Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from ...stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Context:
Denosumab and zoledronic acid (ZOL) are parenteral treatments for patients with osteoporosis.
Objective:
The objective of the study was to compare the effect of transitioning from oral ...bisphosphonates to denosumab or ZOL on bone mineral density (BMD) and bone turnover.
Design and Setting:
This was an international, multicenter, randomized, double-blind trial.
Participants:
A total of 643 postmenopausal women with osteoporosis previously treated with oral bisphosphonates participated in the study.
Interventions:
Subjects were randomized 1:1 to sc denosumab 60 mg every 6 months plus iv placebo once or ZOL 5 mg iv once plus sc placebo every 6 months for 12 months.
Main Outcome Measures:
Changes in BMD and bone turnover markers were measured.
Results:
BMD change from baseline at month 12 was significantly greater with denosumab compared with ZOL at the lumbar spine (primary end point; 3.2% vs 1.1%; P < .0001), total hip (1.9% vs 0.6%; P < .0001), femoral neck (1.2% vs −0.1%; P < .0001), and one-third radius (0.6% vs 0.0%; P < .05). The median decrease from baseline was greater with denosumab than ZOL for serum C-telopeptide of type 1 collagen at all time points after day 10 and for serum procollagen type 1 N-terminal propeptide at month 1 and at all time points after month 3 (all P < .05). Median percentage changes from baseline in serum intact PTH were significantly greater at months 3 and 9 with denosumab compared with ZOL (all P < .05). Adverse events were similar between groups. Three events consistent with the definition of atypical femoral fracture were observed (two denosumab and one ZOL).
Conclusions:
In postmenopausal women with osteoporosis previously treated with oral bisphosphonates, denosumab was associated with greater BMD increases at all measured skeletal sites and greater inhibition of bone remodeling compared with ZOL.
Postmenopausal women with osteoporosis transitioned from oral bisphosphonates had greater BMD increases and greater inhibition of bone turnover with denosumab compared with zoledronic acid.
Although the link between long γ-ray bursts (GRBs) and supernovae has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a ...GRB. In particular, we do not know how the jet that defines a γ-ray burst emerges from the star's surface, nor how a GRB progenitor explodes. Here we report observations of the relatively nearby GRB 060218 (ref. 5) and its connection to supernova SN 2006aj (ref. 6). In addition to the classical non-thermal emission, GRB 060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/ultraviolet band as time passes. We interpret these features as arising from the break-out of a shock wave driven by a mildly relativistic shell into the dense wind surrounding the progenitor. We have caught a supernova in the act of exploding, directly observing the shock break-out, which indicates that the GRB progenitor was a Wolf-Rayet star.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
GRB 130427A: A Nearby Ordinary Monster Maselli, A.; Melandri, A.; Nava, L. ...
Science (American Association for the Advancement of Science),
01/2014, Letnik:
343, Številka:
6166
Journal Article
Recenzirano
Odprti dostop
Long-duration gamma-ray bursts (GRBs) are an extremely rare outcome of the collapse of massive stars and are typically found in the distant universe. Because of its intrinsic luminosity (L ~ 3 × 10⁵³ ...ergs per second) and its relative proximity (z = 0.34), GRB 130427A reached the highest fluence observed in the γ-ray band. Here, we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-meter Liverpool and Faulkes telescopes, and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs, suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early universe and over the full range of GRB isotropie energies.
Bright X-ray Flares in Gamma-Ray Burst Afterglows Burrows, D. N.; Romano, P.; Falcone, A. ...
Science (American Association for the Advancement of Science),
09/2005, Letnik:
309, Številka:
5742
Journal Article
Recenzirano
Odprti dostop
Gamma-ray burst (GRB) afterglows have provided important clues to the nature of these massive explosive events, providing direct information on the nearby environment and indirect information on the ...central engine that powers the burst. We report the discovery of two bright x-ray flares in GRB afterglows, including a giant flare comparable in total energy to the burst itself, each peaking minutes after the burst. These strong, rapid x-ray flares imply that the central engines of the bursts have long periods of activity, with strong internal shocks continuing for hundreds of seconds after the gamma-ray emission has ended.
Gamma-ray bursts (GRBs) come in two classes: long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at ...high redshift (z 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars. In contrast, no short GRB had been accurately (< 10″) and rapidly (minutes) located. Here we report the detection of the X-ray afterglow from-and the localization of-the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect if the origin of this GRB is through the merger of neutron-star or black-hole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Treatment failure in osteoporosis Diez-Perez, A.; Adachi, J. D.; Agnusdei, D. ...
Osteoporosis international,
12/2012, Letnik:
23, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Summary
Guidelines concerning the definition of failure of therapies used to reduce the risk of fracture are provided.
Introduction
This study aims to provide guidelines concerning the definition of ...failure of therapies used to reduce the risk of fracture.
Methods
A working group of the Committee of Scientific Advisors of the International Osteoporosis Foundation was convened to define outcome variables that may assist clinicians in decision making.
Results
In the face of limited evidence, failure of treatment may be inferred when two or more incident fractures have occurred during treatment, when serial measurements of bone remodelling markers are not suppressed by anti-resorptive therapy and where bone mineral density continues to decrease.
Conclusion
The provision of pragmatic criteria to define failure to respond to treatment provides an unmet clinical need and may stimulate research into an important issue.
Summary
We describe the collection of cohorts together with the analysis plan for an update of the fracture risk prediction tool FRAX with respect to current and novel risk factors. The resource ...comprises 2,138,428 participants with a follow-up of approximately 20 million person-years and 116,117 documented incident major osteoporotic fractures.
Introduction
The availability of the fracture risk assessment tool FRAX® has substantially enhanced the targeting of treatment to those at high risk of fracture with FRAX now incorporated into more than 100 clinical osteoporosis guidelines worldwide. The aim of this study is to determine whether the current algorithms can be further optimised with respect to current and novel risk factors.
Methods
A computerised literature search was performed in PubMed from inception until May 17, 2019, to identify eligible cohorts for updating the FRAX coefficients. Additionally, we searched the abstracts of conference proceedings of the American Society for Bone and Mineral Research, European Calcified Tissue Society and World Congress of Osteoporosis. Prospective cohort studies with data on baseline clinical risk factors and incident fractures were eligible.
Results
Of the 836 records retrieved, 53 were selected for full-text assessment after screening on title and abstract. Twelve cohorts were deemed eligible and of these, 4 novel cohorts were identified. These cohorts, together with 60 previously identified cohorts, will provide the resource for constructing an updated version of FRAX comprising 2,138,428 participants with a follow-up of approximately 20 million person-years and 116,117 documented incident major osteoporotic fractures. For each known and candidate risk factor, multivariate hazard functions for hip fracture, major osteoporotic fracture and death will be tested using extended Poisson regression. Sex- and/or ethnicity-specific differences in the weights of the risk factors will be investigated. After meta-analyses of the cohort-specific beta coefficients for each risk factor, models comprising 10-year probability of hip and major osteoporotic fracture, with or without femoral neck bone mineral density, will be computed.
Conclusions
These assembled cohorts and described models will provide the framework for an updated FRAX tool enabling enhanced assessment of fracture risk (PROSPERO (CRD42021227266)).
This paper discusses Swift observations of the g-ray burst GRB 050315 (z = 1.949) from 80 s to 10 days after the onset of the burst. The X-ray light curve displayed a steep early decay (t super(-5)) ...for 6200 s and several breaks. However, both the prompt hard X-ray/g-ray emission (observed by the BAT) and the first 6300 s of X-ray emission (observed by the XRT) can be explained by exponential decays, with similar decay constants. Extrapolating the BAT light curve into the XRT band suggests that the rapidly decaying, early X-ray emission was simply a continuation of the fading prompt emission; this strong similarity between the prompt g-ray and early X-ray emission may be related to the simple temporal and spectral character of this X-ray-rich GRB. The prompt (BAT) spectrum was steep down to 615 keV and appeared to continue through the XRT bandpass, implying a low peak energy, inconsistent with the Amati relation. Following the initial steep decline, the X-ray afterglow did not fade for 61.2x 10 super(4) s, after which time it decayed with a temporal index of a- 0.7, followed by a second break at 62.5 x 10 super(5) s to a slope of a 6 2. The apparent "plateau" in the X-ray light curve, after the early rapid decay, makes this one of the most extreme examples of the steep-flat-steep X-ray light curves revealed by Swift. If the second afterglow break is identified with a jet break, then the jet opening angle was f sub(0) 65, implying E sub(g) 10 super(50) ergs.
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