48 research outputs found
XMM-Newton and INTEGRAL analysis of the Supergiant Fast X-ray Transient IGR J17354-3255
We present the results of combined INTEGRAL and XMM-Newton observations of
the supergiant fast X-ray transient (SFXT) IGR J173543255. Three XMM-Newton
observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first
an initial pointing to identify the correct source in the field of view and the
latter two performed around periastron. Simultaneous INTEGRAL observations
across of the orbital cycle were analysed but the source was neither
detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a
range of moderately bright X-ray activity but there are no particularly strong
flares or outbursts in any of the three observations. We show that the spectral
shape measured by XMM-Newton can be fitted by a consistent model throughout the
observation, suggesting that the observed flux variations are driven by
obscuration from a wind of varying density rather than changes in accretion
mode. The simultaneous INTEGRAL data rule out simple extrapolation of the
simple powerlaw model beyond the XMM-Newton energy range.Comment: 13 pages, 9 figures, This article has been accepted for publication
in Monthly Notices of the Royal Astronomical Society Published by Oxford
University Pres
X-ray, optical and infrared investigation of the candidate Supergiant Fast X-ray Transient IGR J18462-0223
We report on a broad-band X-ray study (0.5-60 keV) of the poorly known
candidate Supergiant Fast X-ray Transient (SFXT) IGR J18462-0223, and on
optical and near-infrared (NIR) followup observations of field objects. The
out-of-outburst X-ray state has been investigated for the first time with
archival INTEGRAL/IBIS, ASCA, Chandra and Swift/XRT observations. This allowed
us to place stringent 3 sigma upper limits on the soft (0.5-10 keV) and hard
(18-60 keV) X-ray emission of 2.9x10^-13 erg cm^-2 s^-1 and 8x10^-12 erg cm^-2
s^-1, respectively; the source was also detected during an intermediate soft
X-ray state with flux equal to 1.6x10^-11 erg cm^-2 s^-1 (0.5-10 keV). In
addition, we report on the INTEGRAL/IBIS discovery of three fast hard X-ray
flares (18-60 keV) having a duration in the range 1-12 hours: the flaring
behavior was also investigated in soft X-rays (3-10 keV) with archival
INTEGRAL/JEM-X observations. The duty cycle (1.2%) and the dynamic ranges (>
1,380 and > 190 in the energy bands 0.5-10 keV and 18-60 keV, respectively)
were measured for the first time. Archival UKIDSS JHK NIR data, together with
our deep R-band imaging of the field, unveiled a single, very red object inside
the intersection of the Swift/XRT and XMM-Newton error circles: this source has
optical/NIR photometric properties compatible with a very heavily absorbed blue
supergiant located at about 11 kpc, thus being a strong candidate counterpart
for IGR J18462-0223. NIR spectroscopy is advised to confirm the association.
Finally, a hint of a possible orbital period was found at about 2.13 days. If
confirmed by further studies, this would make IGR J18462-0223 the SFXT with the
shortest orbital period among the currently known systems.Comment: accepted for publication in A&A, 9 pages, 7 figures, 2 table
New insights on accretion in Supergiant Fast X-ray Transients from XMM-Newton and INTEGRAL observations of IGR J175442619
XMM-Newton observations of the supergiant fast X-ray transient
IGRJ175442619 are reported and placed in the context of an analysis of
archival INTEGRAL/IBIS data that provides a refined estimate of the orbital
period at 4.92720.0004 days. A complete outburst history across the
INTEGRAL mission is reported. Although the new XMM-Newton observations (each
lasting 15 ks) targeted the peak flux in the phase-folded hard X-ray
light curve of IGRJ175442619, no bright outbursts were observed, the
source spending the majority of the exposure at intermediate luminosities of
the order of several 10ergs (0.510keV) and
displaying only low level flickering activity. For the final portion of the
exposure, the luminosity of IGRJ175442619 dropped to
410ergs (0.5 - 10 keV), comparable with the
lowest luminosities ever detected from this source, despite the observations
being taken near to periastron. We consider the possible orbital geometry of
IGRJ175442619 and the implications for the nature of the mass transfer
and accretion mechanisms for both IGRJ175442619 and the SFXT population.
We conclude that accretion under the `quasi-spherical accretion' model provides
a good description of the behaviour of IGRJ175442619, and suggest an
additional mechanism for generating outbursts based upon the mass accumulation
rate in the hot shell (atmosphere) that forms around the NS under the
quasi-spherical formulation. Hence we hope to aid in explaining the varied
outburst behaviours observed across the SFXT population with a consistent
underlying physical model.Comment: 12 pages, 5 figures, accepted for publication in MNRA
Contrasting behaviour from two Be/X-ray binary pulsars: insights into differing neutron star accretion modes
In this paper we present the identification of two periodic X-ray signals
coming from the direction of the Small Magellanic Cloud (SMC). On detection
with the Rossi X-ray Timing Explorer (RXTE), the 175.4s and 85.4s pulsations
were considered to originate from new Be/X-ray binary (BeXRB) pulsars with
unknown locations. Using rapid follow-up INTEGRAL and XMM-Newton observations,
we show the first pulsar (designated SXP175) to be coincident with a candidate
high-mass X-ray binary (HMXB) in the northern bar region of the SMC undergoing
a small Type II outburst. The orbital period (87d) and spectral class
(B0-B0.5IIIe) of this system are determined and presented here for the first
time. The second pulsar is shown not to be new at all, but is consistent with
being SXP91.1 - a pulsar discovered at the very beginning of the 13 year long
RXTE key monitoring programme of the SMC. Whilst it is theoretically possible
for accreting neutron stars to change spin period so dramatically over such a
short time, the X-ray and optical data available for this source suggest this
spin-up is continuous during long phases of X-ray quiescence, where accretion
driven spin-up of the neutron star should be minimal.Comment: 13 pages, 16 figures, accepted for publication in MNRA