State transitions in the 2001/2002 outburst of XTE J1650-500

We present a study of the X-ray transient and black hole candidate XTE J1650-500 during its 2001/2002 outburst. The source made two state transitions between the hard and soft states, at luminosity levels that differed by a factor of ~5-10. The first transition, between hard and soft, lasted for ~30 days and showed two parts; one part in which the spectral properties evolve smoothly away from the hard state and another that we identify as the 'steep power law state'. The two parts showed different behavior of the Fe K emission line and QPO frequencies. The second transition, from soft to hard, lasted only \~15 days and showed no evidence of the presence of the 'steep power law state'. Comparing observations from the early rise and the decay of the outburst, we conclude that the source can be in the hard state in a range of more 10^4 in luminosity. We briefly discuss the state transitions in the framework of a two-flow model.Comment: 4 pages, 5 figures. To appear in Proc. of the II BeppoSAX Meeting: "The Restless High-Energy Universe" (Amsterdam, May 5-8, 2003), E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers Ed

Fast determination of coarse grained cell anisotropy and size in epithelial tissue images using Fourier transform

Mechanical strain and stress play a major role in biological processes such as wound healing or morphogenesis. To assess this role quantitatively, fixed or live images of tissues are acquired at a cellular precision in large fields of views. To exploit these data, large numbers of cells have to be analyzed to extract cell shape anisotropy and cell size. Most frequently, this is performed through detailed individual cell contour determination, using so-called segmentation computer programs, complemented if necessary by manual detection and error corrections. However, a coarse grained and faster technique can be recommended in at least three situations. First, when detailed information on individual cell contours is not required, for instance in studies which require only coarse-grained average information on cell anisotropy. Second, as an exploratory step to determine whether full segmentation can be potentially useful. Third, when segmentation is too difficult, for instance due to poor image quality or too large a cell number. We developed a user-friendly, Fourier transform-based image analysis pipeline. It is fast (typically $10^4$ cells per minute with a current laptop computer) and suitable for time, space or ensemble averages. We validate it on one set of artificial images and on two sets of fully segmented images, one from a Drosophila pupa and the other from a chicken embryo; the pipeline results are robust. Perspectives include \textit{in vitro} tissues, non-biological cellular patterns such as foams, and $xyz$ stacks.Comment: 13 pages; 9 figure

High-frequency Quasi-Periodic Oscillations from GRS 1915+105 in its C state

We report the results of a systematic timing analysis of RXTE observations of GRS 1915+105 when the source was in its variability class theta, characterized by alternating soft and hard states on a time scale of a few hundred seconds. The aim was to examine the high-frequency part of the power spectrum in order to confirm the hecto-Hertz Quasi-Periodic Oscillations (QPO) previously reported from observations from mixed variability behaviours. During the hard intervals (corresponding to state C in the classification of Belloni et al., 2000, A&A, 35, 271), we find a significant QPO at a frequency of ~170 Hz, although much broader (Q~2) than previously reported. No other significant peak is observed at frequencies >30 Hz. A time-resolved spectral analysis of selected observations shows that the hard intervals from class theta show a stronger and steeper (Gamma=2.8-3.0) power-law component than hard intervals from other classes. We discuss these results in the framework of hecto-Hertz QPOs reported from GRS 1915+105 and other black-hole binaries.Comment: 7 pages, 8 figures, accepted for publication on MNRA

The variable radio counterpart and possible large-scale jet of the new Z-source XTE J1701-462

We report radio observations, made with the Australia Telescope Compact Array, of the X-ray transient XTE J1701-462. This system has been classified as a new `Z' source, displaying characteristic patterns of behaviour probably associated with accretion onto a low magnetic field neutron star at close to the Eddington limit. The radio counterpart is highly variable, and was detected in six of sixteen observations over the period 2006 January -- April. The coupling of radio emission to X-ray state, despite limited sampling, appears to be similar to that of other `Z' sources, in that there is no radio emission on the flaring branch. The mean radio and X-ray luminosities are consistent with the other Z sources for a distance of 5--15 kpc. The radio spectrum is unusually flat, or even inverted, in contrast to the related sources, Sco X-1 and Cir X-1, which usually display an optically thin radio spectrum. Deep wide-field observations indicate an extended structure three arcminutes to the south which is aligned with the X-ray binary. This seems to represent a significant overdensity of radio sources for the field and so, although a background source remains a strong possibility, we consider it plausible that this is a large-scale jet associated with XTE J1701-462.Comment: Accepted for publication as a Letter in MNRA

The Parsec-scale Structure, Kinematics, and Polarization of Radio-Loud Narrow-Line Seyfert 1 Galaxies

Several narrow-line Seyfert 1 galaxies (NLS1s) have now been detected in gamma rays, providing firm evidence that at least some of this class of active galactic nuclei (AGN) produce relativistic jets. The presence of jets in NLS1s is surprising, as these sources are typified by comparatively small black hole masses and near- or super-Eddington accretion rates. This challenges the current understanding of the conditions necessary for jet production. Comparing the properties of the jets in NLS1s with those in more familiar jetted systems is thus essential to improve jet production models. We present early results from our campaign to monitor the kinematics and polarization of the parsec-scale jets in a sample of 15 NLS1s through multifrequency observations with the Very Long Baseline Array. These observations are complemented by fast-cadence 15 GHz monitoring with the Owens Valley Radio Observatory 40m telescope and optical spectroscopic monitoring with with the 2m class telescope at the Guillermo Haro Astrophysics Observatory in Cananea, Mexico.Comment: 4 pages, 1 figure. To appear in the Proceedings of the IAU Symposium No. 313: "Extragalactic jets from every angle," Galapagos, Ecuador, 15-19 September 2014, F. Massaro, C. C. Cheung, E. Lopez, and A. Siemiginowska (Eds.), Cambridge University Pres

Discovery of two simultaneous non-harmonically related Quasi-Periodic Oscillations in the 2005 outburst of the black-hole binary GRO J1655-40

We studied the low-frequency quasi-periodic oscillations (LFQPOs) in the black hole GRO J1655-40 during the 2005 outburst, using data from the Rossi X-ray Timing Explorer. All LFQPOs could be identified as either type B or type C using previously proposed classification schemes. In the soft state of the outburst the type-C LFQPOs reached frequencies that are among the highest ever seen for LFQPOs in black holes. At the peak of the outburst, in the ultra-luminous state, the power spectrum showed two simultaneous, non-harmonically related peaks which we identified as a type-B and a type-C QPO. The simultaneous presence of a type-C and type-B QPO shows that at least two of the three known LFQPO types are intrinsically different and likely the result of distinct physical mechanisms. We also studied the properties of a broad peaked noise component in the power spectra of the ultra-luminous state. This noise component becomes more coherent with count rate and there are strong suggestions that it evolves into a type-B QPO at the highest observed count rates.Comment: 14 pages, 6 figures, 2 tables, accepted for publication in MNRA

The evolution of the high-energy cut-off in the X-Ray spectrum of the GX 339-4 across a hard-to-soft transition

We report on X-ray observations of the black-hole candidate GX 339-4 during its 2006/2007 outburst. The hardness-intensity diagram of all RXTE/PCA data combined shows a q-shaped track similar to that observed in previous outbursts. The evolution through the HID suggests that in the early phase of the outburst the source underwent a sequence of state transitions, from the hard to the soft state, which is supported by our timing analysis. Broadband (4-200 keV) spectra, fitted with an exponentially cutoff powerlaw, show that the hard spectral component steepens during the transition from the hard to the soft state. The high-energy cutoff decreased monotonically from 120 to 60 keV during the brightening of the hard state, but increased again to 100 keV during the softening in the hard intermediate state. In the short-lived soft intermediate state the cutoff energy was ~ 130 keV, but was no longer detected in the soft state. This is one of the first times that the high-energy cut-off has been followed in such detail across several state transitions. We find that in comparison to several other spectral parameters, the cut-off energy changes more rapidly, just like the timing properties. The observed behaviour of the high energy cutoff of GX 339-4 is also similar to that observed with RXTE-INTEGRAL-Swift during the 2005 outburst of GRO J1655-40. These results constitute a valuable reference to be considered when testing theoretical models for the production of the hard component in these systems.Comment: 16 pages, 8 figures, 5 tables, accepted for publication in MNRAS Main Journa

X-ray spectral and timing properties of the 2001 superburst of 4U 1636-536

Preliminary results are reported on the spectral and timing properties of the spectacular 2001 superburst of 4U 1636-536 as seen by the RXTE/PCA. The (broad-band) power-spectral and hardness properties during the superburst are compared to those just before and after the superburst. Not all of the superburst emission can be fitted by pure black-body radiation. We also gathered BeppoSAX/WFC and RXTE/ASM data, as well as other RXTE/PCA data, obtained days to months before and after the superburst to investigate the normal X-ray burst behavior around the time of the superburst. The first normal X-ray burst after the 2001 superburst was detected 23 days later. During inspection of all the RXTE/ASM data we found a third superburst. This superburst took place on June 26, 1999, which is ~2.9 yrs after the 1996 superburst and ~1.75 yrs before the 2001 superburst. The above findings are the strongest constraints observed so far on the duration of the cessation of normal X-ray bursts after a superburst and the superburst recurrence times.Comment: 4 pages, 4 figures,to appear in the proceedings of "X-Ray Timing 2003: Rossi and Beyond", eds. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville, NY: AIP