The bright, erratic black hole X-ray binary GRS 1915+105 has long been a target for studies of disk instabilities, radio/infrared jets, and accretion disk winds, with implications that often apply to ...sources that do not exhibit its exotic X-ray variability. With the launch of the Neutron star Interior Composition Explorer (NICER), we have a new opportunity to study the disk wind in GRS 1915+105 and its variability on short and long timescales. Here we present our analysis of 39 NICER observations of GRS 1915+105 collected during five months of the mission data validation and verification phase, focusing on Fe xxv and Fe xxvi absorption. We report the detection of strong Fe xxvi in 32 (>80%) of these observations, with another four marginal detections; Fe xxv is less common, but both likely arise in the well-known disk wind. We explore how the properties of this wind depend on broad characteristics of the X-ray lightcurve: mean count rate, hardness ratio, and fractional rms variability. The trends with count rate and rms are consistent with an average wind column density that is fairly steady between observations but varies rapidly with the source on timescales of seconds. The line dependence on spectral hardness echoes the known behavior of disk winds in outbursts of Galactic black holes; these results clearly indicate that NICER is a powerful tool for studying black hole winds.
We present an X-ray spectral and timing analysis of 4U 1543-47 during its 2002 outburst based on 49 pointed observations obtained using the Rossi X-Ray Timing Explorer. The outburst reached a peak ...intensity of 4.2 crab in the 2-12 keV band and declined by a factor of 32 throughout the month-long observation. A 21.9 plus or minus 0.6 mJy radio flare was detected at 1026.75 MHz two days before the X- ray maximum; the radio source was also detected late in the outburst, after the X-ray source entered the "hard" state. The X-ray light curve exhibits the classic shape of a rapid rise and an exponential decay. The spectrum is soft and dominated by emission from the accretion disk. The continuum is fitted with a multicolor disk blackbody (kT sub(max) = 1.04 keV) and a power law ( gamma approx 2.7). Midway through the decay phase, a strong low-frequency quasi- periodic oscillation ( nu = 7.3-8.1 Hz) was present for several days. The spectra feature a broad Fe Kalpha line that is asymmetric, suggesting that the line is due to relativistic broadening rather than Comptonization. Relativistic Laor models provide much better fits to the line than nonrelativistic Gaussian models, particularly near the beginning and end of our observations. The line fits yield estimates for the inner disk radius that are within 6R sub(g); this result and additional evidence indicates that this black hole may have a nonzero angular momentum.
Many astronomical sources produce transient phenomena at radio frequencies, but the transient sky at low frequencies (<300 MHz) remains relatively unexplored. Blind surveys with new wide-field radio ...instruments are setting increasingly stringent limits on the transient surface density on various timescales. Although many of these instruments are limited by classical confusion noise from an ensemble of faint, unresolved sources, one can in principle detect transients below the classical confusion limit to the extent that the classical confusion noise is independent of time. We develop a technique for detecting radio transients that is based on temporal matched filters applied directly to time series of images, rather than relying on source-finding algorithms applied to individual images. This technique has well-defined statistical properties and is applicable to variable and transient searches for both confusion-limited and non-confusion-limited instruments. Using the Murchison Widefield Array as an example, we demonstrate that the technique works well on real data despite the presence of classical confusion noise, sidelobe confusion noise, and other systematic errors. We searched for transients lasting between 2 minutes and 3 months. We found no transients and set improved upper limits on the transient surface density at 182 MHz for flux densities between ∼20 and 200 mJy, providing the best limits to date for hour- and month-long transients.
Long term variability of Cygnus X–1 Pottschmidt, K.; Wilms, J.; Nowak, M. A. ...
Astronomy and astrophysics (Berlin),
09/2003, Letnik:
407, Številka:
3
Journal Article
Human immunodeficiency virus (HIV) integrase enzyme is required for the integration of viral DNA into the host cell chromosome. Integrase complex assembly and subsequent strand transfer catalysis are ...mediated by specific interactions between integrase and bases at the end of the viral long terminal repeat (LTR). The strand transfer reaction can be blocked by the action of small molecule inhibitors, thought to bind in the vicinity of the viral LTR termini. This study examines the contributions of the terminal four bases of the nonprocessed strand (G2T1C–1A–2) of the HIV LTR on complex assembly, specific strand transfer activity, and inhibitor binding. Base substitutions and abasic replacements at the LTR terminus provided a means to probe the importance of each nucleotide on the different functions. An approach is described wherein the specific strand transfer activity for each integrase/LTR variant is derived by normalizing strand transfer activity to the concentration of active sites. The key findings of this study are as follows. 1) The G2:C2 base pair is necessary for efficient assembly of the complex and for maintenance of an active site architecture, which has high affinity for strand transfer inhibitors. 2) Inhibitor-resistant enzymes exhibit greatly increased sensitivity to LTR changes. 3) The strand transfer and inhibitor binding defects of a Q148R mutant are due to a decreased affinity of the complex for magnesium. 4) Gln148 interacts with G2, T1, and C–1 at the 5′ end of the viral LTR, with these four determinants playing important and overlapping roles in assembly, strand transfer catalysis and high affinity inhibitor binding.
This study evaluated four over the counter venison dry dog foods available from one on-line retail vendor for potential contamination with common known food allergens: soy, poultry or beef. An ...amplified, double sandwich type enzyme linked immunosorbent assay (ELISA) test of soy, poultry and beef proteins were performed by an independent accredited food laboratory. The ELISA test for poultry protein was found to be unreliable when testing in dry dog foods because false negatives occurred. ELISA testing of control diets for both soy and beef proteins performed as expected and could be useful in antigen testing in dry dog foods. Three of the four over the counter (OTC) venison canine dry foods with no soy products named in the ingredient list were ELISA positive for soy; additionally one OTC diet tested positive for beef protein with no beef products listed as an ingredient list. One OTC venison diet was not found to be positive for soy, poultry or beef proteins. However, none of the four OTC venison diets could be considered suitable for a diagnostic elimination trial as they all contained common pet food proteins, some of which were readily identifiable on the label and some that were only detected by ELISA. Therefore, if the four OTC venison products selected in this study are representative of OTC products in general, then the use of OTC venison dry dog foods should not be used during elimination trials in suspected food allergy patients.
We present phase-resolved, high-resolution (1.3 Å) spectroscopy of the brightest near-synchronous polar BY Cam taken on two different occasions in 1998 and 1999. The first tomographic study of such a ...system reveals line emission spread out over a large velocity range forming a crescent at negative vy velocities in the Doppler maps. In contrast to the majority of synchronous AM Her systems there is only weak indication for the presence of a focused accretion stream. These two facts suggest that the majority of the matter is accreted via an extended curtain. Location and extent of the structure in the Doppler maps can be reproduced with a simple curtain model raised over a wide (~180°) range in azimuth implying that the ballistic stream stretches to a point far behind the white dwarf. In order to reach such small magnetospheric radii mass accretion rates a factor of 10 to 20 in excess of that normally seen in polars would be required. In addition to the curtain emission, the Balmer lines show a narrow emission line component likely originating from the heated side of the secondary star. Its velocity amplitude of 190 $\rm km\,s^{-1}$ together with an illumination model of the secondary star suggests a rather heavy white dwarf of $M_{1}\geq 0.8~M_{\odot}$ and an inclination larger than $i \geq 40$°. Timings of this feature in the present and historical data unequivocally determine the orbital period and have been used to establish a high-precision, long-term ephemeris.
We present R-band photometry of the X-ray transient and candidate black hole binary XTE J1650-500 obtained between 2003 May and August with the 6.5 m Clay telescope. A timing analysis of these data ...reveals a photometric period of 0.3205 c 0.0007 days (i.e., 7.63 hr) with a possible alias at 0.3785 days (9.12 hr). Our photometry completely rules out the previously published spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the 15 archival ESO VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.) that were the basis of the previously published spectroscopic period. We used a "rest-frame search" technique that is well suited for cases in which the signal-to-noise ratio of individual spectra is low. For each of roughly 1.1 million binary ephemerides, we summed all of the spectra in a trial rest frame of the secondary star, and each rest-frame spectrum was cross-correlated against a template spectrum. We then searched for the set of orbital parameters that produced the strongest cross-correlation value. The results confirmed the photometric period of 0.3205 days and ruled out the alias period near 0.38 days. The best value for the velocity semiamplitude of the companion star is K sub(2) = 435 c 30 km s super(-1), and the corresponding optical mass function is f(M) = 2.73 c 0.56 M sub( ). The spectral type of the companion star is not well constrained because we only have six template spectra available to us. The K4 V template provides the best match; next-best matches are provided by the G5 V and K2 III templates. We also find that the accretion disk dominates the light in the R band where the disk fraction is 80% or higher, although this value should be treated with caution owing to the poor signal-to-noise ratio and the limited number of templates. The amplitude of the phased R-band light curve is 0.2 mag, which gives a lower limit to the inclination of 50 c 3 in the limiting case of no contribution to the R-band light curve from the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass ratios of other black hole binaries, such as A0620-00 or GRS 1124-683 (e.g., Q 10), then our lower limit to the inclination gives an upper limit to the mass of the black hole in XTE J1650-500 of M sub(1) 7.3 M sub( ). However, the mass can be considerably lower if the R-band flux is dominated by the accretion disk. For example, if the accretion disk does contribute 80% of the flux, as our preliminary results suggest, then the black hole mass would be only about 4 M sub( ).
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