The long-period massive binary HD~54662 revisited

HD54662 is an O-type binary star belonging to the CMa OB1 association. Due to its long-period orbit, this system is an interesting target to test the adiabatic wind shock model. The goal is to improve our knowledge of the orbital and stellar parameters of HD54662 and to analyze its X-ray emission to test the theoretical scaling of the X-ray emission with orbital separation for adiabatic wind shocks. We applied a spectral disentangling code to optical spectra to determine the radial velocities and the individual spectra of each star. The individual spectra were analyzed using the CMFGEN model atmosphere code. We fitted two X-ray spectra using a Markov Chain Monte Carlo algorithm and compared them to the emission expected from adiabatic shocks. We determine an orbital period of 2103.4days, a low orbital eccentricity of 0.11, and a mass ratio m2/m1=0.84. Combined with the orbital inclination inferred in a previous astrometric study, we obtain surprisingly low masses of 9.7 and 8.2Msun. From the individual spectra, we infer O6.5 spectral types for both stars and a brightness ratio of l1/l2~2. The softness of the X-ray spectra, the very small variation of spectral parameters, and the comparison of the X-ray-to-bolometric luminosity ratio with the canonical value for O-type stars allow us to conclude that X-ray emission from the wind interaction region is quite low. We cannot confirm the runaway status previously attributed to HD54662 and we find no X-ray emission associated with the bow shock detected in the infrared. The lack of hard X-ray emission from the wind-shock region suggests that the mass-loss rates are lower than expected and/or that the pre-shock wind velocities are much lower than the terminal wind velocities. The bow shock associated with HD54662 possibly corresponds to a wind-blown arc created by the interaction of the stellar winds with the ionized gas of CMa OB1. (abridged)Comment: Manuscript has been accepted. A&A, in pres

Search for non-thermal X-ray emission in the colliding wind binary Cygnus OB2 #8A⋆

Aims. Cyg OB2 #8A is a massive O-type binary displaying strong non-thermal radio emission. Owing to the compactness of this binary, emission of non-thermal X-ray photons via inverse Compton scattering is expected. Methods. We first revised the orbital solution for Cyg OB2 #8A using new optical spectra. We then reduced and analysed X-ray spectra obtained with XMM-Newton, Swift, INTEGRAL, and NuSTAR. Results. The analysis of the XMM-Newton and Swift data allows us to better characterise the X-ray emission from the stellar winds and colliding winds region at energies below 10 keV. We confirm the variation of the broad-band light curve of Cyg OB2 #8A along the orbit with, for the first time, the observation of the maximum emission around phase 0.8. The minimum ratio of the X-ray to bolometric flux of Cyg OB2 #8A remains well above the level expected for single O-type stars, indicating that the colliding wind region is not disrupted during the periastron passage. The analysis of the full set of publicly available INTEGRAL observations allows us to refine the upper limit on the non-thermal X-ray flux of the Cyg OB2 region between 20 and 200 keV. Two NuSTAR observations (phases 0.028 and 0.085) allow us to study the Cyg OB2 #8A spectrum up to 30 keV. These data do not provide evidence of the presence of non-thermal X-rays, but bring more stringent constraints on the flux of a putative non-thermal component. Finally, we computed, thanks to a new dedicated model, the anisotropic inverse Compton emission generated in the wind shock region. The theoretical non-thermal emission appears to be compatible with observational limits and the kinetic luminosity computed from these models is in good agreement with the unabsorbed flux observed below 10 keV

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

Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed

Context. The supermassive black hole Sagittarius A* (Sgr A*) is located at the dynamical center of the Milky Way. In a recent study of the X-ray flaring activity from Sgr A* using Chandra, XMM-Newton, and Swift observations from 1999 to 2015, it has been argued that the bright flaring rate has increased from 2014 August 31 while the faint flaring rate decreased from around 2013 August. Aims. We tested the persistence of these changes in the flaring rates with new X-ray observations of Sgr A* performed from 2016 to 2018 (total exposure of 1.4 Ms). Methods. We reprocessed the Chandra, XMM-Newton, and Swift observations from 2016 to 2018. We detected 9 flares in the Chandra data and 5 flares in the Swift data that we added to the set of 107 previously detected flares. We computed the intrinsic distribution of flare fluxes and durations corrected for the sensitivity bias using a new method that allowed us to take the error on the flare fluxes and durations into account. From this intrinsic distribution, we determined the average flare detection efficiency for each Chandra, XMM-Newton, and Swift observation. After correcting each observational exposure for this efficiency, we applied the Bayesian blocks algorithm on the concatenated flare arrival times. As in the above-mentioned study, we also searched for a flux and fluence threshold that might lead to a change in flaring rate. We improved the previous method by computing the average flare detection efficiencies for each flux and fluence range. Results. The Bayesian block algorithm did not detect any significant change in flaring rate of the 121 flares. However, we detected an increase by a factor of about three in the flaring rate of the most luminous and most energetic flares that have occurred since 2014 August 30. Conclusions. The X-ray activity of Sgr A* has increased for more than four years. Additional studies about the overall near-infrared and radio behavior of Sgr A* are required to draw strong results on the multiwavelength activity of the black hole

The historical case of Paricutin volcano (Michoacán, México): challenges of simulating lava flows on a gentle slope during a long-lasting eruption

Simulating lava flows on a gentle slope is complex since they can propagate in a wide range of directions. It is an even greater challenge to define lava flow trajectories when an eruption lasts over several years and flows cool down, changing the surrounding topography. In this study, we test Q-LavHA, an open source plug-in that simulates lava flow inundation calculating its probability, and using Paricutin’s eruption (1943–1952) in central Mexico as a case study. We have appropriately calibrated the Q-LavHA plug-in for the Paricutin case study, which provides insights on how to better model lava flows in gentle terrain. From this work, we observe that each phase is characterized by a unique set of parameters requiring a careful calibration and that low-relief topographies require special consideration. Our findings could be useful for real-time hazard evaluation in future volcanic scenarios in the Michoacán–Guanajuato volcanic field and elsewhere, where new monogenetic eruptions similar to Paricutin can be expected.This research was supported by the Government of Spain through “Juan de la Cierva” postdoctoral fellowship awarded to L. Becerril; NSF EAR 1019798 (2014–2016) and a UNAM-DGAPA postdoctoral fellowship (2018–2019) granted to P. Larrea; National Science Foundation (NSF) EAR grant #1019798 awarded to E. Widom. Consejo Nacional de Ciencia y Tecnología (CONACyT-167231) and Dirección General de Asuntos del Personal Académico (UNAM-DGAPA-IN-104221) granted to C. Siebe; and VeTOOLS and EVE projects funded by the European Commission (EC ECHO SI2.695524 and 826292EC ECHO SI2.695524) granted to J. Martí.Peer reviewe

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

Flaring Activity of Sgr A* During the Passage of the G2 Cloud

International audiencePreliminary results of our monitoring of Sgr A* in coordination with Chandra, XMM and HST will be presented. The main focus will be on the cross correlation analysis of radio and X-ray flare emission on September 12, 2013 when a luminous X-ray flare was detected by Chandra. The peak of flare emission at 3.5cm was found to be delayed by more than 130 minutes when compared to the peak of the X-ray emission. The cross correlation of the peak emission at radio and X-rays is consistent with an adiabatic expansion modelof flare emission

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