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تسجيل مستخدم جديدINTEGRAL monitoring of the Black Hole candidate 1E 1740.7-2942
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The brightest persistent Galactic black hole candidate close to the Galactic Centre, 1E 1740.7-2942, has long been observed with INTEGRAL. In this paper, we report on the long-term hard X-ray monitoring obtained during the first year of observations as part of the Galactic Centre Deep Exposure. We discuss the temporal and spectral behaviours in different energy bands up to 250 keV, as well as the hardness-flux correlations.
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The microquasar 1E 1740.7-2942 is one of the most appealing source of the Galactic Centre region. The high energy feature detected once by SIGMA has been searched in the last years by INTEGRAL, but never confirmed. Classified as a persistent source,
on 2004 it showed a quiescent-like state. In fact for few month 1E 1740.7-2942 was below the detector sensitivity level. We present the long term temporal behaviour of 1E 1740.7-2942 observed by INTEGRAL and RXTE in 2004 and 2005, as well as preliminary results on possible spectral transitions.
The microquasar 1E 1740.7-2942 is observed with Integral since Spring 2003. Here, we report on the source high energy behaviour by using the first three years of data collected with SPI and IBIS telescopes, taking advantage of the instruments complem
entarity. Light curves analysis showed two main states for 1E 1740.7-2942: the canonical low/hard state of black-hole candidates and a ``dim state, characterised by a ~ 20 times fainter emission, detected only below 50 keV and when summing more than 1Ms of data. For the first time the continuum of the low/hard state has been measured up to ~ 600 keV with a spectrum that is well represented by a thermal Comptonization plus an additional component necessary to fit the data above 200 keV. This high energy component could be related to non-thermal processes as already observed in other black-hole candidates. Alternatively, we show that a model composed by two thermal Comptonizations provides an equally representative description of the data: the temperature of the first population of electrons results as (kTe)_1 ~ 30 keV while the second, (kTe)_2, is fixed at 100 keV. Finally, searching for 511 keV line showed no feature, either narrow or broad, transient or persistent.
We present results of the monitoring of the black hole candidate 1E 1740.7-2942 with INTEGRAL, in combination with simultaneous observations by RXTE. We concentrate on broad-band spectra from INTEGRAL/IBIS and RXTE/PCA instruments. During our observa
tions, the source spent most of its time in the canonical low/hard state with the measured flux variation within a factor of two. In 2003 September the flux started to decline and in 2004 February it was below the sensitivity level of the INTEGRAL and RXTE instruments. Notably, during the decline phase the spectrum changed, becoming soft and typical of black hole binaries in the intermediate/soft state.
Studies of the long-term spectral variations have been used to constrain the emission processes of black hole candidates. However, a common scenario which is able to explain the emission from soft to hard X-rays has been proposed only recently. Here,
we use XMM and INTEGRAL data on 1E 1740.7-2942 in order to demonstrate that Comptonization plays an important role in producing high energy photons, as predicted by the current modeling scenario.
The black hole system 1E${thinspace}$1740.7$-$2942 is usually the brightest hard X-ray source (above 20 keV) near the Galactic Center, but presents some epochs of low emission (below the INTEGRAL detection limit, for example). In this work, we presen
t the results of studies on 1E${thinspace}$1740.7$-$2942 over 10 years, using the instruments ISGRI/IBIS and JEM-X, both on board the INTEGRAL observatory. We fit the spectra with both the compTT and cutoffpl models. According to the fits and taking the mean value over the 10 years, we have obtained a plasma temperature in the range $sim$20$,-,$90$thinspace$ keV, and an average powerlaw index of 1.41 ($sigma$=0.25). We have also made a Lomb$,-,$Scargle periodogram of the flux in the 50$,-,$20${thinspace}$keV band and found two tentative periods at 2.90 and 3.99${thinspace}$days. We present here the preliminary results of this ongoing work.
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