <p>Background</p> <p>Excessive and abnormal accumulation of alpha-synuclein (α-synuclein) is a factor contributing to pathogenic cell death in Parkinson's disease. The purpose of this study, based on earlier observations of Parkinson's disease cerebrospinal fluid (PD-CSF) initiated cell death, was to determine the effects of CSF from PD patients on the functionally different microglia and astrocyte glial cell lines. Microglia cells from human glioblastoma and astrocytes from fetal brain tissue were cultured, grown to confluence, treated with fixed concentrations of PD-CSF, non-PD disease control CSF, or control no-CSF medium, then photographed and fluorescently probed for α-synuclein content by deconvolution fluorescence microscopy. Outcome measures included manually counted cell growth patterns from day 1-8; α-synuclein density and distribution by antibody tagged 3D model stacked deconvoluted fluorescent imaging.</p> <p>Results</p> <p>After PD-CSF treatment, microglia growth was reduced extensively, and a non-confluent pattern with morphological changes developed, that was not evident in disease control CSF and no-CSF treated cultures. Astrocyte growth rates were similarly reduced by exposure to PD-CSF, but morphological changes were not consistently noted. PD-CSF treated microglia showed a significant increase in α-synuclein content by day 4 compared to other treatments (p †0.02). In microglia only, α-synuclein aggregated and redistributed to peri-nuclear locations.</p> <p>Conclusions</p> <p>Cultured microglia and astrocytes are differentially affected by PD-CSF exposure compared to non-PD-CSF controls. PD-CSF dramatically impacts microglia cell growth, morphology, and α-synuclein deposition compared to astrocytes, supporting the hypothesis of cell specific susceptibility to PD-CSF toxicity.</p
Parkin Deficiency Delays Motor Decline and Disease Manifestation in a Mouse Model of Synucleinopathy
In synucleinopathies, including Parkinson's disease, partially ubiquitylated α-synuclein species phosphorylated on serine 129 (PS129-α-synuclein) accumulate abnormally. Parkin, an ubiquitin-protein ligase that is dysfunctional in autosomal recessive parkinsonism, protects against α-synuclein-mediated toxicity in various models
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