Precision Timing of Two Anomalous X-Ray Pulsars

Area of Science:

• High-energy astrophysics
• X-ray astronomy
• Pulsar physics

Background:

• Anomalous X-ray pulsars (AXPs) are highly magnetized neutron stars emitting X-rays.
• Understanding the emission mechanisms and evolution of AXPs is crucial in astrophysics.

Purpose of the Study:

• To conduct long-term X-ray timing of two specific AXPs: 1RXS J170849.0-400910 and 1E 2259+586.
• To determine the rotational stability and frequency derivatives of these pulsars.
• To test the validity of the magnetar hypothesis versus binary accretion models.

Main Methods:

• Utilized the Rossi X-Ray Timing Explorer (RXTE) for monthly observations.
• Obtained phase-coherent timing solutions over extended periods (1.4 and 2.6 years).
• Analyzed rotational frequencies and their derivatives for both pulsars.

Main Results:

• Achieved highly stable rotational timing solutions for both 1RXS J170849.0-400910 and 1E 2259+586.
• Derived precise rotational frequencies and frequency derivatives for each pulsar.
• Found the derived frequency derivative for 1E 2259+586 to be inconsistent with previous 20-year observations.

Conclusions:

• The observed stable rotation and derived parameters are consistent with the magnetar model for AXPs.
• The findings strongly disfavor binary accretion as the energy source for these pulsars.
• Long-term X-ray timing provides critical data for distinguishing between competing astrophysical models.