Analytical X-ray Astronomy
Analytical X-ray astronomy is applied to an astronomy puzzle in an attempt to provide an acceptable solution. Consider the following puzzle.
High-mass X-ray binaries (HMXBs) are composed of OB supergiant companion stars and compact objects, usually neutron stars (NS) or black holes (BH). Supergiant X-ray binaries (SGXBs) are HMXBs in which the compact objects orbit massive companions with orbital periods of a few days (3–15 d), and in circular (or slightly eccentric) orbits. SGXBs show typical the hard X-ray spectra of accreting pulsars and most show strong absorption as obscured HMXBs. X-ray luminosity (Lx) increases up to 1036 erg·s−1 (1029 watts).
The mechanism triggering the different temporal behavior observed between the classical SGXBs and the recently discovered supergiant fast X-ray transients (SFXT)s is still debated.
Aim: use the discovery of long orbits (>15 d) to help discriminate between emission models and perhaps bring constraints on the models.
Method: analyze archival data on various SGXBs such as has been obtained by INTEGRAL for candidates exhibiting long orbits. Build short- and long-term light curves. Perform a timing analysis in order to study the temporal behavior of each candidate on different time scales.
Compare various astronomical models:
- direct spherical accretion
- Roche-Lobe overflow via an accretion disk on the compact object.
Draw some conclusions: for example, the SGXB SAX J1818.6-1703 was discovered by BeppoSAX in 1998, identified as a SGXB of spectral type between O9I−B1I, which also displayed short and bright flares and an unusually very low quiescent level leading to its classification as a SFXT. The analysis indicated an unusually long orbital period: 30.0 ± 0.2 d and an elapsed accretion phase of ~6 d implying an elliptical orbit and possible supergiant spectral type between B0.5-1I with eccentricities e ~ 0.3–0.4. The large variations in the X-ray flux can be explained through accretion of macro-clumps formed within the stellar wind.
Choose which model seems to work best: for SAX J1818.6-1703 the analysis best fits the model that predicts SFXTs behave as SGXBs with different orbital parameters; hence, different temporal behavior.
Read more about this topic: X-ray Astronomy
Famous quotes containing the words astronomy and/or analytical:
“Awareness of the stars and their light pervades the Koran, which reflects the brightness of the heavenly bodies in many verses. The blossoming of mathematics and astronomy was a natural consequence of this awareness. Understanding the cosmos and the movements of the stars means understanding the marvels created by Allah. There would be no persecuted Galileo in Islam, because Islam, unlike Christianity, did not force people to believe in a fixed heaven.”
—Fatima Mernissi, Moroccan sociologist. Islam and Democracy, ch. 9, Addison-Wesley Publishing Co. (Trans. 1992)
“I have seen too much not to know that the impression of a woman may be more valuable than the conclusion of an analytical reasoner.”
—Sir Arthur Conan Doyle (18591930)