173 research outputs found
A New Frequency-Luminosity Relation for Long GRBs?
We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts
(GRBs). We fitted the PDS with a simple power-law and extracted the exponent of
the power-law (alpha) and the noise-crossing threshold frequency (f_th). We
find that the distribution of the extracted alpha peaks around -1.4 and that of
f_th around 1 Hz. In addition, based on a sub-set of 58 bursts with known
redshifts, we show that the redshift-corrected threshold frequency is
positively correlated with the isotropic peak luminosity. The correlation
coefficient is 0.57 +/- 0.03.Comment: 9 pages, 17 figures, 1 table; Accepted for publication in MNRA
Spectral components in the bright, long GRB 061007: properties of the photosphere and the nature of the outflow
We present a time-resolved spectral analysis of the bright, long GRB 061007
(z=1.261) using Swift BAT and Suzaku WAM data. We find that the prompt emission
of GRB 061007 can be equally well explained by a photospheric component
together with a power law as by a Band function, and we explore the
implications of the former model. The photospheric component, which we model
with a multicolour blackbody, dominates the emission and has a very stable
shape throughout the burst. This component provides a natural explanation for
the hardness-intensity correlation seen within the burst and also allows us to
estimate the bulk Lorentz factor and the radius of the photosphere. The
power-law component dominates the fit at high energies and has a nearly
constant slope of -1.5. We discuss the possibility that this component is of
the same origin as the high-energy power laws recently observed in some Fermi
LAT bursts.Comment: Accepted for publication in MNRA
Temporal properties of gamma-ray bursts as signatures of jets from the central engine
A comprehensive temporal analysis has been performed on the 319 brightest
GRBs with T90>2s from the BATSE current catalog. The rise times, fall times,
full-widths at half maximum (FWHM), pulse amplitudes and pulse areas were
measured and the frequency distributions are presented here. The distribution
of time intervals between pulses is not random but compatible with a lognormal
distribution when allowance was made for the 64 ms time resolution and a small
excess (5%) of long duration intervals that is often referred to as a
Pareto-Levy tail. A range of correlations are presented on pulse and burst
properties. The rise and fall times, FWHM and area of the pulses are highly
correlated with each other. The time intervals between pulses and pulse
amplitudes of neighbouring pulses are correlated with each other. It was also
found that the number of pulses, N, in GRBs is strongly correlated with the
fluence and the duration and that can explain the well known correlation
between duration and fluence. The GRBs were sorted into three catagories based
on N i.e. 3=25. The properties of pulses before and after
the stongest pulse were compared for the three catagories of bursts. This
analysis revealed that the GRBs with large numbers of pulses have narrower and
faster pulses and also larger fluences, longer durations and higher hardness
ratios than the GRBs with smaller numbers of pulses.Comment: 19 pages, 22 figures. Submitted to A&A July 200
Challenging GRB models through the broadband dataset of GRB060908
Context: Multiwavelength observations of gamma-ray burst prompt and afterglow
emission are a key tool to disentangle the various possible emission processes
and scenarios proposed to interpret the complex gamma-ray burst phenomenology.
Aims: We collected a large dataset on GRB060908 in order to carry out a
comprehensive analysis of the prompt emission as well as the early and late
afterglow. Methods: Data from Swift-BAT, -XRT and -UVOT together with data from
a number of different ground-based optical/NIR and millimeter telescopes
allowed us to follow the afterglow evolution from about a minute from the
high-energy event down to the host galaxy limit. We discuss the physical
parameters required to model these emissions. Results: The prompt emission of
GRB060908 was characterized by two main periods of activity, spaced by a few
seconds of low intensity, with a tight correlation between activity and
spectral hardness. Observations of the afterglow began less than one minute
after the high-energy event, when it was already in a decaying phase, and it
was characterized by a rather flat optical/NIR spectrum which can be
interpreted as due to a hard energy-distribution of the emitting electrons. On
the other hand, the X-ray spectrum of the afterglow could be fit by a rather
soft electron distribution. Conclusions: GRB060908 is a good example of a
gamma-ray burst with a rich multi-wavelength set of observations. The
availability of this dataset, built thanks to the joint efforts of many
different teams, allowed us to carry out stringent tests for various
interpretative scenarios showing that a satisfactorily modeling of this event
is challenging. In the future, similar efforts will enable us to obtain
optical/NIR coverage comparable in quality and quantity to the X-ray data for
more events, therefore opening new avenues to progress gamma-ray burst
research.Comment: A&A, in press. 11 pages, 5 figure
Multi-wavelength observations of the energetic GRB 080810: detailed mapping of the broadband spectral evolution
GRB 080810 was one of the first bursts to trigger both Swift and the Fermi
Gamma-ray Space Telescope. It was subsequently monitored over the X-ray and
UV/optical bands by Swift, in the optical by ROTSE and a host of other
telescopes and was detected in the radio by the VLA. The redshift of z= 3.355
+/- 0.005 was determined by Keck/HIRES and confirmed by RTT150 and NOT. The
prompt gamma/X-ray emission, detected over 0.3-10^3 keV, systematically softens
over time, with E_peak moving from ~600 keV at the start to ~40 keV around 100
s after the trigger; alternatively, this spectral evolution could be identified
with the blackbody temperature of a quasithermal model shifting from ~60 keV to
~3 keV over the same time interval. The first optical detection was made at 38
s, but the smooth, featureless profile of the full optical coverage implies
that this originated from the afterglow component, not the pulsed/flaring
prompt emission.
Broadband optical and X-ray coverage of the afterglow at the start of the
final X-ray decay (~8 ks) reveals a spectral break between the optical and
X-ray bands in the range 10^15 - 2x10^16 Hz. The decay profiles of the X-ray
and optical bands show that this break initially migrates blueward to this
frequency and then subsequently drifts redward to below the optical band by
~3x10^5 s. GRB 080810 was very energetic, with an isotropic energy output for
the prompt component of 3x10^53 erg and 1.6x10^52 erg for the afterglow; there
is no evidence for a jet break in the afterglow up to six days following the
burst.Comment: 15 pages, 9 figures, 4 in colour. Accepted for publication in MNRA
Intracellular Trafficking and Synaptic Function of APL-1 in Caenorhabditis elegans
Background: Alzheimer’s disease (AD) is a neurodegenerative disorder primarily characterized by the deposition of b-amyloid plaques in the brain. Plaques are composed of the amyloid-b peptide derived from cleavage of the amyloid precursor protein (APP). Mutations in APP lead to the development of Familial Alzheimer’s Disease (FAD), however, the normal function of this protein has proven elusive. The organism Caenorhabditis elegans is an attractive model as the amyloid precursor-like protein (APL-1) is the single ortholog of APP, and loss of apl-1 leads to a severe molting defect and early larval lethality. Methodology/Principal Findings: We report here that lethality and molting can be rescued by full length APL-1, C-terminal mutations as well as a C-terminal truncation, suggesting that the extracellular region of the protein is essential for viability. RNAi knock-down of apl-1 followed by drug testing on the acetylcholinesterase inhibitor aldicarb showed that loss of apl-1 leads to aldicarb hypersensitivity, indicating a defect in synaptic function. The aldicarb hypersensitivity can be rescued by full length APL-1 in a dose dependent fashion. At the cellular level, kinesins UNC-104/KIF-1A and UNC-116/kinesin-1 are positive regulators of APL-1 expression in the neurons. Knock-down of the small GTPase rab-5 also leads to a dramatic decrease in the amount of apl-1 expression in neurons, suggesting that trafficking from the plasma membrane to the early endosome is important for apl-1 function. Loss of function of a different small GTPase, UNC-108, on the contrary, leads t
Proteomic Analysis of the Dysferlin Protein Complex Unveils Its Importance for Sarcolemmal Maintenance and Integrity
Dysferlin is critical for repair of muscle membranes after damage. Mutations in dysferlin lead to a progressive muscular dystrophy. Recent studies suggest additional roles for dysferlin. We set out to study dysferlin's protein-protein interactions to obtain comprehensive knowledge of dysferlin functionalities in a myogenic context. We developed a robust and reproducible method to isolate dysferlin protein complexes from cells and tissue. We analyzed the composition of these complexes in cultured myoblasts, myotubes and skeletal muscle tissue by mass spectrometry and subsequently inferred potential protein functions through bioinformatics analyses. Our data confirm previously reported interactions and support a function for dysferlin as a vesicle trafficking protein. In addition novel potential functionalities were uncovered, including phagocytosis and focal adhesion. Our data reveal that the dysferlin protein complex has a dynamic composition as a function of myogenic differentiation. We provide additional experimental evidence and show dysferlin localization to, and interaction with the focal adhesion protein vinculin at the sarcolemma. Finally, our studies reveal evidence for cross-talk between dysferlin and its protein family member myoferlin. Together our analyses show that dysferlin is not only a membrane repair protein but also important for muscle membrane maintenance and integrity
DETORQUEO, QUIRKY, and ZERZAUST Represent Novel Components Involved in Organ Development Mediated by the Receptor-Like Kinase STRUBBELIG in Arabidopsis thaliana
Intercellular signaling plays an important role in controlling cellular behavior in apical meristems and developing organs in plants. One prominent example in Arabidopsis is the regulation of floral organ shape, ovule integument morphogenesis, the cell division plane, and root hair patterning by the leucine-rich repeat receptor-like kinase STRUBBELIG (SUB). Interestingly, kinase activity of SUB is not essential for its in vivo function, indicating that SUB may be an atypical or inactive receptor-like kinase. Since little is known about signaling by atypical receptor-like kinases, we used forward genetics to identify genes that potentially function in SUB-dependent processes and found recessive mutations in three genes that result in a sub-like phenotype. Plants with a defect in DETORQEO (DOQ), QUIRKY (QKY), and ZERZAUST (ZET) show corresponding defects in outer integument development, floral organ shape, and stem twisting. The mutants also show sub-like cellular defects in the floral meristem and in root hair patterning. Thus, SUB, DOQ, QKY, and ZET define the STRUBBELIG-LIKE MUTANT (SLM) class of genes. Molecular cloning of QKY identified a putative transmembrane protein carrying four C2 domains, suggesting that QKY may function in membrane trafficking in a Ca2+-dependent fashion. Morphological analysis of single and all pair-wise double-mutant combinations indicated that SLM genes have overlapping, but also distinct, functions in plant organogenesis. This notion was supported by a systematic comparison of whole-genome transcript profiles during floral development, which molecularly defined common and distinct sets of affected processes in slm mutants. Further analysis indicated that many SLM-responsive genes have functions in cell wall biology, hormone signaling, and various stress responses. Taken together, our data suggest that DOQ, QKY, and ZET contribute to SUB-dependent organogenesis and shed light on the mechanisms, which are dependent on signaling through the atypical receptor-like kinase SUB
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