Could AX J1841.0$-$0536 Be an Anti-Magnetar?

Abstract

Recent observations show that supergiant fast X-ray transients (SFXTs) spend most of their lifetime at an intermediate level luminosity $\sim 10^{33}-10^{34}$ ergs${}^{-1}$, and, when a blackbody model for the spectra is adopted, the resulting radii of the emission region are always only a few hundred meters, supporting the idea that during the intermediate state SFXTs are accreting matter from the companion star. From these observational phenomena we derive possible constraints on the magnetic field strengths of the neutron stars in four SFXTs with known spin periods. While IGR J11215$-$5952, IGR J16465$-$4507, and IGR J18483$-$0311 may have magnetic fields (up to a few $10^{11}-10^{12}$ G) similar to those of normal X-ray pulsars, the magnetic field of AX J1841.0$-$0536 is considerably low ($\la 10^{10}$ G). The high-mass companion stars in SFXTs implies that the neutron stars are relatively young objects, with age less than $\sim 10^7$ yr. Analysis of the spin evolution shows that neutron stars like AX J1841.0$-$0536 should be born with relatively long spin periods ($\la 1$ s). Considering the fact that among the four SFXTs only AX J1841.0$-$0536 is a "proper" one, and the other three are either "intermediate" SFXTs or have peculiar characteristics, we suggest that the neutron stars in some of SFXTs may have similar characteristics as several young central compact objects in supernova remnants called "anti-magnetars". These features, combining with accretion from clumpy winds, could make them distinct from standard supergiant X-ray binaries -- the low fields and relatively long spin periods guarantee accretion at very low level, resulting in a large dynamic range ($10^4-10^5$) of X-ray luminosity.

12 pages, accepted for publication in MNRAS

References in corpus (18)

• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• Probing clumpy stellar winds with a neutron star
• An alternative hypothesis for the outburst mechanism in Supergiant Fast X-ray Transients: the case of IGR J11215-5952
• Monitoring Supergiant Fast X-ray Transients with Swift. I. Behavior outside outbursts
• Discovery of a 112 ms X-ray Pulsar in Puppis A: Further Evidence of Neutron Stars Weakly Magnetized at Birth
• Precise Timing of the X-ray Pulsar 1E 1207.4-5209: A Steady Neutron Star Weakly Magnetized at Birth
• IGR J11215-5952: a hard X-ray transient displaying recurrent outbursts
• Monitoring Supergiant Fast X-ray Transients with Swift. Results from the first year
• X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth
• Detection of an orbital period in the supergiant high mass X-ray binary IGR J16465$-$4507 with Swift-BAT
• Monitoring Supergiant Fast X-ray Transients with Swift. Rise to the outburst in IGR J16479-4514
• Swift/XRT monitoring of the Supergiant Fast X-ray Transient IGR J18483-0311 for an entire orbital period
• The orbital period in the supergiant fast X-ray transient IGR J16465--4507
• Two years of monitoring Supergiant Fast X-ray Transients with Swift
• Exploration of the $\ps-\pb$ Relation for Wind-Fed X-Ray Pulsars
• The first broad-band X-ray study of the Supergiant Fast X-ray Transient SAXJ1818.6-1703 in outburst
• Suzaku observes weak flares from IGR J17391-3021 representing a common low-activity state in this SFXT
• The longest observation of a low intensity state from a Supergiant Fast X-ray Transient: Suzaku observes IGRJ08408-4503

Cited by in corpus (1)

• Fast X-ray transients in the Galactic bulge with the Rossi X-ray Timing Explorer