2,986 research outputs found
Fermi detected blazars seen by INTEGRAL
Multiwavelength observations are essential to constrain physical parameters
of the blazars observed by Fermi/LAT. Among the 187 AGN significantly detected
in public INTEGRAL data above 20 keV by the imager IBIS/ISGRI, 20 blazars were
detected. 15 of these sources allowed significant spectral extraction. They
show hard X-ray spectra with an average photon index of 2.1+-0.1 and a hard
X-ray luminosity of L(20-100 keV) = 1.3e46 erg/s. 15 of the INTEGRAL blazars
are also visible in the first 16 months of the Fermi/LAT data, thus allowing to
constrain the inverse Compton branch in these cases. Among others, we analyse
the LAT data of four blazars which were not included in the Fermi LAT Bright
AGN Sample based on the first 3 months of the mission: QSO B0836+710, H
1426+428, RX J1924.8-2914, and PKS 2149-306. Especially for blazars during
bright outbursts, as already observed simultaneously by INTEGRAL and Fermi
(e.g. 3C 454.3 and Mrk 421), INTEGRAL provides unique spectral coverage up to
several hundred keV. We present the spectral analysis of INTEGRAL and Fermi
data and demonstrate the potential of INTEGRAL observations of Fermi detected
blazars in outburst by analysing the combined data set of the persistent radio
galaxy Cen A.Comment: 5 pages, 5 figures, 2009 Fermi Symposium, eConf Proceedings C09112
Compton processes in the bright AGN MCG+8-11-11
We present preliminary results on the hard X-ray emission properties of the
Seyfert 1.5 galaxy MCG+8-11-11 as observed by INTEGRAL and SWIFT. All the
INTEGRAL IBIS/ISGRI data available up to October 2009 have been analyzed
together with two SWIFT/XRT snapshot observations performed in August and
October 2009, quasi-simultaneously to INTEGRAL pointed observations of
MCG+8-11-11. No correlation is observed between the hard X-ray flux and the
spectral slope, while the position of the high-energy cut-off is found to have
varied during the INTEGRAL observations. This points to a change in the
temperature of the Comptonising medium from a minimum value of kT = 30-50 keV
to values larger than 100-150 keV. There is no significant detection of Compton
reflection, with a 3 sigma upper limit of R < 0.2, and no line has been
detected at 112 keV, as previously claimed from HEAT observations (112 keV flux
F < 2.4e-4 ph/cm^2/s). The variability behaviour of MCG+8-11-11 is found to be
similar to that shown by IC 4329A, with different temperatures of the electron
plasma for similar flux levels of the source, while other bright Seyfert
galaxies present different variability patterns at hard X-rays, with spectral
changes correlated to flux variations (e.g. NGC 4151).Comment: 6 pages, 4 figures. Accepted for publication on PoS (contribution
PoS(INTEGRAL 2010)077), proceedings of the 8th INTEGRAL Workshop "The
Restless Gamma-ray Universe" (September 2010, Dublin, Ireland
High-energy emission from NGC 5506, the brightest hard X-ray Narrow Line Seyfert 1 galaxy
We present results on the hard X-ray emission of NGC 5506, the brightest
narrow line Seyfert 1 galaxy above 20 keV. All the recent observations by
INTEGRAL, Swift and Suzaku have been analysed and spectral analysis during nine
separated time periods has been performed. While flux variations by a factor of
2 were detected during the last 7 years, only moderate spectral variations have
been observed, with the hint of a hardening of the X-ray spectrum and a
decrease of the intrinsic absorption with time. Using Suzaku observations it is
possible to constrain the amount of Compton reflection to R = 0.6-1.0, in
agreement with previous results on the source. The signature of Comptonisation
processes can also be found in the detection of a high-energy cut-off during
part of the observations, at Ec = 40-100 keV. When a Comptonisation model is
applied to the Suzaku data, the temperature and the optical depth of the
Comptonising electron plasma are measured at kT = 60-80 keV and tau = 0.6-1.0,
respectively. The properties inferred for NGC 5506 in this study agree with
those based on other data sets for the same AGN, and fit the picture of NLS1
having in general lower high-energy cut-offs at hard X-rays than their broad
line equivalent.Comment: 8 pages, 3 figures, 1 table. Proceedings of the Workshop "Narrow-Line
Seyfert 1 Galaxies and Their Place in the Universe", Milano, April 4-6, 2011
(Proceedings of Science,
http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=126
Plants in the Tapestry (Literally)
Among our studies of ancient Peruvian textiles created in tapestry technique, we have come across some surprising elements, both in the warp and the weft. Andean textiles created over the past 10,000 years have been preserved in certain locations along the Pacific desert coast. They are usually preserved in the cloth bundles that protect and adorn the dead, and composed of fibers from native cotton varieties of Amazonian ancestry, the hair of highland ancestors of today’s llama and alpaca, maguey leaves from the mid-valley canyons, and reeds from coastal marshes. Garment forms, techniques and imagery can indicate textiles produced in different regions of the coast, or produced in the highlands and later deposited in lowland contexts.
In a survey of 450 textiles of all historic periods from sites in the greater Ica region, two objects stand out based on their use of unspun elements of vegetable origin in a tapestry structure. The plant parts are dissimilar, as are the species present, and the way in which they are used. In one case, the unusual elements are used strategically and seem related to object function, while in the other case the choice may have been purely aesthetic. One object is approximately 1000 years old, while the other is over 2000 years old. We present them in the contexts of the textile traditions from which they come, and whose rules they appear to break
Echoes of multiple outbursts of Sagittarius A* revealed by Chandra
The relatively rapid spatial and temporal variability of the X-ray radiation
from some molecular clouds near the Galactic center shows that this emission
component is due to the reflection of X-rays generated by a source that was
luminous in the past, most likely the central supermassive black hole,
Sagittarius A*. Studying the evolution of the molecular cloud reflection
features is therefore a key element to reconstruct Sgr A*'s past activity. The
aim of the present work is to study this emission on small angular scales in
order to characterize the source outburst on short time scales. We use Chandra
high-resolution data collected from 1999 to 2011 to study the most rapid
variations detected so far, those of clouds between 5' and 20' from Sgr A*
towards positive longitudes. Our systematic spectral-imaging analysis of the
reflection emission, notably of the Fe Kalpha line at 6.4 keV and its
associated 4-8 keV continuum, allows us to characterize the variations down to
15" angular scale and 1-year time scale. We reveal for the first time abrupt
variations of few years only and in particular a short peaked emission, with a
factor of 10 increase followed by a comparable decrease, that propagates along
the dense filaments of the Bridge cloud. This 2-year peaked feature contrasts
with the slower 10-year linear variations we reveal in all the other molecular
structures of the region. Based on column density constraints, we argue that
these two different behaviors are unlikely to be due to the same illuminating
event. The variations are likely due to a highly variable active phase of Sgr
A* sometime within the past few hundred years, characterized by at least two
luminous outbursts of a few-year time scale and during which the Sgr A*
luminosity went up to at least 10^39 erg/s.Comment: 17 pages, 16 figures, Accepted for publication in Astronomy &
Astrophysic
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