9,688 research outputs found
INTEGRAL and Swift/XRT observations of IGR J19405-3016
IGR J19405-3016 is reported in the 3rd IBIS catalog as being one of its
lowest significance sources (~4.6 sigma under an exposure of about 371 ks).
This leads to a caveat in multi-wavelength study although the source was
identified in optical as a Seyfert 1. The currently increased INTEGRAL data
stimulate us to investigate the reality of this source. We analyze all
available observations carried out by INTEGRAL and Swift on IGR J19405-3016. We
find that IGR J19405-3016 has a detection significance of ~ 9.4 sigma in the
20-60 keV band during the observational period between March 2003 and March
2008. Thus confirms a real source detection reported previously. The source
position and error location are therefore updated. The source is found to be
constant over years at the hard X-rays. Over the three XRT observations, the
source flux varied by up to 39% from the average, and the spectrum is generally
soft. The combined XRT/ISGRI spectrum is well fitted with a simple power law
model (photon index 2.11+-0.03). Such a photon index is well consistent with
the mean value 1.98 (dispersion 0.27) as obtained from Swift/BAT AGN samples at
14-195 keV. The spectral slope of IGR J19405-3016 is larger than the average
spectral slope found by Molina et al. (2009). A similar discrepancy is found
with the results of Beckmann et al. (2009) regarding Seyfert 1 AGNs. A possible
explanation of this simple spectral description may be that the low level of
the column density allows for the `true' spectrum to appear at soft X-rays as
well.Comment: Astronomy and Astrophysics, in pres
Optical identification of X-ray source 1RXS J180431.1-273932 as a magnetic cataclysmic variable
The X-ray source 1RXS J180431.1-273932 has been proposed as a new member of
the symbiotic X-ray binary (SyXB) class of systems, which are composed of a
late-type giant that loses matter to an extremely compact object, most likely a
neutron star. In this paper, we present an optical campaign of imaging plus
spectroscopy on selected candidate counterparts of this object. We also
reanalyzed the available archival X-ray data collected with XMM-Newton. We find
that the brightest optical source inside the 90% X-ray positional error circle
is spectroscopically identified as a magnetic cataclysmic variable (CV), most
likely of intermediate polar type, through the detection of prominent Balmer,
He I, He II, and Bowen blend emissions. On either spectroscopic or statistical
grounds, we discard as counterparts of the X-ray source the other optical
objects in the XMM-Newton error circle. A red giant star of spectral type M5
III is found lying just outside the X-ray position: we consider this latter
object as a fore-/background one and likewise rule it out as a counterpart of
1RXS J180431.1-273932. The description of the X-ray spectrum of the source
using a bremsstrahlung plus black-body model gives temperatures of around 40
keV and around 0.1 keV for these two components, respectively. We estimate a
distance of about 450 pc and a 0.2-10 keV X-ray luminosity of about 1.7e32
erg/s for this system and, using the information obtained from the X-ray
spectral analysis, a mass of about 0.8 solar masses for the accreting white
dwarf (WD). We also confirm an X-ray periodicity of 494 s for this source,
which we interpret as the spin period of the WD. In summary, 1RXS
J180431.1-273932 is identified as a magnetic CV and its SyXB nature is
excluded.Comment: 9 pages, 7 figures, 3 tables, accepted for publication on Astronomy &
Astrophysics, main journal. Version 2 includes the A&A Language Editor's
correction
Unveiling the nature of INTEGRAL objects through optical spectroscopy. VIII. Identification of 44 newly detected hard X-ray sources
(abridged) Hard X-ray surveys performed by the INTEGRAL satellite have
discovered a conspicuous fraction (up to 30%) of unidentified objects among the
detected sources. Here we continue our identification program by selecting
probable optical candidates using positional cross-correlation with soft X-ray,
radio, and/or optical archives, and performing optical spectroscopy on them. As
a result, we identified or more accurately characterized 44 counterparts of
INTEGRAL sources: 32 active galactic nuclei, with redshift 0.019 < z < 0.6058,
6 cataclysmic variables (CVs), 5 high-mass X-ray binaries (2 of which in the
Small Magellanic Cloud), and 1 low-mass X-ray binary. This was achieved by
using 7 telescopes of various sizes and archival data from two online
spectroscopic surveys. The main physical parameters of these hard X-ray sources
were also determined using the available multiwavelength information. AGNs are
the most abundant population among hard X-ray objects, and our results confirm
this tendency when optical spectroscopy is used as an identification tool. The
deeper sensitivity of recent INTEGRAL surveys enables one to begin detecting
hard X-ray emission above 20 keV from sources such as LINER-type AGNs and
non-magnetic CVs.Comment: 22 pages, 14 figures, 6 tables, accepted for publication on A&A, main
journa
Unveiling the nature of INTEGRAL objects through optical spectroscopy. IX. 22 more identifications, and a glance into the far hard X-ray Universe
(Abridged) 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, 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, 14
are Type 1 AGNs; of these, 6 lie at redshift larger than 0.5 and one 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, and one of them is 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. 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.Comment: 18 pages, 9 figures, 8 tables, accepted for publication on Astronomy
& Astrophysics, main journa
Simultaneous Heavy Ion Dissociation at Ultrarelativistic Energies
We study the simultaneous dissociation of heavy ultrarelativistic nuclei
followed by the forward-backward neutron emission in peripheral collisions at
colliders. The main contribution to this particular heavy-ion dissociation
process, which can be used as a beam luminosity monitor, is expected to be due
to the electromagnetic interaction. The Weizsacker-Williams method is extended
to the case of simultaneous excitation of collision partners which is simulated
by the RELDIS code. A contribution to the dissociation cross section due to
grazing nuclear interactions is estimated within the abrasion model and found
to be relatively small.Comment: Talk given at Bologna 2000 Conference - Structure of the Nucleus at
the Dawn of the Century, May 29 - June 3, 2000, 4 pages, 2 figure
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&
Accurate classification of 29 objects detected in the 39 months Palermo Swift/BAT hard X-ray catalogue
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.Comment: 15 pages, 4 figures, 8 tables, accepted for publication on Astronomy
and Astrophysic
1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet
We present a detailed NIR/optical/UV study of the transient low mass X-ray
binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at
determining the nature of its companion star. We obtained three optical spectra
at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed
optical and NIR photometric observations with both the REM telescope and the
New Technology Telescope (NTT) in La Silla. We obtained optical and UV
observations from the Swift archive. Finally, we performed optical polarimetry
of the source by using the EFOSC2 instrument mounted on the NTT. The optical
spectrum of the source is almost featureless since the hydrogen and He I
emissions lines, typically observed in LMXBs, are not detected. Similarly,
carbon and oxygen lines are neither observed. We marginally detect the He II
4686 AA emission line, suggesting the presence of helium in the accretion disc.
No significant optical polarisation level was observed. The lack of hydrogen
and He I emission lines in the spectrum implies that the companion is likely
not a main sequence star. Driven by the tentative detection of the He II 4686
AA emission line, we suggest that the system could harbour a helium white
dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact
X-ray binary. By combining an estimate of the mass accretion rate together with
evolutionary tracks for a He white dwarf, we obtain a tentative orbital period
of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral
energy distribution (SED) of the source at two different epochs. One SED was
gathered when the source was in the soft X-ray state, and it is consistent with
the presence of a single thermal component. The second SED, obtained when the
source was in the hard X-ray state, shows a thermal component together with a
tail in the NIR, likely indicating the presence of a (transient) jet.Comment: 8 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysics (Section 7
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