325 research outputs found
Diversity of multiwavelength emission bumps in the GRB 100219A afterglow
Context. Multi-wavelength observations of gamma-ray burst (GRB) afterglows
provide important information about the activity of their central engines and
their environments. In particular, the short timescale variability, such as
bumps and/or rebrightening features visible in the multi-wavelength light
curves, is still poorly understood.
Aims. We analyze the multi-wavelength observations of the GRB100219A
afterglow at redshift 4.7. In particular, we attempt to identify the physical
origin of the late achromatic flares/bumps detected in the X-ray and optical
bands.
Methods. We present ground-based optical photometric data and Swift X-ray
observations on GRB100219A. We analyzed the temporal behavior of the X-ray and
optical light curves, as well as the X-ray spectra.
Results. The early flares in the X-ray and optical light curves peak
simultaneously at about 1000 s after the burst trigger, while late achromatic
bumps in the X-ray and optical bands appear at about 20000 s after the burst
trigger. These are uncommon features in the afterglow phenomenology.
Considering the temporal and spectral properties, we argue that both optical
and X-ray emissions come from the same mechanism. The late flares/bumps may be
produced by late internal shocks from long-lasting activity of the central
engine. An off-axis origin for a structured jet model is also discussed to
interpret the bump shapes. The early optical bump can be interpreted as the
afterglow onset, while the early X-ray flare could be caused by the internal
activity. GRB 100219A exploded in a dense environment as revealed by the strong
attenuation of X-ray emission and the optical-to-X-ray spectral energy
distribution.Comment: A&A accepte
The Intracluster Plasma: a Universal Pressure Profile?
The pressure profiles of the Intracluster Plasma in galaxy clusters show a
wide variance when observed in X rays at low redshifts z<0.2. We find the
profiles to follow two main patterns, featuring either a steep or a shallow
shape throughout both core and outskirts. We trace these shapes back to a
physical dichotomy of clusters into two classes, marked by either low entropy
(LE) or high entropy (HE) throughout. From X-ray observations and
Sunyaev-Zel'dovich stacked data at higher 0.2<z<0.4, we elicit evidence of an
increasing abundance of HEs relative to LEs. We propose this to constitute a
systematic trend toward high z; specifically, we predict the pressure profiles
to converge into a truly universal HE-like template for z>0.5. We submit our
physical templates and converging trend for further observational tests, in
view of the current and upcoming measurements of individual, stacked, and
integrated Sunyaev-Zel'dovich signals.Comment: 5 pages, 2 figures. Typos-corrected. Accepted by ApJ
Quantifying Non-circular Streaming Motions in Disc Galaxies
High-quality velocity maps of galaxies frequently exhibit signatures of
non-circular streaming motions. We here apply the software tool, "velfit"
recently proposed by Spekkens & Sellwood, to five representative galaxies from
the THINGS sample. We describe the strengths and weaknesses of the tool, and
show that it is both more powerful and yields results that are more easily
interpreted than the commonly used procedure. We demonstrate that it can
estimate the magnitudes of forced non-circular motions over a broad range of
bar strengths from a strongly barred galaxy, through cases of mild bar-like
distortions to placing bounds on the shapes of halos in galaxies having
extended rotation curves. We identify mild oval distortions in the inner parts
of two dwarf galaxies, NGC 2976 and NGC 7793, and show that the true strength
of the non-axisymmetric gas flow in the strongly barred galaxy NGC 2903 is
revealed more clearly in our fit to an optical Halpha map than to the neutral
hydrogen data. The method can also yield a direct estimate of the ellipticity
of a slowly-rotating potential distortion in the flat part of a rotation curve,
and we use our results to place tight bounds on the possible ellipticity of the
outer halos of NGC 3198 and NGC 2403.Comment: 12 pages, 8 color figures, to appear in MNRAS. Version 2 of the
software can be downloaded from
http://www.physics.rutgers.edu/~spekkens/velfit
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