Recent activity of the Be/X-ray binary system SAX J2103.5+4545

Aims. We present a multiwavelength study of the Be/X-ray binary system SAX J2103.5+4545 with the goal of better characterizing the transient behaviour of this source. Methods. SAX J2103.5+4545 was observed by Swift-XRT four times in 2007 from April 25 to May 5, and during quiescence in 2012 August 31. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain) since 2011 August, and from the TUBITAK National Observatory (Antalya, Turkey) since 2009 June. We have performed spectral and photometric temporal analyses in order to investigate the different states exhibited by SAX J2103.5+4545. Results. In X-rays, an absorbed power law model provided the best fit for all the XRT spectra. An iron-line feature at ~6.42 keV was present in all the observations except for that taken during quiescence in 2012. The photon indexes are consistent with previous studies of SAX J2103.5+4545 in high/low luminosity states. Pulsations were found in all the XRT data from 2007 (2.839(2) mHz; MJD 54222.02), but not during quiescence. Both optical outbursts in 2010 and 2012 lasted for about 8/9 months (as the one in 2007 probably did and the current one in 2014 might do) and were most probably caused by mass ejection events from the Be star that eventually fed the circumstellar disc. All of these outbursts started about 3 months before the triggering of the X-ray activity, and about the same period before the maximum of the H_alpha line equivalent width (in emission) was reached at only ~ -5 \AA. In this work we found that the global correlation between the BV variability and the X-ray intensity was also observed at longer wavelengths in the IR domain.Comment: 11 pages, 7 figures, and online material (2 tables). Submitted to A&A in 2014 Januar

Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+274

We present a multiwavelength study of the Be/X-ray binary system XTE J1946+274 with the main goal of better characterizing its behavior during X-ray quiescence. We aim to shed light on the mechanism which triggers the X-ray activity for this source. XTE J1946+274 was observed by Chandra-ACIS during quiescence in 2013 March 12. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain) since 2011 September, and from the TUBITAK National Observatory (Antalya, Turkey) since 2005 April. We have performed spectral and photometric temporal analyses in order to investigate the quiescent state and transient behavior of this binary system. In 2006, a long mass ejection event took place from the Be star, lasting for about seven years. We also found that a large Be circumstellar disk was present during quiescence, although major X-ray activity was not observed. We made an attempt to explain this scenario by assuming the permanently presence of a tilted and warped Be circumstellar disk. The 0.3-10 keV X-ray spectrum during quiescence was well fitted with either an absorbed blackbody or absorbed power-law models. The main parameters obtained for these models were kT=1.43+/-0.17 and Gamma=0.9+/-0.4 (with N_H~2-7E+22 cm-2). The 0.3-10 keV flux of the source was ~0.8E-12 erg-1 cm-2 s-1. Pulsations were found with P_pulse=15.757(1) s (MJD 56363.115) and an rms pulse fraction of 32.1(3)%. The observed X-ray luminosity during quiescent periods may be explained by the neutron star being in supersonic propeller regimen.Comment: 9 pages, 7 figures, accepte

Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6-0814 observed with NICER and NuSTAR

Swift J1858.6-0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors of >100 in soft X-rays) in its discovery state. We present the detection of five thermonuclear (Type I) X-ray bursts from Swift J1858.6-0814, implying that the compact object in the system is a neutron star (NS). Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, D = 12.8(-0.6)(+0.8) kpc, although systematic effects allow a conservative range of 9-18 kpc. Before one burst, we detect a QPO at 9.6 +/- 0.5 mHz with a fractional rms amplitude of 2.2 +/- 0.2 per cent (0.5-10 keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15 per cent fractional amplitude (over 1-8 keV). Finally, we discuss the implications of the NS accretor and this distance on other inferences which have been made about the system. In particular, we find that Swift J1858.6-0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst

The Changing-look Optical Wind of the Flaring X-Ray Transient Swift J1858.6-0814

We present the discovery of an optical accretion disk wind in the X-ray transient Swift J1858.6-0814. Our 90-spectrum data set, taken with the 10.4 m Gran Telescopio Canarias telescope over eight different epochs and across five months, reveals the presence of conspicuous P-Cyg profiles in He i at 5876 A and Hα. These features are detected throughout the entire campaign, albeit their intensity and main observational properties are observed to vary on timescales as short as 5 minutes. In particular, we observe significant variations in the wind velocity, between a few hundreds and ∼2400 km s; -1. In agreement with previous reports, our observations are characterized by the presence of frequent flares, although the relation between the continuum flux variability and the presence/absence of wind features is not evident. The reported high activity of the system at radio waves indicates that the optical wind of Swift J1858.6-0814 is contemporaneous with the radio jet, as is the case for the handful of X-ray binary transients that have shown so far optical P-Cyg profiles. Finally, we compare our results with those of other sources showing optical accretion disk winds, with emphasis on V404 Cyg and V4641 Sgr, since they also display strong and variable optical wind features as well as similar flaring behavior.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Ionic Conductivity of Ce0.9-xGd0.1SmxO2-delta co-doped Ceria Electrolytes

Ceria doped with heterovalent cations, such as alkaline earth and rare earth ions, has been considered one of the most promising electrolyte materials for intermediate temperature solid oxide fuel cells. The present trend is to investigate the co-doping approach in ceria to improve further its electrical conductivity. In this study, Ce(NO3)(3).6H(2)O, Gd(NO3)(3).6H(2)O, Sm(NO3)(3).6H(2)O nitrate salts were used as the starting materials to form co-doped ceria electrolytes of Ce0.9-xGd0.1SmxO2-delta (x = 0, 0.05, 0.10) using the Pechini method. The samples were characterized by means of X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy methods. The results of the impedance spectroscopy revealed that Ce0.85Gd0.10Sm0.05O1.925 sample exhibited the highest ionic conductivity of 4:23 x 10(-2) Scm(-1) at 750 degrees C in air

Incomplete-Kawasaki disease: A pediatric diagnostic conflict [20]

PubMedID: 17785242[No abstract available

Characterization of Nd and Sm Co-Doped CeO2-Based Systems

Nd0.20SmxCe0.8-xO1.9-x = 2 (x = 0, 0.05, 0.10, 0.15, 0.20) rare-earth-co-doped ceria electrolytes were synthesized by polyol process. Acetate compounds of cerium and dopants (Nd, Sm) were used as starting materials and triethylene glycol was used as a solvent. Structural and ionic conductivity properties of the electrolyte systems were determined by applying characterization techniques such as X-ray diffraction, the Fourier transform infrared spectroscopy, scanning electron microscope, and electrochemical impedance spectroscopy. The results of X-ray diffraction indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 600 degrees C. So, the samples were calcined at 600 degrees C for 4 h and then sintered at 1400 degrees C for 6 h to obtain dense ceramics (between 85 and 90%). The two-probe ac impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria samples. The results of the impedance spectroscopy indicate that the Nd0.20Sm0.05Ce0.75O1.875 composition exhibited highest ionic conductivity value, 3.60 x 10(-2) S cm(-1) at 800 degrees C

Characterization of Sm and Nd Co-Doped Ceria-Based Electrolyte Materials

Ceria doped with trivalent cations, such as rare earth elements, is considered to be one of the most promising electrolyte materials for intermediate-temperature solid oxide fuel cells, which are an alternative to the commercially used ytrium-stabilized zirconia (YSZ). The aim of this work research is to synthesize Sm and Nd co-doped ceria materials using the Pechini method as solid electrolyte for intermediate temperature solid oxide fuel cell. Ce0.75Smo.2oNdo.o501.875, Ce0.65Sm0.2Nd0.15O1.825, and Ce(0.6)oSm(0.2)Nd(0.20)O(1.80) have been chosen as target of this study. Microstructural and physical properties of the samples were characterized with X-ray diffraction, scanning electron microscopy, thermogravimetric analysis methods. The results of the thermogravimetry/differential thermal analysis and X-ray diffraction indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 600 degrees C for 3 h. The two-probe ac impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria ceramics at 800 degrees C. The Ce0.60Sm0.20Nd0.20O1.80 sample showed maximum ionic conductivity