-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we present the hard X-ray spectral analysis of a complete
sample of AGN de- tected by INTEGRAL/IBIS. In conjunction with IBIS spectra, we
make use of Swift/BAT data, with the aim of cross-calibrating the two
instruments, studying source variability and con- straining some important
spectral parameters. We find that flux variability is present in at least 14%
of the sample, while spectral variability is found only in one object. There is
general good agreement between BAT and IBIS spectra, despite a systematic
mismatch of about 22% in normalisation. When fitted with a simple power-law
model, type 1 and type 2 sources appear to have very similar average photon
indices, suggesting that they are powered by the same mechanism. As expected,
we also find that a simple power-law does not always describe the data
sufficiently well, thus indicating a certain degree of spectral complexity,
which can be ascribed to features like a high energy cut-off and/or a
reflection component. Fixing the reflection to be 0, 1 or 2, we find that our
sample covers quite a large range in photon indices as well as cut-off
energies; however, the spread is due only to a small number of objects, while
the majority of the AGN lie within well defined boundaries of photon index
(1<{\Gamma}<2) and cut-off energy (30<Ecut<300 keV).
05/2013;
-
[show abstract]
[hide abstract]
ABSTRACT: With respect to the recent INTEGRAL/IBIS 9-year Galactic Hard X-ray Survey
(Krivonos et al. 2012), we use archival Swift/XRT observations in conjunction
with multi-wavelength information to discuss the counterparts of a sample of
newly discovered objects. The X-ray telescope (XRT, 0.3-10 keV) on board Swift,
thanks to its few arcseconds source location accuracy, has been proven to be a
powerful tool with which the X-ray counterparts to these IBIS sources can be
searched for and studied. In this work, we present the outcome of this analysis
by discussing four objects (SWIFT J0958.0-4208, SWIFT J1508.6-4953, IGR
J17157-5449, and IGR J22534+6243) having either X-ray data of sufficient
quality to perform a reliable spectral analysis or having interesting
multiwaveband properties. We find that SWIFT J1508.6-4953 is most likely a
Blazar, while IGR J22534+6243 is probably a HMXB. The remaining two objects may
be contaminated by nearby X-ray sources and their class can be inferred only by
means of optical follow-up observations of all likely counterparts.
04/2013;
-
P. Parisi,
N. Masetti,
A. F. Rojas,
V. McBride,
L. Steward, L. Bassani,
A. Bazzano,
A. J. Bird,
P. A. Charles,
V. Chavushyan,
G. Galaz,
E. Jimenez-Bailon,
R. Landi,
A. Malizia,
E. Mason,
D. Minniti,
L. Morelli,
E. Palazzi,
J. B Stephen,
P. Ubertini
[show abstract]
[hide abstract]
ABSTRACT: The most recent all-sky surveys performed with the INTEGRAL and SWIFT
satellites allowed the detection of more than 1500 sources in hard X-rays above
20 keV. About one quarter of them has no obvious counterpart at other
wavelengths and therefore could not be associated with any known class of
high-energy emitting objects. Although cross-correlation with catalogues or
surveys at other wavelengths (especially soft X-rays) is of invaluable support
in pinpointing the putative optical candidates, only accurate optical
spectroscopy can reveal the true nature of these sources. With the aim of
identifying them, we started in 2004 an optical spectroscopy program which uses
data from several telescopes worldwide and which proved extremely successful,
leading to the identification of about 200 INTEGRAL objects and nearly 130
Swift sources. Here we want to present a summary of this identification work
and an outlook of our preliminary results on identification of newly-discovered
sources belonging to the 4th IBIS catalog and to the 54 months Palermo
Swift/BAT catalog.
02/2013;
-
[show abstract]
[hide abstract]
ABSTRACT: In this work we present the most comprehensive INTEGRAL AGN sample which
lists 272 objects. Here we mainly use this sample to study the absorption
properties of active galaxies, to probe new AGN classes and to test the AGN
unification scheme. We find that half (48%) of the sample is absorbed while the
fraction of Compton thick AGN is small (~7%). In line with our previous
analysis, we have however shown that when the bias towards heavily absorbed
objects which are lost if weak and at large distance is removed, as it is
possible in the local Universe, the above fractions increase to become 80% and
17%. We also find that absorption is a function of source luminosity, which
implies some evolution in the obscuration properties of AGN. Few peculiar
classes, so far poorly studied in the hard X-ray band, have been detected and
studied for the first time such as 5 XBONG, 5 type 2 QSOs and 11 LINERs. In
terms of optical classification, our sample contains 57% of type 1 and 43% of
type 2 AGN; this subdivision is similar to that found in X-rays if unabsorbed
versus absorbed objects are considered, suggesting that the match between
optical and X-ray classification is overall good. Only a small percentage of
sources (12%) does not fulfill the expectation of the unified theory as we find
22 type 1 AGN which are absorbed and 10 type 2 AGN which are unabsorbed.
Studying in depth these outliers we found that most of the absorbed type 1 AGN
have X-ray spectra characterized by either complex or warm/ionized absorption
more likely due to ionized gas located in an accretion disk wind or in the
biconical structure associated to the central nucleus, therefore unrelated to
the toroidal structure. Among 10 type 2 AGN which resulted to be unabsorbed, at
most 3-4% is still eligible to be classified as a "true" type 2 AGN.
07/2012;
-
P. Parisi,
N. Masetti,
E. Jiménez-Bailón,
V. Chavushyan,
E. Palazzi,
R. Landi,
A. Malizia, L. Bassani,
A. Bazzano,
A. J. Bird,
P. A. Charles,
G. Galaz,
E. Mason,
V. A. McBride,
D. Minniti,
L. Morelli,
F. Schiavone,
P. Ubertini
[show abstract]
[hide abstract]
ABSTRACT: Through an optical campaign performed at 4 telescopes located in the northern
and the southern hemispheres, plus archival data from two on-line sky surveys,
we have obtained optical spectroscopy for 29 counterparts of unclassified or
poorly studied hard X-ray emitting objects detected with Swift/BAT and listed
in the 39 months Palermo catalogue. All these objects have also observations
taken with Swift/XRT or XMM-EPIC which not only allow us to pinpoint their
optical counterpart, but also to study their X-ray spectral properties (column
density, power law photon index and F2-10 keV flux). We find that 28 sources in
our sample are AGN; 7 are classified as type 1 while 21 are of type 2; the
remaining object is a galactic cataclysmic variable. Among our type 1 AGN, we
find 5 objects of intermediate Seyfert type (1.2-1.9) and one Narrow Line
Seyfert 1 galaxy; for 4 out of 7 sources, we have been able to estimate the
central black hole mass. Three of the type 2 AGN of our sample display optical
features typical of the LINER class and one is a likely Compton thick AGN. All
galaxies classified in this work are relatively nearby objects since their
redshifts lie in the range 0.008-0.075; the only galactic object found lies at
an estimated distance of 90 pc. We have also investigated the optical versus
X-ray emission ratio of the galaxies of our sample to test the AGN unified
model. For them, we have also compared the X-ray absorption (due to gas) with
the optical reddening (due to dust): we find that for most of our sources,
specifically those of type 1.9-2.0 the former is higher than the latter
confirming early results by Maiolino et al. (2001); this is possibly due to the
properties of dust in the circumnuclear obscuring torus of the AGN.
06/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We report on the identification of a new soft gamma-ray source, IGR
J12319-0749, detected with the IBIS imager on board the INTEGRAL satellite. The
source, which has an observed 20-100 keV flux of ~8.3 x 10^{-12} erg cm^{-2}
s^{-1}, is spatially coincident with an AGN at redshift z=3.12. The broad-band
continuum, obtained by combining XRT and IBIS data, is flat (Gamma ~ 1.3) with
evidence for a spectral break around 25 keV (100 keV in the source rest frame).
X-ray observations indicate flux variability which is further supported by a
comparison with a previous ROSAT measurement. IGR J12319-0749 is also a radio
emitting object likely characterized by a flat spectrum and high radio
loudness; optically it is a broad-line emitting object with a massive black
hole (2.8 x 10^{9}$ solar masses) at its center. The source Spectral Energy
Distribution is similar to another high redshift blazar, 225155+2217 at
z=3.668: both objects are bright, with a large accretion disk luminosity and a
Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319-0749 is
likely the second most distant blazar detected so far by INTEGRAL.
05/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We present new Suzaku and Fermi data and re-analysed archival hard X-ray data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) and Swift–Burst Alert Telescope (BAT) surveys to investigate the physical properties of the luminous, high-redshift, hard X-ray-selected blazar IGR J22517+2217, through the modelling of its broad-band spectral energy distribution (SED) in two different activity states. Through analysis of new Suzaku data and flux-selected data from archival hard X-ray observations, we build the source SED in two different states, one for the newly discovered flare that occurred in 2005 and one for the following quiescent period. Both SEDs are strongly dominated by the high-energy hump peaked at 1020–1022 Hz, which is at least two orders of magnitude higher than the low-energy (synchrotron) one at 1011–1014 Hz and varies by a factor of 10 between the two states. In both states the high-energy hump is modelled as inverse Compton emission between relativistic electrons and seed photons produced externally to the jet, while the synchrotron self-Compton component is found to be negligible. In our model the observed variability can be accounted for by a variation of the total number of emitting electrons and by a dissipation region radius changing from inside to outside the broad-line region as the luminosity increases. In its flaring activity, IGR J22517+2217 is revealed as one of the most powerful jets among the population of extreme, hard X-ray-selected, high-redshift blazars observed so far.
Monthly Notices of the Royal Astronomical Society 03/2012; 421(1):390 - 397. · 4.90 Impact Factor
-
N Masetti,
P Parisi,
E Jiménez-Bailón,
E Palazzi,
V Chavushyan, L Bassani,
A Bazzano,
A J Bird,
A J Dean,
G Galaz,
R Landi,
A Malizia,
D Minniti,
L Morelli,
F Schiavone,
J B Stephen,
P Ubertini
[show abstract]
[hide abstract]
ABSTRACT: Since its launch in October 2002, the INTEGRAL satellite has revolutionized our knowledge of the hard X–ray sky thanks to its unprecedented imaging capabilities and source detection positional accuracy above 20 keV. Nevertheless, many of the newly-detected sources in the INTEGRAL sky surveys are of unknown nature. The combined use of available information at longer wavelengths (mainly soft X–rays and radio) and of optical spectroscopy on the putative counterparts of these new hard X–ray objects allows us to pinpoint their exact nature. Continuing our long-standing program that has been running since 2004, and using 6 different telescopes of various sizes together with data from an online spectroscopic survey, here we report the classification through optical spectroscopy of 22 more unidentified or poorly studied high-energy sources detected with the IBIS instrument onboard INTEGRAL. We found that 16 of them are active galactic nuclei (AGNs), while the remaining 6 objects are within our Galaxy. Among the identified extragalactic sources, the large majority (14) is made up of Type 1 AGNs (i.e. with broad emission lines); of these, 6 lie at redshift larger than 0.5 and one (IGR J12319−0749) has z = 3.12, which makes it the second farthest object detected in the INTEGRAL surveys up to now. The remaining AGNs are of type 2 (that is, with narrow emission lines only), and one of the two cases is confirmed as a pair of interacting Seyfert 2 galaxies. The Galactic objects are identified as two cataclysmic variables, one high-mass X–ray binary, one symbiotic binary and two chromospherically active stars, possibly of RS CVn type. The main physical parameters of these hard X–ray sources were also determined using the multiwavelength information available in the literature. We thus still find that AGNs are the most abundant population among hard X–ray objects identified through optical spectroscopy. Moreover, we note that the higher sensitivity of the more recent INTEGRAL surveys is now enabling the detection of high-redshift AGNs, thus allowing the exploration of the most distant hard X–ray emitting sources and possibly of the most extreme blazars. Send offprint requests to: N. Masetti (masetti@iasfbo.inaf.it) ⋆ Based on observations collected at the following ob-servatories: Cerro Tololo Interamerican Observatory (Chile); Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (Canary Islands, Spain); Astronomical Observatory of Bologna in Loiano (Italy); Astronomical Observatory of Asiago (Italy); Observatorio Astronómico Nacional (San Pedro Mártir, México); Anglo-Australian Observatory (Siding Spring, Australia).
02/2012;
-
P Parisi,
N. Masetti,
E. Jiménez-Bailón,
V. Chavushyan,
R. Landi,
A. Malizia,
E. Palazzi, L. Bassani,
A. Bazzano,
A. J. Bird,
G. Galaz,
D. Minniti,
L. Morelli,
M. Schiavone,
P. Ubertini
[show abstract]
[hide abstract]
ABSTRACT: Through an optical campaign performed at 4 telescopes located in the northern
and the southern hemispheres, plus archival data from two on-line sky surveys,
we have obtained optical spectroscopy for 28 counterparts of unclassified or
poorly studied hard X-ray emitting objects detected with Swift/BAT and listed
in the 39 months Palermo Swift/BAT hard X-ray catalogue. We have been able to
pinpoint the optical counterpart of these high energy sources by means of X-ray
observations taken with Swift/XRT or XMM which allowed us to restrict the
positional uncertainty from few arcmin to few arcsec; satellite data also
provided information on the X-ray spectra of these objects. We find that 7
sources in our sample are Type 1 AGN while 20 are Type 2 AGN, with their
redshifts lying between 0.009 and 0.075; the remaining object is a Galactic
cataclysmic variable (CV). In this work we provide optical information for all
28 sources and the results of the soft X-ray analysis of 3 out of 5 AGN
observed with XMM/Newton.
12/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Presented in this work is the most comprehensive INTEGRAL AGN sample: it
includes 272 active galaxies for which optical identifications and redshifts
are available. 2-10 keV fluxes and column density measurements are also
collected for all the sample sources. For 33 new hard X-ray discovered AGN with
no previous X-ray coverage, XRT and XMM data analysis is reported for the first
time in this work. Examples of future studies which are being developed using
this large X-ray selected sample are presented together with some early
results.
12/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper we report on the broadband X-ray properties of a complete
sample of 33 absorbed Seyfert galaxies hard X-ray selected with integral. The
high quality broadband spectra obtained with both xmm, and integral-IBIS data
are well reproduced with an absorbed primary emission with a high energy cutoff
and its scattered fraction below 2-3 keV, plus the Compton reflection features.
A high energy cut-off is found in 30% of the sample, with an average value
below 150 keV. The diagnostic plot NH vs Fobs(2-10 keV)/F(20-100 keV) allowed
the isolation of the Compton thick objects, and may represent a useful tool for
future hard X-ray observations of newly discovered AGN. We are unable to
associate the reflection components with the absorbing gas as a torus, a more
complex scenario being necessary. In the Compton thin sources, a fraction (but
not all) of the Fe K line needs to be produced in a gas possibly associated
with the optical Broad Line Region, responsible also for the absorption. We
still need a Compton thick medium (not intercepting the line of sight) likely
associated to a torus, which contributes to the Fe line intensity and produces
the observed reflection continuum above 10 keV. The so-called Iwasawa-Taniguchi
effect can not be confirmed with our data. Finally, the comparison with a
sample of unobscured AGN shows that, type 1 and type 2 (once corrected for
absorption) Seyfert are characterized by the same nuclear/accretion properties
(luminosity, bolometric luminosity, Eddington ratio), supporting the "unified"
view.
12/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present new Suzaku and Fermi data, and re-analyzed archival hard X-ray
data from INTEGRAL and Swift-BAT survey, to investigate the physical properties
of the luminous, high-redshift, hard X-ray selected blazar IGR J22517+2217,
through the modelization of its broad band spectral energy distribution (SED)
in two different activity states. Through the analysis of the new Suzaku data
and the flux selected data from archival hard X-ray observations, we build the
source SED in two different states, one for the newly discovered flare occurred
in 2005 and one for the following quiescent period. Both SEDs are strongly
dominated by the high energy hump peaked at 10^20 -10^22 Hz, that is at least
two orders of magnitude higher than the low energy (synchrotron) one at 10^11
-10^14 Hz, and varies by a factor of 10 between the two states. In both states
the high energy hump is modeled as inverse Compton emission between
relativistic electrons and seed photons produced externally to the jet, while
the synchrotron self-Compton component is found to be negligible. In our model
the observed variability can be accounted for by a variation of the total
number of emitting electrons, and by a dissipation region radius changing from
within to outside the broad line region as the luminosity increases. In its
flaring activity, IGR J22517+2217 shows one of the most powerful jet among the
population of extreme, hard X-ray selected, high redshift blazar observed so
far.
12/2011;
-
N. Masetti,
P Parisi,
E. Jimenez-Bailon, L. Bassani,
A. Bazzano,
A. J. Bird,
V. Chavushyan,
A. J. Dean,
G. Galaz,
R. Landi,
A. Malizia,
D. Minniti,
L. Morelli,
E. Palazzi,
F. Schiavone,
J. B. Stephen,
P. Ubertini
[show abstract]
[hide abstract]
ABSTRACT: Since its launch on October 2002, the INTEGRAL satellite has revolutionized
our knowledge of the hard X-ray sky thanks to its unprecedented imaging
capabilities and source detection positional accuracy above 20 keV.
Nevertheless, many of the newly-detected sources in the INTEGRAL sky surveys
are of unknown nature. The combined use of available information at longer
wavelengths (mainly soft X-rays and radio) and of optical spectroscopy on the
putative counterparts of these new hard X-ray objects allows pinpointing their
exact nature. Continuing our long-standing program running since 2004, here we
report the classification, through optical spectroscopy, of 19 more
unidentified or poorly studied high-energy sources detected with the IBIS
instrument onboard INTEGRAL.
12/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: [Abridged]We report on the broadband X-ray properties of a complete sample of
absorbed Seyfert galaxies hard X-ray selected with INTEGRAL. The sample is
composed of 33 sources: 15 are newly discovered above 20 keV while 18 are
already known AGN. For 17 sources we have performed a broadband analysis with
XMM and INTEGRAL data. We have complemented the analysis of the 16 remaining
sources with existing broadband studies. The spectra are well reproduced with
an absorbed primary emission with a high energy cutoff and its scattered
fraction below 2-3 keV, plus the Compton reflection features. A high energy
cut-off is found in 30% of the sample, with an average value below 150 keV. The
hard X-ray selection favours the detection of more obscured sources, with the
log NH average value of 23.15. The diagnostic plot NH vs
F(corr)(2-10keV)/F(20-100keV) allowed the isolation of the Compton thick
objects and may represent a useful tool for future hard X-ray observations of
newly discovered AGN. We are unable to associate the reflection components
(continuum and Fe line) with the absorbing gas as a torus, a more complex
scenario being necessary. In the Compton thin sources, a fraction (but not all)
of the Fe line needs to be produced in a gas located closer to the BH than the
thick torus, and this is possibly associated with the optical BLR, responsible
also for the absorption. We still need a Compton thick medium (not intercepting
the line of sight) likely associated to a torus, which contributes to the Fe
line and produces the observed reflection continuum above 10 keV. The
Iwasawa-Taniguchi effect can not be confirmed with our data. Finally, the
comparison with a sample of unobscured AGN shows that, type 1 and type 2 (once
corrected for absorption) Seyfert are characterized by the same
nuclear/accretion properties (luminosity, bolometric luminosity, Eddington
ratio), supporting the unified view.
11/2011;
-
E. Maiorano,
R. Landi,
J. B. Stephen, L. Bassani,
N. Masetti,
P. Parisi,
E. Palazzi,
P. Parma,
A. J. Bird,
A. Bazzano,
P. Ubertini,
E. Jiménez-Bailón,
V. Chavushyan,
G. Galaz,
D. Minniti,
L. Morelli
[show abstract]
[hide abstract]
ABSTRACT: We report on a new method to identify active galactic nuclei (AGNs) among unidentified INTEGRAL sources. This method consists of cross-correlating unidentified sources listed in the fourth Imager on Board the INTEGRAL Satellite (IBIS) Survey Catalogue first with infrared and then with radio catalogues and a posteriori verifying, by means of X-ray and optical follow-up observations, the likelihood of these associations. In order to test this method, a sample of eight sources has been extracted from the fourth IBIS catalogue. For seven sources of the sample, we obtained an identification, whereas the last one (IGR J03103+5706) has insufficient information for a clear classification and deserves more in-depth study. We identified three objects (IGR J08190−3835, IGR J17520−6018 and IGR J21441+4640) as AGNs and suggest that three more (IGR J00556+7708, IGRJ17219−1509 and IGR J21268+6203) are likely active galaxies on the basis of their radio spectra, near-infrared photometry and location above the Galaxy plane. One source (IGR J05583−1257) has been classified as a starburst galaxy, but it might have been spuriously associated with the INTEGRAL detection.
Monthly Notices of the Royal Astronomical Society 06/2011; 416(1):531 - 540. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Narrow Line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 AGN
(BLSy1). The X-ray properties of individual objects belonging to this class are
often extreme and associated with accretion at high Eddington ratios. Here we
present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (> 20
keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show
hard X-ray photon indeces flatly distributed (Gamma_{20-100 keV} ranging from
~1.3 to ~3.6) with an average value of <Gamma_{20-100 keV}> = 2.3+/-0.7,
compatible with a sample of hard X-ray BLSy1 average slope. Instead, NLSy1 show
steeper spectral indeces with respect to BLSy1 when broad-band spectra are
considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data
sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on
the high energy cut-off and on the reflection component is achieved only in one
source, Swift J2127.4+5654 (E_{cut-off} ~ 50 keV, R=1.0{+0.5}_{-0.4}). Hard
X-ray selected NLSy1 do not display particularly strong soft excess emission,
while absorption fully or partially covering the continuum is often measured as
well as Fe line emission features. Variability is a common trait in this
sample, both at X-ray and at hard X-rays. The fraction of NLSy1 in the hard
X-ray sky is likely to be ~15%, in agreement with estimates derived in
optically selected NLSy1 samples. We confirm the association of NLSy1 with
small black hole masses with a peak at 10^{7} M_{dot} in the distribution,
however hard X-ray NLSy1 seem to occupy the lower tail of the Eddington ratios
distribution of classical NLSy1.
06/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We report the results from an archival XMM-Newton observation of the
Supergiant Fast X-ray Transient (SFXT) IGR J18483-0311 during its apastron
passage. The measured 0.5--10 keV luminosity state (1.3$\times10^{33}$ erg
s$^{-1}$) is the lowest ever reported in the literature, it is best fitted by
an absorbed black body model yielding parameters consistent with previous
measurements. In addition, we find evidence of an emission line feature at
$\sim$3.3 keV in the 0.5--10 keV EPIC-pn source spectrum. We show that its
physical explanation in terms of atomic emission line appears unlikely and
conversely we attempt to ascribe it to an electron cyclotron emission line
which would implies a neutron star magnetic field of the order of
$\sim3\times10^{11}$ G. A possible hint of the first harmonic is also found. If
firmly confirmed by future longer X-ray observations, this would be the first
detection ever of a cyclotron feature in the X-ray spectrum of a SFXT, with
important implications on theoretical models.
06/2011;
-
E. Maiorano,
R. Landi,
J. B. Stephen, L. Bassani,
N. Masetti,
P Parisi,
E. Palazzi,
P. Parma,
A. J. Bird,
A. Bazzano,
P. Ubertini,
E. Jimenez-Bailon,
V. Chavushyan,
G. Galaz,
D. Minniti,
L. Morelli
[show abstract]
[hide abstract]
ABSTRACT: We report on a new method to identify Active Galactic Nuclei (AGN) among
unidentified INTEGRAL sources. This method consists of cross-correlating
unidentified sources listed in the fourth IBIS Survey Catalogue first with
infrared and then with radio catalogues and a posteriori verifying, by means of
X-ray and optical follow up observations, the likelihood of these associations.
In order to test this method, a sample of 8 sources has been extracted from the
fourth IBIS Catalogue. For 7 sources of the sample we obtained an
identification, whereas the last one (IGR J03103+5706) has insufficient
information for a clear classification and deserves more in-depth study. We
identified three objects (IGR J08190-3835, IGR J17520-6018, IGR J21441+4640) as
AGNs and suggest that three more (IGR J00556+7708, IGRJ17219-1509, IGR
J21268+6203) are likely active galaxies on the basis of their radio spectra,
near-infrared photometry and location above the Galaxy plane. One source (IGR
J05583-1257) has been classified as a starburst galaxy but it might have been
spuriously associated with the INTEGRAL detection.
05/2011;
-
A Bazzano,
A ~J Bird,
E Kuulkers,
L Sidoli,
V ~S ~M Fiocchi,
L Natalucci,
A Tarana,
P Ubertini,
F Capitanio,
M Del Santo,
S Sabatini,
M Tavani, L Bassani,
A Malizia,
S ~P Drave,
C Winkler
The Astronomer's Telegram. 05/2011; 3361:1.
-
[show abstract]
[hide abstract]
ABSTRACT: In this telegram we report the X-ray follow-up observations performed
with Swift-XRT of 2 unidentified INTEGRAL sources listed in Bird et al.
2010 (ApJS, 186, 1). IGR J11014-6103. Within the
IBIS error circle, XRT detects an X-ray source with coordinates
R.A.(J2000) = 11h 01m 46.4s and Dec.(J2000) = -61d 01m 21s and 6 arcsec
positional uncertainty. XRT detection is at 7.7 sigma in the 0.3-10 keV
band and 4.6 sigma above 3 keV.
The Astronomer's Telegram. 03/2011; 3290:1.
