Cетевой мониторинг программного обеспечения в информационной инфраструктуре предприятия

The article is devoted to network monitoring software enterprises. The process of providing functional and technical state of the system are described the actual business needs of the company. The paper proposes a solution to the optimization of this process, based on the scope of activities of the enterprise

A polarised infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots

In this article we summarise and discuss the infrared, radio, and X-ray emission from the supermassive black hole in the Galactic Centre, SgrA*. We include new results from near-infrared polarimetric imaging observations obtained on May 31st, 2006. In that night, a strong flare in Ks band (2.08 microns) reaching top fluxes of ~16 mJy could be observed. This flare was highly polarised (up to ~40%) and showed clear sub-structure on a time scale of 15 minutes, including a swing in the polarisation angle of about 70 degrees. For the first time we were able to observe both polarised flux and short-time variability, with high significance in the same flare event. This result adds decisive information to the puzzle of the SgrA* activity. The observed polarisation angle during the flare peak is the same as observed in two events in 2004 and 2005. Our observations strongly support the dynamical emission model of a decaying plasma hotspot orbiting SgrA* on a relativistic orbit. The observed polarisation parameters and their variability with time might allow to constrain the orientation of accretion disc and spin axis with respect to the Galaxy.Comment: 9 pages, 8 figures, accepted for publication in MNRA

The orbit of the star S2 around SgrA* from VLT and Keck data

Two recent papers (Ghez et al. 2008, Gillessen et al. 2009) have estimated the mass of and the distance to the massive black hole in the center of the Milky Way using stellar orbits. The two astrometric data sets are independent and yielded consistent results, even though the measured positions do not match when simply overplotting the two sets. In this letter we show that the two sets can be brought to excellent agreement with each other when allowing for a small offset in the definition of the reference frame of the two data sets. The required offsets in the coordinates and velocities of the origin of the reference frames are consistent with the uncertainties given in Ghez et al. (2008). The so combined data set allows for a moderate improvement of the statistical errors of mass of and distance to Sgr A*, but the overall accuracies of these numbers are dominated by systematic errors and the long-term calibration of the reference frame. We obtain R0 = 8.28 +- 0.15(stat) +- 0.29(sys) kpc and M(MBH) = 4.30 +- 0.20(stat) +- 0.30(sys) x 10^6 Msun as best estimates from a multi-star fit.Comment: submitted to ApJ

Locating the VHE source in the Galactic Centre with milli-arcsecond accuracy

Very high-energy gamma-rays (VHE; E>100 GeV) have been detected from the direction of the Galactic Centre up to energies E>10 TeV. Up to now, the origin of this emission is unknown due to the limited positional accuracy of the observing instruments. One of the counterpart candidates is the super-massive black hole (SMBH) Sgr A*. If the VHE emission is produced within ~10^{15} cm ~1000 r_G (r_G=G M/c^2 is the Schwarzschild radius) of the SMBH, a decrease of the VHE photon flux in the energy range 100--300 GeV is expected whenever an early type or giant star approaches the line of sight within ~ milli-arcseconds (mas). The dimming of the flux is due to absorption by pair-production of the VHE photons in the soft photon field of the star, an effect we refer to as pair-production eclipse (PPE). Based upon the currently known orbits of stars in the inner arcsecond of the Galaxy we find that PPEs lead to a systematic dimming in the 100--300 GeV band at the level of a few per cent and lasts for several weeks. Since the PPE affects only a narrow energy band and is well correlated with the passage of the star, it can be clearly discriminated against other systematic or even source-intrinsic effects. While the effect is too small to be observable with the current generation of VHE detectors, upcoming high count-rate experiments like the Cherenkov telescope array (CTA) will be sufficiently sensitive. Measuring the temporal signature of the PPE bears the potential to locate the position and size of the VHE emitting region within the inner 1000 r_G or in the case of a non-detection exclude the immediate environment of the SMBH as the site of gamma-ray production altogether.Comment: 7 pages, published in MNRAS 402, pg. 1342-134

Distinguishing an ejected blob from alternative flare models at the Galactic centre with GRAVITY

The black hole at the Galactic centre exhibits regularly flares of radiation, the origin of which is still not understood. In this article, we study the ability of the near-future GRAVITY infrared instrument to constrain the nature of these events. We develop realistic simulations of GRAVITY astrometric data sets for various flare models. We show that the instrument will be able to distinguish an ejected blob from alternative flare models, provided the blob inclination is >= 45deg, the flare brightest magnitude is 14 <= mK <= 15 and the flare duration is >= 1h30.Comment: 11 pages, 9 figures, accepted by MNRA

Massive binaries in the vicinity of Sgr A*

A long-term spectroscopic and photometric survey of the most luminous and massive stars in the vicinity of the super-massive black hole Sgr A* revealed two new binaries; a long-period Ofpe/WN9 binary, GCIRS 16NE, with a modest eccentricity of 0.3 and a period of 224 days and an eclipsing Wolf-Rayet binary with a period of 2.3 days. Together with the already identified binary GCIRS 16SW, there are now three confirmed OB/WR binaries in the inner 0.2\,pc of the Galactic Center. Using radial velocity change upper limits, we were able to constrain the spectroscopic binary fraction in the Galactic Center to $F_{\rm SB}=0.27^{+0.29}_{-0.19}$ at a confidence level of 95%, a massive binary fraction similar to that observed in dense clusters. The fraction of eclipsing binaries with photometric amplitudes $\Delta m>0.4$ is $F^{\rm GC}_{\rm EB}=3\pm2$, which is consistent with local OB star clusters ($F_{\rm EB}=1$). Overall the Galactic Center binary fraction seems to be close to the binary fraction in comparable young clusters.Comment: 5 figures, submitted to Ap

The two states of Sgr A* in the near-infrared: bright episodic flares on top of low-level continuous variability

In this paper we examine properties of the variable source Sgr A* in the near-infrared (NIR) using a very extensive Ks-band data set from NACO/VLT observations taken 2004 to 2009. We investigate the variability of Sgr A* with two different photometric methods and analyze its flux distribution. We find Sgr A* is continuously emitting and continuously variable in the near-infrared, with some variability occurring on timescales as long as weeks. The flux distribution can be described by a lognormal distribution at low intrinsic fluxes (<~5 mJy, dereddened with A_{Ks}=2.5). The lognormal distribution has a median flux of approximately 1.1 mJy, but above 5 mJy the flux distribution is significantly flatter (high flux events are more common) than expected for the extrapolation of the lognormal distribution to high fluxes. We make a general identification of the low level emission above 5 mJy as flaring emission and of the low level emission as the quiescent state. We also report here the brightest Ks-band flare ever observed (from August 5th, 2008) which reached an intrinsic Ks-band flux of 27.5 mJy (m_{Ks}=13.5). This flare was a factor 27 increase over the median flux of Sgr A*, close to double the brightness of the star S2, and 40% brighter than the next brightest flare ever observed from Sgr~A*.Comment: 14 pages, 6 figures, accepted for publication in Ap