2,049 research outputs found
INTEGRAL and Swift observations of IGRJ19294+1816 in outburst
IGRJ19294+1816 was discovered by INTEGRAL in 2009 during a bright X-ray
outburst and was classified as a possible Be X-ray binary or supergiant fast
X-ray transient. On 2010 October 28, the source displayed a second X-ray
outburst and a 2 months-long monitoring with Swift was carried out to follow
the evolution of the source X-ray flux during the event. We report on the
INTEGRAL and Swift observations of the second X-ray outburst observed from
IGRJ19294+1816. We detected pulsations in the X-ray emission from the source at
\sim12.5 s up to 50 keV. The source X-ray flux decreased smoothly during the
two months of observation displaying only marginal spectral changes. Due to the
relatively rapid decay of the source X-ray flux, no significant variations of
the source spin period across the event could be measured. This prevented a
firm confirmation of the previously suggested orbital period of the source at
117 d. This periodicity was also searched by using archival Swift /BAT data. We
detected a marginally significant peak in the periodogram and determined the
best period at 116.2\pm0.6 days (estimated chance probability of a spurious
detection 1%). The smooth decline of the source X-ray flux across the two
months of observations after the onset of the second outburst, together with
its relatively low value of the spin period and the absence of remarkable
changes in the spectral parameters (i.e., the absorption column density),
suggests that IGRJ19294+1816 is most likely another member of the Be X-ray
binaries discovered by INTEGRAL and not a supergiant fast X-ray transient.Comment: Accepted for publication in A&A. 7 pages, 10 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
XMM-Newton observations of IGRJ18410-0535: The ingestion of a clump by a supergiant fast X-ray transient
IGRJ18410-0535 is a supergiant fast X-ray transients. This subclass of
supergiant X-ray binaries typically undergoes few- hour-long outbursts reaching
luminosities of 10^(36)-10^(37) erg/s, the occurrence of which has been
ascribed to the combined effect of the intense magnetic field and rotation of
the compact object hosted in them and/or the presence of dense structures
("clumps") in the wind of their supergiant companion. IGR J18410-0535 was
observed for 45 ks by XMM-Newton as part of a program designed to study the
quiescent emission of supergiant fast X-ray transients and clarify the origin
of their peculiar X-ray variability. We carried out an in-depth spectral and
timing analysis of these XMM-Newton data. IGR J18410-0535 underwent a bright
X-ray flare that started about 5 ks after the beginning of the observation and
lasted for \sim15 ks. Thanks to the capabilities of the instruments on-board
XMM-Newton, the whole event could be followed in great detail. The results of
our analysis provide strong convincing evidence that the flare was produced by
the accretion of matter from a massive clump onto the compact object hosted in
this system. By assuming that the clump is spherical and moves at the same
velocity as the homogeneous stellar wind, we estimate a mass and radius of Mcl
\simeq1.4\times10^(22) g and Rcl \simeq8\times10^(11) cm. These are in
qualitative agreement with values expected from theoretical calculations. We
found no evidence of pulsations at \sim4.7 s after investigating coherent
modulations in the range 3.5 ms-100 s. A reanalysis of the archival ASCA and
Swift data of IGR J18410-0535, for which these pulsations were previously
detected, revealed that they were likely to be due to a statistical fluctuation
and an instrumental effect, respectively.Comment: Accepted for publication on A&A. V2: Inserted correct version of
Fig.1
XMM-Newton and Swift observations of XTE J1743-363
XTEJ1743-363 is a poorly known hard X-ray transient, that displays short and
intense flares similar to those observed from Supergiant Fast X-ray Transients.
The probable optical counterpart shows spectral properties similar to those of
an M8 III giant, thus suggesting that XTEJ1743-363 belongs to the class of the
Symbiotic X-ray Binaries. In this paper we report on the first dedicated
monitoring campaign of the source in the soft X-ray range with XMM-Newton and
Swift/XRT. T hese observations confirmed the association of XTEJ1743-363 with
the previously suggested M8 III giant and the classification of the source as a
member of the Symbiotic X-ray binaries. In the soft X-ray domain, XTEJ1743-363
displays a high absorption (~6x10^22 cm^-2 ) and variability on time scales of
hundreds to few thousand seconds, typical of wind accreting systems. A
relatively faint flare (peak X-ray flux 3x10^-11 erg/cm^2/s) lasting ~4 ks is
recorded during the XMM-Newton observation and interpreted in terms of the wind
accretion scenario.Comment: Accepted for publication on A&
The supergiant fast X-ray transient IGRJ18483-0311 in quiescence: XMM-Newton, Swift, and Chandra observations
IGR J18483-0311 was discovered with INTEGRAL in 2003 and later classified as
a supergiant fast X-ray transient. It was observed in outburst many times, but
its quiescent state is still poorly known. Here we present the results of
XMM-Newton, Swift, and Chandra observations of IGRJ18483-0311. These data
improved the X-ray position of the source, and provided new information on the
timing and spectral properties of IGR J18483-0311 in quiescence. We report the
detection of pulsations in the quiescent X-ray emission of this source, and
give for the first time a measurement of the spin-period derivative of this
source. In IGRJ18483-0311 the measured spin-period derivative of
-(1.3+-0.3)x10^(-9) s/s likely results from light travel time effects in the
binary. We compare the most recent observational results of IGRJ18483-0311 and
SAXJ1818.6-1703, the two supergiant fast X-ray transients for which a similar
orbital period has been measured.Comment: Accepted for publication in MNRA
Swift observations of IGRJ16479-4514 in outburst
The supergiant fast X-ray transient source IGR J16479-4514 was observed in
outburst two times with Swift. Its quiescent state was investigated in-depth
only once in 2008 through a relatively long pointed observation with
XMM-Newton. The latter observation was taken about 1.7 days after the outburst
in 2008, and showed an X-ray eclipse-like event, likely caused by the
supergiant companion. At present, this is the only supergiant fast X-ray
transient that displayed an evidence for an X-ray eclipse. Here we carry out a
comparison between the most recent outburst of IGRJ16479-4514, caught by Swift
on 29 January 2009 and those detected previously from this source. The decay
from the outbursts in 2005, 2008 and 2009 presents many similarities, and
suggests a common mechanism that modulates the mass accretion rate onto the
neutron star in IGRJ16479-4514.Comment: Accepted for publication in A&
IGR J11014-6103: a newly discovered pulsar wind nebula?
Context: IGRJ11014-6103 is one of the still unidentified hard X-ray INTEGRAL
sources, reported for the first time in the 4th IBIS/ISGRI catalog. Aims: We
investigated the nature of IGR J11014-6103 by carrying out a multiwavelength
analysis of the available archival observations performed in the direction of
the source. Methods: We present first the results of the timing and spectral
analysis of all the X-ray observations of IGR J11014-6103 carried out with
ROSAT, ASCA, Einstein, Swift, and XMM-Newton, and then use them to search for
possible counterparts to the source in the optical, infra-red, radio and
gamma-ray domain. Results: Our analysis revealed that IGR J11014-6103 is
comprised of three different X-ray emitting regions: a point-like source, an
extended object and a cometary-like "tail" (~4 arcmin). A possible radio
counterpart positionally coincident with the source was also identified.
Conclusions: Based on these results, we suggest that the emission from IGR
J11014-6103 is generated by a pulsar wind nebula produced by a high-velocity
pulsar. IGR J11014-6103 might be the first of these systems detected with
INTEGRAL IBIS/ISGRI.Comment: A&A accepted, 8 pages, 8 figures, 2 table
Witnessing the magnetospheric boundary at work in Vela X-1
We present an analysis of the Vela X-1's "off-states" based on Suzaku
observations taken in June 2008. Defined as states in which the flux sudden
decreases below the instrumental sensitivity, these "off-states" have been
interpreted by several authors as the onset of the "propeller regime". For the
first time ever, however, we find that the source does not turn off and,
although the flux drops by a factor of 20 during the three recorded
"off-states", pulsations are still observed. The spectrum and the
pulse-profiles of the "off-states" are also presented. Eventually, we discuss
our findings in framework of the "gated accretion" scenario and conclude that
most likely the residual flux is due to the accretion of matter leaking through
the magnetosphere by means of Kelvin-Helmholz instabilities (KHI).Comment: 4 pages 4 figures; accepted for publication in A&A letters
(20/02/2011); v1.1 - some changes in language + added 3 reference
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