Multiwavelength studies of accretion disks around compact objects

Abstract

(cont.) 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.

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