Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate

Recently, in a study the X-ray flaring activity of Sgr A* with Chandra and XMM-Newton public observations from 1999 to 2014 and 2014 Swift data, it has been argued that the "bright and very bright" flaring rate raised from 2014 Aug. 31. Thanks to 482ks of observations performed in 2015 with Chandra, XMM-Newton and Swift, we test the significance of this rise of flaring rate and determine the threshold of unabsorbed flare flux or fluence leading to any flaring-rate change. The mean unabsorbed fluxes of the 107 flares detected in the 1999-2015 observations are consistently computed from the extracted spectra and calibration files, assuming the same spectral parameters. We construct the observed flare fluxes and durations distribution for the XMM-Newton and Chandra flares and correct it from the detection biases to estimate the intrinsic distribution from which we determine the average flare detection efficiency for each observation. We apply the BB algorithm on the flare arrival times corrected from the corresponding efficiency. We confirm a constant overall flaring rate in 1999-2015 and a rise in the flaring rate for the most luminous/energetic flares from 2014 Aug. 31 (4 months after the passage of the DSO/G2 close to Sgr A*). We also identify a decay of the flaring rate for the less luminous and less energetic flares from 2013 Aug. and Nov., respectively (10 and 7 months before the pericenter of the DSO/G2). The decay of the faint flaring rate is difficult to explain by the tidal disruption of the DSO/G2, whose stellar nature is now well established, since it occurred well before its pericenter. Moreover, a mass transfer from the DSO/G2 to Sgr A* is not required to produce the rise in the bright flaring rate since the energy saved by the decay of the number of faint flares during a long time period may be later released by several bright flares during a shorter time period. (abridged)Comment: Accepted in A&A in 2017 April 2

Fe xxv line profiles in colliding wind binaries

Strong wind-wind collisions in massive binaries generate a very hot plasma that frequently produces a moderately strong iron line. The morphology of this line depends upon the properties of the wind interaction zone and its orientation with respect to the line of sight. As the binary components revolve around their common centre of mass, the line profiles are thus expected to vary. With the advent of the next generation of X-ray observatories (Astro-H, Athena) that will offer high-resolution spectroscopy above 6 keV, it will become possible to exploit these changes as the most sensitive probe of the inner parts of the colliding wind interaction. Using a simple prescription of the wind-wind interaction in an early-type binary, we have generated synthetic line profiles for a number of configurations and orbital phases. These profiles can help constrain the properties of the stellar winds in such binary systems.Comment: Accepted for publication in New Astronom

Study of the X-ray activity of Sgr A* during the 2011 XMM-Newton campaign

In Spring 2011 we observed Sgr A*, the supermassive black hole at the center of our Galaxy, with XMM-Newton with a total exposure of ~226 ks in coordination with the 1.3 mm VLBI. We have performed timing analysis of the X-ray emission from Sgr A* using Bayesian blocks algorithm to detect X-ray flares observed with XMM-Newton. Furthermore, we computed X-ray smoothed light curves observed in this campaign in order to have better accuracy on the position and the amplitude of the flares. We detected 2 X-ray flares on the 2011 March 30 and April 3 which have for comparison a peak detection level of 6.8 and 5.9 sigma in the XMM-Newton/EPIC light curve in the 2-10 keV energy range with a 300 s bin. The former is characterized by 2 sub-flares: the first one is very short (~458 s) with a peak luminosity of ~9.4E34 erg/s whereas the second one is longer (~1542 s) with a lower peak luminosity of ~6.8E34 erg/s. The comparison with the sample of X-ray flares detected during the 2012 Chandra XVP campaign favors the hypothesis that the 2011 March 30 flare is a single flare rather than 2 distinct sub-flares. We model the light curve of this flare with the gravitational lensing of a simple hotspot-like structure but we can not satisfactorily reproduce the large decay of the light curve between the 2 sub-flares with this model. From magnetic energy heating during the rise phase of the first sub-flare and assuming an X-ray photons production efficiency of 1 and a magnetic field of 100 G at 2 r_g, we derive an upper limit to the radial distance of the first sub-flare of 100 r_g. We estimate using the decay phase of the first sub-flare a lower limit to the radial distance of 4 r_g from synchrotron cooling in the infrared. The X-ray emitting region of the first sub-flare is located at a radial position of 4-100 and has a corresponding radius of 1.8-2.87 in r_g unit for a magnetic field of 100 G at 2 r_g.Comment: Version published in A&A + corrigendum published in A&

Colliding winds in massive binary systems to be diagnosed with X-IFU

OB and Wolf-Rayet stars feature energetic stellar winds. In massive binary systems, the winds of both components collide. This leads to the formation of a hot X-ray emitting plasma. The properties of this plasma are best studied via Athena/X-IFU observations of the line profiles of the Fe xxv line complex at 6.7 keV. We have designed numerical tools to predict the morphology of those lines for a variety of configurations and to extract a maximum of information from the future observations.PRODEX HERMe

X-ray emission of massive stars as seen with ATHENA

Massive O, B and Wolf-Rayet stars are key drivers of the ecology of the interstellar medium and play an essential role in the feedback processes of matter and energy at the level of their host galaxy. Here we highlight a few science cases where X-ray spectroscopy with ATHENA will provide precious insight into the physics of the stellar winds and the circumstellar environments of massive stars

Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate

Recently, in a study the X-ray flaring activity of Sgr A* with Chandra and XMM-Newton public observations from 1999 to 2014 and 2014 Swift data, it has been argued that the "bright and very bright" flaring rate raised from 2014 Aug. 31. Thanks to 482ks of observations performed in 2015 with Chandra, XMM-Newton and Swift, we test the significance of this rise of flaring rate and determine the threshold of unabsorbed flare flux or fluence leading to any flaring-rate change. The mean unabsorbed fluxes of the 107 flares detected in the 1999-2015 observations are consistently computed from the extracted spectra and calibration files, assuming the same spectral parameters. We construct the observed flare fluxes and durations distribution for the XMM-Newton and Chandra flares and correct it from the detection biases to estimate the intrinsic distribution from which we determine the average flare detection efficiency for each observation. We apply the BB algorithm on the flare arrival times corrected from the corresponding efficiency. We confirm a constant overall flaring rate in 1999-2015 and a rise in the flaring rate for the most luminous/energetic flares from 2014 Aug. 31 (4 months after the passage of the DSO/G2 close to Sgr A*). We also identify a decay of the flaring rate for the less luminous and less energetic flares from 2013 Aug. and Nov., respectively (10 and 7 months before the pericenter of the DSO/G2). The decay of the faint flaring rate is difficult to explain by the tidal disruption of the DSO/G2, whose stellar nature is now well established, since it occurred well before its pericenter. Moreover, a mass transfer from the DSO/G2 to Sgr A* is not required to produce the rise in the bright flaring rate since the energy saved by the decay of the number of faint flares during a long time period may be later released by several bright flares during a shorter time period. (abridged)Comment: Accepted in A&A in 2017 April 2

The X-ray footprint of the circumnuclear disc

We studied the central regions of the Galactic Centre to determine if the circumnuclear disc (CND) acts as an absorber or a barrier for the central X-rays diffuse emission. After reprocessing 4.6 Ms of Chandra observations, we were able to detect, for the first time, a depression in the X-ray luminosity of the diffuse emission whose size and location correspond to those of the CND. We extracted the X-ray spectra for various regions inside the CND footprint as well as for the region where the footprint is observed and for a region located outside the footprint. We simultaneously fitted these spectra as an optically thin plasma whose absorption by the interstellar medium (ISM) and by the local plasma were fitted independently using the Markov chain Monte Carlo method. The hydrogen column density of the ISM is 7.5 x 10(22) cm(-2). The X-ray diffuse emission inside the CND footprint is formed by a 2T plasma of 1 and 4 keV with slightly super-solar abundances except for the iron and carbon that are sub-solar. The plasma from the CND, in turn, is better described by a 1T model with abundances and local hydrogen column density that are very different from those of the innermost regions. The large iron abundance in this region confirms that the CND is dominated by the shock-heated ejecta of the Sgr A East supernova remnant. We deduced that the CND rather acts as a barrier for the Galactic Centre plasma and that the plasma located outside the CND may correspond to the collimated outflow possibly created by Sgr A* or the interaction between the wind of massive stars and the mini-spiral material

LIFELINE: The program for the simulation of the X-ray line profiles in massive colliding wind binaries

The study of the X-ray line profiles produced by massive colliding wind binaries is a powerful tool for the characterisation of the stellar winds. We built a self-consistent program for the computation of line profiles named LIFELINE. The resulting theoretical profiles can be compared to the line profile that will be observed with future high-resolution X-ray spectrographs to retrieve the characteristics of the stellar winds generating them. We considered a grid of 780 O-type binaries and computed, for each of them, the wind velocity distribution of each star, taking the impact of the radiation pressure and gravity force of the companion star into account. We then computed the characteristics of the wind shock region and followed the emitted photons towards the observer to compute their absorption. Finally, the Fe K line profiles near 6.7keV were constructed from the distribution of the photons as a function of the radial velocities of their emitting region. LIFELINE can be used to compare the theoretical line profiles to the observed ones or to compute theoretical profiles for a new binary system. We highlight the results for three systems. While the line profiles created in adiabatic wind collision regions are quite simple, the line profiles arising from regions in the radiative regime, as found in short-period binaries, are more sophisticated notably because of the Coriolis effect on the shape of the shock. The predicted differences in line morphology between systems with different wind properties are quite significant, allowing a detailed comparison between the theoretical profiles and those that will be observed with future high-resolution X-ray spectrometers

Synchrotron Self-Compton Scattering in Sgr A* Derived from NIR and X-Ray Flare Statistics

The flaring activity of Sagittarius A* (Sgr A*) can be analyzed by statistical means to test emission models for its accretion flow. A particular modeling question is whether the observed X-ray flares are the high-energy end of a synchrotron spectrum or if they arise from self-Comptonized photons of a lower-energy synchrotron process. We use already published Chandra X-ray Visionary Project data to statistically investigate the X-ray count-rate distribution of Sgr A*. Two previous workgroups have already undertaken such an analysis on that data. They modeled the flaring part of the emission with a bounded power law, i.e., a power-law distribution with a hard cutoff at the highest measured count rate. With this model, both teams obtain a power-law index a(X) similar to 2. We show that the flare count-rate distribution can also be well described by a truncated, i.e., an exponentially decaying power law. We argue that an exponential truncation is a more natural model than a hard cutoff. With this alternate model, our fit yields a power-law index alpha(X) similar to 1.66. We find that this slope can be canonically explained by a synchrotron self-Compton (SSC) process. Therefore, we argue that SSC models are the best ones suitable to explain the observed X-ray count-rate distribution