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Post Info TOPIC: LSI+61303
Blobrana


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Posts: 131433
Date:
V615 Cassiopeiae
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Title: The Black Hole Candidate LSI+61303
Author: M. Massi, S. Migliari, M. Chernyakova

In recent years, fundamental relationships for the black hole X-ray binaries have been established between their X-ray luminosity L_X and the photon index Gamma of their X-ray spectrum. For the moderate-luminosity regime, an anti-correlation between Gamma and L_X has been observed. In this article, aimed to verify if the moderate luminous X-ray binary system LSI +61303 is a black hole, we analyse Swift observations of LSI +61303. We compare the derived L_X vs Gamma distribution, first with the statistical trend for black hole X-ray binaries, then with the trend of the pulsar PSR B1259-63, and finally with the individual trends of the black hole X-ray binaries Swift J1357.2-0933 and V404 Cygni. We find that the system PSR B1259-63 shows a positive correlation between Gamma and L_X, whereas in contrast LSI +61303 shows the same anti-correlation as for black hole X-ray binaries. Moreover, the trend of LSI +61303 in the L_X/L_Eddington-Gamma plane overlaps with that of the two black holes Swift J1357.2-0933 and V404 Cygni. All three systems, Swift J1357.2-0933, V404 Cygni and LSI +61303 well trace the last part of the evolution of accreting black holes at moderate-luminosity until their drop to quiescence.

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Blobrana


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Posts: 131433
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RE: LSI+61303
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Title: VLBA images of the precessing jet of LSI+61303
Authors: M. Massi, E. Ros, L. Zimmermann

Context: In 2004, changes in the radio morphology of the Be/X-ray binary system LSI+61303 suggested that it is a precessing microquasar. In 2006, a set of VLBA observations performed throughout the entire orbit of the system were not used to study its precession because the changes in radio morphology could tentatively be explained by the alternative pulsar model. However, a recent radio spectral index data analysis has confirmed the predictions of the two-peak microquasar model, which therefore does apply in LSI+61303.
Aims: We revisit the set of VLBA observations performed throughout the orbit to determine the precession period and improve our understanding of the physical mechanism behind the precession.
Methods: By reanalysing the VLBA data set, we improve the dynamic range of images by a factor of four, using self-calibration. Different fitting techniques are used and compared to determine the peak positions in phase-referenced maps.
Results: The improved dynamic range shows that in addition to the images with a one-sided structure, there are several images with a double-sided structure. The astrometry indicates that the peak in consecutive images for the whole set of observations describes a well-defined ellipse, 6-7 times larger than the orbit, with a period of about 28 d.
Conclusions: A double-sided structure is not expected to be formed from the expanding shocked wind predicted in the pulsar scenario. In contrast, a precessing microquasar model can explain the double- and one-sided structures in terms of variable Doppler boosting. The ellipse defined by the astrometry could be the cross-section of the precession cone, at the distance of the 8.4 GHz-core of the steady jet, and 28d the precession period.

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Blobrana


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Posts: 131433
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Title: Observations of LSI+61303 with Swift
Authors: J. Holder, A. Falcone, D. Morris

The TeV emitting high-mass X-ray binary system LSI+61303 was observed with the Swift satellite from early September 2006 to early January 2007. Many of these observations were contemporaneous with TeV observations. The data consist of observations on 24 separate days with durations ranging between 700s and 4700s, and partially cover 4.5 orbital periods of the binary system. We present here an analysis of the 0.2 to 10keV X-ray data from the Swift-XRT instrument. Contemporaneous optical data from UVOT are also available.

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