High Magnetic Field Radio Pulsars Research Articles

The Magnetar Connection

AbstractWe investigate the combined evolution of the dipolar surface magnetic field (Bs) and the spin-period (Ps) of known Magnetars and high magnetic field ( $${{\rm{B}}_s} \mathbin{\lower.3ex\hbox{$\buildrel>\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} {10^{13}}{\rm{G}}$$ ) radio pulsars. We study the long term behaviour of these objects assuming a simple Ohmic dissipation of the magnetic field. Identifying the regions (in the Ps-Bs plane) in which these neutron stars would likely move into, before crossing the death-line to enter the pulsar graveyard, we comment upon the possible connection between the Magnetars and other classes of neutron stars.

On the evolution of high-B radio pulsars with measured braking indices

We have investigated the long-term evolutions of the high-magnetic field radio pulsars (HBRPs) with measured braking indices in the same model that was applied earlier to individual anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs) and dim isolated neutron stars (XDINs). We have shown that the rotational properties (period, period derivative and braking index) and the X-ray luminosity of individual HBRPs can be acquired simultaneously by the neutron stars evolving with fallback discs. The model sources reach the observed properties of HBRPs in the propeller phases, when pulsed radio emission is allowed, at ages consistent with the estimated ages of the supernova remnants of the sources. Our results indicate that the strength of magnetic dipole fields of HBRPs are comparable to and even greater than those of AXP/SGRs and XDINs, but still one or two orders of magnitude smaller than the values inferred from the magnetic dipole torque formula. The possible evolutionary paths of the sources imply that they will lose their seemingly HBRP property after about a few 10^4 yr, because either their rapidly decreasing period derivatives will lead them into the normal radio pulsar population, or they will evolve into the accretion phase switching off the radio pulses.

THE SPIN-DOWN OF SWIFT J1822.3–1606: A NEW GALACTIC MAGNETAR

On 2011 July 14, a new magnetar candidate, Swift J1822.3-1606, was identified via a rate trigger on the Swift/Burst Alert Telescope. Here we present an initial analysis of the X-ray properties of the source, using data from the Rossi X-ray Timing Explorer, Swift, and the Chandra X-ray Observatory, spanning 2011 July 16--September 22. We measure a precise spin period of P=8.43771963(5) s and a spin-down rate of 2.97(28)E-13, at MJD 55761.0, corresponding to an inferred surface dipole magnetic field strength of B=5.1E13 G, the second lowest thus far measured for a magnetar, though similar to 1E~2259+586 as well as to several high-magnetic field radio pulsars. We show that the pulsed X-ray flux decay in the 2--10 keV band is best fit by an exponential with a time constant of 16.4+/-0.3 days. After increasing from ~35% during the first week after the onset of the outburst, the pulsed fraction in the 2--10 keV band remained constant at ~45. We argue that these properties confirm this source to be a new member of the class of objects known as magnetars.

UsingChandrato Unveil the High‐Energy Properties of the High Magnetic Field Radio Pulsar J1119−6127

(shortened) PSR J1119-6127 is a high magnetic field (B=4.1E13 Gauss), young (<=1,700 year-old), and slow (P=408 ms) radio pulsar associated with the supernova remnant (SNR) G292.2-0.5. In 2003, Chandra allowed the detection of the X-ray counterpart of the radio pulsar, and provided the first evidence for a compact pulsar wind nebula (PWN). We here present new Chandra observations which allowed for the first time an imaging and spectroscopic study of the pulsar and PWN independently of each other. The PWN is only evident in the hard band and consists of jet-like structures extending to at least 7 from the pulsar, with the southern `jet' being longer than the northern `jet'. The spectrum of the PWN is described by a power law with a photon index~1.1 for the compact PWN and ~1.4 for the southern long jet (at a fixed column density of 1.8E22/cm2), and a total luminosity of 4E32 ergs/s (0.5-7 keV), at a distance of 8.4 kpc. The pulsar's spectrum is clearly softer than the PWN's spectrum. We rule out a single blackbody model for the pulsar, and present the first evidence of non-thermal (presumably magnetospheric) emission that dominates above ~3keV. A two-component model consisting of a power law component (with photon index ~1.5--2.0) plus a thermal component provides the best fit. The thermal component can be fit by either a blackbody model with a temperature kT~0.21 keV, or a neutron star atmospheric model with a temperature kT~0.14 keV. The efficiency of the pulsar in converting its rotational power, Edot, into non-thermal X-ray emission from the pulsar and PWN is ~5E-4, comparable to other rotation-powered pulsars with a similar Edot. We discuss our results in the context of the X-ray manifestation of high-magnetic field radio pulsars in comparison with rotation-powered pulsars and magnetars.

VLT/NACOobservations of the high-magnetic field radio pulsar PSR J1119-6127

Context. Recent radio observations have unveiled the existence of a number of radio pulsars with spin-down derived magnetic fields in the magnetar range. However, their observational properties appear to be more similar to those of the classical radio pulsars than to the magnetars’s ones. Aims. To shed light on this puzzle we first have to determine whether the spin-down derived magnetic field values for these radio pulsars are indeed representative of the actual neutron star magnetic field or if they are polluted, e.g. by the effects of a torque from a fallback disk. Methods. To investigate this possibility, we have performed deep IR (J,H,Ks bands) observations of one of these high magnetic field radio pulsars (PSR J1119–6127) with the ESO VLT to search for IR emission which can be associated with a disk. Results. No IR emission is detected from the pulsar position down to J ∼ 24, H ∼ 23 and Ks ∼ 22. Conclusions. By comparing our flux upper limits with the predictions of fallback disk models, we have found that we can only exclude the presence of a disk with accretion rate u M > 3 × 10 16 gs −1 . This lower limit cannot rule out the presence of a substantial disk torque on the pulsar, which would then lead to overestimate the value of the magnetic field inferred from P and u P .W e have also compared the upper limit on the IR luminosity of PSR J1119–6127 with the IR luminosities of rotation-powered pulsars and magnetars. We found that, while magnetars are intrinsically more efficient IR emitters than rotation-powered pulsars, possibly because of their higher magnetic field, the relatively low IR emission efficiency of PSR J1119–6127 suggests that it is more similar to the latters than to the former.

PSR J1119–6127 and the X-ray emission from high magnetic field radio pulsars

The existence of radio pulsars having inferred magnetic fields in the magnetar regime suggests that possible transition objects could be found in the radio pulsar population. The discovery of such an object would contribute greatly to our understanding of neutron star physics. Here we report on unusual X-ray emission detected from the radio pulsar PSR J1119–6127 using XMM–Newton. The pulsar has a characteristic age of 1,700 yrs and inferred surface dipole magnetic field strength of 4.1×1013 G. In the 0.5–2.0 keV range, the emission shows a single, narrow pulse with an unusually high pulsed fraction of ∼70%. No pulsations are detected in the 2.0–10.0 keV range, where we derive an upper limit at the 99% level for the pulsed fraction of 28%. The pulsed emission is well described by a thermal blackbody model with a high temperature of ∼2.4×106 K. While no unambiguous signature of magnetar-like emission has been found in high-magnetic-field radio pulsars, the X-ray characteristics of PSR J1119–6127 require alternate models from those of conventional thermal emission from neutron stars. In addition, PSR J1119–6127 is now the radio pulsar with the smallest characteristic age from which thermal X-ray emission has been detected.

Chandra X-Ray Detection of the High Magnetic Field Radio Pulsar PSR J1718-3718

We report on the serendipitous X-ray detection, using the Chandra X-Ray Observatory, of the radio pulsar PSR J1718-3718. This pulsar has one of the highest inferred surface dipole magnetic fields in the radio pulsar population (B = 7.4 × 1013 G), higher than that inferred for one well-known anomalous X-ray pulsar (AXP). The X-ray emission for PSR J1718-3718 appears pointlike and has a purely thermal spectrum, with kT = 0.145 keV and absorbed 0.5-2 keV flux of (6.3-6.9) × 10-15 ergs s-1 cm-2. We show that the pulsar's 2-10 keV luminosity is several orders of magnitude smaller than those of the nontransient AXPs and consistent with the predictions of standard models for initial cooling. The number of high magnetic field radio pulsars observed at X-ray energies now stands at five. All are X-ray faint, suggesting either that there is a significant physical distinction between high magnetic field radio pulsars and AXPs or that high magnetic field radio pulsars are, in fact, quiescent AXPs.

Chandra Detection of the High Magnetic Field Radio Pulsar J1119-6127in the Supernova Remnant G292.2-0.5

We report the Chandra Advanced CCD Imaging Spectrometer detection of the X-ray counterpart of the high magnetic field, ~1600 yr old, 407 ms radio pulsar J1119-6127 associated with the supernova remnant G292.2-0.5. The powerful imaging capability of Chandra also unveiled, for the first time, a faint 3'' × 6'' pulsar wind nebula (PWN) at energies above ~1.2 keV. The X-ray emission from the pulsar and its associated nebula is well described by an absorbed power law model with a photon index Γ = 2.2. The corresponding 0.5-10 keV unabsorbed X-ray luminosity is (5.5) × 1032 ergs s-1 (at 6 kpc). When compared to two other pulsars with similar spin and magnetic properties, J1119-6127 stands out as being the least efficient at turning rotational kinetic energy into X-ray emission. This study shows that high magnetic field radio pulsars can be significant X-ray emitters, and Chandra is needed to study the emission properties of the pulsars and associated faint PWNs.

Magnetically Accreting Isolated Old Neutron Stars

Previous work on the emission from isolated old neutron stars (IONS) accreting the inter-stellar medium (ISM) focussed on gravitational capture - Bondi accretion. We propose a new class of sources which accrete via magnetic interaction with the ISM. While for the Bondi mechanism, the accretion rate decreases with increasing NS velocity, in magnetic accretors (MAGACs=magics) the accretion rate increases with increasing NS velocity. MAGACs will be produced among high velocity (~> 100 km s-1) high magnetic field (B> 1e14 G) radio pulsars - the ``magnetars'' - after they have evolved first through magnetic dipole spin-down, followed by a ``propeller'' phase (when the object sheds angular momentum on a timescale ~ 1e14 G; minimum velocities relative to the ISM of >25-100 km s-1, depending on B, well below the median in the observed radio-pulsar population; spin-periods of >days to years; accretion luminosities of 1e28- 1e31 ergs s-1 ; and effective temperatures kT=0.3 - 2.5 keV if they accrete onto the magnetic polar cap. We find no examples of MAGACs among previously observed source classes (anomalous X-ray pulsars, soft-gamma-ray repeaters or known IONS). However, MAGACs may be more prevelant in flux-limited X-ray catalogs than their gravitationally accreting counterparts.

High Magnetic Field Pulsars and Magnetars: A Unified Picture.

We propose a unified picture of high magnetic field radio pulsars and magnetars by arguing that they are all rotating high-field neutron stars but that their magnetic axes have different orientations with respect to their rotation axes. In strong magnetic fields where photon splitting suppresses pair creation near the surface, the high-field pulsars can have active inner accelerators while the anomalous X-ray pulsars cannot. This can account for the very different observed emission characteristics of the anomalous X-ray pulsar 1E 2259+586 and the high-field radio pulsar PSR J1814-1744. A predicted consequence of this picture is that radio pulsars having surface magnetic fields greater than about 2x1014 G should not exist.