1,237 research outputs found
Uncovering the physics behind the blazar sequence using a realistic model for jet emission
Blazar spectra are one of the most important windows into the physical
processes occurring along jets. The spectrum, composed from the different
emitting regions along the jet, allows us to constrain the physical conditions
in the jet. I present my work modelling blazar spectra using an extended
inhomogeneous jet model with an accelerating, magnetically dominated, parabolic
base transitioning to a slowly decelerating, conical section motivated by
observations, simulations and theory. We set the inner geometry of our
multi-zone model using observations of the jet in M87 which transitions from
parabolic to conical at 10^5 Schwarzschild radii. This model is able to
reproduce quiescent blazar spectra very well across all wavelengths (including
radio observations) for a sample of 42 BL Lacs and FSRQs.
Using this inhomogeneous model we are able to constrain the location at which
the synchrotron emission is brightest in these jets by fitting to the optically
thick to thin synchrotron break. We find that the radius of the jet at which
the synchrotron emission is brightest (where the jet first approaches
equipartition) scales approximately linearly with the jet power. We also find a
correlation between the length of the accelerating, parabolic section of the
jet and the maximum bulk Lorentz factor. In agreement with previous work we
find that BL Lacs are low power blazars whereas FSRQs are high power blazars.
Together with our simple jet power-radius relation this leads us to a deeper
understanding of the physics underlying the blazar sequence.Comment: 5 pages, 5 figures, to appear in "The Innermost Regions of
Relativistic Jets and Their Magnetic Fields" conference proceedings; includes
minor change
Synchrotron and inverse-Compton emission from blazar jets - III. Compton-dominant blazars
In this paper we develop the extended jet model of Potter & Cotter to model
the simultaneous multi-wavelength spectra of six Compton-dominant blazars. We
include an accelerating parabolic base transitioning to a slowly decelerating
conical jet with a geometry set by observations of M87 and consistent with
simulations and theory. We investigate several jet models and find that the
optically thick to thin synchrotron break in the radio spectrum requires the
jet to first come into equipartition at large distances along the jet (10^5
Schwarzschild radii), consistent with the observed transition from parabolic to
conical in the jet of M87. We confirm this result analytically and calculate
the expected frequency core-shift relations for the models under consideration.
We find that a parabolic jet transitioning to a ballistic conical jet, which
starts in equipartition and becomes more particle dominated at larger
distances, fits the multiwavelength data of the six blazars well, whilst an
adiabatic equipartition conical section requires very large bulk Lorentz
factors to reproduce the Compton-dominance of the blazars.
We find that all these blazars require high power, high bulk Lorentz factor
jets observed close to the line of sight as we expect from the blazar sequence
and consistent with the results from Paper II. The inverse-Compton emission in
our fits is due to inverse-Compton scattering of high-redshift CMB photons at
large distances along the jet due to the high bulk Lorentz factors of the jets.
We postulate a new interpretation of the blazar sequence based on the radius of
the transition region of the jet (where the jet is brightest in synchrotron
emission) scaling linearly with black hole mass.Comment: 13 pages, 5 figures, accepted for publication in MNRA
The Feasibility of Magnetic Reconnection Powered Blazar Flares from Synchrotron Self-Compton Emission
Order of magnitude variability has been observed in the blazar sub-class of
Active Galactic Nuclei on minute timescales. These high-energy flares are often
difficult to explain with shock acceleration models due to the small size of
the inferred emitting region, with recent particle-in-cell (PIC) simulations
showing that magnetic reconnection is a promising alternative mechanism. Here,
we present a macroscopic emission model physically motivated by PIC
simulations, where the energy for particle acceleration originates from the
reconnecting magnetic field. We track the radial growth and relative velocity
of a reconnecting plasmoid, modelling particle acceleration and radiative
losses from synchrotron and synchrotron self-Compton (SSC) emission. To test
the viability of magnetic reconnection as the mechanism behind rapid blazar
flares we simultaneously fit our model to the observed light-curve and SED from
the 2016 TeV flare of BL Lacertae. We find generally that, without considering
external photons, reconnecting plasmoids are unable to produce Compton-dominant
TeV flares and so cannot reproduce the observations due to overproduction of
synchrotron emission. Additionally, problematically large plasmoids, comparable
in size to the entire jet radius, are required to emit sufficient SSC
gamma-rays to be observable. However, our plasmoid model can reproduce the
rapid TeV lightcurve of the flare, demonstrating that reconnection is able to
produce rapid, powerful TeV flares on observed timescales. We conclude that
while reconnection can produce SSC flares on the correct timescales, the
primary source of TeV emission cannot be SSC and the size of plasmoids required
may be implausibly large.Comment: Replaced with accepted version. Contains additional figures and
considers the effect of a magnetic guide fiel
Gamma-ray Novae: Rare or Nearby?
Classical Novae were revealed as a surprise source of gamma-rays in Fermi LAT
observations. During the first 8 years since the LAT was launched, 6 novae in
total have been detected to > 5 sigma in gamma-rays, in contrast to the 69
discovered optically in the same period. We attempt to resolve this discrepancy
by assuming all novae are gamma-ray emitters, and assigning peak one-day fluxes
based on a flat distribution of the known emitters to a simulated population.
To determine optical parameters, the spatial distribution and magnitudes of
bulge and disc novae in M31 are scaled to the Milky Way, which we approximate
as a disc with a 20 kpc radius and elliptical bulge with semi major axis 3 kpc
and axis ratios 2:1 in the xy plane. We approximate Galactic reddening using a
double exponential disc with vertical and radial scale heights of r_d = 5 kpc
and z_d = 0.2 kpc, and demonstrate that even such a rudimentary model can
easily reproduce the observed fraction of gamma-ray novae, implying that these
apparently rare sources are in fact nearby and not intrinsically rare. We
conclude that classical novae with m_R < 12 and within ~8 kpc are likely to be
discovered in gamma-rays using the Fermi LAT.Comment: Accepted by MNRAS, 10 pages, 7 figure
A study on the hadroproduction of heavy resonances in ATLAS experiment at the LHC
This work is devoted to the study of the hadroproduction of heavy resonances and related topics. The study begins with a chapter that analyzes some experimental issues on heavy quarkonia production, pointing out the important role that the ATLAS detector at LHC can play in this regard. The main goal of chapter 2 is revising some theoretical aspects on bottomonia production, some relevant heavy quarkonia production models are visited, pointing out the most relevant features involved in this work. Later, chapter 3 describes the most relevant techniques used in order to generate the Upsilon(nS) family, as well as a description on the changes and new implementations in the original software of PYTHIA: In summary, all the tools that we needed when carrying out the bottomonia hadroproduction analysis. In chapter 4 we focused on the study of the information available on Upsilon production, basing our analysis of bottomonia inclusive production on the results from Run IB of the CDF collaboration : We analyze the differential Upsilon(nS) cross sections, extracting some relevant NRQCD matrix elements, paying attention to the problem concerning the factorization of the cross section, etc. In chapter 5 we make some predictions on bottomonium hadroproduction at the forthcoming LHC energies and kinematic conditions: We show the expected differential and integrated cross section for all Upsilon(nS) resonances, etc. In chapter 6 we present a proposal to probe gluon densities in the proton using Upsilon hadroproduction, within the framework of the colour-octet mechanism. Aside the proposal, we included predicted production rates, and details that arose during the development of the idea. Finally, in order to help the reading of this work, a lot of technical details have been separated from the main body of the text, gathering them in the appendices A-B-C
Prospects for probing the gluon density in protons using heavy quarkonium hadroproduction
We examine carefully bottomonia hadroproduction in proton colliders,
especially focusing on the LHC, as a way of probing the gluon density in
protons. To this end we develop some previous work, getting quantitative
predictions and concluding that our proposal can be useful to perform
consistency checks of the parameterization sets of different parton
distribution functions.Comment: LaTeX, 14 pages, 6 EPS figure
Multifunctional device for bicycles
This paper aims at designing a "Multifunctional device composed of load support and anti-theft lock for standard bicycles".
A previous study has been developed in order to justify and validate the final design of the unmet needs of people in their daily lives, with an emphasis on satisfying those that imply specific savings, whether economic, energy or time.
As a result, the use of bicycles as a means of transport in Spain is promoted taking as a frame of reference countries such as the Netherlands or France. This means economic and energy savings (by replacing the car) and an improvement in people's health and quality of life.
Following the steps of the design methodology, once the need was detected, an information search was carried out in order to identify and prioritize the design specifications that meet the demands of potential customers. For this reason, various sources were used,
The boost to use bicycles has allowed to establish a set of measurements and specifications in the design of the device with a double functionality, the transport of merchandise and an anti-theft system.
In addition to meeting the needs of the client, the design must comply with a set of reference regulations both, at the level of security devices and the transport of merchandise at retail.
The result of the work has given rise to patent application with prior examination at a national level, in a first phase, and subsequently, at an international level.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
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