Abstract
Astro-COLIBRI is a novel tool that evaluates alerts of transient observations in real time, filters them by user-specified criteria, and puts them into their multiwavelength and ...multimessenger context. Through fast generation of an overview of persistent sources as well as transient events in the relevant phase space, Astro-COLIBRI contributes to an enhanced discovery potential of both serendipitous and follow-up observations of the transient sky. The software’s architecture comprises a Representational State Transfer Application Programming Interface, both a static and a real-time database, a cloud-based alert system, as well as a website and apps for iOS and Android as clients for users. The latter provide a graphical representation with a summary of the relevant data to allow for the fast identification of interesting phenomena along with an assessment of observing conditions at a large selection of observatories around the world.
We present a new method for the reconstruction of the longitudinal profile of extensive air showers induced by ultra-high energy cosmic rays. In contrast to the typically considered shower size ...profile, this method employs directly the ionization energy deposit of the shower particles in the atmosphere. Due to universality of the energy spectra of electrons and positrons, both fluorescence and Cherenkov light can be used simultaneously as signal to infer the shower profile from the detected light. The method is based on an analytic least-square solution for the estimation of the shower profile from the observed light signal. Furthermore, the extrapolation of the observed part of the profile with a Gaisser–Hillas function is discussed and the total statistical uncertainty of shower parameters like total energy and shower maximum is calculated.
Steady increase of functionality and concurrent reduction of the package size are one of the key driving forces in electronics production. In this paper we will present solutions developed at the ...institute for the automated assembly of highly miniaturized flip-chips with pitches down to 100
μm. In particular the present and future influences of miniaturization on the main process steps wafer bumping, component placement, reflow soldering and inspection are examined as well as the influences on complementary materials used. Results regarding the achievable yield after assembly and the reliability of the structures will be presented in addition to an analysis of the failure mechanisms.
Abstract
We report the discovery of four Fast Radio Bursts (FRBs) in the ongoing SUrvey for Pulsars and Extragalactic Radio Bursts at the Parkes Radio Telescope: FRBs 150610, 151206, 151230 and ...160102. Our real-time discoveries have enabled us to conduct extensive, rapid multimessenger follow-up at 12 major facilities sensitive to radio, optical, X-ray, gamma-ray photons and neutrinos on time-scales ranging from an hour to a few months post-burst. No counterparts to the FRBs were found and we provide upper limits on afterglow luminosities. None of the FRBs were seen to repeat. Formal fits to all FRBs show hints of scattering while their intrinsic widths are unresolved in time. FRB 151206 is at low Galactic latitude, FRB 151230 shows a sharp spectral cut-off, and FRB 160102 has the highest dispersion measure (DM = 2596.1 ± 0.3 pc cm−3) detected to date. Three of the FRBs have high dispersion measures (DM > 1500 pc cm−3), favouring a scenario where the DM is dominated by contributions from the intergalactic medium. The slope of the Parkes FRB source counts distribution with fluences >2 Jy ms is $\alpha =-2.2^{+0.6}_{-1.2}$ and still consistent with a Euclidean distribution (α = −3/2). We also find that the all-sky rate is $1.7^{+1.5}_{-0.9}\times 10^3$FRBs/(4π sr)/day above ${\sim }2{\rm \, }\rm {Jy}{\rm \, }\rm {ms}$ and there is currently no strong evidence for a latitude-dependent FRB sky rate.
Rapid radio brightening of GRB 210702A Anderson, G E; Russell, T D; Fausey, H M ...
Monthly notices of the Royal Astronomical Society,
06/2023, Letnik:
523, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We observed the rapid radio brightening of GRB 210702A with the Australia Telescope Compact Array (ATCA) just 11 h post-burst, tracking early-time radio variability over a 5 h period on ∼15 ...min time-scales at 9.0, 16.7, and 21.2 GHz. A broken power law fit to the 9.0 GHz light curve showed that the 5 h flare peaked at a flux density of 0.4 ± 0.1 mJy at ∼13 h post-burst. The observed temporal and spectral evolution is not expected in the standard internal–external shock model, where forward and reverse shock radio emission evolves on much longer time-scales. The early-time (<1 d) optical and X-ray light curves from the Neil Gehrels Swift Observatory demonstrated typical afterglow forward shock behaviour, allowing us to use blast wave physics to determine a likely homogeneous circumburst medium and an emitting electron population power-law index of p = 2.9 ± 0.1. We suggest that the early-time radio flare is likely due to weak interstellar scintillation (ISS), which boosted the radio afterglow emission above the ATCA sensitivity limit on minute time-scales. Using relations for ISS in the weak regime, we were able to place an upper limit on the size of the blast wave of ≲6 × 1016 cm in the plane of the sky, which is consistent with the theoretical forward shock size prediction of 8 × 1016 cm for GRB 210702A at ∼13 h post-burst. This represents the earliest ISS size constraint on a gamma-ray burst (GRB) blast wave to date, demonstrating the importance of rapid (<1 d) radio follow-up of GRBs using several-hour integrations to capture the early afterglow evolution and to track the scintillation over a broad frequency range.
The blazar Mrk 501 (z = 0.034) was observed at very-high-energy (VHE, E 100 GeV) gamma-ray wavelengths during a bright flare on the night of 2014 June 23-24 (MJD 56832) with the H.E.S.S. phase-II ...array of Cherenkov telescopes. Data taken that night by H.E.S.S. at large zenith angle reveal an exceptional number of gamma-ray photons at multi-TeV energies, with rapid flux variability and an energy coverage extending significantly up to 20 TeV. This data set is used to constrain Lorentz invariance violation (LIV) using two independent channels: a temporal approach considers the possibility of an energy dependence in the arrival time of gamma-rays, whereas a spectral approach considers the possibility of modifications to the interaction of VHE gamma-rays with extragalactic background light (EBL) photons. The non-detection of energy-dependent time delays and the non-observation of deviations between the measured spectrum and that of a supposed power-law intrinsic spectrum with standard EBL attenuation are used independently to derive strong constraints on the energy scale of LIV (EQG) in the subluminal scenario for linear and quadratic perturbations in the dispersion relation of photons. For the case of linear perturbations, the 95% confidence level limits obtained are EQG,1 > 3.6 × 1017 GeV using the temporal approach and EQG,1 > 2.6 × 1019 GeV using the spectral approach. For the case of quadratic perturbations, the limits obtained are EQG,2 > 8.5 × 1010 GeV using the temporal approach and EQG,2 > 7.8 × 1011 GeV using the spectral approach.
Context.
Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible ...for a significant fraction of cosmic rays (CRs) that are accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy, is a prime candidate for studying this hypothesis. While the very-high-energy
γ
-ray source HESS J1646−458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified.
Aims.
We aim to identify the physical processes responsible for the
γ
-ray emission around Westerlund 1 and thus to understand the role of massive stellar clusters in the acceleration of Galactic CRs better.
Methods.
Using 164 h of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the
γ
-ray emission of HESS J1646−458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs.
Results.
We detected large-scale (∼2° diameter)
γ
-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with
γ
-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and it is uniform across the entire source region. We did not find a clear correlation of the
γ
-ray emission with gas clouds as identified through H I and CO observations.
Conclusions.
We conclude that, of the known objects within the region, only Westerlund 1 can explain the majority of the
γ
-ray emission. Several CR acceleration sites and mechanisms are conceivable and discussed in detail. While it seems clear that Westerlund 1 acts as a powerful particle accelerator, no firm conclusions on the contribution of massive stellar clusters to the flux of Galactic CRs in general can be drawn at this point.
The H.E.S.S. Galactic plane survey Angüner, E. O.; Arakawa, M.; Aubert, P. ...
Astronomy and astrophysics (Berlin),
04/2018, Letnik:
612
Journal Article
Recenzirano
Odprti dostop
We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) γ-rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the ...discovery of 16 new sources of VHE γ-rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from ℓ = 250° to 65° and latitudes |b|≤ 3°. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08° ≈ 5 arcmin mean point spread function 68% containment radius), sensitivity (≲1.5% Crab flux for point-like sources), and energy range (0.2–100 TeV). We constructed a catalog of VHE γ-ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood-based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for example, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we individually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible associations with cataloged objects, notably PWNe and energetic pulsars that could power VHE PWNe.
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