Context. A large number of low-mass (≲0.20 M⊙) helium white dwarfs (He WDs) have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close ...binary system; a few examples are found to show pulsations or to have a main-sequence star companion. There appear to be discrepancies between the current theoretical modelling of such low-mass He WDs and a number of key observed cases, indicating that their formation scenario yet remains to be fully understood. Aims. Here we investigate the formation of detached proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). Our prime focus is to examine the thermal evolution and the contraction phase towards the WD cooling track and investigate how this evolution depends on the WD mass. Our calculations are then compared to the most recent observational data. Methods. Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in a large number of close-orbit LMXBs with different initial values of donor star mass, neutron star mass, orbital period, and strength of magnetic braking. Subsequently, we followed the evolution of the detached low-mass proto-He WDs, including stages with residual shell hydrogen burning and vigorous flashes caused by unstable CNO burning. Results. We find that the time between Roche-lobe detachment until the low-mass proto-He WD reaches the WD cooling track is typically Δtproto = 0.5−2 Gyr, depending systematically on the WD mass and therefore on its luminosity. The lowest WD mass for developing shell flashes is ~0.21 M⊙ for progenitor stars of mass M2 ≤ 1.5 M⊙ (and ~0.18 M⊙ for M2 = 1.6 M⊙). Conclusions. The long timescale of low-mass proto-He WD evolution can explain a number of recent observations, including some MSP systems hosting He WD companions with very low surface gravities and high effective temperatures. We find no evidence for Δtproto to depend on the occurrence of flashes and thus question the suggested dichotomy in thermal evolution of proto-WDs.
Formation of Double Neutron Star Systems Tauris, T. M.; Kramer, M.; Freire, P. C. C. ...
Astrophysical journal/The Astrophysical journal,
09/2017, Letnik:
846, Številka:
2
Journal Article
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Odprti dostop
Double neutron star (DNS) systems represent extreme physical objects and the endpoint of an exotic journey of stellar evolution and binary interactions. Large numbers of DNS systems and their mergers ...are anticipated to be discovered using the Square Kilometre Array searching for radio pulsars, and the high-frequency gravitational wave detectors (LIGO/VIRGO), respectively. Here we discuss all key properties of DNS systems, as well as selection effects, and combine the latest observational data with new theoretical progress on various physical processes with the aim of advancing our knowledge on their formation. We examine key interactions of their progenitor systems and evaluate their accretion history during the high-mass X-ray binary stage, the common envelope phase, and the subsequent Case BB mass transfer, and argue that the first-formed NSs have accreted at most . We investigate DNS masses, spins, and velocities, and in particular correlations between spin period, orbital period, and eccentricity. Numerous Monte Carlo simulations of the second supernova (SN) events are performed to extrapolate pre-SN stellar properties and probe the explosions. All known close-orbit DNS systems are consistent with ultra-stripped exploding stars. Although their resulting NS kicks are often small, we demonstrate a large spread in kick magnitudes that may, in general, depend on the past interaction history of the exploding star and thus correlate with the NS mass. We analyze and discuss NS kick directions based on our SN simulations. Finally, we discuss the terminal evolution of close-orbit DNS systems until they merge and possibly produce a short γ-ray burst.
ABSTRACT
We present high-cadence multifrequency radio observations of the long gamma-ray burst (GRB) 190829A, which was detected at photon energies above 100 GeV by the High Energy Stereoscopic ...System (H.E.S.S.). Observations with the Meer Karoo Array Telescope (MeerKAT, 1.3 GHz) and Arcminute Microkelvin Imager – Large Array (AMI-LA, 15.5 GHz) began one day post-burst and lasted nearly 200 d. We used complementary data from Swift X-Ray Telescope (XRT), which ran to 100 d post-burst. We detected a likely forward shock component with both MeerKAT and XRT up to over 100 d post-burst. Conversely, the AMI-LA light curve appears to be dominated by reverse shock emission until around 70 d post-burst when the afterglow flux drops below the level of the host galaxy. We also present previously unpublished observations of the other H.E.S.S.-detected GRB, GRB 180720B from AMI-LA, which shows likely forward shock emission that fades in less than 10 d. We present a comparison between the radio emission from the three GRBs with detected very high energy (VHE) gamma-ray emission and a sensitivity-limited radio afterglow sample. GRB 190829A has the lowest isotropic radio luminosity of any GRB in our sample, but the distribution of luminosities is otherwise consistent, as expected, with the VHE GRBs being drawn from the same parent distribution as the other radio-detected long GRBs.
We report the timing results for PSR J2234+0611, a 3.6 ms pulsar in a 32 day, eccentric (e = 0.13) orbit with a helium white dwarf. The precise timing and eccentric nature of the orbit allow ...measurements of an unusual number of parameters: (a) a precise proper motion of 27.10(3) mas yr−1 and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; enabling an estimate of the transverse velocity, 123(5) km s−1. Together with previously published spectroscopic measurements of the systemic radial velocity, this allows a 3D determination of the system's velocity; (b) precise measurements of the rate of advance of periastron yields a total system mass of M ; (c) a Shapiro delay measurement, h3 = 82 14 ns, despite the orbital inclination not being near 90°; combined with the measurement of the total mass yields a pulsar mass of and a companion mass of (d) we measure precisely the secular variation of the projected semimajor axis and detect a significant annual orbital parallax; together these allow a determination of the 3D orbital geometry of the system, including an unambiguous orbital inclination ( ) and a position angle for the line of nodes ( ). We discuss the component masses to investigate the hypotheses previously advanced to explain the origin of eccentric MSPs. The unprecedented determination of the 3D position, motion, and orbital orientation of the system, plus the precise pulsar and WD masses and the latter's optical detection make this system a unique test of our understanding of white dwarfs and their atmospheres.
Type Ia supernovae (SNe Ia) are manifestations of stars that are deficient in hydrogen and helium, and disrupt in a thermonuclear runaway. While explosions of carbon-oxygen white dwarfs are thought ...to account for the majority of events, part of the observed diversity may be due to varied progenitor channels. We demonstrate that helium stars with masses between ∼1.8 and 2.5
M
⊙
may evolve into highly degenerate cores with near-Chandrasekhar mass and helium-free envelopes that subsequently ignite carbon and oxygen explosively at densities of ∼(1.8−5.9) × 10
9
g cm
−3
. This occurs either due to core growth from shell burning (when the core has a hybrid CO/NeO composition), or following ignition of residual carbon triggered by exothermic electron captures on
24
Mg (for a NeOMg-dominated composition). We argue that the resulting thermonuclear runaway is likely to prevent core collapse, leading to the complete disruption of the star. The available nuclear energy at the onset of explosive oxygen burning suffices to create ejecta with a kinetic energy of ∼10
51
erg, as in typical SNe Ia. Conversely, if these runaways result in partial disruptions, the corresponding transients would resemble SN Iax events similar to SN 2002cx. If helium stars in this mass range indeed explode as SNe Ia, then the frequency of events would be comparable to the observed SN Ib/c rates, thereby sufficing to account for the majority of SNe Ia in star-forming galaxies.
ABSTRACT
We report on a high-precision timing analysis and an astrophysical study of the binary millisecond pulsar, PSR J1909−3744, motivated by the accumulation of data with well improved quality ...over the past decade. Using 15 yr of observations with the Nançay Radio Telescope, we achieve a timing precision of approximately 100 ns. We verify our timing results by using both broad-band and sub-band template matching methods to create the pulse time-of-arrivals. Compared with previous studies, we improve the measurement precision of secular changes in orbital period and projected semimajor axis. We show that these variations are both dominated by the relative motion between the pulsar system and the Solar system barycentre. Additionally, we identified four possible solutions to the ascending node of the pulsar orbit, and measured a precise kinetic distance of the system. Using our timing measurements and published optical observations, we investigate the binary history of this system using the stellar evolution code mesa, and discuss solutions based on detailed WD cooling at the edge of the WD age dichotomy paradigm. We determine the 3D velocity of the system and show that it has been undergoing a highly eccentric orbit around the centre of our Galaxy. Furthermore, we set up a constraint over dipolar gravitational radiation with the system, which is complementary to previous studies given the mass of the pulsar. We also obtain a new limit on the parametrized post-Newtonian parameter, $\left| \hat\alpha_1 \right|$ < 2.1 × 10−5 at 95 per cent confidence level, which is fractionally better than previous best published value and achieved with a more concrete method.
We report on photometric and spectroscopic observations of white dwarf companions to four binary radio millisecond pulsars, leading to the discovery of companions to PSRs J0614−3329, J1231−1411 and ...J2017+0603. We place limits on the brightness of the companion to PSR J0613−0200. Optical spectroscopy of the companion to PSR J0614−3329 identifies it as a DA-type white dwarf with a temperature of T
eff = 6460 ± 80 K, a surface gravity log g = 7.0 ± 0.2 cgs and a mass of M
WD = 0.24 ± 0.04 M⊙. We find that the distance to PSR J0614−3329 is smaller than previously estimated, removing the need for the pulsar to have an unrealistically high γ-ray efficiency. Comparing the photometry with predictions from white dwarf cooling models allows us to estimate temperatures and cooling ages of the companions to PSRs J0613−0200, J1231−1411 and J2017+0603. We find that the white dwarfs in these systems are cool T
eff < 4000 K and old ≳ 5 Gyr. Thin hydrogen envelopes are required for these white dwarfs to cool to the observed temperatures, and we suggest that besides hydrogen shell flashes, irradiation driven mass loss by the pulsar may have been important.
ABSTRACT
Using data from the Large European Array for Pulsars, and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar PSR J0613−0200 over a 7 yr timespan. The ...‘secondary spectrum’ – the 2D power spectrum of scintillation – presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to ${\sim}5 \, \mu {\rm s}$, and measure the bulk scattering delay to be between 50 to 200 ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times of arrival as measured through pulsar timing. The arc curvature varies annually, and is well fitted by a one-dimensional scattering screen ${\sim}40{{\ \rm per\ cent}}$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programmes would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation.
ABSTRACT
In this work, we study variations in the parabolic scintillation arcs of the binary millisecond pulsar PSR J1643−1224 over five years using the Large European Array for Pulsars (LEAP). The ...two-dimensional (2D) power spectrum of scintillation, called the secondary spectrum, often shows a parabolic distribution of power, where the arc curvature encodes the relative velocities and distances of the pulsar, ionized interstellar medium, and Earth. We observe a clear parabolic scintillation arc, which varies in curvature throughout the year. The distribution of power in the secondary spectra is inconsistent with a single scattering screen, which is fully 1D or entirely isotropic. We fit the observed arc curvature variations with two models: an isotropic scattering screen and a model with two independent 1D screens. We measure the distance to the scattering screen to be in the range 114–223 pc, depending on the model, consistent with the known distance of the foreground large-diameter H ii region Sh 2-27 (112 ± 17 pc), suggesting that it is the dominant source of scattering. We obtain only weak constraints on the pulsar’s orbital inclination and longitude of ascending node, since the scintillation pattern is not very sensitive to the pulsar’s motion and the screen is much closer to the Earth than the pulsar. More measurements of this kind – where scattering screens can be associated with foreground objects – will help to inform the origins and distribution of scattering screens within our galaxy.
L’artérite à cellules géantes (ACG) est la vascularite la plus fréquente après 50 ans. L’atteinte inflammatoire des gros vaisseaux (LVV) est fréquente, observée dans 40 à 70 % des cas et concerne ...principalement l’aorte 1. Nous présentons ici trois cas d’ACG avec LVV qui nous ont parus d’intérêt car sans atteinte aortique associée.
Cas n°1
Un patient de 77 ans consultait pour une cécité brutale de l’œil gauche avec céphalées, cervicalgies et claudication de la mâchoire évoluant depuis plusieurs mois. La protéine C réactive (CRP) était à 90mg/L. L’examen ophtalmologique retrouvait une névrite optique ischémique antérieure aiguë. La biopsie de l’artère temporale (BAT) confirmait le diagnostic d’ACG. Une TEP-TDM retrouvait une hyperfixation au niveau des artères vertébrales, sous-clavières et fémorales, sans atteinte aortique. Le suivi a été marqué par une corticodépendance à 3mg/L.
Cas n°2
Un patient de 65 ans était hospitalisé pour une altération de l’état général (AEG) fébrile évoluant depuis 1 mois avec céphalées, hyperesthésie du cuir chevelu, cervicalgies et douleurs des épaules d’horaire mixte. La CRP était à 119mg/L. La TDM retrouvait une atteinte inflammatoire isolée de l’artère mésentérique inférieure. La BAT confirmait le diagnostic d’ACG. Le suivi de ce patient montrait une corticodépendance ainsi que des complications infectieuses digestives à type de sigmoïdite ayant nécessité la mise en place d’une colostomie. Les imageries de suivi ont montré une régression de l’atteinte inflammatoire de l’artère mésentérique inférieure sous cortisone.
Cas n°3
Un patient de 77 ans consultait pour une AEG avec céphalées depuis 4 mois. Il présentait des arthralgies inflammatoires des ceintures avec hyperesthésie du cuir chevelu et induration de l’artère temporale gauche. La CRP était à 195mg/L. Le patient ne présentait pas de manifestations ophtalmologiques. Une TEP-TDM retrouvait une atteinte inflammatoire des artères vertébrales, temporales, carotides internes, occipitales et de la racine des membres, sans atteinte aortique. L’IRM cérébrale montrait des AVC cérébelleux bilatéraux et des lacunes du centre semi-ovale gauche, frontal droit et gauche en lien avec une vascularite cérébrale. Le suivi a été marqué par une rechute d’ACG lors de la décroissance de la cortisone (céphalées et élévation de la CRP), puis une bonne évolution sous décroissance plus douce.
Nous vous présentons ici trois cas d’ACG avec atteinte inflammatoire vasculaire des troncs supra-aortiques, des artères digestives et des membres inférieurs, sans atteinte aortique. Les atteintes des membres sont rares dans l’ACG touchant 1 % des patients 2. Elles sont associées dans 85 % des cas à une atteinte de l’aorte 2. L’atteinte mésentérique est peu décrite avec une trentaine de cas publiés, le plus souvent sur des tableaux d’ischémie mésentérique 3. Le progrès de l’imagerie permet des diagnostics précoces de LVV au cours de l’ACG, aussi nos observations encore rares aujourd’hui sont probablement davantage rapportées à l’avenir.
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