1,095 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&
Chasing extreme blazars with INTEGRAL
Within the blazar population, hard X-ray selected objects are of particular
interest as they tend to lie at each end of the blazar sequence. In particular,
flat spectrum radio quasars located at high redshifts display the most powerful
jets, the largest black hole masses and the most luminous accretion disks:
their spectral energy distribution has a Compton peak in the sub-MeV region
which favours their detection by instruments like INTEGRAL/IBIS and Swift/BAT.
These sources are even more extreme than blazars selected in other wavebands,
like, for example, the gamma-ray range explored by Fermi. Here we report on a
sample of 12 high redshift blazars detected so far by INTEGRAL, including 3
newly identified objects. Some properties of the combined IBIS/BAT sample of
high redshift blazars (z>2) are also compared to those of a similar similar
sample obtained by Fermi.Comment: 4 pages, 2 figures. Proceedings of "An INTEGRAL view of the
high-energy sky (the first 10 years)" the 9th INTEGRAL Workshop, October
15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds.
A. Goldwurm, F. Lebrun and C. Winkler,
(http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id=05
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
Adaptive quasi-unsupervised detection of smoke plume by lidar
The early detection of fire is one of the possible applications of LiDAR techniques. The smoke generated by a fire is mainly compounded of CO2, H2O, particulate, and other combustion products, which involve the local variation of the scattering of the electromagnetic wave at specific wavelengths. The increases of the backscattering coefficient are transduced in peaks on the signal of the backscattering power recorded by the LiDAR system, located exactly where the smoke plume is, allowing not only the detection of a fire but also its localization. The signal processing of the LiDAR signals is critical in the determination of the performances of the fire detection. It is important that the sensitivity of the apparatus is high enough but also that the number of false alarms is small, in order to avoid the trigger of useless and expensive countermeasures. In this work, a new analysis method, based on an adaptive quasi-unsupervised approach was used to ensure that the algorithm is continuously updated to the boundary conditions of the system, such as the weather and experimental apparatus issues. The method has been tested on an experimental campaign of 227 pulses and the performances have been analyzed in terms of sensitivity and specificity
Measurements of vehicle pollutants in a high-traffic urban area by a multiwavelength dial approach: Correlation between two different motor vehicle pollutants
The development and improvement of monitoring techniques to measure the concentration
of pollutants in the atmosphere are a starting point to guarantee high levels of human health and
environmental safety. The combination of lidar and dial techniques, by measuring backscattering
signals and reconstructing the map of their concentrations, can be used to provide detailed information
about the presence of aerosols, particulate and pollutions. Moreover, by using a multiwavelength
approach, it is possible to increase the measurement accuracy and reliability. In this work, the dial
approach is used to monitor the pollution in a very congested urban area with high trac. In order
to provide a validation of the results, correlation analyses between the measured pollutants was
performed. A new lidar analysis method, based on the least-square minimization technique,
was introduced and demonstrated to work properly. The dial capability to detect polluted areas was
shown—and by correlation analysis—also the possibility to identify the source of pollutions can
be performed
- …