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BeppoSAX Observations of Algol: The first observations of an X-ray flare eclipse

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Fig.1: X-ray light curve of Algol measured with the SAX MECS2-MECS3 detectors in the 1.6 - 10 keV band between Aug 30, 1997 3:04 UT and Sep 1, 1997, 20:32 UT with phase calculated from the ephemeris JD = 2445739.003 + 2.8673285 E (E integer) for the times of primary minimum; a hundredth of a phase corresponds to 41.3 minutes. The phasing is such that for Phi(E) = E + 0.5 the X-ray dark early type primary is in front of the X-ray emitting late type secondary. Note the huge flare starting at phase Phi = 1.0 with a rise time of about 8.3 hours and peaking at Phi = 1.12. A rapid initial decay until at Phi = 1.25 is followed by an exponential decay. A clear eclipse of the flaring plasma is seen at Phi = 1.5, when the early type primary is in front of the late-type secondary. The dotted line indicates an estimate of the quiescent out-of-flare rate, extrapolated from the observed ROSAT all-sky survey count rate.

Fig.2: a) Upper panel: MECS count rate vs. phase in the interval 1.3 - 1.7; the solid line represents an exponential fit to the pre- and post eclipse light curve. b) Lower panel: Count rate vs. phase in the interval 1.3 - 1.7 with exponential decay (shown in panel a) removed; the zero line is explicitly shown. The flare eclipse starts at Phi = 1.39 with a somewhat shallow decay, whence at Phi = 1.451 a sharp decay starts (first contact). Totality begins at Phi = 1.488 (second contact) and ends at Phi = 1.505 (third contact). The light curve increases fast until Phi = 1.545 (fourth contact) and then more slowly until Phi = 1.605, when the flare eclipse is over. Below panel (b) the viewing geometry is shown at phases Phi = 1.42, 1.45, 1.50, and 155; the filled circle represents Algol A as it moves across Algol B.

Fig.3: 3D-Visualisation of the Algol system including the maximum volume containing the flare. Shown are the two binary components Algol A (foreground) and Algol B (background) as seen from our line of sight at phase Phi = 1.45. The extension below the ``south'' pole of Algol B is the computed locus of all points satisfying the following requirements: First, they must be totally eclipsed by Algol A between second and third contact. Second, they must be not eclipsed by Algol A and not occulted by Algol B itself before first and after fourth contact. Third, they must be visible between first and second but not between third and fourth contact or vice versa. And fourth, assuming that the flaring plasma originates from the surface of Algol B, along any radial line of sight from the surface of the Algol B to the point under consideration there should be no more than twenty percent rotational modulation. These requirements define the hose-like structure above the ``south'' pole of of Algol B, within which the flare must have occurred. The flare is clearly associated with Algol B and did not occur in the interbinary region.

Stand: Don, 20 Dez 2001 13:45:00

Verantwortlich für den Inhalt: J. Schmitt