117,679 research outputs found
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. 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 IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (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 IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star 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
INTEGRAL and XMM-Newton observations of IGR J16418-4532: evidence of accretion regime transitions in a supergiant fast X-ray transient
No full textWe report on combined INTEGRAL and XMM–Newton observations of the supergiant fast X-ray transient (SFXT) IGR J16418-4532. The observations targeted the X-ray eclipse region of IGR J16418-4532's orbit with continuous INTEGRAL observations across ~25 per cent of orbital phase and two quasi-simultaneous XMM–Newton observations of length 20 and 14 ks, occurring during and just after the eclipse, respectively. An enhanced INTEGRAL emission history is provided with 19 previously unreported outbursts identified in the archival 18–60 keV data set. The XMM–Newton eclipse observation showed prominent Fe emission and a flux of 2.8 × 10-13 erg cm-2 s-1 (0.5–10 keV). Through the comparison of the detected eclipse and post-eclipse flux, the supergiant mass-loss rate through the stellar wind was determined as Ṁw = 2.3–3.8 × 10-7 M⊙ yr-1. The post-eclipse XMM–Newton observation showed a dynamic flux evolution with signatures of the X-ray pulsation, a period of flaring activity, structured nH variations and the first ever detection of an X-ray intensity dip, or ‘off-state’, in a pulsating SFXT. Consideration is given to the origin of the X-ray dip, and we conclude that the most applicable of the current theories of X-ray dip generation is that of a transition between Compton-cooling-dominated and radiative-cooling-dominated subsonic accretion regimes within the ‘quasi-spherical’ model of wind accretion. Under this interpretation, which requires additional confirmation, the neutron star in IGR J16418-4532 possesses a magnetic field of ~1014 G, providing tentative observational evidence of a highly magnetized neutron star in a SFXT for the first time. The implications of these results on the nature of IGR J16418-4532 itself and the wider SFXT class are discussed
Fullerene mixtures as negative electrodes in innovative Na-ion batteries
No full textAfter the successful electrochemical intercalation of C60 with sodium, we report here the preparation of novel negative electrodes for Na-ion batteries composed by commercial C60:C70 mixture, this being significantly less expensive than pure fullerenes. An optimized solid-state Na-poly(ethylene oxide) electrolyte was used for the battery assembly. While pure C60 electrodes show a strong irreversible behavior after the first discharge, the peculiar disordered crystalline arrangement of C60 and C70 in the mixture, increased by a high-energy ball milling treatment, allows to improve the specific capacity at the first discharge up to 320 mAh/g, as well as the overall reversibility
IGR J18175-1530: a new hard X-ray transient detected by INTEGRAL
No full textAuthors: - A. Paizis, V. Beckmann, D. Gotz, L. Sidoli, A. Bazzano, G. Belanger, M. Cadolle-Bel, J. Chenevez, A. De Rosa, E. Kuulkers, M. Falanga, M. Fiocchi, L. Kuiper, J. C. Leyder, S. Mereghetti, S. Piraino, K. Pottschmidt, S. Shaw, J. Tomsick, K. Watanabe, R. Walter, G. Weidenspointnerhttps://www.astronomerstelegram.org/?read=124
BeppoSAX observations of the X-ray pulsar MAXI J1409-619 in low state: DISCOVERY of cyclotron resonance features
No full textThe transient 500 s X-ray pulsar MAXI J1409-619 was discovered by the slit cameras aboard Monitor of All-sky X-ray Image (MAXI) on 2010 October 17, and soon after accurately localized by Swift. We found that the source position was serendipitously observed in 2000 during BeppoSAX observations of the Galactic plane. Two sources are clearly detected in the Medium-Energy Concentrator Spectrometer (MECS): one is consistent with the position of IGR J14043-6148 and the other one with that of MAXI J1409-619. We report on the analysis of this archival BeppoSAX/MECS observation integrated with newly analyzed observation from ASCA and a set of high-energy observations obtained from the offset fields of the BeppoSAX/PDS instrument. For the ON-source observation, the 1.8-100keV spectrum is fit by an absorbed power law with a photon index Γ = 0.87 +0.29-0.19, corresponding to 2-10 and 15-100keV unabsorbed fluxes of 2.7 × 10-12 and 4 × 10 -11ergcm-2 s-1, respectively, and a 2-10keV luminosity of 7 × 1034 erg s-1 for a 15kpc distance. For a PDS offset field observation, performed about one year later and showing a 15-100keV flux of 7 × 10-11ergcm-2 s-1, we clearly pinpoint three spectral absorption features at 44, 73, and 128keV, resolved both in the spectral fit and in the Crab ratio. We interpret these not harmonically spaced features as due to cyclotron resonances. The fundamental energy of 44 3keV corresponds to a magnetic field strength at the neutron star surface of 3.8 × 1012(1 + z) G, where z is the gravitational redshift. We discuss the nature of the source in the light of its possible counterpart. © 2012. The American Astronomical Society. All rights reserved.
Chasing candidate supergiant fast X-ray transients in the 1,000 orbits INTEGRAL/IBIS catalog
No full textWe report results from an investigation at hard X-rays (above 18 keV) and soft X-rays (below 10 keV) of a sample of X-ray transients located on the Galactic plane and detected with the bursticity method, as reported in the latest 1,000 orbits INTEGRAL/IBIS catalog. Our main aim has been to individuate those with X-rays characteristics strongly resembling Supergiant Fast X-ray Transients (SFXTs). As a result, we found four unidentified fast X-ray transients which now can be considered good SFXT candidates. In particular, three transients (IGR J16374−5043, IGR J17375−3022 and IGR J12341−6143) were very poorly studied in the literature before the current work, and our findings largely improved the knowledge of their X-ray characteristics. The other transient (XTE J1829−098) was previously studied in detail only below 10 keV, conversely the current work provides the first detailed study in outburst above 18 keV. In addition we used archival infrared observations of the transients to pinpoint, among the field objects, their best candidate counterpart. We found that their photometric properties are compatible with an early type spectral classification, further supporting our proposed nature of SFXTs. Infrared spectroscopy is advised to confirm or disprove our interpretation. The reported findings allowed a significant increase of the sample of candidate SFXTs known to date, effectively doubling their number
Comparative study of serum and tissue levels after administration of sisomicin and gentamicin
No full textFibroblast interferon from a human amniotic cell line: a strategy for rapid molecular cloning
No full textA strategy for rapid cloning and identification of cDNA clones was employed to obtain fragments of the gene for human fibroblast (beta) interferon. A human amniotic cell line (UAC), widely used for interferon assay, yielded high titers of beta-interferon and was used as a source for cDNA synthesis. Recombinant clones were screened by a combination of hybridization conditions: (a) comparing clones that hybridized with radioactive cDNA from induced UAC cells vs cDNA from cells not induced for beta-IFN; (b) using a synthetic oligonucleotide proble complementary to a region of the beta-IFN gene. Among clones selected on the basis of their positive response to both screening procedure, one (4F7) was sequenced and shown to be highly homologous to the beta-IFN gene. This clone was used as a probe to screen a human chromosomal DNA library, yielding the entire chromosomal beta-IFN gene. A "Northern" hybridization analysis of UAC mRNA from uninduced and induced cells revealed the existence of a single molecular species of mRNA for beta-IFN with the expected molecular weight
Discovery of two new fast X-ray transients with INTEGRAL: IGR J03346+4414 and IGR J20344+3913
No full textWe report on the discovery of two fast X-ray transients (FXTs) from analysis of archival INTEGRAL data. Both are characterized by a remarkable hard X-ray activity above 20?keV, in terms of duration (?15 and 30 min, respectively), peak flux (?10?9?erg?cm?2 s?1) and dynamic range (?2400 and 1360, respectively). Swift/X-ray telescope follow-up observations failed to detect any quiescent or low-level soft X-ray emission from either of the two FXTs, providing an upper limit of the order of a few times 10?12?erg?cm?2 s?1. The main spectral and temporal Imager on Board INTEGRAL Satellite (IBIS)/INTEGRAL Soft Gamma-Ray Imager (ISGRI) characteristics are presented and discussed with the aim of inferring possible hints on their nature
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