ABSTRACT
fink is a broker designed to enable science with large time-domain alert streams such as the one from the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). It ...exhibits traditional astronomy broker features such as automatized ingestion, annotation, selection, and redistribution of promising alerts for transient science. It is also designed to go beyond traditional broker features by providing real-time transient classification that is continuously improved by using state-of-the-art deep learning and adaptive learning techniques. These evolving added values will enable more accurate scientific output from LSST photometric data for diverse science cases while also leading to a higher incidence of new discoveries which shall accompany the evolution of the survey. In this paper, we introduce fink, its science motivation, architecture, and current status including first science verification cases using the Zwicky Transient Facility alert stream.
ABSTRACT
The observation of the transient sky through a multitude of astrophysical messengers has led to several scientific breakthroughs in the last two decades, thanks to the fast evolution of the ...observational techniques and strategies employed by the astronomers. Now, it requires to be able to coordinate multiwavelength and multimessenger follow-up campaigns with instruments both in space and on ground jointly capable of scanning a large fraction of the sky with a high-imaging cadency and duty cycle. In the optical domain, the key challenge of the wide field-of-view telescopes covering tens to hundreds of square degrees is to deal with the detection, identification, and classification of hundreds to thousands of optical transient (OT) candidates every night in a reasonable amount of time. In the last decade, new automated tools based on machine learning approaches have been developed to perform those tasks with a low computing time and a high classification efficiency. In this paper, we present an efficient classification method using convolutional neural networks (CNNs) to discard many common types of bogus falsely detected in astrophysical images in the optical domain. We designed this tool to improve the performances of the OT detection pipeline of the Ground Wide field Angle Cameras (GWAC) telescopes, a network of robotic telescopes aiming at monitoring the OT sky down to R = 16 with a 15 s imaging cadency. We applied our trained CNN classifier on a sample of 1472 GWAC OT candidates detected by the real-time detection pipeline.
We used the TAROT network of telescopes to search for the electromagnetic counterparts of GW150914, GW170104 and GW170814, which were reported to originate from binary black hole merger events by the ...LIGO and Virgo collaborations. Our goal is to constrain the emission from a binary black hole coalescence at visible wavelengths. We developed a simple and effective algorithm to detect new sources by matching the image data with the Gaia catalog data release 1. Machine learning was used and an algorithm was designed to locate unknown sources in a large field of view image. The angular distance between objects in the image and in the catalog was used to find new sources; we then process the candidates to validate them as possible new unknown celestial objects. Though several possible candidates were detected in the three gravitational wave source error boxes studied, none of them were confirmed as a viable counterpart. The algorithm was effective for the identification of unknown candidates in a very large field and provided candidates for GW150914, GW170104 and GW170814. The entire 90% GW170814 error box was surveyed extensively within 0.6 days after the GW emission resulting in an absolute limiting R magnitude of-23.8. This strong limit excludes to a great extent a possible emission of a gamma-ray burst with an optical counterpart associated with GW170814.
Abstract
We present detailed ultraviolet, optical, and near-infrared light curves of the Type Ia supernova (SN) 2012fr, which exploded in the Fornax cluster member NGC 1365. These precise ...high-cadence light curves provide a dense coverage of the flux evolution from −12 to +140 days with respect to the epoch of
B
-band maximum (
t
B
max
). Supplementary imaging at the earliest epochs reveals an initial slow and nearly linear rise in luminosity with a duration of ∼2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of
56
Ni mixing in the ejecta. From our analysis of the light curves, we conclude that: (i) the explosion occurred <22 hr before the first detection of the supernova, (ii) the rise time to peak bolometric (
λ
> 1800 Å) luminosity was 16.5 ± 0.6 days, (iii) the supernova suffered little or no host-galaxy dust reddening, (iv) the peak luminosity in both the optical and near-infrared was consistent with the bright end of normal Type Ia diversity, and (v) 0.60 ± 0.15
M
⊙
of
56
Ni was synthesized in the explosion. Despite its normal luminosity, SN 2012fr displayed unusually prevalent high-velocity Ca
ii
and Si
ii
absorption features, and a nearly constant photospheric velocity of the Si
ii
λ
6355 line at ∼12,000
km
s
−
1
that began ∼5 days before
t
B
max
. We also highlight some of the other peculiarities in the early phase photometry and the spectral evolution. SN 2012fr also adds to a growing number of Type Ia supernovae that are hosted by galaxies with direct Cepheid distance measurements.
Abstract
The Ground Wide Angle Camera Network (GWAC-N) is a network of robotic multi-aperture, multiple field-of-view (FoV) optical telescopes. The main contingent of GWAC-N instruments are provided ...by the Ground Wide Angle Cameras Array (GWAC-A), and additional, narrower FoV telescopes are utilized to provide fast multi-band follow-up capabilities. The primary scientific goal of the GWAC-N is to search for optical counterparts of gamma-ray bursts that will be detected by the Space Variable Object Monitor (SVOM) satellite. The GWAC-N performs many additional observing tasks including follow-up of Target of Opportunities (ToO) targets and the detection (and monitoring) of variable objects and optical transients. To handle these use cases (and to allow for extensibility), we have designed ten observation modes and 175 observation strategies, including a joint strategy with multiple GWAC-N telescopes for the follow-up of gravitational wave (GW) events. To perform these observations, we develop an Automatic Observation Management (AOM) system capable of performing object management, dynamic scheduling, automatic broadcasting across the network, and image handling. The AOM system combines the individual telescopes which comprise the GWAC-N into a network and smoothly organizes all associated operations, completely meeting the requirements dictated by GWAC-N. With its modular design, the AOM is scientifically and technically viable for other general-purpose telescope networks. As the GWAC-N extends and evolves, the AOM will greatly enhance its discovery potential. In this first paper of a series, we present the scientific goals of the GWAC-N and detail the hardware, software, and workflow developed to achieve these goals. The structure, technical design, implementation, and performance of the AOM system are also described in detail. We conclude with a summary of the current status of the GWAC-N and our near-future development plan.
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The transition from prompt to afterglow emission is one of the most exciting and least understood phases in gamma-ray bursts (GRBs). Correlations among optical, X-ray, and gamma-ray emission in GRBs ...have been explored, to attempt to answer whether the earliest optical emission comes from internal and/or external shocks. We present optical photometric observations of GRB 180325A collected with the TAROT and RATIR ground-based telescopes. These observations show two strong optical flashes with separate peaks at ∼50 and ∼120 s, followed by a temporally extended optical emission. We also present X-rays and gamma-ray observations of GRB 180325A, detected by the Burst Alert Telescope and X-ray Telescope, on the Neil Gehrels Swift observatory, which both observed a narrow flash at ∼80 s. We show that the prompt gamma-ray and X-ray early emission shares similar temporal and spectral features consistent with internal dissipation within the relativistic outflow (e.g., by internal shocks or magnetic reconnection), while the early optical flashes are likely generated by the reverse shock that decelerates the ejecta as it sweeps up the external medium.
The Ground Wide Angle Camera Network (GWAC-N) is a network of robotic multi-aperture, multiple field-of-view (FoV) optical telescopes. The main contingent of GWAC-N instruments are provided by the ...Ground Wide Angle Cameras Array (GWAC-A), and additional, narrower FoV telescopes are utilized to provide fast multi-band follow-up capabilities. The primary scientific goal of the GWAC-N is to search for optical counterparts of gamma-ray bursts that will be detected by the Space Variable Object Monitor (SVOM) satellite. The GWAC-N performs many additional observing tasks including follow-up of Target of Opportunities (ToO) targets and the detection (and monitoring) of variable objects and optical transients. To handle these use cases (and to allow for extensibility), we have designed ten observation modes and 175 observation strategies, including a joint strategy with multiple GWAC-N telescopes for the follow-up of gravitational wave (GW) events. To perform these observations, we develop an Automatic Observation Management (AOM) system capable of performing object management, dynamic scheduling, automatic broadcasting across the network, and image handling. The AOM system combines the individual telescopes which comprise the GWAC-N into a network and smoothly organizes all associated operations, completely meeting the requirements dictated by GWAC-N. With its modular design, the AOM is scientifically and technically viable for other general-purpose telescope networks. As the GWAC-N extends and evolves, the AOM will greatly enhance its discovery potential. In this first paper of a series, we present the scientific goals of the GWAC-N and detail the hardware, software, and workflow developed to achieve these goals. The structure, technical design, implementation, and performance of the AOM system are also described in detail. We conclude with a summary of the current status of the GWAC-N and our near-future development plan.
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BFBNIB, NMLJ, NUK, PNG, UL, UM, UPUK
L'Univers est continûement le théâtre d'événements explosifs capables de relâcher une énorme quantité d'énergie sur des courtes échelles de temps. Ces sources transitoires comme les sursauts gamma, ...les supernovae ou les noyaux actifs de galaxie sont souvent associées à des objets extrêmes comme des étoiles à neutrons ou des trous noirs. De manière générale, ces sources émettent des radiations électromagnétiques dans une large bande spectrale voire sur la totalité du spectre pour les cas les plus extrêmes. Dès lors, une analyse multi-longueur d'onde est vitale pour étudier et comprendre la physique complexe de ces objets. De plus, au voisinage de ces sources, des particules (rayons cosmiques, RC) pourraient être efficacement accélérées jusqu'à des énergies très elevées dans des processus de chocs violents. L'interaction de ces RCs avec l'environnement peut conduire à la production d'un nombre significatif de neutrinos de hautes énergies. Par conséquent, l'étude des objets transitoires par le biais de l'astronomie neutrino offre la possibilité d'identifier enfin la nature des puissants accélérateurs cosmiques.Cette thèse est dédiée à l'étude de deux sources transitoires parmi les plus extrêmes dans l'Univers : les sursauts gamma (en anglais, Gamma-Ray Bursts : GRBs) détectés il y a ~ 50 ans et les sursauts radio (en anglais, Fast Radio Bursts : FRBs) fraîchement découverts il y a ~ 15 ans. Ces sources sont caractérisées par l'émission "prompte" d'un flash gamma (keV-MeV) durant de quelques ms à plusieurs secondes dans le cadre des GRBs et d'un flash intense en radio (GHz) durant quelques ms pour les FRBs. Dans le cas des GRBs une émission rémanente dite "afterglow" est observée dans une large gamme spectrale (X, visible et radio) alors que jusqu'à présent aucune autre contrepartie électromagnétique provenant d'un FRB n'a été découverte. Ces dernières années des modèles d'émission multi-longueur d'onde et multi-messager ont été développés afin d'expliquer ces 2 phénomènes. L'objectif majeur de ce travail de thèse est de tester ces modèles d'émission afin de contraindre la physique et la nature de ces deux objets. Pour cela, une analyse détaillée des propriétés physiques de l'émission afterglow des GRBs a été menée grâce à un large échantillon de données collectées ces 20 dernières années par diverses télescopes. Cette étude a permis de mettre en évidence les lacunes et les réussites du modèle GRB dit "standard" mais aussi les liens physiques subtils existant entre l'émission prompte des GRBs et leurs rémanences. Une recherche de signal neutrino en coïncidence avec les GRBs/FRBs a aussi été réalisée avec le télescope à neutrinos ANTARES. Les résultats sont décrits dans cette thèse ainsi que les contraintes apportées sur les processus d'accélération des particules durant ces phénomènes transitoires. Enfin, ce manuscrit rend compte des différents programmes d'observations innovants qui ont été engagés sur les télescopes optiques TAROT et Zadko et le télescope à neutrinos ANTARES afin de contraindre la nature des progéniteurs des GRBs/FRBs.
The Universe is continuously the scene of explosive events capable of releasing a tremendous amount of energy in short time scales. These transients like Gamma-Ray Bursts, Supernovae or Active Galactic Nuclei are often associated with extreme objects such as neutron stars or black holes. Generally, these sources emit light in a large spectral energy range and sometimes in the whole electromagnetic spectrum for the most extreme cases. Thus, a multi-wavelength analysis is crucial to study and understand the complex physical processes at work. Furthermore, in the vicinity of these sources, particles (cosmic-rays, CRs) could be efficiently accelerated up to very high energies by violent shock mecanisms. The interaction of these CRs with the surrounding environment may lead to a substantial production of high-energy neutrinos. Therefore, the study of the high-energy transient objects through neutrino astronomy offer the possibility to finally identify the nature of the powerful cosmic accelerators a hundred year after the discovery of the cosmic-rays.This thesis is dedicated to the study of two transient sources among the most extreme ones observed in the Universe: the Gamma-Ray Bursts (GRBs) detected ~ 50 years ago and the Fast Radio Bursts (FRBs) newly discovered ~ 15 years ago. These sources are characterised by the "prompt" emission of a gamma-ray flash (keV-MeV) lasting few ms up to few seconds for GRBs and an intense pulse of radio light (GHz) lasting few ms for FRBs. In the case of GRBs a late broadband afterglow emission is observed in X-rays/optical/radio domain while up to now no other electromagnetic counterpart has ever been detected in coincidence with any FRBs. These last years, many models predicting a multi-wavelength and a multi-messenger emission from these two phenomena have been developped. The main goal of this thesis work is to test these models in order to constrain the physics and the nature of the GRBs/FRBs. To do so, a detailed analysis on the physical properties of the GRB afterglow emission was made thanks to a large set of data collected these last 20 years by various facilities. The study reveals the major problems but also the successes encountered with the so-called "standard" GRB model. Subtle connections between the prompt and the afterglow emission are also discussed. In addition, a search for a neutrino signal from GRBs/FRBs was realised with the ANTARES neutrino telescope. The results are described in this thesis as well as the constraints on the particle acceleration mecanisms occuring during these transient phenomena.At last, this manuscript presents the different innovative observational programs realised in the optical domain with the TAROT and Zadko telescopes and in the astroparticle side with the ANTARES neutrino telescope in order to probe the nature of the GRBs/FRBs progenitors.
The second (O2) observational campaign of gravitational waves (GWs) organized by the LIGO/Virgo Collaborations has led to several breakthroughs such as the detection of GW signals from merger systems ...involving black holes or neutrons stars. During O2, 14 GW alerts were sent to the astronomical community with sky regions mostly covering over hundreds of square degrees. Among them, six were finally confirmed as real astrophysical events. Since 2013, a new set of ground-based robotic telescopes called Ground-based Wide Angle Camera system (GWAC) project and its pathfinder mini-GWAC has been developed to contribute to the various challenges of multi-messenger and time domain astronomy. The GWAC system is built up in the framework of the ground-segment system of the SVOM mission that will be devoted to the study of the multi-wavelength transient sky in the next decade. During O2, only the mini-GWAC telescope network was fully operational. Due to the wide field of view and fast automatic follow-up capabilities of the mini-GWAC telescopes, they were adept to efficiently cover the sky localization areas of GW event candidates. In this paper, we present the mini-GWAC pipeline we have set up to respond to GW alerts and we report our optical follow-up observations of eight GW alerts detected during the O2 run. Our observations provided the largest coverage of the GW localization areas with a short latency made by any optical facility. We found tens of optical transient candidates in our images, but none of those could be securely associated with any confirmed black hole - black hole merger event. Based on this first experience and the near future technical improvements of our network system, we will be more competitive in detecting the optical counterparts from some GW events that will be identified during the upcoming O3 run, especially those emerging from binary neutron star mergers.
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