106 research outputs found
The failed state transition of the ATOLL source GRS 1724-308
The 2004-2012 X-ray time history of the NS LMXB GRS 1724-308 shows, along
with the episodic brightenings associated to the low-high state transitions
typical of the ATOLL sources, a peculiar, long lasting (about 300 d) flaring
event, observed in 2008. This rare episode, characterised by a high-flux hard
state, has never been observed before for GRS 1724-308 , and in any case is not
common among ATOLL sources. We discuss here different hypotheses on the origin
of this peculiar event that displayed the spectral signatures of a failed
transition, similar in shape and duration to those rarely observed in Black
Hole binaries. We also suggest the possibility that the atypical flare occurred
in coincidence with a new rising phase of the 12-years super-orbital modulation
that has been previously reported by other authors. The analysed data also
confirm for GRS 1724-308 the already reported orbital period of about 90 d.Comment: accepted for publication in MNRA
INTEGRAL high energy behaviour of 4U 1812-12
The low mass X-ray binary system 4U 1812-12 was monitored with the INTEGRAL
observatory in the period 2003-2004 and with BeppoSAX on April 20, 2000. We
report here on the spectral and temporal analysis of both persistent and burst
emission. The full data set confirms the persistent nature of this burster, and
reveals the presence of emission up to 200 keV. The persistent spectrum is well
described by a comptonization (CompTT) model plus a soft blackbody component.
The source was observed in a hard spectral state with a 1-200 keV luminosity of
2*10^(36) ergs/s and L/LEdd~1% and no meaningful flux variation has been
revealed, as also confirmed by a 2004 RXTE observation. We have also detected 4
bursts showing double peaked profiles and blackbody spectra with temperatures
ranging from 1.9 to 3.1 keV.Comment: 6 pages, 4 figures. Accepted for publication by A&
Spectral states evolution of 4U 1728-34 observed by INTEGRAL and RXTE: non-thermal component detection
We report results of a one-year monitoring of the low mass X-ray binary
(LMXB) source (atoll type) 4U 1728-34 with INTEGRAL and RXTE. Three time
intervals were covered by INTEGRAL, during which the source showed strong
spectral evolution. We studied the broad-band X-ray spectra in detail by
fitting several models in the different sections of the hardness-intensity
diagram. The soft states are characterised by prominent blackbody emission plus
a contribution from a Comptonized emission. The hard states are characterised
by the presence of an excess flux with respect to the Comptonization model
above 50 keV while the soft component is fainter. To obtain an acceptable fit
to the data this excess is modeled either with a power law with photon index
Gamma ~ 2 or a Comptonization (CompPS) spectrum implying the presence of hybrid
thermal and non-thermal electrons in a corona. This makes 4U 1728-34 one of the
few LMXBs of atoll type showing non-thermal emission at high energy. From our
analysis, it is also apparent that the presence of the hard tail is more
prominent as the overall spectrum becames harder. We discuss also alternative
models which can discribe these hard states.Comment: Accepted for publication in MNRAS (accepted 2011 April 20. Received
2011 April 20; in original form 2010 December 07); 9 pages, 7 figure
The two INTEGRAL X-ray transients IGR J17091--3624 and IGR J17098--3628: a multi-wavelength long term campaign
IGR J17091-3624 and IGR J17098-3628 are two X-ray transients discovered by
INTEGRAL and classified as possible black hole candidates (BHCs). We present
here the results obtained from the analysis of multi-wavelength data sets
collected by different instruments from 2005 until the end of 2007 on both
sources. IGR J17098-3628 has been regularly detected by INTEGRAL and RXTE over
the entire period of the observational campaign; it was also observed with
pointed observations by XMM and Swift/XRT in 2005 and 2006 and exhibited flux
variations not linked with the change of any particular spectral features. IGR
J17091-3624 was initially in quiescence (after a period of activity between
2003 April and 2004 April) and it was then detected again in outburst in the
XRT field of view during a Swift observation of IGR J17098--3628 on 2007 July
9. The observations during quiescence provide an upper limit to the 0.2-10 keV
luminosity, while the observations in outburst cover the transition from the
hard to the soft state. Moreover, we obtain a refined X-ray position for IGR
J17091-3624 from the Swift/XRT observations during the outburst in 2007. The
new position is inconsistent with the previously proposed radio counterpart. We
identify in VLA archive data a compact radio source consistent with the new
X-ray position and propose it as the radio counterpart of the X-ray transient.Comment: Accepted for publication in Ap
XMMU J174716.1-281048: a "quasi-persistent" very faint X-ray transient?
The X-ray transient XMMU J174716.1-281048 was serendipitously discovered with
XMM-Newton in 2003. It lies about 0.9 degrees off the Galactic Centre and its
spectrum shows a high absorption (~8 x 10E22 cm^(-2)). Previous X-ray
observations of the source field performed in 2000 and 2001 did not detect the
source, indicative of a quiescent emission at least two orders of magnitude
fainter. The low luminosity during the outburst (~5 x 10E34 erg/s at 8 kpc)
indicates that the source is a member of the ``very faint X-ray transients''
class. On 2005 March 22nd the INTEGRAL satellite caught a possible type-I X-ray
burst from the new INTEGRAL source IGR J17464-2811, classified as fast X-ray
transient. This source was soon found to be positionally coincident, within the
uncertainties, with XMMU J174716.1-281048. Here we report data analysis of the
X-ray burst observed with the IBIS and JEM-X telescopes and confirm the type-I
burst nature. We also re-analysed XMM-Newton and Chandra archival observations
of the source field. We discuss the implications of these new findings,
particularly related to the source distance as well as the source
classification.Comment: 4 pages, 8 figures, accepted for publication in A&A Letter
Wear of nanohybrid and microfilled composite resin in occlusal restoration of first permanent molar tooth
This study compared the wear of nanohybrid and microfilled composite restorative material in occlusal restoration of first permanent molar tooth. In total, 60 first permanent molar teeth having carious lesion without any clinical and radiological indication of pulpal involvement, removal of carious dental hard tissues was performed using round carbide bur and a class I cavity was prepared, rinsed with water and then dried with gentle air. These cavities were filled with either nanohybrid or microfilled composite resin by simple random sampling by lottery method. All teeth were subjected to clinical qualitative and quantitative wear test at baseline, 3, 6 and 9 months observation period. The quantitative wear was analyzed by profile meter. The results showed that the wear depth of microfilled was significant than the nanofilled composite resin. It can be concluded that quantitative wear of microfilled had greater wear than that of nanohybrid composite restorations
INTEGRAL Galactic Plane Scans detect enhanced activity from the HMXBs IGR J19294+1816 and 4U 1909+07
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