On the Torsion of Elastic Half Space with Penny Shaped Crack

The investigation deals with the effect of an embedded flaw-a penny-shaped crack in an elastic half-space subject to torsional deformation. The problem is reduced to a system of Fredholm integral equations. Graphical display of the results are included

The first accurate parallax distance to a black hole

Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 +/- 0.024 milliarcseconds, corresponding to a distance of 2.39 +/- 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is less than 1.4 AU at 22 GHz. Astrometric observations of a larger sample of such systems would provide useful insights into the formation and properties of accreting stellar-mass black holes.Comment: Accepted for publication in ApJ Letters. 6 pages, 2 figure

Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC

The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering process in the Coulomb Nuclear Interference (CNI) region was measured using an ultra thin carbon target and polarized proton beam in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100 GeV). A_N was obtained as a function of momentum transfer -t. The results were fit with theoretical models which allow us to assess the contribution from a hadronic spin flip amplitude.Comment: Contribution to the proceedings of the 16th International Spin Physics Symposium, spin2004 (Trieste

Multi-wavelength INTEGRAL NEtwork (MINE) observations of the microquasar GRS 1915+105

We present the international collaboration MINE (Multi-lambda Integral NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries and microquasars simultaneously with the INTEGRAL gamma-ray satellite. We will focus on the 2003 March-April campaign of observations of the peculiar microquasar GRS 1915+105 gathering radio, IR and X-ray data. The source was observed 3 times in the plateau state, before and after a major radio and X-ray flare. It showed strong steady optically thick radio emission corresponding to powerful compact jets resolved in the radio images, bright near-infrared emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without cutoff in the 3-300 keV range. We compare the different observations, their multi-wavelength light curves, including JEM-X, ISGRI and SPI, and the parameters deduced from fitting the spectra obtained with these instruments on board INTEGRAL.Comment: 4 pages, 9 fig., Proc. of the 5th INTEGRAL Workshop (Feb. 16-20 2004), to be published by ES

Simultaneous multi-wavelength observations of microquasars (the MINE collaboration)

We present the international collaboration MINE (Multi-lambda INTEGRAL NEtwork) aimed at conducting multi-wavelength observations of microquasars simultaneously with the INTEGRAL satellite. The first results on GRS 1915+105 are encouraging and those to come should help us to understand the physics of the accretion and ejection phenomena around a compact object.Comment: 2 p, 3 fig., proc. of the IAU Coll. 194, ``Compact Binaries in the Galaxy and Beyond'', Nov. 2003, La Paz, Mexico, to be published in the Conf. Series of Revista Mexicana de Astronomia y Astrofisica, Eds. G. Tovmassian & E. Sio

Multiple relativistic outbursts of GRS 1915+105: radio emission and internal shocks

We present 5-GHz MERLIN radio images of the microquasar GRS 1915+105 during two separate outbursts in 2001 March and 2001 July, following the evolution of the jet components as they move outwards from the core of the system. Proper motions constrain the intrinsic jet speed to be >0.57c, but the uncertainty in the source distance prevents an accurate determination of the jet speed. No deceleration is observed in the jet components out to an angular separation of about 300mas. Linear polarisation is observed in the approaching jet component, with a gradual rotation in position angle and a decreasing fractional polarisation with time. Our data lend support to the internal shock model whereby the jet velocity increases leading to internal shocks in the pre-existing outflow before the jet switches off. The compact nuclear jet is seen to re-establish itself within two days, and is visible as core emission at all epochs. The energetics of the source are calculated for the possible range of distances; a minimum power of 1-10 per cent of the Eddington luminosity is required to launch the jet.Comment: 18 pages, 14 figures, accepted for publication in MNRAS. For higher-resolution versions of Figures 3, 5, and 12, see http://remote.science.uva.nl/~jmiller/grs1915/figures.htm

Cosmological model insensitivity of local H0H_0 from the Cepheid distance ladder

The observed tension ($\sim 9\%$ difference) between the local distance ladder measurement of the Hubble constant, $H_0$, and its value inferred from the cosmic microwave background (CMB) could hint at new, exotic, cosmological physics. We test the impact of the assumption about the expansion history of the universe ($0.01<z<2.3$) on the local distance ladder estimate of $H_0$. In the fiducial analysis, the Hubble flow Type Ia supernova (SN~Ia) sample is truncated to $z < 0.15$ and the deceleration parameter ($q_0$) fixed to -0.55. We create realistic simulations of the calibrator and Pantheon samples and account for a full systematics covariance between these two sets. We fit several physically motivated dark energy models and derive combined constraints from calibrator and Pantheon SNe~Ia and simultaneously infer $H_0$ and dark energy properties. We find that the assumption on the dark energy model does not significantly change the local distance ladder value of $H_0$, with a maximum difference ($\Delta H_0$) between the inferred value for different models of 0.47 km$^{-1}$ s$^{-1}$ Mpc $^{-1}$, i.e. a 0.6$\%$ shift in $H_0$, significantly smaller than the observed tension. Additional freedom in the dark energy models does not increase the error in the inferred value of $H_0$. Including systematics covariance between the calibrators, low redshift SNe, and high redshift SNe can induce small shifts in the inferred value for $H_0$. The SN~Ia systematics in this study contribute $\lesssim 0.8 \%$ to the total uncertainty on $H_0$.Comment: 11 pages, 3 figures, accepted to Ap

A weak compact jet in a soft state of Cygnus X-1

We present evidence for the presence of a weak compact jet during a soft X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change, showing the hard state jet to be suppressed by a factor of about 3-5 in radio flux and unresolved to direct imaging observations (i.e. < 1 mas at 4 cm). High time-resolution X-ray observations with the RXTE-PCA were also taken during the radio monitoring period, showing the source to make the transition from the hard state to a softer state (via an intermediate state), although the source may never have reached the canonical soft state. Using astrometric VLBI analysis and removing proper motion, parallax and orbital motion signatures, the residual positions show a scatter of ~0.2 mas (at 4 cm) and ~3 mas (at 13 cm) along the position angle of the known jet axis; these residuals suggest there is a weak unresolved outflow, with varying size or opacity, during intermediate and soft X-ray states. Furthermore, no evidence was found for extended knots or shocks forming within the jet during the state transition, suggesting the change in outflow rate may not be sufficiently high to produce superluminal knots.Comment: Accepted in MNRAS; 4 figures and 1 tabl

Searching for the 511 keV annihilation line from galactic compact objects with the IBIS gamma ray telescope

The first detection of a gamma ray line with an energy of about 500 keV from the center our Galaxy dates back to the early seventies. Thanks to the astrophysical application of high spectral resolution detectors, it was soon clear that this radiation was due to the 511 keV photons generated by electron-positron annihilation. Even though the physical process are known, the astrophysical origin of this radiation is still a mystery. The spectrometer SPI aboard the INTEGRAL gamma-ray satellite has been used to produce the first all-sky map in light of the 511 keV annihilation, but no direct evidence for 511 keV galactic compact objects has been found [...] We present the first deep IBIS 511 keV all-sky map, obtained by applying standard analysis to about 5 years of data. Possible 511 keV signals are also searched over hour-day-month timescales. The IBIS sensitivity at 511 keV depends on the detector quantum efficiency at this energy and on the background. Both these quantities were estimated in this work. We find no evidence of Galactic 511 keV point sources. With an exposure of 10 Ms in the center of the Galaxy, we estimate a $1.6 \times 10^{-4}\,ph\,cm^{-2}\,s^{-1}$ flux 2 sigma upper limit. A similar limit is given in a wide area in the Galactic center region with similar exposures. The IBIS 511 keV flux upper limits for microquasars and supernova remnants detected in the hard X domain ($E > 20\, keV$) are also reported. Our results are consistent with a diffuse $e^{+}e^{-}$ annihilation scenario. If positrons are generated in compact objects, we expect that a significant fraction of them propagate in the interstellar medium before there are annihilated away from their birth places.Comment: To appear in A&