Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

We report the detection of the two-dimensional structure of the radio source associated with the Galactic Center black hole, Sagittarius A*, obtained from Very Long Baseline Array observations at a wavelength of 7 mm. The intrinsic source is modeled as an elliptical Gaussian with major-axis size 35.4 × 12.6 RS in position angle 95° east of north. This morphology can be interpreted in the context of both jet and accretion disk models for the radio emission. There is supporting evidence in large angular-scale multi-wavelength observations for both source models for a preferred axis near 95°. We also place a maximum peak-to-peak change of 15% in the intrinsic major-axis size over five different epochs. Three observations were triggered by detection of near infrared (NIR) flares and one was simultaneous with a large X-ray flare detected by NuSTAR. The absence of simultaneous and quasi-simultaneous flares indicates that not all high energy events produce variability at radio wavelengths. This supports the conclusion that NIR and X-ray flares are primarily due to electron excitation and not to an enhanced accretion rate onto the black hole. © 2014. The American Astronomical Society. All rights reserved..

AX J1745.6-2901 is a high-inclination (eclipsing) neutron star Low Mass X-ray Binary (LMXB) located less than ~1.5 arcmin from Sgr A*. Ongoing monitoring campaigns have targeted Sgr A* frequently and these observations also cover AX J1745.6-2901. We present here an X-ray analysis of AX J1745.6-2901 using a large dataset of 38 XMM-Newton observations, including eleven which caught AX J1745.6-2901 in outburst. Fe K absorption is clearly seen when AX J1745.6-2901 is in the soft state, but disappears during the hard state. The variability of these absorption features does not appear to be due to changes in the ionizing continuum. The small Kalpha/Kbeta ratio of the equivalent widths of the Fe xxv and Fe xxvi lines suggests that the column densities and turbulent velocities of the absorbing ionised plasma are in excess of N_H ~ 10^23 cm^-2 and v_turb >~ 500 km s^-1. These findings strongly support a connection between the wind (Fe K absorber) and the accretion state of the binary. These results reveal strong similarities between AX J1745.6-2901 and the eclipsing neutron star LMXB, EXO 0748-676, as well as with high-inclination black hole binaries, where winds (traced by the same Fe K absorption features) are observed only during the accretion-disc-dominated soft states, and disappear during the hard states characterised by jet emission.

We present a study of the X-ray flaring activity of Sgr A* during all the 150 XMM-Newton and Chandra observations pointed at the Milky Way center over the last 15 years. This includes the latest XMM-Newton and Chandra campaigns devoted to monitoring the closest approach of the very red Br-Gamma emitting object called G2. The entire dataset analysed extends from September 1999 through November 2014. We employed a Bayesian block analysis to investigate any possible variations in the characteristics (frequency, energetics, peak intensity, duration) of the flaring events that Sgr A* has exhibited since their discovery in 2001. We observe that the total bright-or-very bright flare luminosity of Sgr A* increased between 2013-2014 by a factor of 2-3 (~3.5 sigma significance). We also observe an increase (~99.9% significance) from 0.27+-0.04 to 2.5+-1.0 day^-1 of the bright-or-very bright flaring rate of Sgr A*, starting in late summer 2014, which happens to be about six months after G2's peri-center passage. This might indicate that clustering is a general property of bright flares and that it is associated with a stationary noise process producing flares not uniformly distributed in time (similar to what is observed in other quiescent black holes). If so, the variation in flaring properties would be revealed only now because of the increased monitoring frequency. Alternatively, this may be the first sign of an excess accretion activity induced by the close passage of G2. More observations are necessary to distinguish between these two hypotheses.