Swiss CTA Day 2020

Tuesday 24 Nov 2020, 09:00 → 20:35 Europe/Zurich

Building on the technology of the current generation ground-based high-energy gamma-ray telescopes, the Cherenkov Telescope Array Observatory (CTAO), made of about 100 telescopes located in La Palma and in Chile, will be ten times more sensitive than current instruments and have unprecedented energy coverage and accuracy. The CTAO will be the first ground-based gamma-ray observatory open to the worldwide scientific community.

Swiss scientists are members of the Cherenkov Telescope Array Consortium since 2006. The University of Geneva is a shareholder of the Cherenkov Telescope Array Observatory gGmbH, representing the Swiss interest. 

The countries participating in CTA are currently in the process of establishing the CTAO European Research Infrastructure Consortium (CTAO ERIC) which will construct, commission and operate CTA for an intended period of 30 years.

In preparation for the positioning of Switzerland in the CTAO ERIC, we are pleased to invite you to participate to the Swiss CTA Day 2020, where we will discuss the status of the project, the ambitions of Switzerland in this endeavour and the Science.

The science talks of this meeting will present the result of working groups discussions fostering scientific exchange between non members and members of the CTA project.

Poster contributions are also encouraged. An on-line poster (2 min talk) will be organised during the lunch break.

Following  the latest federal COVID-19 ordinance and the Geneva state rules, the meeting with be held remotely on https://unige.zoom.us/j/95762716052

Poster.pdf

09:15 → 11:00 Introduction to the CTA Project and the Swiss Landscape: The CTA Project

Convener: Dr Roland Walter (University of Geneva)

09:15 Scope of the Meeting

Speaker: Prof. Teresa Montaruli (Universite de Geneve (CH))

09:20 CTA at the Départment de Physique Nucléaire et Corpusculaire

Speaker: Prof. Federico Sanchez (Universite de Geneve (CH))

CTA_DPNC.key

CTA_DPNC.pdf

09:30 CTA at Départment d'Astronomie

Speaker: Prof. Stéphane Paltani (Université de Genève)

2020-11-24-Swiss CTA days_SPaltani.pdf

09:40 Welcome: the role of the University of Geneva in CTA

Speaker: Prof. Brigitte Galliot (ViceRector UNIGE)

09:55 SERI remarks

Speaker: Dr Kevin Reymond

10:10 Status of the Cherenkov Telescope Array Observatory (CTAO)

CTAO Managing Director

Speaker: Prof. Federico Ferrini (INFN Sezione di Pisa (INFN))

Slides CH.pdf

10:35 CTA key science projects

Spokesperson of CTAC

Speaker: Prof. Werner Hofmann (Max Planck Institut für Kernphysik)

2020_11_CTA_KSP_Swiss_Day.pdf

11:00 → 11:20 Coffee Break

11:20 → 13:05 CTA in Switzerland: The Swiss Landscape

Convener: Prof. Stéphane Paltani (Université de Genève)

11:20 The CTA Large Size Telescope project (LST)

Spokesperson of LST

Speaker: Prof. Masahiro Teshima (Max-Planck-Institute for Physics)

2020_1124_LST_SWISS.pdf

2020_1124_LST_SWISS.pptx

11:45 Inheritance of gamma-ray astronomy in Switzerland

Speaker: Prof. Adrian Biland (Eidgenossische Technische Hochschule Zurich/ETH (ETH))

SwissCTAday_Biland2.pdf

12:05 Swiss Contributions to CTA

Speaker: Prof. Teresa Montaruli (Universite de Geneve (CH))

CTA_CH_DAY_Montaruli.pdf

12:25 Technology expertise for CTA in Switzerland

Speaker: Prof. Edoardo Charbon (EPFL)

CTA November 24 2020 Charbon_v3_compressed.pdf

12:45 Why CTA matters and its computing challenges

Speaker: Roland Walter (University of Geneva)

2020 CTA Day.pdf

13:10 → 13:50 Poster Lunch: 2 minutes presentations

There will be 2 minutes for each poster and questions. Poster presentation will be registered and has to be posted.

Convener: Dr Matthieu Heller (Universite de Geneve (CH))

13:10 The Single Mirror Small-Sized Telescope project

In this work we present the status of the Single Mirror Small-Sized Telescope project: its design, previous observation campaigns, simulation results and future.

Speakers: Matthieu Heller (Universite de Geneve (CH)), Andrii Nagai (Universite de Geneve (CH)), Cyril Martin Alispach (Universite de Geneve (CH)), Domenico Della Volpe (Universitè de Genève), Etienne Lyard (University of Geneva), Matteo Balbo (Université de Genève), Roland Walter (University of Geneva), Teresa Montaruli (Universite de Geneve (CH)), Dr Vitalii Sliusar (University of Geneva)

CTASwissDays_Pitch_SST1M.pdf

CTASwissDays_Poster_SST1MProject.pdf

13:13 Multi-messenger searches of neutrino sources driven by gamma-ray observations

After more than 100 years since their discovery, cosmic rays (CRs) are still one of the most intriguing open questions in astrophysics. Intrinsic difficulties are unavoidable when trying to identify the sites of production and acceleration of these charged particles due to the magnetic deflections they undergo when travelling across galactic and extragalactic distances. However, in the era of multimessenger astrophysics, hints of a cosmic accelerator might come from the detection of high-energy $\gamma$ rays and/or neutrinos that are expected to be produced by the interactions of CRs with the ambient matter and radiation in the vicinity of a potential source. IceCube, the largest neutrino telescope ever built, provided some years ago the most emblematic and fruitful example of synergy between $\gamma$-rays and astrophysical neutrinos in the identification of a potential source of CRs. A high-energy neutrino alert detected from a restricted region of the sky, compatible with the location of the known blazar TXS 0506+056, triggered a follow-up of several $\gamma$-ray experiments that observed an enriched activity from the same location and coincident with the neutrino event. Additionally, an analysis of the data at the same location but prior to the alert time revealed a prominent neutrino flare in 2014/2015. Recently, IceCube has also presented an evidence at $3.3\sigma$-level of a time-integrated neutrino excess from four sources in a catalog of astrophysical objects selected on the basis of $\gamma$-ray observations. Such an excess is due to the Seyfert galaxy NGC 1068 (also reported as the most significant northern spot in a time-integrated all-sky search), the aforementioned blazar TXS 0506+056 and the BL Lacs PKS 1424+240 and GB6 J1542+6129. A subsequent time-dependent investigation of the same catalog confirmed the neutrino excess and provided interesting results at the location of M87, the most significant time-dependent source of the catalog and a well known emitter of ultra-relativistic jets of particles, recently popular also for the first picture of the black hole at its center. Gamma-ray experiments are expected to provide attractive insights in the following years: in particular, with a sensitivity that is 10 times better than any existing gamma-ray instrument and reaching energies up to 300 TeV, the Cherenkov Telescope Array project and its multi-messenger program might unveil new potential neutrino sources and help to reveal the origin of ultra high-energy cosmic rays.

Speakers: Francesco Lucarelli (Universite de Geneve (CH)), Teresa Montaruli

Poster_Multi-messenger_searches_of_neutrino_sources_driven_by_gamma-ray_observations.pdf

Slides_Multi-messenger_searches_of_neutrino_sources_driven_by_gamma-ray_observations.pdf

13:16 Search for dark matter annihilation in the dwarf irregular galaxy WLM with H.E.S.S.

We search for an indirect signal of dark matter through high-energy γ rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would produce Standard Model particles in the final state such as γ rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. five-telescope array observed the dwarf irregular galaxy WLM for 18 hours. These observations are the very first ones made by an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant signal excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation 〈σv〉 as a function of the darkmatter particle mass for various continuum channels as well as the prompt emission γγ. For the τ+τ− channel the limits reach a value of 〈σv〉 = 4×10−22 cm3 s−1 for a dark matter particle mass of 1 TeV. For the prompt γγ channel, the upper limit reaches a value of 〈σv〉 = 5×10−24 cm3 s−1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200 with respect to previous results for the dwarf irregular galaxies for TeV dark matter search.

Speakers: Celine Armand (LAPTh), Vincent Poireau (Laboratoire d'Annecy-le-Vieux de Physique des Particules (LAPP)), Emmanuel Moulin (CEA Saclay), Lucia Rinchiuso (CEA Saclay)

WLM_poster_2020.pdf

13:19 The CTA Multi-messenger and multi-wavelength program

The Cherenkov Telescope Array (CTA) will allow observations in the >10 GeV range with unprecedented photon statistics and sensitivity to investigate the yet-unexplored physics of short-time-scale transient events. The CTA Transient program includes follow-up observations of a wide range of multi-wavelength and multi-messenger alerts, ranging from Galactic compact object binary systems to extragalactic events such as GRBs. In recent years, the proven connection between gravitational waves and short GRBs as well as the detection of VHE signal associated to GRB and the possible neutrino-blazar association on TXS 0506+056 has shown the importance of coordinated follow-up observations triggered by these different cosmic signals. In the next years, CTA will play a major role in this type of observations by taking advantage of its fast slewing (for LSTs), large effective area and good sensitivity, opening new opportunities for time-domain astrophysics in an energy range not affected by selective absorption processes typical of other wavelengths.

Speakers: Alessandro Carosi (Universite de Geneve (CH)), Francesco Longo (Univ. + INFN)

CTAMMessengerProgram_Carosi_v5.pdf

CTAMMessengerProgram_slides_carosi.pdf

13:22 Transient Handler for the LST-1 prototype

In 2019, the first firm detection of a very high energy (VHE, E>100 GeV) emission component from Gamma-ray Bursts (GRBs) has definitely opened a new observational window for the study of those enigmatic transient events.These discoveries did not arrive unexpectedly but they represent the result of a 20-years-long-lasting hunt by the major Cherenkov telescope collaborations. Furthermore, the recently discovered high-energy neutrinos and gravitational waves from astrophysical sources have opened the era of the so-called multi-messenger astrophysics. The proven connection between gravitational waves and short GRBs has shown the importance of coordinated follow-up observations triggered by different cosmic signals. However, the unpredictable nature of the transient sky makes it difficult for the large ground-based IACTs to point and start follow-up of these sources rapidly enough to catch their early emission phase(s). The instrument response to external triggers (GRB and multi-messenger transients) relies on a dedicated transient handler. In this contribution , I will report about the first implementation of transient handler within the LST-1 framework.

Speaker: Alessandro Carosi (Universite de Geneve (CH))

LST_TransientHandler_Carosi_v4.pdf

LST_TransientHandler_slides_carosi.pdf

13:26 Neural Networks for the Gamma/Hadron Separation of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be the largest ground-based gamma-ray observatory. CTA will detect the signature of gamma rays and cosmic
rays hadrons and electrons interacting with the Earth’s atmosphere. Making the best possible use of this facility requires to be able to separate events
generated by gamma rays from the particle-induced background. Deep neural networks produced encouraging results, but so far there has been no
evaluation of their performance for gamma/hadron separation with respect to well established approaches. In this paper we compare convolutional neural
networks and a standard analysis technique, namely boosted decision trees. We compare the performance of the two techniques as applied to simulated
observation data. We then looked at the Receiver Operating Characteristics (ROC) curves produced by the two approaches and discuss the similarities
and differences between both.

Speakers: Etienne Lyard (University of Geneva), Nicolas Produit (Universite de Geneve (CH)), Roland Walter (University of Geneva), Vitalii Sliusar (University of Geneva)

Poster_ACAT2019_326.pdf

Slides_Swiss_CTA_day_2020_lyard.pdf

13:29 LST-1 telescope performance and preliminary data analysis

Large Size Telescope (LST) is the biggest from three main telescope types of CTA. Both CTA sites shall be equipped with four LSTs, located in the middle of each array. Having the largest reflector of 23 m diameter, the LSTs will lower the energy threshold of the whole observatory down to about 20 GeV and will be crucial for the CTA sensitivity from that energy up to about 200 GeV. As the first telescope for CTA, a fully equipped LST-1 was installed and inaugurated at the CTA-N site in October 2018.

We present a performance estimation of the LST-1 prototype located at La Palma together with a preliminary analysis of the data from the first and second Crab observation campaigns conducted during the author’s stay at Institut de Fisica d’Altes Energies (IFAE) of Universitat Autònoma de Barcelona in the cooperation with members of the LST Consortium.

Speaker: Jakub Jurysek (Institute of Physics, ASCR)

slides_lst.pdf

SwissCTA_lst1_jurysek_v3.pdf

13:32 Trigger rate studies with LST-1 prototype

In-depth analysis and comparison of simulated and observed trigger rates provides a good verification on the correctness of the telescope simulation. Presented method uses the full simulation of cosmic rays induced showers with the large size telescope prototype (LST-1) which is installed at the Roque de los Muchachos Observatory, La Palma, Spain. It compliments the results obtained with the analysis of detected muons. Good agreement achieved through entire range of scanned trigger threshold points.

Speaker: Dr Mykhailo Dalchenko (University of Geneva)

SwissCTA_LST-1_trigger_slides.pdf

SwissCTA_poster_LST-1_trigger_dalchenko_nagai.pdf

13:35 An alternative way to monitor telescope pointing: application to LST-1

The first prototype of the Large Size Telescopes (LST) proposed for the forthcoming Cherenkov Telescope Array (CTA) has recently started to operate in La Palma and is finalizing its commissioning period. The large structure of LST-1 (24 m diameter mirror) imposes a strict control of the telescope bending and deformations that could affect the pointing accuracy and its overall performances. According to CTA specifications, LST pointing accuracy should be better than 14 arcseconds. To achieve this, the LST-1 pointing accuracy is monitored by means of dedicated devices, for example a starguider camera and a Camera Displacement Monitor. In this work, we propose an alternative approach by using the stars that are naturally present in the field of view during observations. By cleaning from the Cherenkov showers the events registered by the camera, it is possible to obtain a picture of the sky at the pointed direction. The reconstructed positions of the stars in the field of view can be compared to their nominal expected position, providing a direct measurement of the mispointing of the telescope.

Speakers: Dr Luca Foffano (Universite de Geneve (CH)), Alessandro Carosi (Universite de Geneve (CH))

Foffano_Carosi_CTA_Swiss_day_approved.pdf

LucaFoffano_poster_presentation_slides.pdf

13:38 IACT image reconstruction using a spatio-temporal likelihood for LST

Imaging Atmospheric Cherenkov Telescopes (IACTs) collect the Cherenkov light emitted in Extensive Air Showers (EASs) from highly energetic particles in the atmosphere. One of the main challenges of IACT based astronomy is to discriminate between images from very high energy photons and other particles, mainly protons, and to identify the energy and direction of the primary photons. Here, an innovative method using the maximization of a likelihood function describing the spatial and temporal distributions of the signal in the camera is presented. It allows propagating the calibration parameters in the extraction of the image parameters. These parameters are used to estimate the gammaness of the event, the energy, and the arrival direction of the photon.

Speakers: Cyril Martin Alispach (Universite de Geneve (CH)), Gabriel Emery (Universite de Geneve (CH))

2min_slides.pdf

SwissCTA_Poster_LHfit.pdf

13:41 Long-term multi-wavelength analysis Mrk 421 variability

We are using the longest and densest unbiased observing campaign obtained at TeV and GeV energies during 5.5 years with the FACT telescope and the Fermi LAT detector together with contemporaneous multi-wavelength observations to characterize the variability of the source and constrain the underlying physical mechanisms. We study and correlate light curves obtained by ten different instruments and found two significant results. The TeV and X-ray light curves are very well correlated with a \textbf{lag $<0.6$ day}. The GeV light curve accurately leads the variations observed at long wavelengths and in particular in the radio band by 43 days with a broad response.

Speaker: Dr Vitalii Sliusar (University of Geneva)

Mrk_421_Poster.pdf

V.Sliusar_Mrk421_CTA_Swiss_Day_slides.pdf

13:44 A Mini-Imaging Air Cherenkov Telescope

In this work we present the design and realization of a mini-telescope based on the optical module of the SST-1M project. The result of the observation campaign in the St Luc Observatory will also be presented.

Speakers: Matthieu Heller (Universite de Geneve (CH)), Andrii Neronov (Universite de Geneve (CH)), Theodore Njoh Ekoume (Universite de Geneve (CH)), Domenico Della Volpe (Universitè de Genève), Teresa Montaruli (Universite de Geneve (CH))

CTASwissDays_Poster_MiniCamera.pdf

13:47 Towards a polarization prediction for LISA via intensity interferometry

Compact Galactic binary systems with orbital periods of a few hours are expected to be detected in gravitational waves (GW) by LISA or a similar mission. At present, these so-called verification binaries provide predictions for GW frequency and amplitude. A full polarisation prediction would provide a new method to calibrate LISA and other GW observatories, but requires resolving the orientation of the binary on the sky, which is not currently possible. We suggest a method to determine the elusive binary orientation and hence predict the GW polarisation, using km-scale optical intensity interferometry. The most promising candidate is CD–30◦ 11223, consisting of a hot helium subdwarf with 𝑚𝐵 = 12 and a much fainter white dwarf companion, in a nearly edge-on orbit with period 70.5 min. We estimate that the brighter star is tidally stretched by 6%. Resolving the tidal stretching would provide the binary orientation. The resolution needed is far beyond any current instrument, but not beyond current technology. We consider scenarios where an array of telescopes with km- scale baselines and/or the Very Large Telescope (VLT) and Extremely Large Telescope (ELT) are equipped with recently-developed kilo-pixel sub-ns single-photon counters and used for intensity interferometry. We estimate that a team-up of the VLT and ELT could measure the orientation to ±1◦ at 2𝜎 confidence in 24 hours of observation.

Speaker: Mr Benno Neuenschwander

cta_poster.pdf

ezgif.com-gif-maker.gif

14:00 → 15:15 CTA Science - The Galaxy

Convener: Prof. Thierry Courvoisier (University of Geneva)

14:00 Fundamental Physics and Dark Matter searches with CTA

Speakers: Dr Alexey Boyarsky (EPFL), Prof. Andrii Neronov (APC and University of Geneva)

CTA_day_Boyarsky.pdf

CTA_fundamental_neronov1.pdf

14:30 Galactic Sources

Speakers: Matteo Balbo (Université de Genève), Dr Mitchell Alison (University of Zurich)

Galactic_Sources_Mitchell_Balbo.pdf

14:55 Cosmic Rays & Positrons

Speaker: Prof. Xin Wu (University of Geneva)

SwissCTAday_Nov2020_Wu.pdf

SwissCTAday_Nov2020_Wu.pptx

15:15 → 15:35 Coffe Break

15:35 → 17:20 CTA Science - The extragalactic space

This session is divided into two parts, one mostly on the Galaxy and the other on the extragalactic space

Convener: Prof. Xin Wu (Universite de Geneve (CH))

15:35 The expansion of the Universe and what do we learn from CTA

Speaker: Prof. Jean-Paul Kneib (EPFL)

cta_cosmo2020nov24_jpkneib.pdf

15:55 Multi-messenger Astrophysics with CTA

Speaker: Dr Volodymyr Savchenko (University of Geneva)

Slides

16:15 Relativistic Jets with CTA

Speaker: Dr Andrea Tramacere (University of Geneva)

CTA_relativistic_jets_Tramacere.pdf

16:35 Stellar intensity Interferometry with CTA

Speaker: Prof. Prasenjit Saha (Universität Zürich)

Stellar Intensity Interferometry with the CTA

16:55 Wrap up and Discussion