Monitoring the Dusty S-Cluster Object (DSO/G2) on its Orbit towards the Galactic Center Black Hole

We analyse and report in detail new near-infrared (1.45 - 2.45 microns) observations of the Dusty S-cluster Object (DSO/G2) during its approach to the black hole at the center of the Galaxy that were carried out with ESO VLT/SINFONI between February and September 2014. Before May 2014 we detect spatially compact Br-gamma and Pa-alpha line emission from the DSO at about 40mas east of SgrA*. The velocity of the source, measured from the red-shifted emission, is 2700+-60 km/s. No blue-shifted emission above the noise level is detected at the position of SgrA* or upstream the presumed orbit. After May we find spatially compact Br-gamma blue-shifted line emission from the DSO at about 30mas west of SgrA* at a velocity of -3320+-60 km/s and no indication for significant red-shifted emission. We do not detect any significant extension of velocity gradient across the source. We find a Br-gamma-line full width at half maximum of 50+-10 Angstroem before and 15+-10 Angstroem after the peribothron transit, i.e. no significant line broadening with respect to last year is observed. Br-gamma line maps show that the bulk of the line emission originates from a region of less than 20mas diameter. This is consistent with a very compact source on an elliptical orbit with a peribothron time passage in 2014.39+-0.14. For the moment, the flaring activity of the black hole in the near-infrared regime has not shown any statistically significant increment. Increased accretion activity of SgrA* may still be upcoming. We discuss details of a source model according to which the DSO is rather a young accreting star than a coreless gas and dust cloud.Comment: 32 pages - 3 tables - 17 figure - accepted by Ap

<i>Hazagora: will you survive the next disaster?</i> &ndash; A serious game to raise awareness about geohazards and disaster risk reduction

Natural disasters are too often presented as resulting from extreme natural phenomena affecting helpless populations, with people being insufficiently aware of the factors leading to disasters and of the existing strategies to mitigate their impacts. We developed a board game aimed at raising awareness about geohazards and disaster risk reduction strategies. The target groups are (1) secondary school students and citizens and (2) scientists and stakeholders involved in risk management activities. For the first group, the aim is to induce a better understanding of the geohazards and disasters they are confronted with in the media or in their daily lives; for the second, the objective is to generate discussion about risk management strategies. The game was tested with students in Belgium and with citizens, earth scientists, and risk managers in several African countries. Based on analysis of the most common game strategies observed, the players' reactions during the game, and their answers to a short questionnaire, we analyzed the main learning outcomes conveyed by this game. The game <i>Hazagora</i> appears to positively enhance the players' insights into processes involved in disasters. As such, the game is an effective, fun learning tool to introduce participants to the concepts of geohazards and disasters and to generate discussion

Multiwavelength study of the flaring activity of Sagittarius A* in 2014 February-April

International audienceWe studied the flaring activity of the Galactic Center supermassive black hole Sgr A* close to the DSO/G2 pericenter passage with XMM-Newton, HST/WFC3, VLT/SINFONI, VLA and CARMA. We detected 3 and 2 NIR and 2 X-ray flares with HST, VLT and XMM-Newton, respectively. The Mar. 10 X-ray flare has a long rise and a rapid decay. Its NIR counterpart peaked before the X-ray peak implying a variation in the X-ray-to-NIR flux ratio. This flare may be one flare created by the adiabatic compression of a plasmon or 2 close flares with simultaneous X-ray/NIR peaks. The rising radio flux-density observed on Mar. 10 with the VLA could be the delayed emission from a NIR/X-ray flare preceding our observations. On Apr. 2, we observed the start of the NIR counterpart of the X-ray flare and the end of a bright NIR flare without X-ray counterpart. We studied the physical parameters of the flaring region for each NIR flare but none of the radiative processes can be ruled out for the X-ray flares creation. Our X-ray flaring rate is consistent with those observed in the 2012 Chandra/XVP campaign. No increase in the flaring activity was thus triggered close to the DSO/G2 pericenter passage

Modelización del flujo de lava del volcán Pico de Bandama (Gran Canaria, Islas Canarias)

Lava flow emplacement modelling provides about possible future eruptions in a given area and helps, consequently, to better design volcanic hazards zonation maps. The open access plugin Quantum-Lava Hazard Assessment (Q-LavHA), integrated into a Geographic Information System (GIS), includes three different models, two probabilistic and one deterministic, for the simulation of lava flow emplacement and establishes the overlap degree with actual flows. Pico de Bandama volcano lava flow (1970 ± 70 AP) was modelled with Q-LavHA. A high degree of reliability between the model and the reality is obtained, even with the simplest probabilistic models. For a high degree of reliability in modelling ancient eruptions, a detailed palaeogeomorphological reconstruction of the relief prior to the eruption is essential. © 2019 Sociedad Geologica de Espana. All rights reserved.Este trabajo ha sido financiado por el Cabildo de Gran Canaria, programa de Becas de Investigación Simón Benítez Padilla-2016 (referenciaCPH249/16). Este estudio se realizó en el marco de los Grupos de Investigación Consolidados GEOVOL (Gobierno de Canarias,ULPGC) y GEOPAM (Generalitat de Catalunya, 2017 SGR 1494).Peer reviewe

Comparison of real and simulated lava flows in the Holocene volcanism of Gran Canaria (Canary Islands, Spain) with Q-LavHA: contribution to volcanic hazard management

Lava flow simulations are valuable tools for forecasting and assessing the areas potentially affected by new eruptions, interpreting past volcanic events and understanding the lava flow behaviour’s controls. Q-LavHA (v 2.0) plug-in of Mossoux et al. (Mossoux et al., Comput Geosci 97:98–109, 2016) combines and improves existing deterministic (FLOWGO) and probabilistic ("Maximum Length" and "Decreasing Probability") codes which allow calculating the probability of lava flow spatial propagation and terminal length. We investigate the Q-LavHA algorithm’s effectiveness in twenty Holocene ʻaʻā lava flows of Gran Canaria (Canary Islands). Pre-eruptive and updated digital elevation models (DEMs) (25 m of resolution) and associated topographic and morphometric parameters have been used as essential input data to simulate the lava flows. Besides, thermo-rheological properties of the studied Holocene lavas have also been provided in the deterministic approach. The probabilistic lava flow maps produced by Q-LavHA and the fitness indexes calculated for assessing the simulated lava flow’ accuracy indicate that the probabilistic "Maximum Length" constraint provides the best simulations. By using this method, many of the simulations in Gran Canaria almost overlap the real lava flow entirely even if overestimated areas are, in some cases, relatively high. By contrast, underestimated areas are generally low. The best results are those in which the highest inundation probability is observed within the main channel where the actual lava flow is emplaced, and even if overestimated areas are high, they are associated with low pixel inundation.Financial support was provided by the Cabildo de Gran Canaria Research Program "Simon Benitez Padilla" (CPH249/16) and by Project LAJIAL (ref. PGC2018-101027-B-I00, MCIU/AEI/ FEDER, EU). This study was carried out in the framework of the Research Consolidated Groups GEOVOL (Canary Islands Government, ULPGC) and GEOPAM (Generalitat de Catalunya, 2017 SGR 1494).Peer reviewe

Multiwavelength study of the flaring activity of Sgr A* in 2014 February-April

International audienceThe supermassive black hole Sgr A* is located at the Milky Way center. We studied its flaring activity close to the DSO/G2 pericenter passage with XMM-Newton, HST/WFC3, VLT/SINFONI, CARMA and VLA to constrain the physical properties and origin of the flares. We detected two X-ray and three NIR flares on 2014 Mar. 10 and Apr. 2 with XMM-Newton and HST and two NIR flares on 2014 Apr. 3 and 4 with VLT. The 2014 Mar. 10 X-ray flare has a long rise and a rapid decay. Its NIR counterpart peaked 4320 s before the X-ray peak implying a variation in the X-ray-to-NIR flux ratio. This flare may be a single flare where change in the flux ratio is explained by the adiabatic compression of a plasmon or two close flares with simultaneous X-ray/NIR peaks. We observed an increase in the rising radio flux density on 2014 Mar. 10 with the VLA. It could be the delayed emission from a NIR/X-ray flare preceding our observation. The 2014 Apr. 2 X-ray flare occurred for HST in the Earth occultation of Sgr A*. We thus only observed the start of its NIR counterpart. After the occultation, we observed the decay phase of a bright NIR flare with no X-ray counterpart. On 2014 Apr. 3, two CARMA flares were observed. The first one may be the delayed emission of a VLT NIR flare. We thus observed a total of seven NIR flares whose three have an X-ray counterpart. We studied the physical parameters of the flaring region for each NIR flare but none of the possible radiative processes can be ruled out for the X-ray flares creation. Our X-ray flaring rate is consistent with those observed in the 2012 Chandra XVP campaign. No increase in the flaring activity was thus triggered close to the DSO/G2 pericenter passage. Moreover, higher X-ray flaring rates had already been observed with no increase in the quiescent level. There is thus no direct link between an X-ray flaring-rate increase and an accretion-rate change

Multiwavelength study of the flaring activity of Sagittarius A in 2014 February−April

International audienc

Assessing lava flow susceptibility at neighbouring volcanoes: Nyamulagira and Nyiragongo volcanoes, Virunga Volcanic Province

Abstract Assessing volcanic hazards in locations exposed to multiple central volcanoes requires to consider multiple potential eruption sources and their respective characteristics. While this is common practice in ashfall hazard assessment, this is generally not considered for topography-controlled volcanic flow processes. Yet, in volcanic areas with closely spaced volcanic systems, eruptions fed from several contrasted volcanic systems might threaten one given area. Considering the case of the Nyiragongo and Nyamulagira volcanoes in the Virunga Volcanic Province (D.R.Congo), we present a method to produce a combined lava flow inundation susceptibility map that integrates both volcanoes. The spatial distribution of the probability of vent opening for the next eruption is separately constrained for both volcanoes based on the mapping of historical and pre-historical eruptive vents and fissures. The Q-LavHa lava flow probability model is then calibrated separately for each volcano, considering several historical lava flows of Nyamulagira (2004, 2006, 2010) and Nyiragongo (2002). The maps for the two volcanoes are thereafter integrated based on a weighted sum of both individual lava flow inundation probability maps, assuming historically-based relative eruption frequency of the two volcanoes. The accuracy of this probabilistic susceptibility map for the most active volcanic region in Africa was unfortunately validated by the May 2021 lava flow produced by Nyiragongo. This map was discussed and validated in 2019 with local scientists, as well as representatives of disaster management and urban planning institutions, but was not included in the regional contingency plan ahead of the 2021 eruption crisis. Updating the volcanic crisis and evacuation management plans with this lava flow probability map could contribute to reinforce risk awareness among the population and inform the future development of the city of Goma