300 research outputs found
Observational Constraints on Cosmological Models with the Updated Long Gamma-Ray Bursts
In the present work, by the help of the newly released Union2 compilation
which consists of 557 Type Ia supernovae (SNIa), we calibrate 109 long
Gamma-Ray Bursts (GRBs) with the well-known Amati relation, using the
cosmology-independent calibration method proposed by Liang {\it et al.}. We
have obtained 59 calibrated high-redshift GRBs which can be used to constrain
cosmological models without the circularity problem (we call them ``Hymnium''
GRBs sample for convenience). Then, we consider the joint constraints on 7
cosmological models from the latest observational data, namely, the combination
of 557 Union2 SNIa dataset, 59 calibrated Hymnium GRBs dataset (obtained in
this work), the shift parameter from the WMAP 7-year data, and the distance
parameter of the measurement of the baryon acoustic oscillation (BAO) peak
in the distribution of SDSS luminous red galaxies. We also briefly consider the
comparison of these 7 cosmological models.Comment: 19 pages, 3 tables, 10 figures, revtex4; v2: accepted for publication
in JCAP; v3: published versio
Gamma Ray Bursts as Probes of Quantum Gravity
Gamma ray bursts (GRBs) are short and intense pulses of -rays
arriving from random directions in the sky. Several years ago Amelino-Camelia
et al. pointed out that a comparison of time of arrival of photons at different
energies from a GRB could be used to measure (or obtain a limit on) possible
deviations from a constant speed of light at high photons energies. I review
here our current understanding of GRBs and reconsider the possibility of
performing these observations.Comment: Lectures given at the 40th winter school of theretical physics:
Quantum Gravity and Phenomenology, Feb. 2004 Polan
Jet disc coupling in black hole binaries
In the last decade multi-wavelength observations have demonstrated the
importance of jets in the energy output of accreting black hole binaries. The
observed correlations between the presence of a jet and the state of the
accretion flow provide important information on the coupling between accretion
and ejection processes. After a brief review of the properties of black hole
binaries, I illustrate the connection between accretion and ejection through
two particularly interesting examples. First, an INTEGRAL observation of Cygnus
X-1 during a 'mini-' state transition reveals disc jet coupling on time scales
of orders of hours. Second, the black hole XTEJ1118+480 shows complex
correlations between the X-ray and optical emission. Those correlations are
interpreted in terms of coupling between disc and jet on time scales of seconds
or less. Those observations are discussed in the framework of current models.Comment: Invited talk at the Fifth Stromlo Symposium: Disks, Winds & Jets -
from Planets to Quasars. Accepted for publication in Astrophysics & Space
Scienc
Low-Luminosity Accretion in Black Hole X-ray Binaries and Active Galactic Nuclei
At luminosities below a few percent of Eddington, accreting black holes
switch to a hard spectral state which is very different from the soft
blackbody-like spectral state that is found at higher luminosities. The hard
state is well-described by a two-temperature, optically thin, geometrically
thick, advection-dominated accretion flow (ADAF) in which the ions are
extremely hot (up to K near the black hole), the electrons are also
hot ( K), and thermal Comptonization dominates the X-ray
emission. The radiative efficiency of an ADAF decreases rapidly with decreasing
mass accretion rate, becoming extremely low when a source reaches quiescence.
ADAFs are expected to have strong outflows, which may explain why relativistic
jets are often inferred from the radio emission of these sources. It has been
suggested that most of the X-ray emission also comes from a jet, but this is
less well established.Comment: To appear in "From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales" edited by T. Maccarone, R. Fender, L. Ho, to be published as
a special edition of "Astrophysics and Space Science" by Kluwe
Magnetoluminescence
Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain
regions where the electromagnetic energy density greatly exceeds the plasma
energy density. These sources exhibit dramatic flaring activity where the
electromagnetic energy distributed over large volumes, appears to be converted
efficiently into high energy particles and gamma-rays. We call this general
process magnetoluminescence. Global requirements on the underlying, extreme
particle acceleration processes are described and the likely importance of
relativistic beaming in enhancing the observed radiation from a flare is
emphasized. Recent research on fluid descriptions of unstable electromagnetic
configurations are summarized and progress on the associated kinetic
simulations that are needed to account for the acceleration and radiation is
discussed. Future observational, simulation and experimental opportunities are
briefly summarized.Comment: To appear in "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts
and Blazars: Physics of Extreme Energy Release" of the Space Science Reviews
serie
Gamma-Ray Bursts: The Underlying Model
A pedagogical derivation is presented of the ``fireball'' model of gamma-ray
bursts, according to which the observable effects are due to the dissipation of
the kinetic energy of a relativistically expanding wind, a ``fireball.'' The
main open questions are emphasized, and key afterglow observations, that
provide support for this model, are briefly discussed. The relativistic outflow
is, most likely, driven by the accretion of a fraction of a solar mass onto a
newly born (few) solar mass black hole. The observed radiation is produced once
the plasma has expanded to a scale much larger than that of the underlying
``engine,'' and is therefore largely independent of the details of the
progenitor, whose gravitational collapse leads to fireball formation. Several
progenitor scenarios, and the prospects for discrimination among them using
future observations, are discussed. The production in gamma- ray burst
fireballs of high energy protons and neutrinos, and the implications of burst
neutrino detection by kilometer-scale telescopes under construction, are
briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture
Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure
Characterization of Antibodies against Receptor Activity-Modifying Protein 1 (RAMP1): A Cautionary Tale
Calcitonin gene-related peptide (CGRP) is a key component of migraine pathophysiology, yielding effective migraine therapeutics. CGRP receptors contain a core accessory protein subunit: receptor activity-modifying protein 1 (RAMP1). Understanding of RAMP1 expression is incomplete, partly due to the challenges in identifying specific and validated antibody tools. We profiled antibodies for immunodetection of RAMP1 using Western blotting, immunocytochemistry and immunohistochemistry, including using RAMP1 knockout mouse tissue. Most antibodies could detect RAMP1 in Western blotting and immunocytochemistry using transfected cells. Two antibodies (844, ab256575) could detect a RAMP1-like band in Western blots of rodent brain but not RAMP1 knockout mice. However, cross-reactivity with other proteins was evident for all antibodies. This cross-reactivity prevented clear conclusions about RAMP1 anatomical localization, as each antibody detected a distinct pattern of immunoreactivity in rodent brain. We cannot confidently attribute immunoreactivity produced by RAMP1 antibodies (including 844) to the presence of RAMP1 protein in immunohistochemical applications in brain tissue. RAMP1 expression in brain and other tissues therefore needs to be revisited using RAMP1 antibodies that have been comprehensively validated using multiple strategies to establish multiple lines of convincing evidence. As RAMP1 is important for other GPCR/ligand pairings, our results have broader significance beyond the CGRP field
Reconstructing the Cosmic Expansion History up to Redshift z=6.29 with the Calibrated Gamma-Ray Bursts
Recently, Gamma-Ray Bursts (GRBs) were proposed to be a complementary
cosmological probe to type Ia supernovae (SNIa). GRBs have been advocated to be
standard candles since several empirical GRB luminosity relations were proposed
as distance indicators. However, there is a so-called circularity problem in
the direct use of GRBs. Recently, a new idea to calibrate GRBs in a completely
cosmology independent manner has been proposed, and the circularity problem can
be solved. In the present work, following the method proposed by Liang {\it et
al.}, we calibrate 70 GRBs with the Amati relation using 307 SNIa. Then,
following the method proposed by Shafieloo {\it et al.}, we smoothly
reconstruct the cosmic expansion history up to redshift with the
calibrated GRBs. We find some new features in the reconstructed results.Comment: 12 pages, 4 figures, 1 table, revtex4; v2: title changed, accepted by
Eur. Phys. J. C; v3: published versio
General Overview of Black Hole Accretion Theory
I provide a broad overview of the basic theoretical paradigms of black hole
accretion flows. Models that make contact with observations continue to be
mostly based on the four decade old alpha stress prescription of Shakura &
Sunyaev (1973), and I discuss the properties of both radiatively efficient and
inefficient models, including their local properties, their expected stability
to secular perturbations, and how they might be tied together in global flow
geometries. The alpha stress is a prescription for turbulence, for which the
only existing plausible candidate is that which develops from the
magnetorotational instability (MRI). I therefore also review what is currently
known about the local properties of such turbulence, and the physical issues
that have been elucidated and that remain uncertain that are relevant for the
various alpha-based black hole accretion flow models.Comment: To be published in Space Science Reviews and as hard cover in the
Space Sciences Series of ISSI: The Physics of Accretion on to Black Holes
(Springer Publisher
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