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Continuous Long Term Observations of Accreting Pulsars


Koh, Danny Towsian (1998) Continuous Long Term Observations of Accreting Pulsars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ch1h-0w87.


The all-sky monitoring ability of the BATSE instrument on the GRO has enabled the first uniform, continuous and long term observations of the torque and fluxes of many known accreting pulsars. In the first part of this thesis, I describe the capabilities of BATSE for detecting hard X-rays, the techniques developed to perform timing and flux measurements, and the steps involved in reducing the raw data sets to a standardized database of data products for each accreting pulsar monitored by BATSE.

In the second part of this thesis, I describe several studies performed with this database. The first is a broad overview of all the accreting pulsars monitored by BATSE. For each source, I display the frequency and pulsed flux histories from ≈ five years of BATSE observations, and provide a brief summary of the BATSE findings.

I then focus on the wind-fed accreting pulsar GX 301-2. The most striking features in the pulsar frequency history are two steady and rapid spin-up episodes, with v [over-dot] ≈ (3-5) x 10⁻¹² Hz s⁻¹, each lasting for about 30 days. They probably represent the formation of transient accretion disks in this wind-fed pulsar. Except for these spin-up episodes, there are virtually no net changes in the neutron star spin frequency on long time scales. We suggest that the long-term spin-up trend observed since 1984 (v [over-dot] ≈ 2 x 10⁻¹³ Hz s⁻¹) may be due entirely to brief (≈ 20 d) spin-up episodes similar to those we have discovered.

Next, I highlight the most significant trends revealed by the BATSE observations and discuss their implications for our current understanding of the spin-evolution and torque-luminosity relations in accreting pulsars. Alternating episodes of steady spin-up and spin-down were found to be a surprisingly common characteristic of many persistent sources. Pulsed flux and accretion torque are strongly correlated in outbursts of transient accreting pulsars, but uncorrelated, or even anticorrelated, in persistent sources. I describe the various competing models that currently exist and critically assess each model within the context of the BATSE observations.

Finally, I describe how BATSE observations of the recurrence rate of transient systems can be used to infer the galactic population of high-mass Be-transient systems.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Prince, Thomas A.
Group:Space Radiation Laboratory, Astronomy Department
Thesis Committee:
  • Prince, Thomas A. (chair)
  • Weinstein, Alan Jay
  • Blandford, Roger D.
  • Soifer, B. Thomas
Defense Date:11 July 1997
Record Number:CaltechETD:etd-08292008-082313
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3272
Deposited By: Imported from ETD-db
Deposited On:10 Sep 2008
Last Modified:26 Oct 2021 18:54

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