49 research outputs found
Observations of giant outbursts from Cygnus X-1
We present interplanetary network localization, spectral, and time history
information for 7 episodes of exceptionally intense gamma-ray emission from
Cygnus X-1. The outbursts occurred between 1995 and 2003, with durations up to
\~28000 seconds. The observed 15 - 300 keV peak fluxes and fluences reached
3E-7 erg /cm2 s, and 8E-4 erg / cm2 respectively. By combining the
triangulations of these outbursts we derive an ~1700 square arcminute (3 sigma)
error ellipse which contains Cygnus X-1 and no other known high energy sources.
The outbursts reported here occurred both when Cyg X-1 was in the hard state as
well as in the soft one, and at various orbital phases. The spectral data
indicate that these outbursts display the same parameters as those of the
underlying hard and soft states, suggesting that they represent another
manifestation of these states.Comment: 27 pages, 9 figures. Revised version. Accepted for publication in the
Astrophysical Journal, tentatively scheduled for October 20, 2003 Part
Неоднородное строение магнитоактивного слоя Курильской островной дуги
An innovative technology of anomalous magnetic field inversion was applied to construct 2D models of the magnetic layer using three profiles crossing the southern, central and northern parts of the Kuril Island Arc. In the frontal area of the northern and southern parts, a zone of increased effective magnetization is clearly distinguished. In the central part of the island arc, increased magnetization is much less pronounced. Anomalous zones of positive effective magnetization have a deep part, the so-called "serpentinite wedge". The inhomogeneous lateral structure of the magnetic layer of the Kuril Island Arc suggests differences in the fluid regime and is reflected in the distribution of modern seismicity. На основе оригинальной технологии инверсии аномального магнитного поля построены двумерные модели магнитоактивного слоя по трем профилям, пересекающим Курильскую островную дугу в южной, центральной и северной части. В северной и южной части островной дуги во фронтальной зоне уверенно выделяется зона повышенной эффективной намагниченности. В центральной части дуги зона повышенной намагниченности выражена существенно слабее. Аномальные зоны положительной эффективной намагниченности имеют глубинную часть, которая соответствует так называемому «серпентинитовому валу». Выявленное неоднородное латеральное строение магнитоактивного слоя Курильской островной дуги свидетельствует о различиях во флюидном режиме и находит свое отражение в распределении современной сейсмичности
Multi-Wavelength Studies of the Optically Dark Gamma-Ray Burst 001025A
We identify the fading X-ray afterglow of GRB 001025A from XMM-Newton
observations obtained 1.9-2.3 days, 2 years, and 2.5 years after the burst. The
non-detection of an optical counterpart to an upper limit of R=25.5, 1.20 days
after the burst, makes GRB 001025A a ``dark'' burst. Based on the X-ray
afterglow spectral properties of GRB 001025A, we argue that some bursts appear
optically dark because their afterglow is faint and their cooling frequency is
close to the X-ray band. This interpretation is applicable to several of the
few other dark bursts where the X-ray spectral index has been measured. The
X-ray afterglow flux of GRB 001025A is an order of magnitude lower than for
typical long-duration gamma-ray bursts. The spectrum of the X-ray afterglow can
be fitted with an absorbed synchrotron emission model, an absorbed thermal
plasma model, or a combination thereof. For the latter, an extrapolation to
optical wavelengths can be reconciled with the R-band upper limit on the
afterglow, without invoking any optical circumburst absorption, provided the
cooling frequency is close to the X-ray band. Alternatively, if the X-ray
afterglow is due to synchrotron emission only, seven magnitudes of extinction
in the observed R-band is required to meet the R-band upper limit, making GRB
001025A much more obscured than bursts with detected optical afterglows. Based
on the column density of X-ray absorbing circumburst matter, an SMC gas-to-dust
ratio is insufficient to produce this amount of extinction. The X-ray tail of
the prompt emission enters a steep temporal decay excluding that the tail of
the prompt emission is the onset of the afterglow (abridged).Comment: 32 pages, 8 figures, ApJ in pres
Under-ice convection dynamics in a boreal lake
We investigated radiatively driven under-ice convection in Lake Onego (Russia) during 3 consecutive late winters. In ice-covered lakes, where the temperature of water is below the temperature of maximum density, radiatively driven heating in the upper water column induces unstable density distributions leading to gravitational convection. In this work, we quantified the key parameters to characterise the radiatively driven under-ice convection: (1) the effective buoyancy flux, B∗ (driver), and its vertical distribution; (2) the convective mixed-layer thickness, hCML (depth scale); and (3) the convective velocity,w∗(kinematic scale). We compared analytical w∗ scaling estimates to in situ observations from high-resolution acoustic Doppler current profilers. The results show a robust correlation between w∗and the direct observations, except during the onset and decay of the solar radiation. Our results highlight the importance of accurately defining the upper limit of hCML in highly turbid water and the need for spectrally resolving solar radiation measurements and their attenuation for accurate B∗ estimates. Uncertainties in the different parameters were also investigated. We finally examined the implications of under-ice convection for the growth rate of nonmotile phytoplankton and provide a simple heuristic model as a function of easily measurable parameters
Prevalence of Risk Factors of Thromboembolic Complications in Women after Major Joint Arthroplasty in the Republic of Sakha (Yakutia)
The aim of this study was to assess the risk factors for thromboembolic complications after total arthroplasty of large joints in women in Yakutia conditions to optimize the management tactics of this category of patients. The average age of women was 59.98±11.56 years in the age range from 50 to 70 years. In order to validate the study, women were divided into 2 groups. The main group consisted of 284 women undergoing total knee arthroplasty (Group 1). The comparison group included 147 women undergoing total hip arthoplasty (Group 2). The study demonstrated that hypertension was more common in patients of Group 1 than in patients of Group 2. However, the incidence of coronary heart disease and heart rhythm disorder was detected most frequently in patients with total hip arthroplasty. Obesity, thrombosis of the veins of the lower extremities, and liver disease were detected with almost the same frequency in women with total knee arthroplasty and those with total hip arthroplasty. The frequency of occurrence of complications depending on the risk factors for thromboembolic complications and the type of surgical treatment of the joint was equal in the two groups of studied patients
On the Possibility of Identification of a Short/Hard Burst GRB 051103 with the Giant Flare from a Soft Gamma Repeater in the M81 Group of Galaxies
The light curve, energy characteristics, and localization of a short/hard GRB
051103 burst are considered. Evidence in favor of identifying this event with a
giant flare from a soft gamma repeater in the nearby M81 group of interacting
galaxies is discussed.Comment: 11 pages, 4 figures, accepted for publication in Astronomy Letters,
correction of a typo on page