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Register a new userHard X-ray diffuse emission from the Galactic Center seen by INTEGRAL
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We study the hard X-ray (20-100 keV) variability of the Galactic Center (GC) and of the nearby sources on the time scale of 1000 s. We find that 3 of the 6 hard X-ray sources detected by INTEGRAL within the central 1 degree of the Galaxy are not variable on this time scale: the GC itself (the source IGR J1745.6-2901) as well as the source 1E 1743.1-2843 and the molecular cloud Sgr B2. We put an upper limit of 5 x 10^{-12} erg/(cm^2 sec) (in 20 to 60 keV band) on the variable emission form the supermassive black hole (the source Sgr A*) which powers the activity of the GC(although we can not exclude the possibility of rare stronger flares). The non-variable 20-100 keV emission from the GC turns out to be the high-energy non-thermal tail of the diffuse hard ``8 keV component of emission from Sgr A region. Combining the XMM-Newton and INTEGRAL data we find that the size of the extended hard X-ray emission region is about 20 pc. The only physical mechanism of production of diffuse non-thermal hard X-ray flux, which does not contradict the multi-wavelength data on the GC, is the synchrotron emission from electrons of energies 10-100 TeV.
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We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with $Gammasim1.3$-$2.3$ up to ~50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4 keV Fe K$alpha$ fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broad-band X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density ($sim10^{23}$ cm$^{-2}$), primary X-ray spectra (power-laws with $Gammasim2$) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to $L_X stackrel{>}{sim} 10^{38}$ erg s$^{-1}$. Above ~20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95-0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses $M_{rm WD} sim 0.9 M_{odot}$. Spectral energy distribution analysis suggests that G359.95-0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745-290, strongly favoring a leptonic origin of the GC TeV emission.
This letter presents the first results of an observational campaign to study the Galactic Centre with INTEGRAL. The mosaicked images obtained with the IBIS/ISGRI coded aperture instrument in the energy ranges 20-40 and 40-100 keV, give a yet unseen view of the high-energy sources of this region in hard X- and gamma-rays with an angular resolution of 12 arcmin (FWHM). We report on the discovery of a source, IGR J17456-2901, coincident with the Galactic Nucleus SgrA* to within 0.9 arcmin. Located at R.A.(J2000.0) = 17h45m38.5s, Dec.(J2000.0) = -29:01:15, the source is visible up to about 100 keV with a 20-100 keV luminosity at 8 kpc of (2.89 +/- 0.41) x 10^35 ergs/s. Although the new INTEGRAL source cannot unequivocally be associated to the Galactic Nucleus, this is the first report of significant hard X-ray emission from within the inner 10 arcmin of the Galaxy and a contribution from the galactic supermassive black hole itself cannot be excluded.
We analyse new results of Chandra and Suzaku which found a flux of hard X-ray emission from the compact region around Sgr A$^ast$ (r ~ 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbounded part of captured stars obtains an additional momentum. As a result a flux of subrelativistic protons is generated near the Galactic center which heats the background plasma up to temperatures about 6-10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.
We examine the spectrum of diffuse emission detected in the 17 by 17 field around Sgr A* during 625 ks of Chandra observations. The spectrum exhibits He-like and H-like lines from Si, S, Ar, Ca, and Fe, that are consistent with originating in a two-temperature plasma, as well as a prominent low-ionization Fe line. The cooler, kT=0.8 keV plasma differs in surface brightness across the image by a factor of 9. This soft plasma is probably heated by supernovae. The radiative cooling rate of the plasma within the inner 20 pc of the Galaxy could be balanced by 1% of the kinetic energy of one supernova every 300,000 y. The hotter, kT=8 keV component is more spatially uniform, ranging over a factor of 2 in surface brightness. The intensity of the hard plasma is correlated with that of the soft, but they are probably only indirectly related, because supernova remnants are not observed to produce thermal plasma hotter than kT=3 keV. Moreover, a kT=8 keV plasma is too hot to be bound to the Galactic center, and therefore would form a slow wind or fountain of plasma. The energy required to sustain such a freely-expanding plasma within the inner 20 pc of the Galaxy is ~10^40 erg/s, which corresponds to the entire kinetic energy of one supernova every 3000 y. This rate is unreasonably high. However, alternative explanations for the kT=8 keV diffuse emission are equally unsatisfying. We are left to conclude that either the diffuse emission is heated by an unanticipated source of energy, or that a population of faint (< 10^31 erg/s), hard X-ray sources that are a factor of 10 more numerous than CVs remains to be discovered. (Abridged)
This paper reports that the X-ray spectrum from the Galactic Center X-ray Emission (GCXE) is expressed by the assembly of active binaries, non-magnetic Cataclysmic Variables, magnetic Cataclysmic Variables (X-ray active star: XAS), cold matter and diffuse sources. In the fitting of the limited components of the XASs, the GCXE spectrum exhibits significant excesses with $chi^2/d.o.f. =5.67$. The excesses are found at the energies of K$alpha$, He$alpha$, Ly$alpha$ and radiative recombination continuum of S, Fe and Ni. By adding components of the cold matter and the diffuse sources, the GCXE spectrum is nicely reproduced with $chi^2/d.o.f. = 1.53$, which is a first quantitative model for the origin of the GCXE spectrum. The drastic improvement is mainly due to the recombining plasmas in the diffuse sources, which indicate the presence of high-energy activity of Sgr A$^*$ in the past of $> 1000$~years.
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