Recycled Pulsars Discovered at High Radio Frequency

We present the timing parameters of nine pulsars discovered in a survey of intermediate Galactic latitudes at 1400 MHz with the Parkes radio telescope. Eight of these pulsars possess small pulse periods and period derivatives thought to be indicative of ``recycling''. Six of the pulsars are in circular binary systems, including two with relatively massive white dwarf companions. We discuss the implications of these new systems for theories of binary formation and evolution. One long-period pulsar (J1410-7404) has a moderately weak magnetic field and an exceedingly narrow average pulse profile, similar to other recycled pulsars.Comment: 9 pages, 4 figures. Accepted for publication in Ap

Multi-D Simulations of Ultra-Stripped Supernovae to Shock Breakout

The recent discoveries of many double neutron star systems and their detection as LIGO-Virgo merger events call for a detailed understanding of their origin. Explosions of ultra-stripped stars in binary systems have been shown to play a key role in this context and have also generated interest as a potential explanation for rapidly evolving hydrogen-free transients. Here we present the first attempt to model such explosions based on binary evolution calculations that follow the mass transfer to the companion to obtain a consistent core-envelope structure as needed for reliable predictions of the supernova transient. We simulate the explosion in 2D and 3D, and confirm the modest explosion energies ~10^50erg and small kick velocities reported earlier in 2D models based on bare carbon-oxygen cores. The spin-up of the neutron star by asymmetric accretion is small in 3D with no indication of spin-kick alignment. Simulations up to shock breakout show the mixing of sizeable amounts of iron group material into the helium envelope. In view of recent ideas for a mixing-length treatment (MLT) of Rayleigh-Taylor instabilities in supernovae, we perform a detailed analysis of the mixing, which reveals evidence for buoyancy-drag balance, but otherwise does not support the MLT approximation. The mixing may have implications for the spectroscopic signatures of ultra-stripped supernovae that need to be investigated in the future. Our stellar evolution calculation also predicts presupernova mass loss due to an off-centre silicon deflagration flash, which suggests that supernovae from extremely stripped cores may show signs of interactions with circumstellar material.Comment: 15 pages, 15 figures, submitted to MNRA

White Dwarf Donors in Ultracompact Binaries: The Stellar Structure of Finite Entropy Objects

We discuss the mass-radius (M-R) relations for low-mass (M<0.1 Msun) white dwarfs (WDs) of arbitrary degeneracy and evolved (He, C, O) composition. We do so with both a simple analytical model and models calculated by integration of hydrostatic balance using a modern equation of state valid for fully ionized plasmas. The M-R plane is divided into three regions where either Coulomb physics, degenerate electrons or a classical gas dominate the WD structure. For a given M and central temperature, T_c, the M-R relation has two branches differentiated by the model's entropy content. We present the M-R relations for a sequence of constant entropy WDs of arbitrary degeneracy parameterized by M and T_c for pure He, C, and O. We discuss the applications of these models to the recently discovered accreting millisecond pulsars. We show the relationship between the orbital inclination for these binaries and the donor's composition and T_c. In particular we find from orbital inclination constraints that the probability XTE J1807-294 can accommodate a He donor is approximately 15% while for XTE J0929-304, it is approximately 35%. We argue that if the donors in ultracompact systems evolve adiabatically, there should be 60-160 more systems at orbital periods of 40 min than at orbital periods of 10 min, depending on the donor's composition.Comment: emulateapj style, 11 pages, 12 figures. Accepted to the Astrophysical Journal. Tables with interpolation routines of the M-R relations are available at http://www.physics.ucsb.edu/~cjdeloye/research.htm

Optical Detection of Two Intermediate Mass Binary Pulsar Companions

We report the detection of probable optical counterparts for two Intermediate Mass Binary Pulsar (IMBP) systems, PSR J1528-3146 and PSR J1757-5322. Recent radio pulsar surveys have uncovered a handful of these systems with putative massive white dwarf companions, thought to have an evolutionary history different from that of the more numerous class of Low Mass Binary Pulsars (LMBPs) with He white dwarf companions. The study of IMBP companions via optical observations offers us several new diagnostics: the evolution of main sequence stars near the white-dwarf-neutron star boundary, the physics of white dwarfs close to the Chandrasekhar limit, and insights into the recycling process by which old pulsars are spun up to high rotation frequencies. We were unsuccessful in our attempt to detect optical counterparts of PSR J1141-6545, PSR J1157-5112, PSR J1435-6100, and PSR J1454-5846.Comment: 9 pages, 2 figures, accepted for publication in ApJ

Timing of a Young Mildly Recycled Pulsar with a Massive White Dwarf Companion

We report on timing observations of the recently discovered binary pulsar PSR J1952+2630 using the Arecibo Observatory. The mildly recycled 20.7-ms pulsar is in a 9.4-hr orbit with a massive, M_WD > 0.93 M_sun, white dwarf (WD) companion. We present, for the first time, a phase-coherent timing solution, with precise spin, astrometric, and Keplerian orbital parameters. This shows that the characteristic age of PSR J1952+2630 is 77 Myr, younger by one order of magnitude than any other recycled pulsar-massive WD system. We derive an upper limit on the true age of the system of 50 Myr. We investigate the formation of PSR J1952+2630 using detailed modelling of the mass-transfer process from a naked helium star on to the neutron star following a common-envelope phase (Case BB Roche-lobe overflow). From our modelling of the progenitor system, we constrain the accretion efficiency of the neutron star, which suggests a value between 100 and 300% of the Eddington accretion limit. We present numerical models of the chemical structure of a possible oxygen-neon-magnesium WD companion. Furthermore, we calculate the past and the future spin evolution of PSR J1952+2630, until the system merges in about 3.4 Gyr due to gravitational wave emission. Although we detect no relativistic effects in our timing analysis we show that several such effects will become measurable with continued observations over the next 10 years; thus PSR J1952+2630 has potential as a testbed for gravitational theories.Comment: 12 pages, 10 figures, to be published in MNRA

Deeper, Wider, Sharper: Next-Generation Ground-Based Gravitational-Wave Observations of Binary Black Holes

Next-generation observations will revolutionize our understanding of binary black holes and will detect new sources, such as intermediate-mass black holes. Primary science goals include: Discover binary black holes throughout the observable Universe; Reveal the fundamental properties of black holes; Uncover the seeds of supermassive black holes.Comment: 14 pages, 3 figures, White Paper Submitted to Astro2020 (2020 Astronomy and Astrophysics Decadal Survey) by GWIC 3G Science Case Team (GWIC: Gravitational Wave International Committee

Interstellar Scintillation Velocities of a Relativistic Binary PSR B1534+12 and Three Other Millisecond Pulsars

We present interstellar scintillation velocity measurements for four millisecond pulsars obtained from long-term monitoring observations with the Arecibo radio telescope at 430 MHz. We also derive explicit expressions that relate the measured scintillation velocity to the effective transverse velocity responsible for the motion of the diffraction pattern for both binary and solitary pulsars. For B1257+12, B1534+12, J1640+2224, and J1713+0747 we derive velocity estimates of 197, 192, 38, and 82 km/s, respectively. These values are in good agreement with proper motion measurements for the four pulsars. For PSR B1534+12, we use the ISS velocity dependence on orbital phase to determine the longitude of the ascending node (Omega) of the pulsar's orbit and to derive an estimate of the effective scattering screen location. The two possible values of Omega are 70+/-20 and 290+/-20 degrees and the approximate screen location is 630+/-200 pc with the assumed pulsar distance of 1.1 kpc.Comment: 16 pages, 3 PostScript figures, submitted to the Astrophysical Journa

UCE: A uracil excision (USER™)-based toolbox for transformation of cereals

<p>Abstract</p> <p>Background</p> <p>Cloning of gene casettes and other DNA sequences into the conventional vectors for biolistic or <it>Agrobacterium</it>-mediated transformation is hampered by a limited amount of unique restriction sites and by the difficulties often encountered when ligating small single strand DNA overhangs. These problems are obviated by "The Uracil Specific Excision Reagent (USER™)" technology (New England Biolabs) which thus offers a new and very time-efficient method for engineering of big and complex plasmids.</p> <p>Results</p> <p>By application of the USER™ system, we engineered a collection of binary vectors, termed UCE (USER cereal), ready for use in cloning of complex constructs into the T-DNA. A series of the vectors were tested and shown to perform successfully in <it>Agrobacterium</it>-mediated transformation of barley (<it>Hordeum vulgare </it>L.) as well as in biolistic transformation of endosperm cells conferring transient expression.</p> <p>Conclusions</p> <p>The USER™ technology is very well suited for generating a toolbox of vectors for transformation and it opens an opportunity to engineer complex vectors, where several genetic elements of different origin are combined in a single cloning reaction.</p

Timing of a Young Mildly Recycled Pulsar with a Massive White Dwarf Companion

We report on timing observations of the recently discovered binary pulsar PSR J1952+2630 using the Arecibo Observatory. The mildly recycled 20.7-ms pulsar is in a 9.4-hr orbit with a massive, M_WD > 0.93 M_sun, white dwarf (WD) companion. We present, for the first time, a phase-coherent timing solution, with precise spin, astrometric, and Keplerian orbital parameters. This shows that the characteristic age of PSR J1952+2630 is 77 Myr, younger by one order of magnitude than any other recycled pulsar-massive WD system. We derive an upper limit on the true age of the system of 50 Myr. We investigate the formation of PSR J1952+2630 using detailed modelling of the mass-transfer process from a naked helium star on to the neutron star following a common-envelope phase (Case BB Roche-lobe overflow). From our modelling of the progenitor system, we constrain the accretion efficiency of the neutron star, which suggests a value between 100 and 300% of the Eddington accretion limit. We present numerical models of the chemical structure of a possible oxygen-neon-magnesium WD companion. Furthermore, we calculate the past and the future spin evolution of PSR J1952+2630, until the system merges in about 3.4 Gyr due to gravitational wave emission. Although we detect no relativistic effects in our timing analysis we show that several such effects will become measurable with continued observations over the next 10 years; thus PSR J1952+2630 has potential as a testbed for gravitational theories

The violent past of Cygnus X-2

Cygnus X-2 appears to be the descendant of an intermediate-mass X-ray binary (IMXB). Using Mazzitelli's (1989) stellar code we compute detailed evolutionary sequences for the system and find that its prehistory is sensitive to stellar input parameters, in particular the amount of core overshooting during the main-sequence phase. With standard assumptions for convective overshooting a case B mass transfer starting with a 3.5 M_sun donor star is the most likely evolutionary solution for Cygnus X-2. This makes the currently observed state rather short-lived, of order 3 Myr, and requires a formation rate > 1e-7 - 1e-6 per yr of such systems in the Galaxy. Our calculations show that neutron star IMXBs with initially more massive donors (> 4 M_sun) encounter a delayed dynamical instability; they are unlikely to survive this rapid mass transfer phase. We determine limits for the age and initial parameters of Cygnus X-2 and calculate possible dynamical orbits of the system in a realistic Galactic potential, given its observed radial velocity. We find trajectories which are consistent with a progenitor binary on a circular orbit in the Galactic plane inside the solar circle that received a kick velocity < 200 km/s at the birth of the neutron star. The simulations suggests that about 7% of IMXBs receiving an arbitrary kick velocity from a standard kick velocity spectrum would end up in an orbit similar to Cygnus X-2, while about 10% of them reach yet larger Galactocentric distances.Comment: 9 pages, 12 figures, accepted for publication in MNRA