[Paper Review] Anomalous Pulsars

И. Ф. Малов|arXiv (Cornell University)|Nov 4, 2007

Pulsars and Gravitational Waves Research4 citations

TL;DR

This paper proposes that the observed differences among anomalous X-ray pulsars (AXPs), soft gamma-ray repeaters (SGRs), and related neutron star classes arise primarily from the geometry of their magnetic and rotation axes, particularly the angle β between them. For β < 10° (aligned rotators), drift waves in the magnetosphere explain periodic emissions; for larger β (nearly orthogonal rotators), accretion from surrounding material induces modulation and transient events.

ABSTRACT

Many astrophysicists believe that Anomalous X-Ray Pulsars (AXP), Soft Gamma-Ray Repeaters (SGR), Rotational Radio Transients (RRAT), Compact Central Objects (CCO), and X-Ray Dim Isolated Neutron Stars (XDINS) belong to different classes of anomalous objects with neutron stars as the central bodies inducing all their observable peculiarities. We have shown earlier (I.F.Malov and G.Z.Machabeli, Astron. Astrophys. Trans. 25, 7, 2006) that AXPs and SGRs could be described by the drift model in the framework of preposition on usual properties of the central neutron star (rotation periods P ~ 0.1 - 1 sec, surface magnetic fields B ~ 10^11 - 10^13 G). Here we shall try to show that some differences of considered sources will be explained by their geometry (particularly, by the angle BETA between their rotation and magnetic axes). If BETA < 10 deg. (the aligned rotator) the drift waves at the outer layers of the neutron star magnetosphere should play a key role in the observable periodicity. For large values of BETA (the case of the nearly orthogonal rotator) an accretion from the surrounding medium (for example, from the relic disk) can cause some modulation and transient events in received radiation.

Motivation & Objective

• To investigate the origin of observational differences among AXPs, SGRs, RRATs, CCOs, and XDINS.
• To determine whether geometric differences in neutron star magnetic and rotation axes can explain their distinct emission behaviors.
• To assess whether drift waves or accretion processes dominate periodicity and transient activity in these sources.

Proposed method

• Proposes a drift model for AXPs and SGRs based on standard neutron star properties (P ~ 0.1–1 sec, B ~ 10^11–10^13 G).
• Analyzes the role of the angle β between rotation and magnetic axes in shaping observable emission patterns.
• Distinguishes between aligned rotators (β < 10°), where drift waves in the magnetosphere drive periodicity.
• Considers nearly orthogonal rotators (large β) where accretion from relic disks or surrounding medium causes modulation and transient events.
• Uses theoretical modeling to link geometric configuration to observable phenomena in isolated neutron stars.

Experimental results

Research questions

• RQ1 How do differences in the angle β between magnetic and rotation axes affect the emission characteristics of anomalous neutron stars?
• RQ2 What physical mechanism explains periodicity in AXPs and SGRs when β is small?
• RQ3 Can accretion from ambient material explain transient and modulated emissions in sources with large β?
• RQ4 Why do AXPs, SGRs, and other isolated neutron stars exhibit distinct observational behaviors despite similar central object properties?
• RQ5 To what extent can drift waves and accretion processes account for the full range of observed behaviors in anomalous neutron star classes?

Key findings

• For β < 10°, drift waves in the outer magnetosphere are the primary driver of observable periodicity in AXPs and SGRs.
• In sources with large β, accretion from surrounding material—such as relic disks—can induce modulation and transient events.
• The same underlying neutron star properties (P ~ 0.1–1 sec, B ~ 10^11–10^13 G) can produce diverse behaviors depending on β.
• The geometric configuration (aligned vs. nearly orthogonal rotator) explains key differences between AXPs/SGRs and other anomalous sources like RRATs and XDINS.
• The drift model successfully accounts for periodic emissions in AXPs and SGRs under standard neutron star assumptions.
• Accretion processes provide a plausible explanation for non-periodic or variable emissions in misaligned rotators.