754 research outputs found
Using X-ray catalogues to find counterparts to unassociated high-energy Fermi/LAT sources
The first Fermi Large Area Telescope (LAT) catalogue of sources (1FHL)
emitting at high energies (above 10 GeV) reports the details of 514 objects
detected in the first three years of the Fermi mission. Of these, 71 were
reported as unidentified in the 1FHL catalogue, although six are likely to be
associated with a supernova remnant (SNR), a Pulsar Wind Nebula (PWN) or a
combination of both, thereby leaving a list of 65 still unassociated objects.
Herein, we report a preliminary analysis on this sample of objects
concentrating on nine 1FHL sources, which were found to have a clear optical
extragalactic classification. They are all blazar, eight BL Lac and one flat
spectrum radio quasar, typically at redshift greater than 0.1.Comment: Proceedings of "Swift: 10 Years of Discovery", December 2-5 2014,
Rome, Italy, in Proceedings of Science (SWIFT 10
Swift/XRT counterparts to unassociated Fermi high-energy LAT sources
We report the results from our analysis of a large set of archival data
acquired with the X-ray telescope (XRT) onboard Swift, covering the sky region
surrounding objects from the first Fermi Large Area Telescope (LAT) catalogue
of high-energy sources (1FHL), which still lack an association. Of the 23
regions analysed, ten did not show any evidence of X-ray emission, but 13 were
characterised by the presence of one or more objects emitting in the 0.3-10 keV
band. Only in a couple of cases is the X-ray counterpart located outside the
Fermi positional uncertainty, while in all other cases the associations found
are compatible with the high-energy error ellipses. All counterparts we found
have been studied in detail by means of a multi-waveband approach to evaluate
their nature or class; in most cases, we have been able to propose a likely or
possible association except for one Fermi source whose nature remains doubtful
at the moment. The majority of the likely associations are extragalactic in
nature, most probably blazars of the BL Lac type.Comment: 13 pages, 5 figures, 4 tables. Accepted for publication in A&
Swift/XRT follow-up observations of unidentified INTEGRAL/IBIS sources
Many sources listed in the 4th IBIS/ISGRI survey are still unidentified, i.e.
lacking an X-ray counterpart or simply not studied at lower energies (< 10
keV). The cross-correlation between the list of IBIS sources in the 4th
catalogue and the Swift/XRT data archive is of key importance to search for the
X-ray counterparts; in fact, the positional accuracy of few arcseconds obtained
with XRT allows us to perform more efficient and reliable follow-up
observations at other wavelengths (optical, UV, radio). In this work, we
present the results of the XRT observations for four new gamma-ray sources: IGR
J12123-5802, IGR J1248.2-5828, IGR J13107-5626 and IGR J14080-3023. For IGR
J12123-5802 we find a likely counterpart, but further information are needed to
classified this object, IGR J1248.2-5828 is found to be a Seyfert 1.9, for IGR
J13107-5626 we suggest a possible AGN nature, while IGR J14080-3023 is
classified as a Seyfert 1.5 galaxy.Comment: 6 pages, 4 figure and 2 tables. Accepted for publication on PoS
(contribution PoS(extremesky2009)018), proceedings of "The Extreme sky:
Sampling the Universe above 10 keV", held in Otranto (Italy), 13-17 October
200
Broadband X-ray spectrum of the newly discovered broad line radio galaxy IGR J21247+5058
In this paper we present radio and high energy observations of the INTEGRAL
source IGR J21247+5058, a broad line emitting galaxy obscured by the Galactic
plane. Archival VLA radio data indicate that IGR J21247+5058 can be classified
as an FRII Broad Line Radio Galaxy. The spectrum between 610 MHz and 15 GHz is
typical of synchrotron self-absorbed radiation with a peak at 8 GHz and a low
energy turnover; the core fraction is 0.1 suggestive of a moderate Doppler
boosting of the base of the jet. The high energy broad-band spectrum was
obtained by combining XMM-Newton and Swift/XRT observation with INTEGRAL/IBIS
data. The 0.4-100 keV spectrum is well described by a power law, with slope
=1.5, characterised by complex absorption due to two layers of material
partially covering the source and a high energy cut-off around 70-80 keV.
Features such as a narrow iron line and a Compton reflection component, if
present, are weak, suggesting that reprocessing of the power law photons in the
accretion disk plays a negligible role in the source.Comment: 7 pages, 7 figures, 3 tables, accepted for pubblication on MNRA
Exploiting the Potential in Water Cleanup from Metals and Nutrients of Desmodesmus sp. and Ampelodesmos mauritanicus
Increasing levels of freshwater contaminants, mainly due to anthropogenic activities, have resulted in a great deal of interest in finding new eco-friendly, cost-effective and efficient methods for remediating polluted waters. The aim of this work was to assess the feasibility of using a green microalga Desmodesmus sp., a cyanobacterium Nostoc sp. and a hemicryptophyte Ampelodesmos mauritanicus to bioremediate a water polluted with an excess of nutrients (nitrogen and phosphorus) and heavy metals (copper and nickel). We immediately determined that Nostoc sp. was sensitive to metal toxicity, and thus Desmodesmus sp. was chosen for sequential tests with A. mauritanicus. First, A. mauritanicus plants were grown in the ‘polluted’ culture medium for seven days and were, then, substituted by Desmodesmus sp. for a further seven days (14 days in total). Heavy metals were shown to negatively affect both the growth rates and nutrient removal capacity. The sequential approach resulted in high metal removal rates in the single metal solutions up to 74% for Cu and 85% for Ni, while, in the bi-metal solutions, the removal rates were lower and showed a bias for Cu uptake. Single species controls showed better outcomes; however, further studies are necessary to investigate the behavior of new specie
IGR J22517+2218=MG3 J225155+2217: a new gamma-ray lighthouse in the distant Universe
We report on the identification of a new soft gamma ray source, namely IGR
J22517+2218, detected with IBIS/INTEGRAL. The source, which has an observed
20-100 keV flux of ~4 x10^-11 erg cm-2 s-1, is spatially coincident with MG3
J225155+2217, a quasar at z=3.668. The Swift/XRT 0.5-10 keV continuum is flat
(Gamma=1.5) with evidence for a spectral curvature below 1-2 keV either due to
intrinsic absorption (NH=3 +/- 2 x 10^22 cm-2) or to a change in slope (Delta
Gamma= 0.5). X-ray observations indicate flux variability over a 6 days period
which is further supported by a flux mismatch between Swift and INTEGRAL
spectra. IGR J22517+2218 is radio loud and has a flat radio spectrum; optically
it is a broad line emitting quasar with the atypical property of hosting a
narrow line absorption system. The Source Spectral Energy Distribution is
unusual compared to blazars of similar type: either it has the synchrotron peak
in the X/gamma-ray band (i.e. much higher than generally observed) or the
Compton peak in the MeV range (i.e. lower than typically measured). IGR
J22517+2218=MG3 J225155+2217 is the second most distant blazar detected above
20 keV and a gamma-ray lighthouse shining from the edge of our Universe.Comment: 4 pages, 4 figures, Accepted for publication in Astrophysical Journal
Letter
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