Bridging the gap between stellar-mass black holes and ultraluminous X-ray sources

The X-ray spectral and timing properties of ultraluminous X-ray sources (ULXs) have many similarities with the very high state of stellar-mass black holes (power-law dominated, at accretion rates greater than the Eddington rate). On the other hand, their cool disk components, large characteristic inner-disk radii and low characteristic timescales have been interpreted as evidence of black hole masses ~ 1000 Msun (intermediate-mass black holes). Here we re-examine the physical interpretation of the cool disk model, in the context of accretion states of stellar-mass black holes. In particular, XTE J1550-564 can be considered the missing link between ULXs and stellar-mass black holes, because it exhibits a high-accretion-rate, low-disk-temperature state (ultraluminous branch). On the ultraluminous branch, the accretion rate is positively correlated with the disk truncation radius and the bolometric disk luminosity, while it is anti-correlated with the peak temperature and the frequency of quasi-periodic-oscillations. Two prototypical ULXs (NGC1313 X-1 and X-2) also seem to move along that branch. We use a phenomenological model to show how the different range of spectral and timing parameters found in the two classes of accreting black holes depends on both their masses and accretion rates. We suggest that ULXs are consistent with black hole masses ~ 50-100 Msun, moderately inefficiently accreting at ~20 times Eddington.Comment: 11 pages, accepted for publication in Astrophysics and Space Science. Based on work presented at the Fifth Stromlo Symposium, Australian National University, Dec 200

The Swift X-Ray Te1escope: Status and Performance

We present science highlights and performance from the Swift X-ray Telescope (XRT), which was launched on November 20,2004. The XRT covers the 0.2-10 keV band, and spends most of its time observing gamma-ray burst (GRB) afterglows, though it has also performed observations of many other objects. By mid-August 2007, the XRT had observed over 220 GRB afterglows, detecting about 96% of them. The XRT positions enable followup ground-based optical observations, with roughly 60% of the afterglows detected at optical or near IR wavelengths. Redshifts are measured for 33% of X-ray afterglows. Science highlights include the discovery of flaring behavior at quite late times, with implications for GRB central engines; localization of short GRBs, leading to observational support for compact merger progenitors for this class of bursts; a mysterious plateau phase to GRB afterglows; as well as many other interesting observations such as X-ray emission from comets, novae, galactic transients, and other objects

Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the Ultraviolet Anomaly in NGC 5548 with X-Ray Spectroscopy

During the Space Telescope and Optical Reverberation Mapping Project observations of NGC 5548, the continuum and emission-line variability became decorrelated during the second half of the six-month-long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with the Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all three observations: the UV emission-line flux decrease, the soft-excess increase, and the emission-line anomaly

Space telescope and optical reverberation mapping project. I. Ultraviolet observations of the Seyfert 1 galaxy NGC 5548 with the cosmic origins spectrograph on <i>Hubble Space Telescope</i>

We describe the first results from a six-month long reverberation-mapping experiment in the ultraviolet based on 171 observations of the Seyfert 1 galaxy NGC 5548 with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Significant correlated variability is found in the continuum and broad emission lines, with amplitudes ranging from ~30% to a factor of two in the emission lines and a factor of three in the continuum. The variations of all the strong emission lines lag behind those of the continuum, with He ii $\lambda 1640$ lagging behind the continuum by ~2.5 days and Lyα $\lambda 1215$, C iv $\lambda 1550$, and Si iv $\lambda 1400$ lagging by ~5–6 days. The relationship between the continuum and emission lines is complex. In particular, during the second half of the campaign, all emission-line lags increased by a factor of 1.3–2 and differences appear in the detailed structure of the continuum and emission-line light curves. Velocity-resolved cross-correlation analysis shows coherent structure in lag versus line of sight velocity for the emission lines; the high-velocity wings of C iv respond to continuum variations more rapidly than the line core, probably indicating higher velocity broad-line region clouds at smaller distances from the central engine. The velocity-dependent response of Lyα, however, is more complex and will require further analysis

Estudo anatomopatológico e imunoistoquímico da pitiose em eqüinos naturalmente infectados Anatomopathological and immunohistochemical study of pythiosis in naturally infected horses

O trabalho teve como objetivo comparar a técnica de Grocott metanamina de prata (GMS) com o método imunoistoquímico de streptavidina-biotina marcada (LSAB) no diagnóstico da pitiose. Fragmentos de feridas cutâneas suspeitas de pitiose provenientes de 55 eqüinos foram processados pelas técnicas de hematoxilina/eosina, GMS e imunoperoxidase (LSAB). Trinta e quatro casos foram positivos pelo GMS, dos quais 28 apresentaram imunomarcação (LSAB) positiva para Pythium insidiosum. Os seis casos restantes apresentaram diagnóstico compatível de zigomicose. Foram diagnosticados como tecido de granulação com infiltração de eosinófilos sem áreas de necrose (nove casos), tecido de granulação com infiltrado de eosinófilos e presença de áreas de necrose (sete), habronemose (quatro) e sarcóide (um). Concluiu-se que a imunoperoxidase pelo método LSAB apresenta maior especificidade no diagnóstico de infecção pelo P. insidiosum do que pelo método GMS.<br>The main goals of this study were to perform an anatomopathological evaluation of equine tissue naturally infected with Pythium insidiosus and to compare the reliability of Grocott methenamine silver nitrate (GMS) and the labeled streptavidin-biotin (LSAB) techniques for the diagnosis of pythiosis. Samples of cutaneous wounds suggestive of pythiosis obtained from 55 horses were histologically studied using hematoxylin-eosin and GMS stains, and LSAB. Twenty eight, out of 34 GMS-positive samples, were LSAB-positive for Pythiuminsidiosum. The six LSAB-negative samples were apparently cases of zygomicosis. The remaining samples were diagnosed as follow: granulation tissue with eosinophilic infiltration without necrotic areas (nine cases); granulation tissue with eosinophilic infiltration and necrotic areas (seven); habronemiasis (four); sarcoid (one). In conclusion, the LSAB method was more specific for the diagnosis of P. insidiosum when compared to GMS