Abstracts of Interest
Selected by:
Olaf König
Abstract: 2309.08219
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Title:CTA contributions to the 38th International Cosmic Ray Conference (ICRC 2023)
No PDF available, click to view other formatsAbstract:This index contains the proceedings submitted to the 38th International Cosmic Ray Conference (ICRC 2023) in the name of the CTA consortium.
Abstract: 2309.08753
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Title:Optimal Fitting, Debiasing, and Cosmic Ray Rejection for Detectors Read Out Up-the-Ramp
Download PDFAbstract:This paper derives the optimal fit to a pixel's count rate in the case of an ideal detector read out nondestructively in the presence of both read and photon noise. The approach is general for any readout scheme, provides closed-form expressions for all quantities, and has a computational cost that is linear in the number of resultants (groups of reads). I also derive the bias of the fit from estimating the covariance matrix and show how to remove it to first order. The ramp-fitting algorithm I describe provides the $\chi^2$ value of the fit of a line to the accumulated counts, enabling hypothesis testing for cosmic ray hits using the entire ramp. I show that this approach can be substantially more sensitive than one that only uses the difference between sequential resultants, especially for long ramps and for jumps that occur in the middle of a group of reads. It can also be implemented for a computational cost that is linear in the number of resultants. I provide and describe a pure Python implementation of these algorithms that can process a 10-resultant ramp on a $4096 \times 4096$ detector in $\approx$8 seconds with bias removal, or in $\approx$20 seconds including iterative cosmic ray detection and removal, on a single core of a 2020 Macbook Air. This Python implementation, together with tests and a tutorial notebook, are available at this https URL.
Abstract: 2309.08772
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Title:Non-linear Diffusive Shock Acceleration of Cosmic Rays -- Quasi-thermal and Non-thermal Particle Distributions
Download PDFAbstract:Diffusive shock acceleration (DSA) of particles at collisionless shocks is the major accepted paradigm about the origin of cosmic rays (CRs). As a theory it was developed during the late 1970s in the so-called test-particle case. If one considers the influence of CR particles at shock structure, then we are talking about non-linear DSA. We use semi-analytical Blasi's model of non-linear DSA to obtain non-thermal spectra of both protons and electrons, starting from their quasi-thermal spectra for which we assumed the $\kappa$-distribution, a commonly observed distribution in out-of-equilibrium space plasmas. We treated more carefully than in previous work the jump conditions at the subshock and included electron heating, resonant and, additionally, non-resonant magnetic field instabilities produced by CRs in the precursor. Also, corrections for escaping flux of protons and synchrotron losses of electrons have been made.
Abstract: 2309.08823
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Title:The Source Spectra and Residence Times of Galactic Cosmic Rays Derived from CALET and AMS measurements
Download PDFAbstract:The recent measurements of the spectral intensities of cosmic-ray nuclei have suggested that the ratio of Boron to Carbon nuclei, $R(E)$, comprises two components, one which carries all of the energy dependence and the other a constant independent of energy per nucleon. This supports the earlier theoretical expectations and results of gamma-ray astronomy that one of these components is attributable to spallation in a cocoon like region surrounding the sources and the other in the general interstellar medium before cosmic rays leak away from the Galaxy. A new way of analyzing cosmic-ray spectra is presented here to shed light on the recent findings: based solely on the assumption that the B nuclei in cosmic rays are entirely the products of spallation of heavier nuclei, we solve a cascade of propagation equations to derive both the source-spectra of p, C, O, and Fe nuclei prior to any spallation effects and the energy dependence of the leakage lifetime, $\tau(E)$, implied by the energy dependence of $R(E)$. We find that the source spectra of these nuclei are nearly power laws with the same index, in the nested leaky-box model where the energy-dependent part of the matter is traversed in a cocoon surrounding the sources, and the constant part of the traversal is in the interstellar medium. This is not the case for the alternate choice with the grammage in the sources being a constant. We briefly discuss our results and comment on some aspects of cosmic-ray propagation.
Abstract: 2309.08930
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Title:Radial Outflow Explains the Rotation Curves of Disk Galaxies
Download PDFAbstract:The circular velocities of the inner region of disk galaxies are predicted by standard physics but velocities beyond the stellar disks are not consistent with Newtonian physics if the material there is in stable circular orbits. However, this material is not gravitationally bound and so does not trace the gravitational field in the way that is usually assumed. The gravitational attraction near the edge of a flattened mass distribution is significantly greater than that of an equal mass in a spherical distribution. The size of the effect depends on the specifics of the mass distribution but is greater than a factor of two for reasonable models. In fact, the circular velocity can exceed the escape velocity so that these galaxies are gravitationally unstable in way not previously considered and disk material is lost due to thermal escape, bars or other disturbances. The nearly constant velocity observed in the outer disk region has been interpreted to mean that the dynamical mass of galaxies is much larger than the observed mass. In fact, there is no great discrepancy and no need to invoke dark matter at these scales. The gravitational field of a disk galaxy is determined at all radii by the observed mass. In the region of the stellar disk, stars and gas move in nearly circular orbits at velocities consistent with the gravitational field. In the outer regions the gravitational force drops rapidly so that stars and gas move outward almost unaffected by the attraction of the host galaxy.
Abstract: 2309.09116
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Title:A Hierarchical Framework for explaining the Cosmic Ray Spectrum using Diffusive Shock Acceleration
Download PDFAbstract:The hypothesis that the entire cosmic ray spectrum, from $\lesssim1\,{\rm GeV}$ to $\gtrsim100\,{\rm EeV}$ energy, can be accounted for by diffusive shock acceleration on increasingly large scales is critically examined. Specifically, it is conjectured that Galactic cosmic rays, up to $\sim3\,{\rm PeV}$, are mostly produced by local supernova remnants, from which they escape upstream. These cosmic rays initiate a powerful magnetocentrifugal wind, removing disk mass and angular momentum before passing through the Galactic Wind Termination Shock at a radius $\sim200\,{\rm kpc}$, where they can be re-accelerated to account for observed cosmic rays up to $\sim30\,{\rm PeV}$. The cosmic rays transmitted downstream from more powerful termination shocks associated with other galaxies can be further accelerated at Intergalactic Accretion Shocks to the highest energies observed. In this interpretation, the highest rigidity observed particles are protons; the highest energy particles are heavy nuclei, such as iron. A universal "bootstrap" prescription, coupling the energy density of the magnetic turbulence to that of the resonant cosmic rays, is proposed, initially for the highest energy particles escaping far ahead of the shock front and then scattering, successively, lower energy particles downstream. Observable implications of this general scheme relate to the spectrum, composition and sky distribution of Ultra-High-Energy Cosmic Rays, the extragalactic radio background, the Galactic halo magnetic field and Pevatrons.
Abstract: 2309.09139
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Title:Energy-dependent flavour ratios in neutrino telescopes from charm
Download PDFAbstract:The origin of the observed diffuse neutrino flux is not yet known. Studies of the relative flavour content of the neutrino flux detected at Earth can give information on the production mechanisms at the sources and on flavour mixing, complementary to measurements of the spectral index and normalisation. Here we demonstrate the effects of neutrino fluxes with different spectral shapes and different initial flavour compositions dominating at different energies, and we study the sensitivity of future measurements with the IceCube Neutrino Observatory. Where one kind of flux gives way to another, this shows up as a non-trivial energy dependence in the flavour compositions. We explore this in the context of slow-jet supernovae and magnetar-driven supernovae -- two examples of astrophysical sources where charm production may be effective. Using current best-fit neutrino mixing parameters and their projected 2040 uncertainties, we use event ratios of different event morphologies at IceCube to illustrate the possibilities of distinguishing the energy dependence of neutrino flavour ratios.
Abstract: 2309.09213
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Title:SN 2022vqz: A Peculiar SN 2002es-like Type Ia Supernova with Prominent Early Excess Emission
Download PDFAbstract:We present extensive photometric and spectroscopic observations of a peculiar type Ia supernova (SN Ia) 2022vqz. It shares many similarities with the SN 2002es-like SNe Ia, such as low luminosity (i.e., $M_{B,\rm max}=-18.11\pm0.16$ mag) and moderate post-peak decline rate (i.e., $\Delta m_{15,B}=1.33\pm0.11$ mag). The nickel mass synthesized in the explosion is estimated as $0.20\pm0.04~{\rm M}_\odot$ from the bolometric light curve, which is obviously lower than normal SNe Ia. SN 2022vqz is also characterized by a slow expanding ejecta, with Si II velocities persisting around 7000 km s$^{-1}$ since 16 days before the peak, which is unique among all known SNe Ia. While all these properties imply a less energetic thermonuclear explosion that should leave considerable amount of unburnt materials, however, absent signature of unburnt carbon in the spectra of SN 2022vqz is puzzling. A prominent early peak is clearly detected in the $c$- and $o$-band light curves of ATLAS and in the $gr$-band data of ZTF within days after the explosion. Possible mechanisms for the early peak are discussed, including sub-Chandrasekhar mass double detonation model and interaction of SN ejecta with circumstellar material (CSM). We found both models face some difficulties in replicating all aspects of the observed data. As an alternative, we propose a hybrid CONe white dwarf as progenitor of SN 2022vqz which can simultaneously reconcile the tension between low ejecta velocity and absence of carbon. We further discuss the diversity of 02es-like objects and possible origins of different scenarios.