292 research outputs found
VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50
We report the discovery of the gamma-ray burst GRB 000131 and its optical
afterglow. The optical identification was made with the VLT 84 hours after the
burst following a BATSE detection and an Inter Planetary Network localization.
GRB 000131 was a bright, long-duration GRB, with an apparent precursor signal
62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m
follow-up observations. Broad-band and spectroscopic observations of the
spectral energy distribution reveals a sharp break at optical wavelengths which
is interpreted as a Ly-alpha absorption edge at 6700 A. This places GRB 000131
at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in
gamma rays alone was approximately 10^54 erg (depending on the assumed
cosmology). The rapid power-law decay of the afterglow (index alpha=2.25,
similar to bursts with a prior break in the lightcurve), however, indicates
collimated outflow, which relaxes the energy requirements by a factor of < 200.
The afterglow of GRB 000131 is the first to be identified with an 8-m class
telescope.Comment: 8 pages, 7 figures, accepted to A&A Letter
GRB 000301C: a possible short/intermediate duration burst connected to a DLA system
We discuss two main aspects of the GRB 000301C afterglow (Fynbo et al. 2000,
Jensen et al. 2000); its short duration and its possible connection with a
Damped Ly-alpha Absorber (DLA). GRB 000301C falls in the short class of bursts,
though it is consistent with belonging to the proposed intermediate class or
the extreme short end of the distribution of long-duration GRBs. Based on two
VLT spectra we estimate the HI column density to be Log(N(HI))=21.2+/-0.5. This
is the first direct indication of a connection between GRB host galaxies and
Damped Ly-alpha Absorbers.Comment: 3 pages, 3 postscript figures. To appear in the proceedings of the
October 2000 Rome Workshop on ``Gamma-Ray Bursts in the Afterglow Era'
The bright Gamma-Ray Burst of February 10, 2000: a case study of an optically dark GRB
The gamma-ray burst GRB000210 had the highest gamma-ray peak flux of any
event localized by BeppoSAX as yet but it did not have a detected optical
afterglow. It is therefore one of the events recently classified as dark GRBs
or GHOST (GRB Hiding Optical Source Transient), whose origin is still unclear.
Chandra observations allowed us to localize this GRB within ~1" and a radio
transient was detected with the VLA. We identify the likely (P=0.01) host
galaxy of this burst at z=0.846. The X-ray spectrum of the afterglow shows
intrinsic absorption N_H=5x10**21 cm-2. The amount of dust needed to absorb the
optical flux of this object is consistent with the above HI column density,
given a dust-to-gas ratio similar to that of our Galaxy. We do not find
evidence for a partially ionized absorber expected if the absorption takes
place in a Giant Molecular Cloud. We therefore conclude that either the gas is
local to the GRB, but is condensed in small-scale high-density (n>~10**9 cm-3)
clouds, or that the GRB is located in a dusty, gas-rich region of the galaxy.
Finally, if GRB000210 lies at z>5, its X-ray absorbing medium would have to be
substantially different from that observed in GRBs with optical afterglows.Comment: 29 pages, 7 fig.s, some revisions, ApJ, in pres
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
Insulin and GH Signaling in Human Skeletal Muscle In Vivo following Exogenous GH Exposure: Impact of an Oral Glucose Load
GH induces acute insulin resistance in skeletal muscle in vivo, which in rodent models has been attributed to crosstalk between GH and insulin signaling pathways. Our objective was to characterize time course changes in signaling pathways for GH and insulin in human skeletal muscle in vivo following GH exposure in the presence and absence of an oral glucose load.Eight young men were studied in a single-blinded randomized crossover design on 3 occasions: 1) after an intravenous GH bolus 2) after an intravenous GH bolus plus an oral glucose load (OGTT), and 3) after intravenous saline plus OGTT. Muscle biopsies were taken at tâ=â0, 30, 60, and 120. Blood was sampled at frequent intervals for assessment of GH, insulin, glucose, and free fatty acids (FFA).GH increased AUC(glucose) after an OGTT (p<0.05) without significant changes in serum insulin levels. GH induced phosphorylation of STAT5 independently of the OGTT. Conversely, the OGTT induced acute phosphorylation of the insulin signaling proteins Akt (ser(473) and thr(308)), and AS160.The combination of OGTT and GH suppressed Akt activation, whereas the downstream expression of AS160 was amplified by GH. WE CONCLUDED THE FOLLOWING: 1) A physiological GH bolus activates STAT5 signaling pathways in skeletal muscle irrespective of ambient glucose and insulin levels 2) Insulin resistance induced by GH occurs without a distinct suppression of insulin signaling proteins 3) The accentuation of the glucose-stimulated activation of AS 160 by GH does however indicate a potential crosstalk between insulin and GH.ClinicalTrials.gov NCT00477997
Impact of Non-HIV and HIV Risk Factors on Survival in HIV-Infected Patients on HAART: A Population-Based Nationwide Cohort Study
BACKGROUND: We determined the impact of three factors on mortality in HIV-infected patients who had been on highly active antiretroviral therapy (HAART) for at least one year: (1) insufficient response to (HAART) and presence of AIDS-defining diseases, (2) comorbidity, and (3) drug and alcohol abuse and compared the mortality to that of the general population. METHODOLOGY/PRINCIPAL FINDINGS: In a Danish nationwide, population-based cohort study, we used population based registries to identify (1) all Danish HIV-infected patients who started HAART in the period 1 January 1998-1 July 2009, and (2) a comparison cohort of individuals matched on date of birth and gender (Nâ=â2,267 and 9,068, respectively). Study inclusion began 1 year after start of HAART. Patients were categorised hierarchically in four groups according to the three risk factors, which were identified before study inclusion. The main outcome measure was probability of survival from age 25 to 65 years. The probability of survival from age 25 to age 65 was substantially lower in HIV patients [0.48 (95% confidence interval (CI) 0.42-0.55)] compared to the comparison cohort [0.88 (0.86 to 0.90)]. However, in HIV patients with no risk factors (Nâ=â871) the probability of survival was equivalent to that of the general population [0.86 (95% CI 0.77-0.92)]. In contrast, the probability of survival was 0.58 in patients with HIV risk factors (Nâ=â704), 0.30 in patients with comorbidities (Nâ=â479), and 0.03 in patients with drug or alcohol abuse (Nâ=â313). CONCLUSIONS: The increased risk of death in HIV-infected individuals is mainly attributable to risk factors that can be identified prior to or in the initial period of antiretroviral treatment. Mortality in patients without risk factors on a successful HAART is almost identical to that of the non-HIV-infected population
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