The Spectrum and Dips of RE 0751+14: A joint evaluation of ROSAT and ASCA Archival Data

Using archival ASCA and ROSAT observations of RE 0751+14, X-ray energy spectra, pulse profiles and the results of pulse timing analysis are presented. The energy spectra are well-fitted by a blackbody model at low energy and a Raymond-Smith model at high energy, together with a partial covering absorber. A fluorescence emission line at 6.4 keV with an equivalent width $\sim 220$ eV was resolved for the first time.Comment: To appear on Astrophysics and Space Science, vol 259, pages 191-203, January 199

The Timing Noise of PSR 0823+26, PSR 1706-16, PSR 1749-28, PSR 2021+51 and The Anomalous Braking Indices

We have investigated the stability of the pulse frequency second derivatives ($\ddot \nu$) of PSR 0823+26, PSR 1706-16, PSR 1749-28, PSR 2021+51 which show significant quadratic trends in their pulse frequency histories in order to determine whether the observed second derivatives are secular or they arise as part of noise processes. We have used TOA data extending to more than three decades which are the longest time spans ever taken into account in pulse timing analyses. We investigated the stability of pulse frequency second derivative in the framework of low resolution noise power spectra (Deeter 1984) estimated from the residuals of pulse frequency and TOA data. We have found that the $\ddot \nu$ terms of these sources arise from the red torque noise in the fluctuations of pulse frequency derivatives which may originate from the external torques from the magnetosphere of pulsar

ROTSE observations of the young cluster IC 348

CCD observations of stars in the young cluster IC 348 were obtained from 2004 August to 2005 January with a 0.45 m ROTSEIIId robotic reflecting telescope at the Turkish National Observatory site, Bakirlitepe, Turkey. The timing analysis of selected stars whose X-Ray counterpart were detected by Chandra X-Ray Observatory were studied. The time series of stars were searched for rotational periodicity by using different period search methods. 35 stars were found to be periodic with periods ranging from 0.74 to 32.3 days. Eighteen of the 35 periodic stars were new detections. Four of the new detections were CTTSs and the others were WTTSs and G type (or unknown spectral class) stars. In this study, we confirmed the stability of rotation periods of TTauri stars. The periods obtained by Cohen et al. and us were different by 1%. We also confirmed the 3.24 h pulsation period of H254 which is a delta Scuti type star as noted by Ripepi et al. but the other periods detected by them were not found. We examined correlation between X-ray luminosity and rotational period of our sample of TTSs. There is a decline in the rotational period with X-ray luminosity for late type TTSs.Comment: 15 pages, 14 figures, accepted for publication in Astronomical Journa

Design and evaluation of an ontology based information extraction system for radiological reports

Cataloged from PDF version of article.This paper describes an information extraction system that extracts and converts the available information in free text Turkish radiology reports into a structured information model using manually created extraction rules and domain ontology. The ontology provides flexibility in the design of extraction rules, and determines the information model for the extracted semantic information. Although our information extraction system mainly concentrates on abdominal radiology reports, the system can be used in another field of medicine by adapting its ontology and extraction rule set. We achieved very high precision and recall results during the evaluation of the developed system with unseen radiology reports. (C) 2010 Elsevier Ltd. All rights reserved

Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14

We present evidence of a 6.4 keV emission line during a burst from the soft gamma-ray repeater SGR 1900+14. The Rossi X-ray Timing Explorer (RXTE) monitored this source extensively during its outburst in the summer of 1998. A strong burst observed on August 29, 1998 revealed a number of unique properties. The burst exhibits a precursor and is followed by a long (~ 1000 s) tail modulated at the 5.16 s stellar rotation period. The precursor has a duration of 0.85 s and shows both significant spectral evolution as well as an emission feature centered near 6.4 keV during the first 0.3 s of the event, when the X-ray spectrum was hardest. The continuum during the burst is well fit with an optically thin thermal bremsstrahlung (OTTB) spectrum with the temperature ranging from about 40 to 10 keV. The line is strong, with an equivalent width of 400 eV, and is consistent with Fe K-alpha fluorescence from relatively cool material. If the rest-frame energy is indeed 6.4 keV, then the lack of an observed redshift indicates that the source is at least 80 km above the neutron star surface. We discuss the implications of the line detection in the context of models for SGRs.Comment: AASTex preprint, 14 pages, 3 embedded figures. Accepted for Publication in Astrophysical Journal Letter

Spin-down rate of 1E 2259+586 from RXTE observation

We present new X-ray observations of the X-ray pulsar 1E 2259+586, obtained during March 1997, with the Rossi X-Ray Timing Explorer (RXTE). We have measured the pulse frequency derivative $\dot \nu = (-1.08 \pm 0.04) \times 10^{-14}$ Hz s$^{-1}$ from pulse arrival times obtained in a sequence of 5 observations spread over one month. This $\dot\nu$ is consistent with the long term spin-down trend. We also found that the observed X-ray luminosity is consistent with that measured at quiescent X-ray flux levels by previous missions. Our observations imply that 1E 2259+586 was spinning down steadily without exhibiting any stochastic torque noise fluctuations during the month covered by our observations.Comment: 4 pages, Latex (l-aa), Accepted for publication in Astronomy and Astrophysic

Evidence of a Change in the Long Term Spin-down Rate of the X-ray Pulsar 4U 1907+09

We analyzed RXTE archival observations of 4U 1907+09 between 17 February 1996 and 6 March 2002. The pulse timing analysis showed that the source stayed at almost {\bf{constant}} period around August 1998 and then started to spin-down at a rate of $(-1.887\mp 0.042)\times 10^{-14}$ Hz s$^-1$ which is $\sim$ 0.60 times lower than the long term ($\sim 15$ years) spin-down rate (Baykal et al. 2001). Our pulse frequency measurements for the first time resolved significant spin-down rate variations since the discovery of the source. We also presented orbital phase resolved X-ray spectra during two stable spin down episodes during November 1996 - December 1997 and March 2001 - March 2002. The source has been known to have two orbitally locked flares. We found that X-ray flux and spectral parameters except Hydrogen column density agreed with each other during the flares.We interpreted the similar values of X-ray fluxes as an indication of the fact that the source accretes not only via transient retrograde accretion disc (in't Zand et al. 1998) but also via the stellar wind of the companion (Roberts et al. 2001), so that the variation of the accretion rate from the disc does not cause significant variation in the observed X-ray flux. Lack of significant change in spectral parameters except Hydrogen column density was interpreted as a sign of the fact that the change in the spin-down rate of the source was not accompanied by a significant variation in the accretion geometry.Comment: Revised version. Accepted for publication in MNRA

Design and evaluation of an ontology based information extraction system for radiological reports

This paper describes an information extraction system that extracts and converts the available information in free text Turkish radiology reports into a structured information model using manually created extraction rules and domain ontology. The ontology provides flexibility in the design of extraction rules, and determines the information model for the extracted semantic information. Although our information extraction system mainly concentrates on abdominal radiology reports, the system can be used in another field of medicine by adapting its ontology and extraction rule set. We achieved very high precision and recall results during the evaluation of the developed system with unseen radiology reports. © 2010 Elsevier Ltd

Recent X-ray measurements of the accretion-powered pulsar 4U 1907+09

X-ray observations of the accreting X-ray pulsar 4U~1907+09, obtained during February 1996 with the Proportional Counter Array on the Rossi X-ray Timing Experiment (RXTE), have enabled the first measurement of the intrinsic pulse period Ppulse since 1984: Ppulse=440.341[+0.012,-0.017] s. 4U 1907+09 is in a binary system with a blue supergiant. The orbital parameters were solved and this enabled the correction for orbital delay effects of a measurement of Ppulse obtained in 1990 with Ginga. Thus, three spin down rates could be extracted from four pulse periods obtained in 1983, 1984, 1990, and 1996. These are within 8% equal to a value of dPpulse/dt=+0.225 s/yr. This suggest that the pulsar is perhaps in a monotonous spin down mode since its discovery in 1983. Furthermore, the RXTE observations show transient ~18 s oscillations during a flare that lasted about 1 hour. The oscillations may be interpreted as Keplerian motion of an accretion disk near the magnetospheric radius. This, and the notion that the co-rotation radius is much larger than any conceivable value for the magnetospheric radius (because of the long spin period), renders it unlikely that this pulsar spins near equilibrium like is suspected for other slowing accreting X-ray pulsars. We suggest as an alternative that perhaps the frequent occurrence of a retrograde transient accretion disk may be consistently slowing the pulsar down. Further observations of flares can provide more evidence of this.Comment: 26 pages, 11 figures, to be published in Astrophysical Journal part I on March 20, 199