76,008 research outputs found
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM–Newton observations (each lasting ?15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (0.5–10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model
Synchrotron X-ray topographic analysis of the impact of processing steps on the fabrication of AlGaAs/InGaAs p-HEMT's
No full textSynchrotron X-Ray Topography (SXRT) has been uniquely applied to nondestructively reveal and evaluate the damage throughout the depth of the wafer, caused by the deposition of source/gate/drain metallization and of so-called “passivation” dielectric layers on power Al ₀.₂₂Ga₀.₇₈As/In₀.₂₁Ga₀.₇₉As pseudomorphic HEMT's. Device metallization is visible due to the stress imposed on the underlying substrate and is detected as a strain field by SXRT. Experimental results are in good agreement with simulation. The quality and detail of the initial control topographs disappear when the Si₃N₄ dielectric layer is deposited. This is believed due to the passivating layer introducing such strain into the crystal that it overwhelms the metallization strain, in addition to producing a significant amount of stress-induced defect and dislocation generatio
On the binary nature of the γ-ray sources AGL J2241+4454 (= MWC 656) and HESS J0632+057 (= MWC 148)
No full textWe present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the gamma-ray sources AGL J2241+4454 and HESS J0632+0 57, respectively. The main parameters of the Halpha emission line (EW, FWHM and centroid velocity) in these stars are modulated on the proposed orbital periods of 60.37 and 321 days, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two gamma-ray sources thus confirming their binary nature. Our orbital solution support eccentricities e~0.4 and 0.83+-0.08 for MWC 656 and MWC 148, respectively. Further, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ~0.3 orbital phases after periastron passage, similarly to the case of LS I +61 303. In addition, the optical photometric light curve maxima in AGL J2241+4454/MWC 656 occur ~0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with orbital period for the known gamma-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of VHE radiation. Another correlation between the EW of Halpha and orbital period is also observed, similarly to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters Porb and e from the Halpha line in future Be gamma-ray binary candidates
Inelastic X-ray scattering
No full textThe first- and second-order terms of the X-ray scattering cross section are given
and an overview is provided of the excitations that can be studied using inelastic
X-ray scattering. The second-order (resonant) term is then elaborated on and
the role of the core-hole lifetime broadening is explained. Approximations and
the one-electron transitions that describe the scattering process are briefly
addressed in a simplified equation. X-ray emission (fluorescence) and outline
momentum, angular and polarization dependence of the resonant scattering
process are discussed
Update of the search for Gamma Ray Bursts with ARGO-YBJ in scaler mode
No full textWe report an update of the search for emission from Gamma Ray Bursts (GRBs) in the energy range 1−100 GeV in coincidence with the prompt emission detected by satellites, using the large field of view (about 2 sr) air shower detector ARGO-YBJ, appropriate to monitor unpredictable and short duration events like GRBs. The search has been carried out using the single particle technique in time coincidence with satellite detections both for single events and by stacking GRBs in time and phase. Between December 2004 and April 2011, 131 GRBs detected by different satellites occurred in the ARGO-YBJ field of view (zenith angle within 45 degrees). For 110 of these we searched for a high
energy counterpart in the ARGO-YBJ data, finding no statistically significant signal. The resulting fluence upper limits between 1 and 100 GeV reach values as low as 10^(−5) erg/cm2, and in one case (GRB090902B) can be compared with observations by the LAT instrument on the Fermi satellite
Relations between x-ray timing features and spectral parameters of galactic black hole x-ray binaries
No full textWe present a study of correlations between spectral and timing parameters for a sample of black hole X-ray binary candidates. Data are taken from GX
339-4, H 1743-322, and XTE J1650-500, as the Rossi X-ray Timing Explorer
(RXTE) observed complete outbursts of these sources. In our study we investigate outbursts that happened before the end of 2009 to make use of the high-energy coverage of the HEXTE detector and select observations that
show a certain type of quasi-periodic oscillations (type-C QPOs). The spectral parameters are derived using the empirical convolution model simpl to model the Comptonized component of the emission together with a disc blackbody for the emission of the accretion disc. Additional spectral features, namely a reflection component, a high-energy cut-off, and excess emission at 6.4 keV, are taken into account. Our investigations confirm the known positive
correlation between photon index and centroid frequency of the QPOs and reveal an anti-correlation between the fraction of up-scattered photons and the QPO frequency. We show that both correlations behave as expected in the “sombrero”
geometry. Furthermore, we find that during outburst decay the correlation between photon index and QPO frequency follow a general track, independent of individual outbursts
Ray P. Holland to Horace Kephart, December 31, 1928
No full textIn a letter to Horace Kephart on December 21, 1928, Ray P. Holland, Editor of “Field & Stream” writes to tell Kephart that his article “Afoot and Awing in the Great Smokies” was chosen as one of the ten best stories of the month by a committee of judges of the Franklin Square Agency.RAY P. HOLLAND
EDITOR
ELTINGE F. WARNER
PUBLISHER
578 Madison Avenue
at fifty-seventh street
New York City
Field & Stream's
CONSERVATION
COUNCIL
D. R. ANTHONY, JR.
Congressman; joint Introducer of the Game Refuge Bill.
HORACE M.ALBRIGHT
Superintendent of Yellowstone National Park.
BROOKE ANDERSON
Member of the Federal
Advisory Board of the
Migratory Bird Treaty
Act.
J. B. HARKIN
Commissioner of the
Canadian National Parks.
GEORGE A. LAWYER
Former Chief United
States Game Warden.
WM. B. MERSHON
Sportsman — Author —
Conservationist.
E. W. NELSON
Ex-Chief of the U. S.
Biological Survey.
HARRY S. NEW
U. S. Postmaster General;
joint Introducer of the
Game Refuge Bill in the
United States. Senate.
T. GILBERT PEARSON
President of the National
Association of Audubon
Societies.
THEO. ROOSEVELT
First Executive Chairman
of the National Conference on Outdoor Recreation.
December 31, 1928
Mr. Horace Kephart,
Bryson City, N. C.
Dear Mr. Kephart:
I thought you would be interested
in knowing that your story "Afoot and Awing in
the Great Smokies", published in the January
issue, was chosen by a committee of judges of
the Franklin Square Agency, which is owned by
Harper Brothers, as one of the ten best stories
of the month.
With the best of the holiday greetings,
I am
Sincerely yours,
RPHsFTC
Edito
Deformation density studies of ring systems. 2. The deformation density of the diazirine ring in the X-ray structure of 3-[(p-Nitrophenoxy) methyl]-3-chlorodiazirine
No full textThe crystal structure and electron density of 3-[(p-nitrophenoxy)methyl]-3-chlorodiazirine have been analyzed using single crystal X-ray diffraction at 208 K with Mo K alpha radiation to a resolution of sin(theta(max))/lambda = 1.126 Angstrom(-1). A total of 10 440 measured reflections gave 7742 unique reflections with R(m) = 0.026. A multipole atomic density model was fitted to these reflections to give an R(F) = 0.0311. The deformation density of the phenyl portion of the compound is as expected. The dynamic deformation density of the diazirine ring, however, suggests that the bonding in the three-membered ring is a combination of the classical severely-strained cr bonding system with a significant contribution of a a donation from the N=N to an sp(2) carbon. This observation is placed in the context of similar proposals for the bonding in cyclopropanes.PT: J; CR: ALLEN FH, 1987, J CHEM SOC PERK T 2, S1 BAERT F, 1982, ACTA CRYSTALLOGR A, V38, P143 BATTAGLIA R, 1980, Z NATURFORSCH B, V35, P719 BLESSING R, ACA T, P26 CAMERON TS, 1992, J AM CHEM SOC, V114, P1889 CAMERON TS, 1994, J AM CHEM SOC, V116, P1211 CREMER D, 1985, J AM CHEM SOC, V107, P3800 CREMER D, 1985, J AM CHEM SOC, V107, P3811 DEWAR MJS, 1979, J AM CHEM SOC, V101, P783 DOMENICANO A, 1975, ACTA CRYSTALLOGR B, V31, P221 DUNITZ JD, 1983, HELV CHIM ACTA, V66, P123 HANSEN NK, 1978, ACTA CRYSTALLOGR A, V34, P909 HIRSHFELD FL, 1991, CRYST REV, V2, P169 LINDEN A, 1988, J ORG CHEM, V53, P1085 LIU MTH, 1986, J CHEM SOC PERK T 2, P211 SCHMIDT MW, 1990, QCPE B, V10, P52 SEILER P, 1988, HELV CHIM ACTA, V71, P2100 SMITH VH, 1977, ISRAEL J CHEM, V16, P87 SOUHASSOU M, 1992, J AM CHEM SOC, V114, P2371 STEINER T, 1993, ACTA CRYSTALLOGR A, V49, P379 STEVENS IDR, 1990, J CHEM SOC P2, P661 STEWART RF, 1969, J CHEM PHYS, V51, P4569 WALSH AD, 1949, T FARADAY SOC, V45, P179 WIBERG KB, 1987, J AM CHEM SOC, V109, P985; NR: 24; TC: 4; J9: J AMER CHEM SOC; PG: 7; GA: NV421Source type: Electronic(1
Diagnosing and mapping pulmonary emphysema on X-ray projection images
No full textTo assess whether grating-based X-ray dark-field imaging can increase the sensitivity of X-ray projection images in the diagnosis of pulmonary emphysema and allow for a more accurate assessment of emphysema distribution. Lungs from three mice with pulmonary emphysema and three healthy mice were imaged ex vivo using a laser-driven compact synchrotron X-ray source. Median signal intensities of transmission (T), dark-field (V) and a combined parameter (normalized scatter) were compared between emphysema and control group. To determine the diagnostic value of each parameter in differentiating between healthy and emphysematous lung tissue, a receiver-operating-characteristic (ROC) curve analysis was performed both on a per-pixel and a per-individual basis. Parametric maps of emphysema distribution were generated using transmission, dark-field and normalized scatter signal and correlated with histopathology. Transmission values relative to water were higher for emphysematous lungs than for control lungs (1.11 vs. 1.06, p<0.001). There was no difference in median dark-field signal intensities between both groups (0.66 vs. 0.66). Median normalized scatter was significantly lower in the emphysematous lungs compared to controls (4.9 vs. 10.8, p<0.001), and was the best parameter for differentiation of healthy vs. emphysematous lung tissue. In a per-pixel analysis, the area under the ROC curve (AUC) for the normalized scatter value was significantly higher than for transmission (0.86 vs. 0.78, p<0.001) and dark-field value (0.86 vs. 0.52, p<0.001) alone. Normalized scatter showed very high sensitivity for a wide range of specificity values (94% sensitivity at 75% specificity). Using the normalized scatter signal to display the regional distribution of emphysema provides color-coded parametric maps, which show the best correlation with histopathology. In a murine model, the complementary information provided by X-ray transmission and dark-field images adds incremental diagnostic value in detecting pulmonary emphysema and visualizing its regional distribution as compared to conventional X-ray projections
- …
