479 research outputs found
Low energy cut-offs and hard X-ray spectra in high-z radio-loud quasars: the Suzaku view of RBS315
We present the results from the Suzaku observation of the powerful radio-loud
quasar RBS315 (z=2.69), for which a previous XMM-Newton observation showed an
extremely flat X-ray continuum up to 10 keV (photon index Gamma=1.26) and
indications of strong intrinsic absorption (N_H~10^22 cm^{-2} assuming neutral
gas). The instrument for hard X-rays HXD/PIN allows us a detection of the
source up to 50 keV. The broad-band continuum (0.5-50 keV) can be well modeled
with a power-law with slope Gamma=1.5 (definitively softer than the continuum
measured by XMM-Newton) above 1 keV with strong deficit of soft photons. The
low-energy cut-off can be well fitted either with intrinsic absorption (with
column density N_H~10^22 cm^{-2} in the quasar rest frame) or with a break in
the continuum, with an extremely hard (Gamma =0.7) power-law below 1 keV. We
construct the Spectral Energy Distribution of the source, using also optical-UV
measurements obtained through a quasi-simultaneous UVOT/SWIFT observation. The
shape of the SED is similar to that of other Flat Spectrum Radio Quasars
(FSRQs) with similar power, making this source an excellent candidate for the
detection in gamma-rays by GLAST. We model the SED with the synchrotron-Inverse
Compton model usually applied to FSRQs, showing that the deficit of soft
photons can be naturally interpreted as due to an intrinsic curvature of the
spectrum near the low energy end of the IC component rather than to intrinsic
absorption, although the latter possibility cannot be ruled out. We propose
that in at least a fraction of the radio-loud QSOs at high redshift the cut-off
in the soft X-ray band can be explained in a similar way. Further studies are
required to distinguish between the two alternatives.Comment: Accepted for publication in Ap
High-Energy sources before INTEGRAL -- INTEGRAL reference catalog --
We describe the INTEGRAL reference catalog which classifies previously known
bright X-ray and gamma-ray sources before the launch of INTEGRAL. These sources
are, or have been at least once, brighter than ~1 mCrab above 3 keV, and are
expected to be detected by INTEGRAL. This catalog is being used in the INTEGRAL
Quick Look Analysis to discover new sources or significantly variable sources.
We compiled several published X-ray and gamma-ray catalogs, and surveyed recent
publications for new sources. Consequently, there are 1122 sources in our
INTEGRAL reference catalog. In addition to the source positions, we show an
approximate spectral model and expected flux for each source, based on which we
derive expected INTEGRAL counting rates. Assuming the default instrument
performances and at least ~10^5 sec exposure time for any part of the sky, we
expect that INTEGRAL will detect at least ~700 sources below 10 keV and ~400
sources above 20 keV over the mission life.Comment: Accepted to A&A Letter INTEGRAL special issu
The first gamma-ray outburst of a Narrow-Line Seyfert 1 Galaxy: the case of PMN J0948+0022 in July 2010
We report on a multiwavelength campaign on the radio-loud Narrow-Line Seyfert
1 (NLS1) Galaxy PMN J0948+0022 (z=0.5846) performed in 2010 July-September and
triggered by a high-energy gamma-ray outburst observed by the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. The peak flux in
the 0.1-100 GeV energy band exceeded, for the first time in this type of
source, the value of 10^-6 ph cm^-2 s^-1, corresponding to an observed
luminosity of 10^48 erg s^-1. Although the source was too close to the Sun
position to organize a densely sampled follow-up, it was possible to gather
some multiwavelength data that confirmed the state of high activity across the
sampled electromagnetic spectrum. The comparison of the spectral energy
distribution of the NLS1 PMN J0948+0022 with that of a typical blazar - like 3C
273 - shows that the power emitted at gamma rays is extreme.Comment: 8 pages, 7 figures, 2 tables. Accepted for the publication on MNRAS
Main Journal. Typo in bibliography correcte
INTEGRAL observation of 3EG J1736-2908
The possible identification by INTEGRAL of the EGRET source 3EG J1736-2908
with the active galactic nucleus GRS 1734-292 is discussed. The latter was
discovered in 1990 and later identified with a Seyfert 1 galaxy. At the time of
the compilation of the 3rd EGRET Catalog, it was not considered as a possible
counterpart of the source 3EG J1736-2908, which remained unidentified. A
detailed multiwavelength study of the EGRET error circle is presented, by
including archival radio, soft- and hard-X observations, suggesting that GRS
1734-292 could be a likely counterpart of 3EG J1736-2908, even though this
poses very interesting questions about the production mechanisms of gamma-rays
with energies greater than 100 MeV.Comment: 6 pages, 3 figures. Accepted for publication on A&A Main Journa
Relativistic jets in Narrow-Line Seyfert 1
Narrow-Line Seyfert 1 (NLS1) class of active galactic nuclei (AGNs) is
generally radio-quiet, but a small percent of them are radio-loud. The recent
discovery by Fermi/LAT of high-energy gamma-ray emission from 4 NLS1s proved
the existence of relativistic jets in these systems. It is therefore important
to study this new class of gamma-ray emitting AGNs. Here we report preliminary
results about the observations of the July 2010 gamma-ray outburst of PMN
J0948+0022, when the source flux exceeded for the first time 10^-6 ph cm^-2
s^-1 (E > 100 MeV).Comment: 2 pages, 1 figure. To be presented at IAU Symposium 275 "Jets at all
scales", Buenos Aires, 13-17 September 201
The application of slim disk models to ULX: the case of M33 X-8
A comparative XMM-Newton archival data spectral study of the ultraluminous
X-ray source (ULX) M33 X-8 has been performed by using both the standard disk
model and the newly developed slim disk models. The results of this analysis
tend to confirm the hypothesis that M33 X-8 is an X-ray binary with a
stellar-mass black hole accreting at super-Eddington rate.Comment: 6 pages, 4 figures, accepted for publication on Advances in Space
Research, Special Issue Proceedings of 35th COSPAR (Paris, France, 18-25 July
2004
Chasing the heaviest black holes of jetted Active Galactic Nuclei
We investigate the physical properties of the 10 blazars at redshift greater
than 2 detected in the 3-years all sky survey performed by the Burst Alert
Telescope (BAT) onboard the Swift satellite. We find that the jets of these
blazars are among the most powerful known. Furthermore, the mass of their
central black hole, inferred from the optical-UV bump, exceeds a few billions
of solar masses, with accretion luminosities being a large fraction of the
Eddington one. We compare their properties with those of the brightest blazars
of the 3-months survey performed by the Large Area Telescope (LAT) onboard the
Fermi satellite. We find that the BAT blazars have more powerful jets, more
luminous accretion disks and larger black hole masses than LAT blazars. These
findings can be simply understood on the basis of the blazar sequence, that
suggests that the most powerful blazars have a spectral energy distribution
with a high energy peak at MeV (or even sub-MeV) energies. This implies that
the most extreme blazars can be found more efficiently in hard X-rays, rather
than in the high energy gamma-ray band. We then discuss the implications of our
findings for future missions, such as the New Hard X-ray Mission (NHXM) and
especially the Energetic X-ray Imaging Survey Telescope (EXIST) mission which,
during its planned 2 years all sky survey, is expected to detect thousands of
blazars, with a few of them at z greater than 6.Comment: Accepted for publication in MNRAS. Absorption due to Lyman-alpha
clouds calculated, and optical-UV data de-absorbed. 16 figures, 15 page
Exploring the parent population of beamed NLS1s: from the black hole to the jet
The aim of this work is to understand the nature of the parent population of
beamed narrow-line Seyfert 1 galaxies (NLS1s), by studying the physical
properties of three parent candidates samples: steep-spectrum radio-loud NLS1s,
radio-quiet NLS1s and disk-hosted radio-galaxies. In particular, we focused on
the black hole mass and Eddington ratio distribution and on the interactions
between the jet and the narrow-line region.Comment: 6 pages, 2 figures, to appear in Proceedings of High Energy Phenomena
in Relativistic Outflows (HEPRO) V, Workshop Series of the Argentinian
Astronomical Societ
Unveiling the parent population of beamed narrow-line Seyfert 1s
Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN)
recently identified as a new class of -ray sources. The high energy
emission is explained by the presence of a relativistic jet observed at small
angles, just like in the case of blazars. When the latter are observed at
larger angles they appear as radio-galaxies, but an analogue parent population
for beamed NLS1s has not yet been determined. In this work we analyze this
problem by studying the physical properties of three different samples of
parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s,
and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In
our approach, we first derived black hole mass and Eddington ratio from the
optical spectra, then we investigated the interaction between the jet and the
narrow-line region from the [O III] 4959,5007 lines. Finally,
the radio luminosity function allowed us to compare their jet luminosity and
hence determine the relations between the samples.Comment: 6 pages, no figures. Proceedings of the 28th Texas Symposium, Geneva,
December 13-18, 201
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