Are There Magnetars in High Mass X-ray Binaries? The Case of SuperGiant Fast X-Ray Transients

In this paper we survey the theory of wind accretion in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. We concentrate on the different types of interaction between the inflowing wind matter and the neutron star magnetosphere that are relevant when accretion of matter onto the neutron star surface is largely inhibited; these include the inhibition through the centrifugal and magnetic barriers. Expanding on earlier work, we calculate the expected luminosity for each regime and derive the conditions under which transition from one regime to another can take place. We show that very large luminosity swings (~10^4 or more on time scales as short as hours) can result from transitions across different regimes. The activity displayed by supergiant fast X-ray transients, a recently discovered class of high mass X-ray binaries in our galaxy, has often been interpreted in terms of direct accretion onto a neutron star immersed in an extremely clumpy stellar wind. We show here that the transitions across the magnetic and/or centrifugal barriers can explain the variability properties of these sources as a results of relatively modest variations in the stellar wind velocity and/or density. According to this interpretation we expect that supergiant fast X-ray transients which display very large luminosity swings and host a slowly spinning neutron star are characterized by magnetar-like fields, irrespective of whether the magnetic or the centrifugal barrier applies. Supergiant fast X-ray transients might thus provide a new opportunity to detect and study magnetars in binary systems.Comment: Accepted for publication in ApJ. 16 pages, 6 figure

From Trees to the Forest: Genes to Genomics

Crick, Watson, and colleagues revealed the genetic code in 1953, and since that time, remarkable progress has been made in understanding what makes each of us who we are. Identification of single genes important in disease, and the development of a mechanistic understanding of genetic elements that regulate gene function, have cast light on the pathophysiology of many heritable and acquired disorders. In 1990, the human genome project commenced, with the goal of sequencing the entire human genome, and a “first draft” was published with astonishing speed in 2001. The first draft, although an extraordinary achievement, reported essentially an imaginary haploid mix of alleles rather than a true diploid genome. In the years since 2001, technology has further improved, and efforts have been focused on filling in the gaps in the initial genome and starting the huge task of looking at normal variation in the human genome. This work is the beginning of understanding human genetics in the context of the structure of the genome as a complete entity, and as more than simply the sum of a series of genes. We present 3 studies in this review that apply genomic approaches to leukemia and to transplantation to improve and extend therapies

The Gluon Propagator on a Large Volume, at β=6.0\beta=6.0

We present the results of a high statistics lattice study of the gluon propagator, in the Landau gauge, at $\beta=6.0$. As suggested by previous studies, we find that, in momentum space, the propagator is well described by the expression $G(k^2)= \Big[ M^2 + Z\cdot k^2(k^2/\Lambda^2)^\eta\Big]^{-1}$. By comparing $G(k^2)$ on different volumes, we obtain a precise determination of the exponent $\eta=0.532(12)$, and verify that $M^2$ does not vanish in the infinite volume limit. The behaviour of $\eta$ and $M^2$ in the continuum limit is not known, and can only be studied by increasing the value of $\beta$.Comment: 21 pages, uuencoded LATEX plus 5 postscript figures. ROME prep. 94/1042, SHEP prep. 93/94-3

Identifying Religious and/or Spiritual Perspectives of Adolescents and Young Adults Receiving Blood and Marrow Transplants: A Prospective Qualitative Study

AbstractThe potential benefits (or detriments) of religious beliefs in adolescent and young adults (AYA) are poorly understood. Moreover, the literature gives little guidance to health care teams or to chaplains about assessing and addressing the spiritual needs of AYA receiving hematopoietic stem cell transplants (HSCT). We used an institutional review board–approved, prospective, longitudinal study to explore the use of religion and/or spirituality (R/S) in AYA HSCT recipients and to assess changes in belief during the transplantation experience. We used the qualitative methodology, grounded theory, to gather and analyze data. Twelve AYA recipients were interviewed within 100 days of receiving HSCT and 6 participants were interviewed 1 year after HSCT; the other 6 participants died. Results from the first set of interviews identified 5 major themes: using R/S to address questions of “why me?” and “what will happen to me;” believing God has a reason; using faith practices; and benefitting from spiritual support people. The second set of interviews resulted in 4 major themes: believing God chose me; affirming that my life has a purpose; receiving spiritual encouragement; and experiencing strengthened faith. We learned that AYA patients were utilizing R/S far more than we suspected and that rather than losing faith in the process of HSCT, they reported using R/S to cope with illness and HSCT and to understand their lives as having special purpose. Our data, supported by findings of adult R/S studies, suggest that professionally prepared chaplains should be proactive in asking AYA patients about their understanding and use of faith, and the data can actively help members of the treatment team understand how AYA are using R/S to make meaning, address fear, and inform medical decisions

Young pre-Low-Mass X-ray Binaries in propeller phase : Nature of the 6.7-hour periodic X-ray source 1E 161348-5055 in RCW 103

Discovery of the 6.7-hour periodicity in the X-ray source 1E 161348-5055 in RCW 103 has led to investigations of the nature of this periodicity. We explore a model for 1E 161348-5055, wherein a fast-spinning neutron star with a magnetic field $\sim 10^{12}$ G in a young pre-Low-Mass X-ray Binary (pre-LMXB) with an eccentric orbit of period 6.7 hr operates in the "propeller" phase. The 6.7-hr light curve of 1E 161348-5055 can be quantitatively accounted by a model of orbitally-modulated mass transfer through a viscous accretion disk and subsequent propeller emission (both Illarionov-Sunyaev type and Romanova-Lovelace et al type), and spectral and other properties are also in agreement. Formation and evolution of model systems are shown to be in accordance both with standard theories.Comment: 11 pages, 4 figures, accepted for publication in Astronomy and Astrophysics on 23/08/200

Stochastic background of gravitational waves emitted by magnetars

Two classes of high energy sources in our galaxy are believed to host magnetars, neutron stars whose emission results from the dissipation of their magnetic field. The extremely high magnetic field of magnetars distorts their shape, and causes the emission of a conspicuous gravitational waves signal if rotation is fast and takes place around a different axis than the symmetry axis of the magnetic distortion. Based on a numerical model of the cosmic star formation history, we derive the cosmological background of gravitational waves produced by magnetars, when they are very young and fast spinning. We adopt different models for the configuration and strength of the internal magnetic field (which determines the distortion) as well as different values of the external dipole field strength (which governs the spin evolution of magnetars over a wide range of parameters). We find that the expected gravitational wave background differs considerably from one model to another. The strongest signals are generated for magnetars with very intense toroidal internal fields ($\sim 10^{16}$ G range) and external dipole fields of $\sim 10^{14}$, as envisaged in models aimed at explaining the properties of the Dec 2004 giant flare from SGR 1806-20. Such signals should be easily detectable with third generation ground based interferometers such as the Einstein Telescope.Comment: 9 pages, 5 figures, accepted for publication in MNRA

X-ray and optical observations of the unique binary system HD49798/RXJ0648.0-4418

We report the results of XMM-Newton observations of HD49798/RXJ0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P=13.2 s) and has a dynamically measured mass of 1.28+/-0.05 M_sun. Its X-ray emission consists of a strongly pulsed, soft component, well fit by a blackbody with kT~40 eV, accounting for most of the luminosity, and a fainter hard power-law component (photon index ~1.6). A luminosity of ~10^{32} erg/s is produced by accretion onto the white dwarf of the helium-rich matter from the wind of the companion, which is one of the few hot sub-dwarfs showing evidence of mass-loss. A search for optical pulsations at the South African Astronomical Observatory 1.9-m telescope gave negative results. X-rays were detected also during the white dwarf eclipse. This emission, with luminosity 2x10^{30} erg/s, can be attributed to HD 49798 and represents the first detection of a hot sub-dwarf star in the X-ray band. HD49798/RXJ0648.0-4418 is a post-common envelope binary which most likely originated from a pair of stars with masses ~8-10 M_sun. After the current He-burning phase, HD 49798 will expand and reach the Roche-lobe, causing a higher accretion rate onto the white dwarf which can reach the Chandrasekhar limit. Considering the fast spin of the white dwarf, this could lead to the formation of a millisecond pulsar. Alternatively, this system could be a Type Ia supernova progenitor with the appealing characteristic of a short time delay, being the descendent of relatively massive stars.Comment: Accepted for publication on The Astrophysical Journa

Twenty Years of Unrelated Donor Bone Marrow Transplantation for Pediatric Acute Leukemia Facilitated by the National Marrow Donor Program

AbstractThe National Marrow Donor Program (NMDP) has facilitated unrelated donor hematopoietic cell transplants for more than 20 years. In this time period, there have been many changes in clinical practice, including improvements in HLA typing and supportive care, and changes in the source of stem cells. Availability of banked unrelated donor cord blood (incorporated into the NMDP registry in 2000) as a source of stem cells has become an important option for children with leukemia, offering the advantages of immediate availability for children with high-risk disease, the need for a lesser degree of HLA match, and expanding access for those with infrequent HLA haplotypes. Overall survival (OS) in children with acute leukemia transplanted with unrelated donor bone marrow (BM) is markedly better in more recent years, largely attributable to less treatment-related mortality (TRM). Within this cohort, 2-year survival was markedly better for patients with acute lymphoblastic leukemia (ALL) in first complete response (CR1) (74%) versus second complete response (CR2) (62%) or more advanced disease (33%). Similar findings are observed with patients with AML, suggesting earlier referral to bone marrow transplant (BMT) is optimal for survival. Notably, this improvement over time was not observed in unmodified peripheral blood stem cell (PBSC) recipients, suggesting unmodified PBSC may not be the optimal stem cell source for children

Fast Spectral Variability from Cygnus X-1

We have developed an algorithm that, starting from the observed properties of the X-ray spectrum and fast variability of an X-ray binary allows the production of synthetic data reproducing observables such as power density spectra and time lags, as well as their energy dependence. This allows to reconstruct the variability of parameters of the energy spectrum and to reduce substantially the effects of Poisson noise, allowing to study fast spectral variations. We have applied the algorithm to Rossi X-ray Timing Explorer data of the black-hole binary Cygnus X-1, fitting the energy spectrum with a simplified power law model. We recovered the distribution of the power law spectral indices on time-scales as low as 62 ms as being limited between 1.6 and 1.8. The index is positively correlated with the flux even on such time-scales.Comment: 14 pages, 19 figures, accepted by MNRA