Occultation of X-Rays from Scorpius X-1 by Small Trans-Neptunian Objects (2006, Nature Letters)

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Occultation of X-Rays from Scorpius X-1 by Small Trans-Neptunian Objects (2006, Nature Letters). Hsiang-Kuang Chang, Sun-Kun King, Jau-Shian Liang, Ping-Shien Wu, Lupin Chun-Che Lin,& Jeng-Lun Chiu1. Kuiper Belt Object. [ Conceptual illustration of KBO detection ]. Optical occultation search: - PowerPoint PPT Presentation

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<ul><li><p>Occultation of X-Rays from Scorpius X-1 by Small Trans-Neptunian Objects (2006, Nature Letters)Hsiang-Kuang Chang, Sun-Kun King, Jau-Shian Liang, Ping-Shien Wu, Lupin Chun-Che Lin,&amp; Jeng-Lun Chiu1</p></li><li><p>Kuiper Belt Object</p></li><li><p>[ Cumulative sky density vs. apparent red magnitude of KBOs (Bernstein et al. 2004) ]</p></li><li><p>[ Conceptual illustration of KBO detection ]</p></li><li><p>Optical occultation search:</p><p>TAOS CfA, NCU, ASIAA</p><p>French Roques et al. Paris Observatory</p><p>Australian Georgevits et al. UNSW, AAO</p><p>Canadian Kavelaars et al. NRC, McMaster U</p><p>(Whipple CfA, JPL)</p><p>No definite detections so far</p></li><li><p>Why X-ray occultation?faster photometryless diffractionshorter eventssmaller bodiesbetter chance to detect* The background X-ray source needs to be bright enough.* Sco X-1 is the brightest in the Sky.* RXTE/PCA has the largest effective area.* The typical PCA count rate of Sco X-1 is 105 cps. * Detection of msec time-scale occultation is possible.* The RXTE/PCA data used in this search spans over 7 years from 1996 to 2002. The total exposure is 564.3 ksec.</p></li><li><p>* In the 564-ksec data, 107 events were found.* What are they? Instrumental? Intrinsic variation of Sco X-1? Objects moving around Sco X-1? Objects in the interstellar space moving across the line of sight? The main belt asteroids?* Assuming a distance of 43 AU and a circular orbital with a minimum inclination, the corresponding size of these occulting TNOs can be estimated from its speed relative to the RXTE spacecraft at each event epoch. </p></li><li><p>Direct imaging is possible only for larger ones (e.g. Trujillo et al. 2001).A pains-taking HST observation reports 3 detections (Bernstein et al. 2004).Models predict a turnover in the power law at small sizes (e.g. Kenyon et al. 2004).Optical occultation survey may be able to detect objects down to km size (e.g. the Taiwan-America Occultation Survey, TAOS).</p></li><li><p>Summary</p><p>&gt; The discovery of X-ray occultation by small TNOs opens up a new window in this field.</p><p>&gt; The first result indicates a small turnover radius (less than about 100 meters) in the size distribution of TNOs, or, a second component at small sizes. The total mass in the trans-Neptunian region can be several earth masses, much more than previously thought. </p><p>&gt; More detailed analysis and more observations will be very rewarding in deriving the size and spatial distribution of TNOs and in resolving the X-ray emitting region of Sco X-1.</p></li></ul>