Long-term evolution of anomalous X-ray pulsars and soft gamma repeaters

We have investigated the long-term evolution of individual anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) with relatively well constrained X-ray luminosity and rotational properties. In the frame of the fallback disc model, we have obtained the ranges of disc mass and dipole field strength that can produce the observed source properties. We have compared our results with those obtained earlier for dim isolated neutron stars (XDINs). Our results show that (1) the X-ray luminosity, period and period derivative of the individual AXP/SGR sources can be produced self-consistently in the fallback disc model with very similar basic disc parameters to those used earlier in the same model to explain the long-term evolution of XDINs, (2) except two sources, AXP/SGRs are evolving in the accretion phase; these two exceptional sources, like XDINs, completed their accretion phase in the past and are now evolving in the final propeller phase and still slowing down with the disc torques, (3) the dipole field strength (at the poles) of XDINs are in the $10^{11}-10^{12}$ G range, while AXP/SGRs have relatively strong dipole fields between $1-6 \times 10^{12}$ G, and (4) the source properties can be obtained with large ranges of disc masses which do not allow a clear test of correlation between disc masses and the magnetic dipole fields for the whole AXP/SGRs and XDIN population.Comment: 10 pages, 6 figures, Accepted for publication in MNRA

Central Compact Objects: some of them could be spinning up?

Among confirmed central compact objects (CCOs), only three sources have measured period and period derivatives. We have investigated possible evolutionary paths of these three CCOs in the fallback disc model. The model can account for the individual X-ray luminosities and rotational properties of the sources consistently with their estimated supernova ages. For these sources, reasonable model curves can be obtained with dipole field strengths $\sim$ a few $\times 10^9$ G on the surface of the star. The model curves indicate that these CCOs were in the spin-up state in the early phase of evolution. The spin-down starts, while accretion is going on, at a time $t \sim 10^3 - 10^4$ yr depending on the current accretion rate, period and the magnetic dipole moment of the star. This implies that some of the CCOs with relatively long periods, weak dipole fields and high X-ray luminosities could be strong candidates to show spin-up behavior if they indeed evolve with fallback discs.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Investigation of young neutron star populations with fallback disk model

Young isolated neutron stars manifest themselves as members of different populations, namely anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated neutron stars (XDINs), rotating radio transients (RRATs), central compact objects (CCOs) and the so-called "high-magnetic-field" radio pulsars (HBRPs). In this thesis, we have investigated the long-term evolution, short-term X-ray enhancement/outburst, optical and infra-red disk emission properties and the radio properties of members of different young neutron star populations in the frame of the fallback disk model. (i) We have first investigated the X-ray enhancement and the long-term evolution of the recently discovered second "low-B magnetar" Swift J1822.3–1606. The model could produce the observed long-term source properties (P, _P , Lx) simultaneously. During a soft gamma burst episode, the inner disk matter is pushed back to larger radii, forming a density gradient at the inner disk. Subsequent relaxation of the inner disk could account for the observed X-ray enhancement light curve of Swift J1822.3–1606. (ii) We have analysed the long-term evolution and the X-ray outburst light curve of a typical AXP/SGR source, SGR 0501+4516, with the similar technique applied to Swift J1822.3–1606. We have further shown that the optical/infrared data of SGR 0501+4516 are in good agreement with the emission from an irradiated fallback disk. In two separate works, we have applied the fallback disk model to (iii) six XDIN and (iv) twelve AXP/SGR sources with relatively well constrained X-ray luminosity and rotational properties. We have found that the individual source properties (P, _P , Lx) of AXP/SGRs and XDINs could be obtained with similar basic disk parameters. Our results showed that the XDINs have gone through an accretion epoch in the past, while most of the AXP/SGRs are evolving in the accretion phase at present

Chronic Constrictive Pericarditis

Constrictive pericarditis is the result of a chronic inflammation of the pericardium. Chronic constrictive pericarditis is still a rare disease but is being recognized more frequently. It is characterized by fibrous thickening and calcification of pericardium that impairs diastolic filling, reduced cardiac output, and ultimately leads to diastolic heart failure. Clinically, chronic constrictive pericarditis is characterized by dyspnea during exercise, symptoms of right heart failure. Pericardiectomy with complete decortication is the treatment of choice for constrictive pericarditis

Long-term evolution of dim isolated neutron stars

The X-ray dim isolated neutron stars (XDINs) have periods in the same range as the anomalous X-ray pulsars (AXPs) and the soft gamma-ray repeaters (SGRs). We apply the fallback disc model, which explains the period clustering and other properties of AXP/SGRs, to the six XDINs with measured periods and period derivatives. Present properties of XDINs are obtained in evolutionary scenarios with surface dipole magnetic fields B-0 similar to 10(12) G. The XDINs have gone through an accretion epoch with rapid spin-down earlier, and have emerged in their current state, with the X-ray luminosity provided by neutron star cooling and no longer by accretion. Our results indicate that the known XDINs are not likely to be active radio pulsars, as the low B-0, together with their long periods place these sources clearly below the 'death valley'

X-ray enhancement and long-term evolution of swift J1822.3-1606

We investigate the X-ray enhancement and the long-term evolution of the recently discovered second "low-B magnetar" Swift J1822.3-1606 in the frame of the fallback disk model. During a soft gamma burst episode, the inner disk matter is pushed back to larger radii, forming a density gradient at the inner disk. Subsequent relaxation of the inner disk could account for the observed X-ray enhancement light curve of Swift J1822.3-1606. We obtain model fits to the X-ray data with basic disk parameters similar to those employed to explain the X-ray outburst light curves of other anomalous X-ray pulsars and soft gamma repeaters. The long period (8.4 s) of the neutron star can be reached by the effect of the disk torques in the long-term accretion phase ((1-3) x 10(5) yr). The currently ongoing X-ray enhancement could be due to a transient accretion epoch, or the source could still be in the accretion phase in quiescence. Considering these different possibilities, we determine the model curves that could represent the long-term rotational and the X-ray luminosity evolution of Swift J1822.3-1606, which constrain the strength of the magnetic dipole field to the range of (1-2) x 10(12) G on the surface of the neutron star

On the peculiar torque reversals and the X-ray luminosity history of the accretion-powered X-ray pulsar 4U 1626--67

International audienceThe X-ray luminosity (L_x) and the rotational properties of 4U 1626–67 have been measured at regular intervals during the last four decades. It has been recorded that the source underwent torque reversals twice. We have tried to understand whether these eccentrical sign-switches of the spin period derivative (⁠|$\dot{P}$|⁠) of 4U 1626–67 could be accounted for with the existing torque models. We have found that the observed source properties are better estimated with the distances close to the lower limit of the previously predicted distance range (5−13 kpc). Furthermore, assuming an inclined rotator, we have considered the partial accretion/ejection from the inner disc radius that leads to different L_x–|$\dot{P}$| profiles than the aligned rotator cases. We have concluded that the oblique rotator assumption with the inclination angle χ ∼ (10°−30°) brings at least equally best fitting to the observed L_x and |$\dot{P}$| of 4U 1626–67. More importantly, the estimated change of the mass accretion rate, which causes the change in observed L_x of 4U 1626–67 is much less than that is found in an aligned rotator case. In other words, without the need for a substantial modification of mass accretion rate from the companion star, the range of the observed L_x could be explained naturally with an inclined magnetic axis and rotation axis of the neutron star

The Effects of Temperature and Thermal Stresses on Impact Damage in Laminated Composites

The aim of this study is to investigate the effects of temperature and thermal residual stresses on the impact behavior and damage of unidirectional glass/epoxy laminated composites. To this end, thermal stress analyses of the laminates with lay-ups [90/0/0/90]s, [90/0/45/45]s, [0/90/45/-45]s were carried out under temperatures of 20, 90 and -50 °C by using ANSYS software. Damage parameters proposed by Hou et al. [13] were used for failure analyses. Also, the impact tests on the laminated composites were performed at the impact energies ranging from 5 J to 55 J under the mentioned temperatures. The specific energy values and impact parameters were obtained and compared for each type of specimens and temperatures. The results obtained from both thermal stress analyses and impact tests indicated that the contribution of thermal stresses to impact damage increases with decreasing temperature and therefore, the stresses at low temperatures have a significant effect on the impact damage and parameters of unidirectional laminated composites

Rotational and X-ray luminosity evolution of high-B radio pulsars

In continuation of our earlier work on the long-term evolution of the so-called high-B radio pulsars (HBRPs) with measured braking indices, we have investigated the long-term evolution of the remaining five HBRPs for which braking indices have not been measured yet. This completes our source-by-source analyses of HBRPs in the fallback disc model that was also applied earlier to anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), and dim isolated neutron stars (XDINs). Our results show that the X-ray luminosities and the rotational properties of these rather different neutron star populations can be acquired by neutron stars with fallback discs as a result of differences in their initial conditions, namely the initial disc mass, initial period and the dipole field strength. For the five HBRPs, unlike for AXPs, SGRs and XDINs, our results do not constrain the dipole field strengths of the sources. We obtain evolutionary paths leading to the properties of HBRPs in the propeller phase with dipole fields sufficiently strong to produce pulsed radio emission