[Paper Review] Young pre-Low-Mass X-ray Binaries in propeller phase : Nature of the 6.7-hour periodic X-ray source 1E 161348-5055 in RCW 103

Harshal Bhadkamkar, Pranab Ghosh|Sep 1, 2009

Astrophysical Phenomena and Observations31 references11 citations

TL;DR

This paper proposes that 1E 161348-5055, a 6.7-hour periodic X-ray source in the young supernova remnant RCW 103, is a young pre-Low-Mass X-ray Binary (pre-LMXB) with a fast-spinning neutron star in the propeller phase, where orbital modulation of mass transfer in an eccentric orbit produces the observed periodic X-ray emission. The model successfully reproduces the light curve and spectral properties using both Illarionov-Sunyaev and Romanova-Lovelace propeller torque prescriptions, offering a standard astrophysical explanation without requiring exotic magnetar-like fields.

ABSTRACT

Discovery of the 6.7-hour periodicity in the X-ray source 1E 161348-5055 in RCW 103 has led to investigations of the nature of this periodicity. We explore a model for 1E 161348-5055, wherein a fast-spinning neutron star with a magnetic field $\sim 10^{12}$ G in a young pre-Low-Mass X-ray Binary (pre-LMXB) with an eccentric orbit of period 6.7 hr operates in the "propeller" phase. The 6.7-hr light curve of 1E 161348-5055 can be quantitatively accounted by a model of orbitally-modulated mass transfer through a viscous accretion disk and subsequent propeller emission (both Illarionov-Sunyaev type and Romanova-Lovelace et al type), and spectral and other properties are also in agreement. Formation and evolution of model systems are shown to be in accordance both with standard theories.

Motivation & Objective

• To explain the 6.7-hour X-ray periodicity in 1E 161348-5055 as orbital modulation in a young pre-LMXB system.
• To test whether the observed light curve and spectral properties can be quantitatively reproduced by propeller models with canonical neutron star magnetic fields (~10^12 G).
• To assess the viability of the pre-LMXB model as an alternative to the recently proposed magnetar model for 1E 161348-5055.
• To examine the formation and tidal evolution of eccentric binaries formed in He-star supernovae, consistent with the observed system age and environment.
• To identify potential observational discriminators between the pre-LMXB and magnetar models for this class of sources.

Proposed method

• Modeling the 6.7-hour light curve using orbitally modulated mass transfer through a viscous accretion disk in an eccentric binary system.
• Applying two distinct theoretical frameworks for propeller torques: Illarionov-Sunyaev and Romanova-Lovelace et al., to simulate X-ray emission from the neutron star's magnetospheric ejection of matter.
• Simulating the tidal circularization timescale of eccentric orbits in young binaries to assess the longevity of orbital modulation.
• Comparing the predicted spectral and luminosity evolution of the propeller phase with observed properties of 1E 161348-5055 and soft X-ray transients like Aquila X-1 in quiescence.
• Evaluating the consistency of the model with standard binary evolution theories, including common-envelope evolution and He-star supernova scenarios.
• Assessing the impact of mass and angular momentum loss on orbital eccentricity enhancement in pre-LMXBs.

Experimental results

Research questions

• RQ1 Can the 6.7-hour periodic X-ray modulation in 1E 161348-5055 be explained by orbital modulation in a young, eccentric pre-LMXB with a neutron star in the propeller regime?
• RQ2 Do the observed spectral and luminosity characteristics of 1E 161348-5055 match those predicted by disk-fed propeller emission models with canonical magnetic fields (~10^12 G)?
• RQ3 Is the formation and evolution of such a system consistent with standard binary evolution pathways, including common-envelope evolution and He-star supernova explosions?
• RQ4 What distinguishes the pre-LMXB model from the recently proposed magnetar model in terms of observable signatures?
• RQ5 Can the observed properties of 1E 161348-5055 be explained without invoking superstrong magnetic fields (~10^15 G) or exotic neutron star states?

Key findings

• The 6.7-hour light curve of 1E 161348-5055 is quantitatively reproduced by models of both Illarionov-Sunyaev and Romanova-Lovelace type propeller torques, confirming the viability of the propeller mechanism.
• The spectral and luminosity properties of 1E 161348-5055 are consistent with those of soft X-ray transients like Aquila X-1 in their low/quiescent states, supporting the analogy to propeller-phase systems.
• The model predicts that orbital modulation of X-ray emission is expected only during the eccentric phase of pre-LMXBs, which aligns with the observed periodicity and the young age of RCW 103 (~2000 yr).
• The lifetime of the eccentric-binary phase in pre-LMXBs is estimated to be ~10^6–10^7 years, consistent with the expected population ratio of ~1 such system per 100 LMXBs, matching current observational statistics.
• The model remains viable even when considering eccentricity-enhancing effects from mass and angular momentum loss, though these are found to be minor at the inferred mass transfer rates.
• The study suggests that no compelling evidence currently exists for invoking magnetars in 1E-type systems, as standard pre-LMXB evolution with canonical magnetic fields can explain all observed features.