670 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
The INTEGRAL high energy cut-off distribution of type 1 AGN
In this letter we present the primary continuum parameters, the photon index
Gamma and the high energy cut-off Ec, of 41 type-1 Seyfert galaxies extracted
from the INTEGRAL complete sample of AGN. We performed a broad band (0.3-100
keV) spectral analysis by fitting simultaneously the soft and hard X-ray
spectra obtained by XMM and INTEGRAL/IBIS-Swift/BAT respectively in order to
investigate the general properties of these parameters in particular their
distribution and mean values. We find a mean photon index for the whole sample
of 1.73 with a standard deviation of 0.17 and a mean high energy cut-off of 128
keV with a standard deviation of 46 keV. This is the first time that the
cut-off energy is constrained in a such large number of AGN. We have 26
measurements of the cut-off, which corresponds to 63% of the entire sample,
distributed between 50 and 200 keV. There are a further 11 lower limits mostly
below 300 keV. Using the main parameters of the primary continuum, we have been
able to obtain the actual physical parameters of the Comptonizing region i.e.
the plasma temperature kT_e from 20 to 100 keV and the optical depth tau <4.
Finally, with the high S/N spectra starting to come from NuSTAR it will soon be
possible to better constrain the cut-off values in many AGN, allowing the
determination of more physical models and so to better understand the continuum
emission and geometry of the region surrounding black holes.Comment: 21 pages, 4 figures, 1 table. Accepted for publication on ApJ Letter
Unveiling the nature of three INTEGRAL sources through optical spectroscopy
The results of an optical spectroscopy campaign performed at the Astronomical
Observatory of Bologna in Loiano (Italy) on three hard X-ray sources detected
by INTEGRAL (IGR J17303-0601, IGR J18027-1455 and IGR J21247+5058) are
presented. These data have allowed a determination of the nature for two of
them, with IGR J17303-0601 being a low mass X-ray binary in the Galaxy and IGR
J18027-1455 a background Type 1 Seyfert galaxy at redshift z = 0.035. IGR
J21247+5058, instead, has a quite puzzling spectroscopic appearance, with a
broad, redshifted H_alpha complex superimposed onto a `normal' F/G-type
Galactic star continuum: these features, together with the spatially coincident
extended radio emission, might suggest a chance alignment between a relatively
nearby star and a background radio galaxy. These results underline the still
non-negligible importance of smaller telescopes in modern astrophysics.Comment: 4 pages, 2 figures. Accepted for publication in A&A Letter
The IBIS soft gamma-ray sky after 1000 INTEGRAL orbits
We report here an all-sky soft gamma-ray source catalog based on IBIS
observations performed during the first 1000 orbits of INTEGRAL. The database
for the construction of the source list consists of all good quality data
available from launch in 2002 up to the end of 2010. This corresponds to
110 Ms of scientific public observations with a concentrated coverage on
the Galactic Plane and extragalactic deep exposures. This new catalog includes
939 sources above a 4.5 sigma significance threshold detected in the 17-100 keV
energy band, of which 120 represent previously undiscovered soft gamma-ray
emitters. The source positions are determined, mean fluxes are provided in two
main energy bands, and are reported together with the overall source exposure.
Indicative levels of variability are provided, and outburst times and durations
are given for transient sources. Comparison is made with previous IBIS
catalogs, and those from other similar missions.Comment: 65 pages, 9 figures, 2 tables, accepted for publication in ApJ
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