267 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
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
Mitral Regurgitation Severity and Left Ventricular Systolic Dimension Predict Survival in Young Cavalier King Charles Spaniels
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
On the Afterglow of the X-ray Flash of 2003 July 23: Photometric evdence for an Off-Axis Gamma-Ray burst with an Associated Supernova
Peer reviewe
Very high column density and small reddening towards GRB 020124 at z = 3.20
We present optical and near-infrared observations of the dim afterglow of GRB
020124, obtained between 2 and 68 hours after the gamma-ray burst. The burst
occurred in a very faint (R > 29.5) Damped Ly-alpha Absorber (DLA) at a
redshift of z = 3.198 +- 0.004. The derived column density of neutral hydrogen
is log(N_H) = 21.7 +- 0.2 and the rest-frame reddening is constrained to be
E(B-V) < 0.065, i.e., A_V < 0.20 for standard extinction laws with R_V ~ 3. The
resulting dust-to-gas ratio is less than 11 % of that found in the Milky Way,
but consistent with the SMC and high-redshift QSO DLAs, indicating a low
metallicity and/or a low dust-to-metals ratio in the burst environment. A grey
extinction law (large R_V), produced through preferential destruction of small
dust grains by the GRB, could increase the derived A_V and dust-to-gas ratio.
The dimness of the afterglow is however fully accounted for by the high
redshift: If GRB 020124 had been at z = 1 it would have been approximately 1.8
mag brighter--in the range of typical bright afterglows.Comment: 23 pages, 6 figures, ApJ, in pres
Detection of the optical afterglow of GRB 000630: Implications for dark bursts
We present the discovery of the optical transient of the long-duration
gamma-ray burst GRB000630. The optical transient was detected with the Nordic
Optical Telescope 21.1 hours after the burst. At the time of discovery the
magnitude of the transient was R = 23.04+-0.08. The transient displayed a
power-law decline characterized by a decay slope of alpha = -1.035+-0.097. A
deep image obtained 25 days after the burst shows no indication of a
contribution from a supernova or a host galaxy at the position of the
transient. The closest detected galaxy is a R=24.68+-0.15 galaxy 2.0 arcsec
north of the transient.
The magnitudes of the optical afterglows of GRB980329, GRB980613 and
GRB000630 were all R>=23 less than 24 hours from the burst epoch. We discuss
the implications of this for our understanding of GRBs without detected optical
transients. We conclude that i) based on the gamma-ray properties of the
current sample we cannot conclude that GRBs with no detected OTs belong to
another class of GRBs than GRBs with detected OTs and ii) the majority (>75%)
of GRBs for which searches for optical afterglow have been unsuccessful are
consistent with no detection if they were similar to bursts like GRB000630 at
optical wavelengths.Comment: accepted for publication in A&
Understanding plant cell-wall remodelling during the symbiotic interaction between Tuber melanosporum and Corylus avellana using a carbohydrate microarray
Developmental features of cotton fibre middle lamellae in relation to cell adhesion and cell detachment in cultivars with distinct fibre qualities.
Background: Cotton fibre quality traits such as fibre length, strength, and degree of maturation are determined by genotype and environment during the sequential phases of cotton fibre development (cell elongation, transition to secondary cell wall construction and cellulose deposition). The cotton fibre middle lamella (CFML) is crucial for both cell adhesion and detachment processes occurring during fibre development. To explore the relationship between fibre quality and the pace at which cotton fibres develop, a structural and compositional analysis of the CFML was carried out in several cultivars with different fibre properties belonging to four commercial species: Gossypium hirsutum, G. barbadense, G. herbaceum and G. arboreum. Results: Cotton fibre cell adhesion, through the cotton fibre middle lamella (CFML), is a developmentally regulated process determined by genotype. The CFML is composed of de-esterified homogalacturonan, xyloglucan and arabinan in all four fibre-producing cotton species: G. hirsutum, G. barbadense, G. herbaceum and G. arboreum. Conspicuous paired cell wall bulges are a feature of the CFML of two G. hirsutum cultivars from the onset of fibre cell wall detachment to the start of secondary cell wall deposition. Xyloglucan is abundant in the cell wall bulges and in later stages pectic arabinan is absent from these regions. Conclusions: The CFML of cotton fibres is re-structured during the transition phase. Paired cell wall bulges, rich in xyloglucan, are significantly more evident in the G. hirsutum cultivars than in other cotton species
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