1. Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episodeJ. C. Algaba, M. Baloković, S. Chandra, W.-Y. Cheong, Y.-Z. Cui, F. D'Ammando, A. D. Falcone, N. M. Ford, M. Giroletti, Gabrijela Zaharijas, 2024, original scientific article Keywords: galaxies, active, individual, M 87, jets, nuclei Published in RUNG: 13.01.2025; Views: 261; Downloads: 6
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2. The Cherenkov Telescope Array sensitivity to the transient skyValentina Fioretti, Christopher Eckner, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, published scientific conference contribution Abstract: The Cherenkov Telescope Array (CTA) will be able to perform unprecedented observations of the transient very high-energy sky. An on-line science alert generation (SAG) pipeline, with a required 30 second latency, will allow the discovery or follow-up of gamma ray bursts (GRBs) and flaring emission from active galactic nuclei, galactic compact objects and electromagnetic counterparts of gravitational waves or neutrino messengers. The CTA sensitivity for very short exposures does not only depend on the technological performance of the array (e.g. effective area, background discrimination efficiency). The algorithms to evaluate the significance of the detection also define the sensitivity, together with their computational efficiency in order to satisfy the SAG latency requirements. We explore the aperture photometry and likelihood analysis techniques, and the associated parameters (e.g. on-source to off-source exposure ratio, minimum number of required signal events), defining the CTA ability to detect a significant signal at short exposures. The resulting CTA differential flux sensitivity as a function of the observing time, obtained using the latest Monte Carlo simulations, is compared to the sensitivities of Fermi–LAT and current-generation IACTs obtained in the overlapping energy ranges. Keywords: very-high-energy gamma rays, Cherenkov Telescope Array (CTA) Observatory, transient astrophysical sources, gamma-ray bursts, active galactic nuclei Published in RUNG: 15.11.2024; Views: 525; Downloads: 10
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3. Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger ObservatoryA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2024, original scientific article Abstract: The combined fit of the measured energy spectrum and shower maximum depth
distributions of ultra-high-energy cosmic rays is known to constrain the parameters of
astrophysical models with homogeneous source distributions. Studies of the distribution of
the cosmic-ray arrival directions show a better agreement with models in which a fraction of
the flux is non-isotropic and associated with the nearby radio galaxy Centaurus A or with
catalogs such as that of starburst galaxies. Here, we present a novel combination of both
analyses by a simultaneous fit of arrival directions, energy spectrum, and composition data
measured at the Pierre Auger Observatory. The model takes into account a rigidity-dependent magnetic field blurring and an energy-dependent evolution of the catalog contribution shaped by interactions during propagation.
We find that a model containing a flux contribution from the starburst galaxy catalog
of around 20% at 40 EeV with a magnetic field blurring of around 20◦ for a rigidity of
10EV provides a fair simultaneous description of all three observables. The starburst galaxy
model is favored with a significance of 4.5σ (considering experimental systematic effects)
compared to a reference model with only homogeneously distributed background sources.
By investigating a scenario with Centaurus A as a single source in combination with the
homogeneous background, we confirm that this region of the sky provides the dominant
contribution to the observed anisotropy signal. Models containing a catalog of jetted active
galactic nuclei whose flux scales with the γ-ray emission are, however, disfavored as they
cannot adequately describe the measured arrival directions. Keywords: ultra high energy cosmic rays, cosmic ray experiments, Pierre Auger Observatory, active galactic nuclei Published in RUNG: 19.01.2024; Views: 1738; Downloads: 43
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4. Cosmic-ray Heavy Nuclei Spectra Using the ISS-CREAM InstrumentS.C. Kang, Jon Paul Lundquist, 2022, published scientific conference contribution Abstract: Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) was designed to study high-energy cosmic rays up to PeV and recorded data from August 22nd, 2017 to February 12th, 2019 on the ISS. In this analysis, the Silicon Charge Detector (SCD), CALorimeter (CAL), and Top and Bottom Counting Detectors (TCD/BCD) are used. The SCD is composed of four layers and provides the measurement of cosmic-ray charges with a resolution of ∼0.2e. The CAL comprises 20 interleaved tungsten plates and scintillators, measures the incident cosmic-ray particles' energies, and provides a high energy trigger. The TCD/BCDs consist of photodiode arrays and plastic scintillators and provide a low-energy trigger. In this analysis, the SCD top layer is used for charge determination. Here, we present the heavy nuclei analysis using the ISS-CREAM instrument. Keywords: ISS-CREAM, silicon charge detector, calorimeter, direct detection, heavy nuclei, cosmic rays, energy spectrum, composition Published in RUNG: 26.09.2023; Views: 1854; Downloads: 6
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5. Active Galactic Nuclei population studies with the Cherenkov Telescope ArrayAnthony M. Brown, Saptashwa Bhattacharyya, Barbara MARČUN, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, published scientific conference contribution Abstract: The Cherenkov Telescope Array (CTA) observatory is the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Building on the strengths of current IACTs, CTA is designed to achieve an order of magnitude improvement in sensitivity, with unprecedented angular and energy resolution. CTA will also increase the energy reach of IACTs, observing photons in the energy range from 20 GeV to beyond 100 TeV. These advances in performance will see CTA heralding in a new era for high-energy astrophysics, with the emphasis shifting from source discovery, to population studies and precision measurements. In this talk we discuss CTA’s ability to conduct source population studies of �-ray bright active galactic nuclei and how this ability will enhance our understanding on the redshift evolution of this dominant �-ray source class. Keywords: Cherenkov Telescope Array, high-energy astrophysics, active galactic nuclei Published in RUNG: 19.09.2023; Views: 1804; Downloads: 7
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6. Southern African Large Telescope Spectroscopy of BL Lacs for the CTA projectEli Kasai, Saptashwa Bhattacharyya, Barbara MARČUN, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, published scientific conference contribution Abstract: n the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum-dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory. Keywords: Cherenkov Telescope Array, very-high-energy gamma-ray astronomy, Active Galactic Nuclei, high-frequency peaked BL Lacs, Southern African Large Telescope Published in RUNG: 18.09.2023; Views: 2249; Downloads: 7
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7. Bright blazar flares with CTAM. Cerruti, Saptashwa Bhattacharyya, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2023, published scientific conference contribution Abstract: The TeV extragalactic sky is dominated by blazars, radio-loud active galactic nuclei with a
relativistic jet pointing towards the Earth. Blazars show variability that can be quite exceptional
both in terms of flux (orders of magnitude of brightening) and time (down to the minute timescale).
This bright flaring activity contains key information on the physics of particle acceleration and
photon production in the emitting region, as well as the structure and physical properties of the
jet itself. The TeV band is accessed from the ground by Cherenkov telescopes that image the
pair cascade triggered by the interaction of the gamma ray with the Earth’s atmosphere. The
Cherenkov Telescope Array (CTA) represents the upcoming generation of imaging atmospheric
Cherenkov telescopes, with a significantly higher sensitivity and larger energy coverage with
respect to current instruments. It will thus provide us with unprecedented statistics on blazar
light-curves and spectra. In this contribution we present the results from realistic simulations of
CTA observations of bright blazar flares, taking as input state-of-the-art numerical simulations of
blazar emission models and including all relevant observational constraints. Keywords: active galactic nuclei, radio-loud AGN, blazars Published in RUNG: 15.09.2023; Views: 2446; Downloads: 6
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8. The UHECR-FR0 radio galaxy connection : a multi-messenger study of energy spectra/composition emission and intergalactic magnetic field propagationJon Paul Lundquist, Lukas Merten, Serguei Vorobiov, Margot Boughelilba, Anita Reimer, Paolo Da Vela, Fabrizio Tavecchio, Giacomo Bonnoli, Chiara Righi, 2023, published scientific conference contribution Abstract: This study investigates low luminosity Fanaroff-Riley Type 0 (FR0) radio galaxies as a potentially
significant source of ultra-high energy cosmic rays (UHECRs). Due to their much higher prevalence
in the local universe compared to more powerful radio galaxies (about five times more than
FR-1s), FR0s may provide a substantial fraction of the total UHECR energy density. To determine
the nucleon composition and energy spectrum of UHECRs emitted by FR0 sources, simulation
results from CRPropa3 are fit to Pierre Auger Observatory data. The resulting emission spectral
indices, rigidity cutoffs, and nucleon fractions are compared to recent Auger results. The FR0 simulations
include the approximately isotropic distribution of FR0 galaxies and various intergalactic
magnetic field configurations (including random and structured fields) and predict the fluxes of
secondary photons and neutrinos produced during UHECR propagation through cosmic photon
backgrounds. This comprehensive simulation allows for investigating the properties of the FR0
sources using observational multi-messenger data. Keywords: ultra-high energy cosmic rays, UHECR propagation, CRPropa, active galactic nuclei, jetted AGN, FR0 radio galaxies, Pierre Auger Observatory, UHECR energy spectrum Published in RUNG: 24.08.2023; Views: 2108; Downloads: 5
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9. Spine-sheath jet model for low-luminosity AGNsMargot Boughelilba, Anita Reimer, Lukas Merten, Jon Paul Lundquist, 2023, published scientific conference contribution Abstract: In several jetted AGNs, structured jets have been observed. In particular spine-sheath configurations
where the jet is radially divided into two or more zones of different flow velocities.
We present a model based on the particle and radiation transport code CR-ENTREES. Here,
interaction rates and secondary particle and photon yields are pre-calculated by Monte Carlo
event generators or semi-analytical approximations. These are then used to create transition
matrices, that describe how each particle spectrum evolves with time. This code allows for
arbitrary injection of primary particles, and the possibility to choose which interaction to include
(photo-meson production, Bethe-Heitler pair-production, inverse-Compton scattering, �-� pair
production, decay of all unstable particles, synchrotron radiation — from electrons, protons, and
all relevant secondaries before their respective decays — and particle escape).
In addition to the particle and radiation interactions taking place in each homogeneous zone, we
implement the feedback between the two zones having different bulk velocities. The main mechanism
at play when particles cross the boundary between the two zones is shear acceleration. We
follow a microscopic description of this acceleration process to create a corresponding transition
matrix and include it in our numerical setup. Furthermore, each zone’s radiation field can be
used as an external target photon field for the other zone’s particle interactions. We present here
the first results of the effect of a two-zone spine-sheath jet, by applying this model to typical
low-luminosity AGNs. Keywords: active galactic nuclei, low-luminosity jetted AGN, spine-sheath jet structure Published in RUNG: 24.08.2023; Views: 1880; Downloads: 5
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10. The rise and fall of the nuclear transient PS16dtmTanja Petrushevska, 2023, published scientific conference contribution abstract (invited lecture) Abstract: Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centres of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. I will present PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy which has been proposed to be a TDE candidate. I will show our multi-year spectroscopic and photometric study of PS16dtm, which can help us to better understand the outbursts originating in NLSy1 galaxies. Keywords: active galactic nuclei, tidal disruption events Published in RUNG: 10.08.2023; Views: 2102; Downloads: 5
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