| 1. |
- Aleksic, J., et al.
(författare)
-
DETECTION OF VERY HIGH ENERGY gamma-RAY EMISSION FROM THE PERSEUS CLUSTER HEAD-TAIL GALAXY IC 310 BY THE MAGIC TELESCOPES
- 2010
-
Ingår i: The Astrophysical Journal Letters. - 2041-8205. ; 723:2, s. l207-L212
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the detection with the MAGIC telescopes of very high energy (VHE) gamma-rays from IC 310, a head-tail radio galaxy in the Perseus galaxy cluster, observed during the interval 2008 November to 2010 February. The Fermi satellite has also detected this galaxy. The source is detected by MAGIC at a high statistical significance of 7.6 sigma in 20.6 hr of stereo data. The observed spectral energy distribution is flat with a differential spectral index of -2.00 +/- 0.14. The mean flux above 300 GeV, between 2009 October and 2010 February, (3.1 +/- 0.5) x 10(-12) cm(-2) s(-1), corresponds to (2.5 +/- 0.4)% of Crab Nebula units. Only an upper limit, of 1.9% of Crab Nebula units above 300 GeV, was obtained with the 2008 data. This, together with strong hints (>3 sigma) of flares in the middle of 2009 October and November, implies that the emission is variable. The MAGIC results favor a scenario with the VHE emission originating from the inner jet close to the central engine. More complicated models than a simple one-zone synchrotron self-Compton (SSC) scenario, e. g., multi-zone SSC, external Compton, or hadronic, may be required to explain the very flat spectrum and its extension over more than three orders of magnitude in energy.
|
|
| 2. |
- Soffitta, Paolo, et al.
(författare)
-
XIPE : the X-ray imaging polarimetry explorer
- 2013
-
Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 36:3, s. 523-567
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017. The proposal was, unfortunately, not selected. To be compliant with this schedule, we designed the payload mostly with existing items. The XIPE proposal takes advantage of the completed phase A of POLARIX for an ASI small mission program that was cancelled, but is different in many aspects: the detectors, the presence of a solar flare polarimeter and photometer and the use of a light platform derived by a mass production for a cluster of satellites. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2-10 keV band in 10(5) s for pointed observations, and 0.6 % for an X10 class solar flare in the 15-35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin x 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 mu s. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut fur extraterrestrische Physik (MPE, Germany). XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil). The data policy is organized with a Core Program that comprises three months of Science Verification Phase and 25 % of net observing time in the following 2 years. A competitive Guest Observer program covers the remaining 75 % of the net observing time.
|
|
| 3. |
- Miranda, Maria, et al.
(författare)
-
Antioxidants rescue photoreceptors in rd1 mice: Relationship with thiol metabolism
- 2010
-
Ingår i: Free Radical Biology & Medicine. - : Elsevier BV. - 0891-5849. ; 48:2, s. 216-222
-
Tidskriftsartikel (refereegranskat)abstract
- We have previously shown that the use of a combination of antioxidants delayed the degeneration process in rd1 mouse retina. In an effort to understand the mechanism of action of these substances (zeaxanthin, lutein, alpha-lipoic acid, glutathione, and Lycium barbarum extract) the changes in the levels of several proteins and oxidative stress markers in the rd1 retina have been studied. The treatment increased glutathione peroxidase activity and glutathione levels and decreased cystine concentrations in rd1 retinas. Considering all the results obtained from treated and untreated animals, a high correlation was present between glutathione concentration and glutathione peroxidase activity, and there was a negative correlation between glutathione retinal concentration and number of TUNEL-positive cells. No difference was observed between the numbers of nNOS- and NADPH-diaphorase-positive cells in treated and untreated rd1 mice. Thiol contents and thiol-dependent peroxide metabolism seem to be directly related to the survival of photoreceptors in rd1 mouse retina. (C) 2009 Elsevier Inc. All rights reserved.
|
|
