195 research outputs found
BeppoSAX Observations of the Maser Sy2 Galaxy: ESO103-G35
We have made BeppoSAX observations of the Seyfert 2/1.9 galaxy ESO103-G35,
which contains a nuclear maser source and is known to be heavily absorbed in
the X-rays. Analysis of the X-ray spectra observed by SAX in October 1996 and
1997 yields a spectral index 0.74+/-0.07, typical of Seyfert galaxies and
consistent with earlier observations of this source. The strong, soft X-ray
absorption has column density 1.79E(23)/cm^2, again consistent with earlier
results. The best fitting spectrum is that of a power law with a high energy
cutoff at 29+/-10 keV, a cold, marginally resolved Fe Kalpha line with EW 290
eV (1996) and a mildly ionized Fe K-edge at 7.37 keV. The Kalpha line and cold
absorption are consistent with origin in a accretion disk/torus through which
our line-of-sight passes at a radial distance of pc. The Fe K-edge is
mildly ionized suggesting the presence of ionized gas probably in the inner
accretion disk, close to the central source or in a separate warm absorber. The
data quality is too low to distinguish between these possibilities but the
edge-on geometry implied by the water maser emission favors the former.
Comparison with earlier observations of ESO103-G35 shows little/no change in
spectral parameters while the flux changes by factors of a few on timescales of
a few months. The 2--10 keV flux decreased by a factor of 2.7 between Oct 1996
and Oct 1997 with no detectable change in the count rate >20 keV suggesting a
constant or delayed response reflection component. The high energy cutoff is
lower than the typical 300keV values seen in Seyfert galaxies. A significant
subset of similar sources would affect current models of the AGN contribution
to the cosmic X-ray background which generally assume a high energy cutoff of
300 keV.Comment: 22 pages, postscript file, accepted for publication in Ap
Study of shock waves generation, hot electron production and role of parametric instabilities in an intensity regime relevant for the shock ignition
We present experimental results at intensities relevant to Shock Ignition
obtained at the sub-ns Prague Asterix Laser System in 2012 . We studied shock waves
produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at
1ω (1315 nm) at 7 × 10 13 W/cm 2 to create a pre-plasma on the front side of the target and
a second at 3ω (438 nm) at ∼ 10 16 W/cm 2 to create the shock wave. Multilayer targets
composed of 25 (or 40 μm) of plastic (doped with Cl), 5 μm of Cu (for Kα diagnostics)
and 20 μm of Al for shock measurement were used. We used X-ray spectroscopy of Cl
to evaluate the plasma temperature, Kα imaging and spectroscopy to evaluate spatial and
spectral properties of the fast electrons and a streak camera for shock breakout measurements.
Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and
Two Plasmon Decay) were studied by collecting the back scattered light and analysing its
spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum
pressure reached in our experiment we performed hydro simulations with CHIC and DUED
codes. The maximum shock pressure generated in our experiment at the front side of the
target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was
estimated to be of the order of ∼ 0.1% and their mean energy in the order ∼50 keV.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributio
Swift XRT and VLT Observations of the Afterglow of GRB 041223
The Swift Gamma-Ray Burst Explorer, launched on 2004 November 20, is a
multiwavelength, autonomous, rapid-slewing observatory for gamma-ray burst
(GRB) astronomy. On 2004 December 23, during the activation phase of the
mission, the Swift X-Ray Telescope (XRT) was pointed at a burst discovered
earlier that day by the Swift Burst Alert Telescope. A fading, uncataloged
X-ray source was discovered by the XRT and was observed over a period of about
3 hours, beginning 4.6 hours after the burst. The X-ray detection triggered a
VLT observation of the optical/NIR counterpart, located about 1.1 arcseconds
from the XRT position. The X-ray counterpart faded rapidly, with a power law
index of -1.72 +/- 0.20. The average unabsorbed X-ray flux 4.6-7.9 hours after
the burst was 6.5 x 10^{-12} erg cm^{-2} s^{-1} in the 0.5-10 keV band, for a
power-law spectrum of photon index 2.02 +/- 0.13 with Galactic absorption. The
NIR counterpart was observed at three epochs between 16 and 87 hours after the
burst, and faded with a power-law index of -1.14 +/- 0.08 with a
reddening-corrected SED power-law slope of -0.40 +/- 0.03. We find that the
X-ray and NIR data are consistent with a two-component jet in a wind medium,
with an early jet break in the narrow component and an underlying electron
index of 1.8-2.0.Comment: 16 pages, including 4 figures. Accepted by Astrophysical Journal
(Letters) on 15 February 200
The Imaging X-ray Polarimetry Explorer (IXPE): Technical Overview
The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding linear polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, including polarization maps of several x-ray-bright extended sources and phase-resolved polarimetry of many bright pulsating x-ray sources
The rapid spread of SARS-COV-2 Omicron variant in Italy reflected early through wastewater surveillance
The SARS-CoV-2 Omicron variant emerged in South Africa in November 2021, and has later been identified worldwide, raising serious concerns. A real-time RT-PCR assay was designed for the rapid screening of the Omicron variant, targeting characteristic mutations of the spike gene. The assay was used to test 737 sewage samples collected throughout Italy (19/21 Regions) between 11 November and 25 December 2021, with the aim of assessing the spread of the Omicron variant in the country. Positive samples were also tested with a real-time RT-PCR developed by the European Commission, Joint Research Centre (JRC), and through nested RT-PCR followed by Sanger sequencing. Overall, 115 samples tested positive for Omicron SARS-CoV-2 variant. The first occurrence was detected on 7 December, in Veneto, North Italy. Later on, the variant spread extremely fast in three weeks, with prevalence of positive wastewater samples rising from 1.0% (1/104 samples) in the week 5-11 December, to 17.5% (25/143 samples) in the week 12-18, to 65.9% (89/135 samples) in the week 19-25, in line with the increase in cases of infection with the Omicron variant observed during December in Italy. Similarly, the number of Regions/Autonomous Provinces in which the variant was detected increased from one in the first week, to 11 in the second, and to 17 in the last one. The presence of the Omicron variant was confirmed by the JRC real-time RT-PCR in 79.1% (91/115) of the positive samples, and by Sanger sequencing in 66% (64/97) of PCR amplicons. In conclusion, we designed an RT-qPCR assay capable to detect the Omicron variant, which can be successfully used for the purpose of wastewater-based epidemiology. We also described the history of the introduction and diffusion of the Omicron variant in the Italian population and territory, confirming the effectiveness of sewage monitoring as a powerful surveillance tool
IXPE and XMM-Newton observations of the Soft Gamma Repeater SGR 1806-20
Recent observations with the Imaging X-ray Polarimetry Explorer (IXPE) of two
anomalous X-ray pulsars provided evidence that X-ray emission from magnetar
sources is strongly polarized. Here we report on the joint IXPE and XMM-Newton
observations of the soft {\gamma}-repeater SGR 1806-20. The spectral and timing
properties of SGR 1806-20 derived from XMM-Newton data are in broad agreement
with previous measurements; however, we found the source at an all-time-low
persistent flux level. No significant polarization was measured apart from the
4-5 keV energy range, where a probable detection with PD=31.6\pm 10.5% and
PA=-17.6\pm 15 deg was obtained. The resulting polarization signal, together
with the upper limits we derive at lower and higher energies 2-4 and 5-8 keV,
respectively) is compatible with a picture in which thermal radiation from the
condensed star surface is reprocessed by resonant Compton scattering in the
magnetosphere, similar to what proposed for the bright magnetar 4U 0142+61.Comment: 11 pages, 3 figures, accepted for publication in Ap
VERY HIGH ENERGY γ-RAYS from the UNIVERSE'S MIDDLE AGE: DETECTION of the z = 0.940 BLAZAR PKS 1441+25 with MAGIC
The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale is estimated to be 6.4 ±1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy
Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands
GRAWITA: VLT Survey Telescope observations of the gravitational wave sources GW150914 and GW151226
We report the results of deep optical follow-up surveys of the first two gravitational-wave sources, GW150914 and GW151226, done by the GRAvitational Wave Inaf TeAm Collaboration (GRAWITA). The VLT Survey Telescope (VST) responded promptly to the gravitational wave alerts sent by the LIGO and Virgo Collaborations, monitoring a region of 90 and 72 deg2 for GW150914 and GW151226, respectively, and repeated the observations over nearly two months. Both surveys reached an average limiting magnitude of about 21 in the r band. The paper describes the VST observational strategy and two independent procedures developed to search for transient counterpart candidates in multi-epoch VST images. Several transients have been discovered but no candidates are recognized to be related to the gravitational wave events. Interestingly, among many contaminant supernovae, we find a possible correlation between the supernova VSTJ57.77559-59.13990 and GRB 150827A detected by Fermi-GBM. The detection efficiency of VST observations for different types of electromagnetic counterparts of gravitational wave events is evaluated for the present and future follow-up surveys
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