Multi wavelength studies of accretion disks around compact objects
Abstract
In this thesis, I present multiwavelength studies of phenomena related to accretion disks around compact objects. The observations were made mainly with ground-based telescopes and the Hubble Space Telescope . I observed several known and candidate ultracompact low-mass X-ray binaries (LMXBs) and found that their optical spectra all show a lack of hydrogen emission lines, supporting the theoretical prediction that mass donors in ultracompact LMXBs must be H- depleted. Time-resolved photometry of the candidate source 4U 1543-624 revealed an 18 minute orbital periodicity, verifying the ultracompact nature of this binary. These studies strongly support the identification of several candidate systems with similar X-ray spectral features as ultracompact binaries. In the ultracompact binary 4U 1820-30, which has the shortest orbital period (685 s) among the known LMXBs, I discovered a 692-s periodicity from its far- ultraviolet (FUV) time series data. I interpret this longer-period FUV signal as a superhump oscillation, arising from a tidal resonance in the accretion disk of an extreme-mass-ratio binary.
I also present multiband imaging of the fields surrounding five newly discovered X-ray millisecond pulsars (MSPs) in an effort to identify and study their optical/IR counterparts. For the MSP SAX J1808.4-3658, the optical light curve taken during its 1998 X-ray outburst shows an exponential decay in intensity, roughly following the X-ray light curve early in the outburst. An optical counterpart of XTE J1814-338 was also detected. Finally, optical/IR observations of anomalous X-ray pulsars (AXPs) and X-ray point sources (XPSs) in young supernova remnants (SNRs) identified the IR counterpart to the AXP 1E 1048.1-5937 and a likely IR counterpart to the XPS in SNR RCW 103. The multiple IR band measurements of 1E 1048.1-5937 provide marginal evidence for spectral flattening, and cannot rule out an accretion disk scenario for AXPs. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)- Publication:
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Ph.D. Thesis
- Pub Date:
- 2004
- Bibcode:
- 2004PhDT.........8W
- Keywords:
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- Accretion disks;
- X-ray binaries;
- Pulsars;
- Astronomy, Astrophysics