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Ariel Perera - "Searching for Undetected Gamma Ray Bursts in Fermi GBM Data"
Pádraig Mc Dermott - "Gamma ray detection with EIRSAT-1: Ireland’s first satellite!"
Marianna Dafčíková - "The First GRBAlpha and VZLUSAT-2 catalogue: gamma-ray transients and detector sensitivity"
Manuele Maistrello - "The dispersion of the 𝐸𝑝,𝑖− 𝐿𝑖𝑠𝑜 correlation of long gamma-ray bursts is partially due to assembling different sources"
Tuesday, June 4 Part 2
Rafael Diaz - "Studying VHE variability and flare for blazar B2 1811+31"
Thunyapong Mahapol - "A Theoretical Fourier-Transformation Model for the Formation of X-ray Time Lags from Black Hole Accretion Disks"
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| Abstract: The complex and rapidly varying X-ray emission from active galactic nuclei (AGNs) may provide insights to the thermal and dynamical structure of the central black hole accretion disk. To analyze the observed variability, X-ray time lags which are the temporal delays between Fourier transforms of light curves in hard and soft X-ray energy channels can be used. These time lags may be either hard lags or soft lags, depending on whether the variability in the hard energy channel follows that in the soft channel or vice versa. The source for the observed X-ray time lags from AGNs has been a subject of debate. In this study, we investigate the scenario where the X-ray time lags are generated by thermal and bulk Comptonization, as well as spatial reverberation of iron L-line and K-line seed photons, which are produced via fluorescence due to local instability. We model the inner region of the accretion flow as a hot, geometrically thick ADAF disc, with the outer radius equal to the shock formation radius located just outside the centrifugal barrier. Using a Fourier-transformed, vertically-averaged transport equation in cylindrical coordinates, we analyze the time-dependent radiative transfer in the inner ADAF region and simulate the X-ray time lag data. We then compare the simulated time lags to the observed time lags for model fitting. Our new model successfully reproduces the complex X-ray variability data for the Seyfert 1 galaxies 1H 0707-495 and Ark 564. |
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Wednesday, June 5
Adithiya Dinesh - "A systematic search for extreme gamma-ray blazars using Fermi-LAT"
Laenita De Jonge - "Study of the hadronic synchrotron mirror model for orphan flares in blazars - Application to 3C279"
Paolo Cristarella Orestano - "Study of Periodicity in Blazar Light Curves"
Ao Zhang - "Search for anisotropic pair halos associated with blazar jets"
Thursday, June 6
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| Abstract: The recent discovery of simultaneous gravitational wave (GW) emission and short gamma-ray burst from a binary neutron star (BNS) merger has opened a new window to study such compact binary systems. The joint detection rate from this event is estimated at approximately 0.1 to 1.4 per year, with no other confirmed sources identified yet. In my research, I develop a GRB detection pipeline with rigorous statistical analysis to scan the Fermi GBM data, with the aim of increasing the search sensitivity. This will result in a larger number of known GRBs, and hence increased probability of another joint GRB-GW detection. This expectation is supported by a comparison of the detection probability of the pipeline and the significance of GBM triggering algorithm; our pipeline shows between 2 to 15 times higher signal-to-noise ratio, depending on source direction and intrinsic spectrum. Another feature of this pipeline is a statistical estimation of the location of the burst and discrimination between cosmological, terrestrial, and stellar origins. This allows for a robust classification of the signal, lowering the contamination of the sample. Our analysis includes operating the pipeline on ”time-slided” copies of the data, which allows exact significance assessment and pastro computation, akin to the state-of-the-art GW data analysis pipelines. This, along with a sky-map for the direction to the GRB, will facilitate a rigorous joint GW-GRB search on O3 and O4 LVK data. |
Pádraig Mc Dermott - "Gamma ray detection with EIRSAT-1: Ireland’s first satellite!"
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| Abstract: EIRSAT-1 is Ireland’s first satellite, it was developed by students in University College Dublin as a part of ESAs Fly your Satellite program. On December 1st 2023 EIRSAT-1 was launched into a Sun Synchronous Orbit from Vandenberg Space Base on a Space-X Falcon 9. It is a 2U CubeSat equipped with three payloads, one of which is GMOD; a gamma ray detecting module. GMOD uses a CeBr3 scintillator which produces flashes of light in the visible range when struck by gamma ray photons. The scintillations are measured with silicone photomultipliers (SiPMs) and read using an application specific integrated circuit (ASIC) known as SIPHRA. EIRSAT-1 is performing well in orbit and will soon be producing scientific data. This presentation will give an overview of the satellite subsystems with particular focus on the gamma ray detection module. The challenges faced in the lead up to launch and in the early operations phase will be presented. The results of the first few months of gamma ray detection with EIRSAT-1 will be discussed. Finally, the advantages and disadvantages of gamma ray detection with CubeSats will be presented using EIRSAT-1 as an example. |
Marianna Dafčíková - "The First GRBAlpha and VZLUSAT-2 catalogue: gamma-ray transients and detector sensitivity"
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| Abstract: In recent years there have been numerous efforts to build a constellation of small satellites which would provide an all-sky coverage and quick localization of gamma-ray bursts (GRBs). One of the mission proposals is the CAMELOT constellation with a newly developed gamma-ray detector composed of a CsI(Tl) scintillator coupled with silicon photomultipliers (SiPMs). The prototype of this detector is already employed in two space missions, GRBAlpha 1U CubeSat launched in March 2021 and VZLUSAT-2 3U CubeSat launched in January 2022. To date, the satellites have detected over 150 gamma-ray transients. In this presentation, I will show the first catalogue of the transients detected by these two missions and present the empirical sensitivity of the detector. The weakest GRB detection belongs to the faintest 10% of those observed by Fermi/GBM which demonstrates the detector potential for routine observation of GRBs. |
Manuele Maistrello - "The dispersion of the 𝐸𝑝,𝑖− 𝐿𝑖𝑠𝑜 correlation of long gamma-ray bursts is partially due to assembling different sources"
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| Abstract: Despite the prompt emission of gamma-ray bursts (GRBs) was discovered more than 50 years ago, there are still several aspects that need to be understood. One of them concerns some correlations that emerge when considering time-integrated spectra of long GRBs with known redshift. Specifically, it was found that the intrinsic peak energy, 𝐸𝑝,𝑖, of the 𝜐𝐹 𝜐 spectrum correlates with the isotropic-equivalent gamma-ray peak luminosity, 𝐿𝑝,𝑖𝑠𝑜. This correlation is also characterized by an intrinsic dispersion, 𝜎𝑖𝑛𝑡, whose origin is still unknown. Discovering the origin of the dispersion would give us insights about the radiative process (or processes) and dissipation mechanism at play, and would unlock the possibility of using GRBs as cosmological probes. Even if the 𝐸𝑝,𝑖− 𝐿𝑝,𝑖𝑠𝑜 correlation was discovered starting from time-integrated spectra of different GRBs, it was found that it holds within individual GRBs too, if the corresponding time-resolved quantities are considered, namely 𝐸𝑝,𝑖 and 𝐿𝑖𝑠𝑜. In this work, we focus on the time-resolved 𝐸𝑝,𝑖− 𝐿𝑖𝑠𝑜 correlation. The fact that the dispersion does not vanish within individual bursts is evidence that its origin cannot be entirely ascribed to properties that differ for each GRB. Yet, the question remains as to which extent the dispersion must be ascribed to the dissipation mechanism operating within individual bursts and what is, instead, due to assembling different sources. The aim of this work is to compare the values of the dispersion of individual GRBs with thedispersion of a whole sample of GRBs. In order to do so, we perform a time-resolved spectral analysis of 20 long GRBs detected by Fermi-GBM with known redshift and estimates of the jet opening angle, 𝜃 𝑗, and/or the Lorentz factor, Γ 0. In addition, we want to search for possible correlations between 𝜎𝑖𝑛𝑡, considered as a characteristic of individual bursts, and key observables related to the GRB physics, such as 𝜃 𝑗 and Γ 0. |
Tuesday, June 4 Part 2
Rafael Diaz - "Studying VHE variability and flare for blazar B2 1811+31"
M Thunyapong Mahapol - "A Theoretical Fourier-Transformation Model for the Formation of X-ray Time Lags from Black Hole Accretion Disks"
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| Abstract: The complex and rapidly varying X-ray emission from active galactic nuclei (AGNs) may provide insights to the thermal and dynamical structure of the central black hole accretion disk. To analyze the observed variability, X-ray time lags which are the temporal delays between Fourier transforms of light curves in hard and soft X-ray energy channels can be used. These time lags may be either hard lags or soft lags, depending on whether the variability in the hard energy channel follows that in the soft channel or vice versa. The source for the observed X-ray time lags from AGNs has been a subject of debate. In this study, we investigate the scenario where the X-ray time lags are generated by thermal and bulk Comptonization, as well as spatial reverberation of iron L-line and K-line seed photons, which are produced via fluorescence due to local instability. We model the inner region of the accretion flow as a hot, geometrically thick ADAF disc, with the outer radius equal to the shock formation radius located just outside the centrifugal barrier. Using a Fourier-transformed, vertically-averaged transport equation in cylindrical coordinates, we analyze the time-dependent radiative transfer in the inner ADAF region and simulate the X-ray time lag data. We then compare the simulated time lags to the observed time lags for model fitting. Our new model successfully reproduces the complex X-ray variability data for the Seyfert 1 galaxies 1H 0707-495 and Ark 564. |
Aminabi Thekkoth - "Unprecedented Outburst in 4C 31.03: Exploring variability and multi-wavelength spectral properties."
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| Abstract: The blazar 4C 31.03 has bee reported by Fermi-LAT for exhibiting a major 𝛾- ray outburst at the beginning of 2023 after a prolonged quiescent phase. We performed a comprehensive study of this extraordinary outbreak in temporal and multi-wavelength aspects. From the statistical analysis of the 𝛾gamma-ray lightcurves using Bayesian blocks, we identified 3 epochs of prominent flares. The variability analysis performed using a 12 hour binned 𝛾gamma-ray lightcurve resulted the shortest timescale of 5.453 hours. The highest energy of gamma-ray photons found from the source during the active phase is ∼ 82 GeV. Subsequently, using the transparency of gamma-rays against pair production and light crossing time argument, we could obtain the minimum jet Doppler factor as ∼ 17 and the upper limit on emission region size to be∼1016cm. The broadband spectral energy distribution study performed using synchrotron, SSC and EC emission processes supports the external Compton scattering of IR photons as the likely mechanism for the 𝛾gamma-ray emission from the source. The results of our analysis support the scenario of the emission site in 4C 31.03, being located beyond the Broad line region from the central black-hole. The long-term 𝛾gamma-ray flux distribution depicts a double log-normal variability, indicating that two distinct flux states are active in this energy band. The index distribution also reveals a two distinct variability pattern and hints that the 𝛾gamma-ray spectrum can be more precisely described by two photon indices. |
Krishna Teja Vedula - "Study of Blazar Polarization in Gamma Rays with COSI"
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| Abstract: The Compton Spectrometer and Imager (COSI) Mission, slated for launch in 2027 is focused on bridging the MeV gap in gamma-ray observations. COSI employs innovative polarimetric data collection methods using Compton scattering which puts it in a very unique position in addressing the challenging MeV range. The cutting-edge technology and analytical tools employed by COSI, including MEGAlib and Python-based frameworks which are being built on the same principles and frameworks as the Fermi Tools, underscore its potential to revolutionize the understanding of blazars, contributing to the elucidation of particle acceleration mechanisms, magnetic field order, and turbulence in extragalactic gamma-ray objects. Preliminary blazar analyses for COSI depend upon spectra from the Fermi mission. |
Wednesday, June 5
Adithiya Dinesh - "A systematic search for extreme gamma-ray blazars using Fermi-LAT"
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| Abstract: Blazars are active galactic nuclei with relativistic jets pointing towards our line of sight. These sources are the most powerful persistent gamma-ray emitters in the Universe, and can be classified by the frequency of their synchrotron peak emission from low to extreme synchrotron peak blazars at frequencies larger than 10 is an ongoing observational challenge in gamma-ray astrophysics. In this pioneering search, we will systematically look for the most extreme of these blazars, by finding a transition between a synchrotron peak and the inverse Compton region that could lie at the GeV energy range, where the Large Area Telescope on board the Fermi Gamma-ray Space Telescope is most sensitive. Our results will allows us to understand the recurrence, time-scales, and energetics of these events, which are expected to happen in flares, and their role in the blazar sequence. |
Laenita De Jonge - "Study of the hadronic synchrotron mirror model for orphan flares in blazars - Application to 3C279"
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| Abstract: Blazars are a class of Active Galactic Nuclei (AGN), found in the centres of elliptical galaxies, that are radio loud and have a small angle between the jet and the observer’s line of sight. In some cases, flaring events in one frequency band are not accompanied by flaring in other bands. Such events are called orphan flares. The causes of this variability and conditions in and location of the high energy emission region are not completely understood. As a possible explanation for rapid orphan gamma-ray variability, the hadronic synchrotron mirror model has been suggested in previous work. A TeV orphan flare was observed on the 28th of January 2018 by the H.E.S.S. observatory from 3C 279. A primary flare was observed 11 days earlier by Fermi-LAT. The hadronic synchrotron mirror model, is applied to this flare. A study is done using the SED and multi-wavelength light curve results to see which parameters provide the best fit and to draw conclusions about the radiation mechanism that caused this orphan flare. A search for neutrino emission is also conducted to establish if orphan flares are a possible source. |
Paolo Cristarella Orestano - "Study of Periodicity in Blazar Light Curves"
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| Abstract: Long term periodicity in gamma-ray Blazar light curves could be linked to the innermost zone of the complex structure of AGN, like possible presence of binary system of supermassive black holes, or it could shed light on the origin of gamma-rays emission. The work analyses 1525 sources, whose 14 years light curves come from the Fermi LAT Light Curve Repository (LCR), making use of Lomb-Scargle Periodogram (LSP) and wavelet weighted Z transform (WWZ), to express the significance we performed simulations using the Emmanoulopoulos algorithm. All the available possibilities for the light curves in the LCR, such as different temporal samplings and the use of photon flux and energy flux, are taken into account in order to ensure more reliable results. We found out high significance periodicity in less than 1% of the sources considered, and in few other sources hints of possible periodicity. Our results are compliant with the findings of recent literature focused on searches of periodic modulation in AGNs. |
Olive Zhang - "Search for anisotropic pair halos associated with blazar jets"
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| Abstract: Magnetic fields found in the galaxies are believed to grow from weaker “seed” fields whose origin is still unknown. The weaker “seed” fields might be preserved in the interstellar medium. However, its strength is too weak to be measured by traditional methods such as the Faraday rotation and Zeeman effect. Pair halos around the blazar jets might provide a way to measure the strength of the intergalactic magnetic field (IGMF). Because the IGMFs deflect the charged particles produced by TeV photons emitted by the blazars, extended GeV gamma-rays will develop around the projected jet direction. We propose to use Fermi-LAT data to look at certain high-synchrotron-peaked BL lacs (HBLs) and intermediate-synchrotron-peaked BL Lacs (IBLs) objects and search for any anisotropic pair halos. |
Thursday, June 6
Eliza Neights - "Studying GRBs Using COSI"
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| Abstract: Gamma-ray bursts (GRBs) are energetic phenomena that serve as probes for extreme physics, but their emission mechanisms, jet geometry, and magnetic field structure are not well understood and require new detection capabilities. The Compton Spectrometer and Imager (COSI) is a gamma-ray space telescope set to launch in 2027 that aims to further our understanding of GRBs, in addition to studying positron annihilation and nucleosynthesis in the Galaxy. COSI’s wide field-of-view, excellent energy resolution, sub-degree localizations, and polarization capabilities may reveal insight into GRB prompt emission. In this presentation, I will give a brief overview of the COSI mission and discuss the GRB science it enables. |
Cuán de Barra - "GIFTS (Gamma-Ray Investigation of the Full Transient Sky)"
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| Abstract: Gravitational waves were detected in 2015 for the first time. In 2017, gravitational waves from a binary neutron star merger were detected in coincidence with a gamma-ray burst (GRB) confirming that some short events are produced by mergers. The multi-messenger astrophysics era began, and the discovery highlighted the importance of space missions to detect and localise bursts at a time when gravitational wave systems are becoming more sensitive to merger events. Currently there is a lack of large future gamma-ray missions to enable similar measurements and scientific discovery. Consequently we propose to build Gamma-ray Investigation of the Full Transient Sky (GIFTS), a novel 6U CubeSat, which has been designed, prototyped and demonstrated previous work by the PI. The proposed design is based on detailed in-house instrument development and on the gamma-ray detector in the 2U CubeSat EIRSAT-1 which launched in 2023. GIFTS will comprise six gamma-ray detectors and will detect and localise 70 GRBs per year including 11 short GRBs. Detailed design and simulations demonstrate it will detect up to 2 GRBs per year coincident with GW detections. We will build and prepare GIFTS for operation when GW detectors reach peak sensitivity. |
Zoe Brisson-Tsavoussis - 1-slide
Ieva Jankute - 1-slide
Group Photos
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