arXiv subjects

M. Blank

Publications and source records attributed to M. Blank.

13 recordsLinked to original sources

arXiv2023

Detection of the Crab Nebula using a Random Forest Analysis of the first TAIGA IACT Data

The Tunka Advanced Instrument for Gamma- and cosmic-ray Astronomy (TAIGA) is a multicomponent experiment for the measurement of TeV to PeV gamma- and cosmic rays. Our goal is to establish a novel hybrid direct air shower technique, sufficient to access the energy domain of the long-sought Pevatrons. The hybrid air Cherenkov light detection technique combines the strengths of the HiSCORE shower front sampling array, and two $\thicksim$4 m class, $\sim$9.6 deg field of view Imaging Air Cherenkov Telescopes (IACTs). The HiSCORE array provides good angular and shower core position resolution, while the IACTs provide the image shape and orientation for gamma-hadron separation. In future, an additional muon detector will be used for hadron tagging at $\ge$ 100 TeV energies. Here, only data from the first IACT of the TAIGA experiment are used. A random forest algorithm was trained using Monte Carlo (MC) simulations and real data, and applied to 85 h of selected observational data tracking the Crab Nebula at a mean zenith angle of 33.5 deg, resulting in a threshold energy of 6 TeV for this dataset. The analysis was performed using the gammapy package. A total of 163.5 excess events were detected, with a statistical significance of 8.5 sigma. The observed spectrum of the Crab Nebula is best fit with a power law above 6 TeV with a flux normalisation of $(3.20\pm0.42)\cdot10^{-10} TeV^{-1} cm^{-2} s^{-1})$ at a reference energy of 13 TeV and a spectral index of $-2.74\pm0.16$.

astro-ph.IM↗

arXiv2021

Search for Astrophysical Nanosecond Optical Transients with TAIGA-HiSCORE Array

A wide-angle Cerenkov array TAIGA-HiSCORE (FOV $\sim$0.6 sr), was originally created as a part of TAIGA installation for high-energy gamma-ray astronomy and cosmic ray physics. Array now consist on nearly 100 optical stations on the area of 1 km$^2$. Due to high accuracy and stability ($\sim$1 ns) of time synchronization of the optical stations the accuracy of EAS arrival direction reconstruction is reached 0.1$^\mathrm{o}$. It was proven that the array can also be used to search for nanosecond events of the optical range. The report discusses the method of searching for optical transients using the HiSCORE array and demonstrates its performance on a real example of detecting signals from an artificial Earth satellite. The search for this short flares in the HiSCORE data of the winter season 2018--2019 is carried out. One candidate for double repeater has been detected, but the estimated probability of random simulation of such a transient by background EAS events is not less than 10%, which does not allow us to say that the detected candidate corresponds to a real astrophysical transient. An upper bound on the frequency of optical spikes with flux density of more than $10^{-4} \mathrm{erg/s/cm}^2$ and a duration of more than 5\,ns is established as $\sim 2 \times 10^{-3}$ events/sr/hour.

astro-ph.IM↗

arXiv2017

Mirror Position Determination for the Alignment of Cherenkov Telescopes

Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures to map the faint Cherenkov light emitted in extensive air showers onto their image sensors. Segmented reflectors fulfill these needs using mass produced and light weight mirror facets. However, as the overall image is the sum of the individual mirror facet images, alignment is important. Here we present a method to determine the mirror facet positions on a segmented reflector in a very direct way. Our method reconstructs the mirror facet positions from photographs and a laser distance meter measurement which goes from the center of the image sensor plane to the center of each mirror facet. We use our method to both align the mirror facet positions and to feed the measured positions into our IACT simulation. We demonstrate our implementation on the 4 m First Geiger-mode Avalanche Cherenkov Telescope (FACT).

astro-ph.IM↗

arXiv2016

Bokeh Mirror Alignment for Cherenkov Telescopes

Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment remains a challenge. Here we present a simple, yet extendable method, to align a segmented reflector using its Bokeh. Bokeh alignment does not need a star or good weather nights but can be done even during daytime. Bokeh alignment optimizes the facet orientations by comparing the segmented reflectors Bokeh to a predefined template. The optimal Bokeh template is highly constricted by the reflector's aperture and is easy accessible. The Bokeh is observed using the out of focus image of a near by point like light source in a distance of about 10 focal lengths. We introduce Bokeh alignment on segmented reflectors and demonstrate it on the First Geiger-mode Avalanche Cherenkov Telescope (FACT) on La Palma, Spain.

astro-ph.IM↗

arXiv2016

Normalized and Asynchronous Mirror Alignment for Cherenkov Telescopes

Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and as they are composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment is a challenge. Here we present a computer vision based star tracking alignment method, which also works for limited or changing star light visibility. Our method normalizes the mirror facet reflection intensities to become independent of the reference star's intensity or the cloud coverage. Using two CCD cameras, our method records the mirror facet orientations asynchronously of the telescope drive system, and thus makes the method easy to integrate into existing telescopes. It can be combined with remote facet actuation, but does not require one to work. Furthermore, it can reconstruct all individual mirror facet point spread functions without moving any mirror. We present alignment results on the 4 meter First Geiger-mode Avalanche Cherenkov Telescope (FACT).

astro-ph.IM↗

arXiv2011

Bottomonium in a Bethe-Salpeter-equation study

Using a well-established effective interaction in a rainbow-ladder truncation model of QCD, we fix the remaining model parameter to the bottomonium ground-state spectrum in a covariant Bethe-Salpeter equation approach and find surprisingly good agreement with the available experimental data including the 2^{--} Upsilon(1D) state. Furthermore, we investigate the consequences of such a fit for charmonium and light-quark ground states.

hep-ph↗

arXiv2010

A covariant study of tensor mesons

We investigate tensor mesons as quark-antiquark bound states in a fully covariant Bethe-Salpeter equation. As a first concrete step we report results for masses of J^{PC}=2^{++} mesons from the chiral limit up to bottomonium and sketch a comparison to experimental data. All covariant structures of the fermion-antifermion system are taken into account and their roles and importance discussed in two different bases. We also present the general construction principle for covariant Bethe-Salpeter amplitudes of mesons with any spin and find eight covariant structures for any J>0.

hep-ph↗

arXiv2010

Light-meson properties from the Bethe-Salpeter equation

We discuss how to extract observables from an inhomogeneous vertex Bethe-Salpeter equation without resorting to the corresponding homogeneous equation. As an example we present a prediction for the $e^+e^-$ decay width of the $ρ(1450)$ or $ρ'$ meson. We also attempt to identify the momentum range contributing to a vector meson's decay constant.

hep-ph↗

arXiv2010

Matrix algorithms for solving (in)homogeneous bound state equations

In the functional approach to quantum chromodynamics, the properties of hadronic bound states are accessible via covariant integral equations, e.g. the Bethe-Salpeter equations for mesons. In particular, one has to deal with linear, homogeneous integral equations which, in sophisticated model setups, use numerical representations of the solutions of other integral equations as part of their input. Analogously, inhomogeneous equations can be constructed to obtain off-shell information in addition to bound-state masses and other properties obtained from the covariant analogue to a wave function of the bound state. These can be solved very efficiently using well-known matrix algorithms for eigenvalues (in the homogeneous case) and the solution of linear systems (in the inhomogeneous case). We demonstrate this by solving the homogeneous and inhomogeneous Bethe-Salpeter equations and find, e.g. that for the calculation of the mass spectrum it is more efficient to use the inhomogeneous equation. This is valuable insight, in particular for the study of baryons in a three-quark setup and more involved systems.

hep-ph↗

arXiv2010

The QCD chiral transition temperature in a Dyson-Schwinger-equation context

We analyze the chiral phase transition with the help of the QCD gap equation. Various models for the effective interaction in rainbow truncation are contrasted with regard to the resulting chiral transition temperatures. In particular, we investigate possible systematic relations of the details of the effective interaction and the value of T_c. In addition, we quantify changes to the transition temperature beyond the rainbow truncation.

hep-ph↗

arXiv1997

A KAM type theorem for systems with round-off errors

Perturbations due to round-off errors in computer modeling are discontinuous and therefore one cannot use results like KAM theory about smooth perturbations of twist maps. We elaborate a special approximation scheme to construct two smooth periodic on the angle perturbations of the twist map, bounding the discretized map from above and from below. Using the well known Moser's theorem we prove the existence of invariant curves for these smooth approximations. As a result we are able to prove that any trajectory of the discretized twist map is eventually periodic. We discuss also some questions, concerning the application of the intersection property in Moser's theorem and the generalization of our results for the twist map in Lobachevski plane.

chao-dyn↗

arXiv1996

Bifractality of the Devil's staircase appearing in the Burgers equation with Brownian initial velocity

It is shown that the inverse Lagrangian map for the solution of the Burgers equation (in the inviscid limit) with Brownian initial velocity presents a bifractality (phase transition) similar to that of the Devil's staircase for the standard triadic Cantor set. Both heuristic and rigorous derivations are given. It is explained why artifacts can easily mask this phenomenon in numerical simulations.

chao-dyn↗

arXiv1993

Chaotic Cascades with Kolmogorov 1941 Scaling

We define a (chaotic) deterministic variant of random multiplicative cascade models of turbulence. It preserves the hierarchical tree structure, thanks to the addition of infinitesimal noise. The zero-noise limit can be handled by Perron-Frobenius theory, just as the zero-diffusivity limit for the fast dynamo problem. Random multiplicative models do not possess Kolmogorov 1941 (K41) scaling because of a large-deviations effect. Our numerical studies indicate that deterministic multiplicative models can be chaotic and still have exact K41 scaling. A mechanism is suggested for avoiding large deviations, which is present in maps with a neutrally unstable fixed point.

cond-mat↗