141 research outputs found
IGR J18483-0311: a new intermediate supergiant fast X-ray transient
IGR J18483-0311 is a high-mass X-ray binary recently discovered by INTEGRAL.
Its periodic fast X-ray transient activity and its position in the Corbet
diagram - although ambiguous - led to the conclusion that the source was a
likely Be/X-ray binary (BeXB), even if a supergiant fast X-ray transient (SFXT)
nature could not be excluded. We aimed at identifying the companion star of IGR
J18483-0311 to discriminate between the BeXB and the SFXT nature of the source.
Optical and near-infrared photometry, as well as near-infrared spectroscopy of
the companion star were performed to identify its spectral type. We also
assembled and fitted its broad-band spectral energy distribution to derive its
physical parameters. We show that the companion star of IGR J18483-0311 is an
early-B supergiant, likely a B0.5Ia, and that its distance is about 3-4 kpc.
The early-B supergiant nature of its companion star, as well as its fast X-ray
transient activity point towards an SFXT nature of IGR J18483-0311.
Nevertheless, the long duration and the periodicity of its outbursts, as well
as its high level of quiescence, are consistent with IGR J18483-0311 being an
intermediate SFXT, in between classical supergiant X-ray binaries (SGXBs)
characterised by small and circular orbits, and classical SFXTs with large and
eccentric orbits.Comment: 5 pages, 2 figures, 3 tables, accepted in A&
The not-so-massive black hole in the microquasar GRS1915+105
We present a new dynamical study of the black hole X-ray transient GRS1915+105 making use of near-infrared spectroscopy obtained with X-shooter at the VLT. We detect a large number of donor star absorption features across a wide range of wavelengths spanning the H and K bands. Our 24 epochs covering a baseline of over 1 year permit us to determine a new binary ephemeris including a refined orbital period of P=33.85 +/- 0.16 d. The donor star radial velocity curves deliver a significantly improved determination of the donor semi-amplitude which is both accurate (K_2=126 +/- 1 km/s) and robust against choice of donor star template and spectral features used. We furthermore constrain the donor star's rotational broadening to vsini=21 +/-4 km/s, delivering a binary mass ratio of q=0.042 +/- 0.024. If we combine these new constraints with distance and inclination estimates derived from modelling the radio emission, a black hole mass of M_BH=10.1 +/- 0.6 M_sun is inferred, paired with an evolved mass donor of M_2=0.47 +/- 0.27 M_sun. Our analysis suggests a more typical black hole mass for GRS1915+105 rather than the unusually high values derived in the pioneering dynamical study by Greiner et al. (2001). Our data demonstrate that high-resolution infrared spectroscopy of obscured accreting binaries can deliver dynamical mass determinations with a precision on par with optical studies
Unveiling the nature of IGR J16283-4838
Context. One of the most striking discoveries of the INTEGRAL observatory is
the existence of a previously unknown population of X-ray sources in the inner
arms of the Galaxy. The investigations of the optical/NIR counterparts of some
of them have provided evidence that they are highly absorbed high mass X-ray
binaries hosting supergiants. Aims. We aim to identify the optical/NIR
counterpart of one of the newly discovered INTEGRAL sources, IGR J16283-4838,
and determine the nature of this system. Methods. We present optical and NIR
observations of the field of IGR J16283-4838, and use the astrometry and
photometry of the sources within it to identify its counterpart. We obtain its
NIR spectrum, and its optical/NIR spectral energy distribution by means of
broadband photometry. We search for the intrinsic polarization of its light,
and its short and long-term photometric variability. Results. We demonstrate
that this source is a highly absorbed HMXB located beyond the Galactic center,
and that it may be surrounded by a variable circumstellar medium.Comment: 6 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Monitoring Supergiant Fast X-ray Transients with Swift. Rise to the outburst in IGR J16479-4514
IGR J16479-4514 is a Supergiant Fast X-ray Transient (SFXT), a new class of
High Mass X-ray Binaries, whose number is rapidly growing thanks to the
observations of the Galactic plane performed with the INTEGRAL satellite. IGR
J16479-4514 has been regularly monitored with Swift/XRT since November 2007, to
study the quiescent emission, the outburst properties and their recurrence. A
new bright outburst, reaching fluxes above 10 erg cm s,
was caught by the Swift/BAT.
Swift immediately re-pointed at the target with the narrow-field instruments
so that, for the first time, an outburst from a SFXT where a periodicity in the
outburst recurrence is unknown could be observed simultaneously in the 0.2--150
keV energy band. The X-ray emission is highly variable and spans almost four
orders of magnitude in count rate during the Swift/XRT observations covering a
few days before and after the bright peak. The X-ray spectrum in outburst is
hard and highly absorbed. The power-law fit resulted in a photon index of
0.98, and in an absorbing column density of
cm. These observations demonstrate that in this source (similarly to
what was observed during the 2007 outburst from the periodic SFXT IGR
J11215-5952), the accretion phase lasts much longer than a few hours.Comment: Accepted for publication on Astrophysical Journal Letters. 5 pages, 4
figure
IGRJ16479-4514: the first eclipsing supergiant fast X-ray transient?
Supergiant fast X-ray transients are a new class of high mass X-ray binaries
recently discovered with INTEGRAL. Hours long outbursts from these sources have
been observed on numerous occasions at luminosities of ~1E36-1E37 erg/s,
whereas their low level activity at ~1E32-1E34 erg/s has not been deeply
investigated yet due to the paucity of long pointed observations with high
sensitivity X-ray telescopes. Here we report on the first long (~32 ks) pointed
XMM-Newton observation of IGR J16479-4514, a member of this new class. This
observation was carried out in March 2008, shortly after an outburst from this
source, with the main goal of investigating its low level emission and physical
mechanisms that drive the source activity. Results from the timing, spectral
and spatial analysis of the EPIC-PN XMM-Newton observation show that the X-ray
source IGRJ16479-4514 underwent an episode of sudden obscuration, possibly an
X-ray eclipse by the supergiant companion. We also found evidence for a soft
X-ray extended halo around the source that is most readily interpreted as due
to scattering by dust along the line of sight to IGRJ16479-4514. We discuss
this result in the context of the gated accretion scenarios that have been
proposed to interpret the behaviour of supergiant fast X-ray transient.Comment: Accepted for publication in MNRAS letter. 6 pages and 5 figures. We
updated one reference and the acknowledgment
Discovery of x-ray pulsations from the integral source IGR J11014−6103
published_or_final_versio
Swift follow-up observations of 17 INTEGRAL sources of uncertain or unknown nature
(abridged) We analysed data from observations of 17 INTEGRAL sources made
with the Swift satellite. We refine the position of the hard X-ray sources to
an accuracy of a few arcsec. We then browsed the online catalogs (e.g., NED,
SIMBAD, 2MASS, 2MASX, USNO) to search for counterparts at other wavelengths. We
also made use of the X-ray spectral parameters to try to identify the nature of
those sources. We provide the X-ray position with arcsec accuracy, identify
possible infrared and optical counterparts (when found), give the magnitudes in
those bands and in the optical and UV as seen with the Swift/UVOT telescope
when observations are available. We confirm the previously suggested
associations and source types for IGR J03532-6829, J05346-5759, J10101-5654,
J13000+2529, J13020-6359, J15479-4529, J18214-1318, and J23206+6431. We
identify
IGR J09025-6814 as an AGN for the first time, and we suggest that it may be a
Seyfert 2. We suggest that IGR J05319-6601, J16287-5021, J17353-3539 and
J17476-2253 are X-ray binaries, with J05319-6601 being located in the LMC and
the other three possibly being HMXBs in our Galaxy. For IGR J15161-3827 and
J20286+2544, we find several possible X-ray counterparts in the IBIS error
region, and we discuss which, if any, are the likely counterparts. Both are
likely AGNs, although the latter could be a blend of two AGNs. For IGR
J03184-0014 and J19267+1325, we find X-ray sources slightly outside the IBIS
error circle. In the former, we do not favour an association of the Swift and
INTEGRAL source, while it is very likely that IGR J19267+1325 and the Swift
source are the same.Comment: 12 pages, 3 figures, accepted for publication in A&
X-ray Pulsations from the region of the Supergiant Fast X-ray Transient IGR J17544-2619
Phase-targeted RXTE observations have allowed us to detect a transient 71.49
\pm 0.02 s signal that is most likely to be originating from the supergiant
fast X-ray transient IGR J17544-2619. The phase-folded light curve shows a
possible double-peaked structure with a pulsed flux of ~4.8*10^-12 erg cm^-2
s^-1 (3-10 keV). Assuming the signal to indicate the spin period of the neutron
star in the system, the provisional location of IGR J17544-2619 on the Corbet
diagram places the system within the classical wind-fed supergiant XRB region.
Such a result illustrates the growing trend of supergiant fast X-ray transients
to span across both of the original classes of HMXB in Porb - Pspin space.Comment: 7 pages, 6 figures, Accepted for publication in Astronomy and
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