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

Antidepressant Dosing in Major Depression: A Pharmacogenomic Approach

Major depressive disorder (MDD) is the most predominant mental disorder in the United States, with serious and costly health risks if not successfully managed. Pharmacotherapy is a standard option for MDD treatment, but patients often require extensive therapy adjustments to find a suitable regimen. Pharmacogenomics may enable greater precision in antidepressant therapy. Genotypic variations in CYP2D6 and CYP2C19 metabolic enzymes are reliable predictors of serum drug concentration, but the complex dose-response relationship of antidepressants prevents such variations from predicting therapy success. Additionally, ABCBl has been examined for its role in P-glycoprotein efflux of antidepressants in the brain, yet it is still inconclusive as to which variations are correlated with drug response. Current genotypic guidelines are largely proactive and clinical trials utilizing genotypic dosing have shown significant reductions in side effects and health care costs. Further studies of genotypic targets are needed and, if the possible clinical benefits are confirmed, the use of genotyping will be an important tool in optimizing antidepressant therapy

A transient low-frequency QPO from the black hole binary GRS 1915+105

We present the results of the timing analysis of five Rossi X-ray Timing Explorer observations of the Black Hole Candidate GRS 1915+105 between 1996 September and 1997 December. The aim was to investigate the possible presence of a type-B quasi-periodic oscillation (QPO). Since in other systems this QPO is found to appear during spectral transitions from Hard to Soft states, we analyzed observations characterized by a fast and strong variability, in order to have a large number of transitions. In GRS 1915+105, transitions occur on very short time scales (~ sec): to single them out we averaged Power Density Spectra following the regular path covered by the source on a 3D Hardness-Hardness-Intensity Diagram. We identified both the type-C and the type-B quasi-periodic oscillations (QPOs): this is the first detection of a type-B QPO in GRS 1915+105. As the spectral transitions have been associated to the emission and collimation of relativistic radio-jets, their presence in the prototypical galactic jet source strengthens this connection.Comment: 13 pages, 9 figures, accepted for publication on MNRA

Discovery of mHz X-ray Oscillations in a Transient Ultraluminous X-ray Source in M82

We report the discovery of X-ray quasi-periodic oscillations (QPOs) at frequencies of 3-4 mHz from a transient ultraluminous X-ray source (ULX) X42.3+59 in M82. The QPOs are strong and broad and appear with weak or absent red noise, and are detected only in Chandra observations when the source is brighter than 10^40 ergs/s. The QPO behavior is similar to the type A-I QPOs found in XTE J1550-564, which is a subclass of low frequency QPOs with properties in between type A and B. Therefore, we identify the QPOs in X42.3+59 as of type A or B, and rule out the possibility of type C. With this identification, the mass of the black hole in X42.3+59 can be inferred as in the range of 12,000-43,000 solar masses by scaling the QPO frequency to that of the type A/B QPOs in stellar mass black holes. Cool disk emission is detected in one Chandra observation, and the disk inner radius suggests a similar black hole mass range. Black holes of such a high mass are able to produce an energy output in a manner similar to X42.3+59 by accreting from the interstellar medium directly.Comment: 5 pages, 1 figure, accepted for publication in The Astrophysical Journal Letter

High-Frequency Quasi-Periodic Oscillations from GRS 1915+105

We report the results of a systematic timing analysis of all archival Rossi X-Ray Timing Explorer (RXTE) observations of the bright black-hole binary GRS 1915+105 in order to detect high-frequency quasi-periodic oscillations (HFQPO). We produced power-density spectra in two energy bands and limited the analysis to the frequency range 30-1000 Hz. We found 51 peaks with a single trial significance larger than 3 sigma. As all but three have centroid frequencies that are distributed between 63 and 71 Hz, we consider most of them significant regardless of the number of trials involved. The average centroid frequency and FWHM are 67.3 +/- 2.0 Hz and 4.4 +/- 2.4 Hz respectively. Their fractional rms varies between 0.4% and 2% (total band detections) and between 0.5% and 3% (hard ban detections). As GRS 1915+105 shows large variability on time scales longer than 1s, we analysed the data in 16s intervals and found that the detections are limited to a specific region in the colour-colour diagram, corresponding to state B of the source, when the energy spectrum is dominated by a bright accretion disk component. However, the rms spectrum of the HFQPO is very hard and does not show a flattening up to 40 keV, where the fractional rms reaches 11%. We discuss our findings in terms of current proposed models and compare them with the results on other black-hole binaries and neutron-star binaries.Comment: 9 pages, 6 figures, Accepted for publication in MNRA

Zika Virus: Infectious Process and Public Health Response

The Zika virus has become a growing concern as a global pandemic. Since being identified in Uganda in 1947, the virus has spread around the world, recently emerging in South America with a great impact on Brazil. As of 2016, Zika has made its appearance in the United States and is now actively being transmitted in Florida. The virus is a mosquito-vectored flavivirus primarily transmitted by the Aedes mosquito which infects a human through biting. Transmission through sexual intercourse is also possible as well as transmission from a pregnant woman to her fetus. This latter form of transmission presents the primary problem with the Zika virus; transmission to the fetus can cause microcephaly as well as other brain and developmental problems. Proper precautions should be taken based on these identified modes of transmission. Symptoms of Zika are similar to flu-like symptoms, such as low-grade fever, muscle pain and headache. About 20 percent of patients that come in contact with the Zika virus will originally present as asymptomatic and will not display symptoms until almost two weeks after initial contact with the virus. Zika virus can remain in the blood for about a week, but can remain in the semen for months. There are a number of methods used to detect the Zika virus—urine, blood or semen samples may be used to assess if a patient is infected

Black-Hole Transients : From QPOs to Relativistic Jets

Due to the impressive amount of new data provided by the RXTE satellite in the past decade, our knowledge of the phenomenology of accretion onto black holes has increased considerably. In particular, it has been possible to schematize the outburst evolution of transient systems on the basis of their spectral and timing properties, and link them to the ejection of relativistic jets as observed in the radio. Here, I present this scheme, concentrating on the properties of the quasi-periodic oscillations observed in the light curves and on the link with jet ejection.Comment: 6 pages; to appear in the Proceedings of COSPAR Colloquium "Spectra & Timing of Compact X-ray Binaries," January 17-20, 2005, Mumbai, India [new version, references corrected

A microquasar classification from a disk instability perspective

The spectacular variability of microquasars has led to a long string of efforts in order to classify their observed behaviors in a few states. The progress made in the understanding of the Quasi-Periodic Oscillations observed in these objects now makes it possible to develop a new way to find order in their behavior, based on the theorized physical processes associated with these oscillations. This will also have the interest of reuniting microquasars in a single classification based on the physical processes at work and therefore independent of their specificities (mass, variation timescale, outburst history, etc.). This classification is aimed to be a tool to further our understanding of microquasars behavior and not to replace phenomenological states. We start by considering three instabilities that can cause accretion in the disk. We compare the conditions for their development, and the Quasi-Periodic Oscillations they can be expected to produce, with the spectral states in which these Quasi-Periodic Oscillations are observed and sometimes coexist. From the three instabilities that we proposed to explain the three states of GRS 1915+105 we actually found the theoretical existence of four states. We compared those four states with observations and also how those four states can be seen in a model-independent fashion. Those four state can be used to find an order in microquasar observations, based on the properties of the Quasi-Periodic Oscillations and the physics of the associated instabilities.Comment: accepted by A&

Studies of Quasi Periodic Oscillations in the Black Hole Transient XTE J 1817-330

We have used archival RXTE PCA data to investigate timing and spectral characteristics of the transient XTE J1817-330. The data pertains to 160 PCA pointed observations made during the outburst period 2006, January 27 to August 2. A detailed analysis of Quasi-Periodic Oscillations (QPOs) in this black hole X-ray binary is carried out. Power density spectra were obtained using the light curves of the source. QPOs have been detected in the 2-8 keV band in 10 of the observations. In 8 of these observations, QPOs are present in the 8-14 keV and in 5 observations in the 15-25 keV band. XTE J1817-330 is the third black hole source from which the low frequency QPOs are clearly detected in hard X-rays. The QPO frequency lies in ~ 4-9 Hz and the rms amplitude in 1.7-13.3% range, the amplitude being higher at higher energies. We have fitted the PDS of the observations with Lorentzian and power law models. Energy spectra are derived for those observations in which the QPOs are detected to investigate any dependence of the QPO characteristic on the spectral parameters. These spectra are well fitted with a two component model that includes the disk black body component and a power law component. The QPO characteristics and their variations are discussed and its implication on the origin of the QPOs are examinedComment: 16 page, 9 figures and 2 tables. Accepted in MNRAS Journa

A General Relativistic Magnetohydrodynamic Model of High Frequency Quasi-periodic Oscillations in Black Hole Low-Mass X-ray Binaries

We suggest a possible explanation for the high frequency quasi-periodic oscillations (QPOs) in black hole low mass X-ray binaries. By solving the perturbation general relativistic magnetohydrodynamic equations, we find two stable modes of the Alf\'ven wave in the the accretion disks with toroidal magnetic fields. We suggest that these two modes may lead to the double high frequency QPOs if they are produced in the transition region between the inner advection dominated accretion flow and the outer thin disk. This model naturally accounts for the 3 : 2 relation for the upper and lower frequencies of the QPOs, and the relation between the black hole mass and QPO frequency.Comment: Accepted for publication in The Astrophysical Journa