Tracing the formation and evolution of all supermassive black holes, including the obscured ones, understanding how black holes influence their surroundings and how matter behaves under extreme conditions, are recognized as key science objectives to
be addressed by the next generation of instruments. These are the main goals of the COSPIX proposal, made to ESA in December 2010 in the context of its call for selection of the M3 mission. In addition, COSPIX, will also provide key measurements on the non thermal Universe, particularly in relation to the question of the acceleration of particles, as well as on many other fundamental questions as for example the energetic particle content of clusters of galaxies. COSPIX is proposed as an observatory operating from 0.3 to more than 100 keV. The payload features a single long focal length focusing telescope offering an effective area close to ten times larger than any scheduled focusing mission at 30 keV, an angular resolution better than 20 arcseconds in hard X-rays, and polarimetric capabilities within the same focal plane instrumentation. In this paper, we describe the science objectives of the mission, its baseline design, and its performances, as proposed to ESA.
The radiative counterpart of the supermassive black hole at the Galactic center (GC), Sgr A*, is subject to frequent flares visible simultaneously in X-rays and near-infrared (NIR). Often, enhanced radio variability from centimeter to sub-millimeter
wavelengths is observed to follow these X-ray/NIR eruptions. We present here a multi-wavelength campaign carried out in April 2009, with the aim of characterizing this broadband flaring activity. Concurrent data from the XMM-Newton/EPIC (2-10 keV), VLT/NACO (2.1 microns, 3.8 microns), APEX/LABOCA (870 microns), and Fermi/LAT (0.1-200 GeV) instruments are employed to derive light curves and spectral energy distributions of new flares from Sgr A*. We detected two relatively bright NIR flares both associated with weak X-ray activity, one of which was followed by a strong sub-mm outburst 200 min later. Photometric spectral information on a NIR flare was obtained for the first time with NACO giving a power-law photon index alpha=-0.4pm0.3. The first attempt to detect flaring activity from the Fermi GC source 1FGL J1745.6-2900 is also reported. NIR, X-ray, and sub-mm flares are finally modeled in the context of non-thermal emission processes. It is found that the simplest scenario involving a single expanding plasmoid releasing synchrotron NIR/sub-mm and synchrotron self-Compton X-ray radiation is inadequate to reproduce the data, but suggestions to reconcile the basic elements of the theory and the observations are proposed.
Sagittarius A* (Sgr A*) is the supermassive black hole residing at the center of the Milky Way. It has been the main target of an extensive multiwavelength campaign we carried out in April 2007. Herein, we report the detection of a bright flare from
the vicinity of the horizon, observed simultaneously in X-rays (XMM/EPIC) and near infrared (VLT/NACO) on April 4th for 1-2 h. For the first time, such an event also benefitted from a soft gamma-rays (INTEGRAL/ISGRI) and mid infrared (VLT/VISIR) coverage, which enabled us to derive upper limits at both ends of the flare spectral energy distribution (SED). We discuss the physical implications of the contemporaneous light curves as well as the SED, in terms of synchrotron, synchrotron self-Compton and external Compton emission processes.
The neutron star low-mass X-ray binary GRS 1741.9-2853 is a known type-I burster of the Galactic Center. It is transient, faint, and located in a very crowded region, only 10 arcmin from the supermassive black hole Sgr A*. Therefore, its bursting beh
avior has been poorly studied so far. In particular, its persistent emission has rarely been detected between consecutive bursts, due to lack of sensitivity or confusion. This is what made GRS 1741.9-2853 one of the nine burst-only sources identified by BeppoSAX a few years ago. The physical properties of GRS 1741.9-2853 bursts are yet of great interest since we know very little about the nuclear regimes at stake in low accretion rate bursters. We examine here for the first time several bursts in relation with the persistent emission of the source, using INTEGRAL, XMM-Newton, and Swift observations. We investigate the source flux variability and bursting behavior during its 2005 and 2007 long outbursts. The persistent luminosity of GRS 1741.9-2853 varied between ~1.7 and 10.5 10^36 erg s^-1, i.e. 0.9-5.3% of the Eddington luminosity. The shape of the spectrum as described by an absorbed power-law remained with a photon index Gamma ~ 2 and a column density $N_{rm H} ~ 12 10^22 cm^-2 throughout the outbursts. We discovered 11 type-I bursts with INTEGRAL, and inspected 4 additional bursts: 2 recorded by XMM-Newton and 2 by Swift. From the brigthest burst, we derive an upper limit on the source distance of ~7 kpc. The observed bursts characteristics and source accretion rate suggest pure helium explosions igniting at column depths y_{ign} ~ 0.8-4.8 10^8 g cm^-1, for typical energy releases of ~1.2-7.4 10^39 erg.
