Table of contents

We study the hydrodynamical behavior occurring in the turbulent interaction zone of a fast-moving red supergiant star, where the circumstellar and interstellar material collide. In this wind–interstellar-medium collision, the familiar bow shock, contact discontinuity, and wind termination shock morphology form, with localized instability development. Our model includes a detailed treatment of dust grains in the stellar wind and takes into account the drag forces between dust and gas. The dust is treated as pressureless gas components binned per grain size, for which we use 10 representative grain size bins. Our simulations allow us to deduce how dust grains of varying sizes become distributed throughout the circumstellar medium. We show that smaller dust grains (radius <0.045 μm) tend to be strongly bound to the gas and therefore follow the gas density distribution closely, with intricate fine structure due to essentially hydrodynamical instabilities at the wind-related contact discontinuity. Larger grains which are more resistant to drag forces are shown to have their own unique dust distribution, with progressive deviations from the gas morphology. Specifically, small dust grains stay entirely within the zone bound by shocked wind material. The large grains are capable of leaving the shocked wind layer and can penetrate into the shocked or even unshocked interstellar medium. Depending on how the number of dust grains varies with grain size, this should leave a clear imprint in infrared observations of bow shocks of red supergiants and other evolved stars.

We present the simultaneous Swift and Fermi observations of the bright GRB 100728A and its afterglow. The early X-ray emission is dominated by a vigorous flaring activity continuing until 1 ks after the burst. In the same time interval, high-energy emission is significantly detected by the Fermi/Large Area Telescope. Marginal evidence of GeV emission is observed up to later times. We discuss the broadband properties of this burst within both the internal and external shock scenarios, with a particular emphasis on the relation between X-ray flares, the GeV emission, and a continued long-duration central engine activity as their power source.

We report Chandra evidence for a 200 kpc scale shock in the cluster surrounding the powerful radio galaxy 3C 444. Our 20 ks observation allows us to identify a clear surface brightness drop around the outer edge of the radio galaxy, which is likely to correspond to a spheroidal shock propagating into the intracluster medium. We measure a temperature jump across this drop of a factor ∼1.7, which corresponds to a Mach number of ∼1.7. This is likely to be an underestimate due to the need to average over fairly large regions. We also detect clear cavities corresponding to the positions of the radio lobes, which is only the second such detection associated with an FRII radio galaxy. We estimate that the total energy transferred to the environment is >8.2 × 10⁶⁰ erg, corresponding to a jet power >2.9 × 10⁴⁵ erg s⁻¹. Our results suggest that energy input from FRII radio galaxies is likely to exceed substantially estimates based on cluster cavity scaling relations.

We present a spectroscopic study of the eclipsing binary system AS Camelopardalis, the first such study based on phase-resolved CCD échelle spectra. Via a spectral disentangling analysis we measure the minimum masses of the stars to be M_Asin ³i = 3.213 ± 0.032 M_☉ and M_Bsin ³i = 2.323 ± 0.032 M_☉, their effective temperatures to be T_eff(A) = 12, 840 ± 120 K and T_eff(B) = 10, 580 ± 240 K, and their projected rotational velocities to be v_Asin i_A = 14.5 ± 0.1 km s⁻¹ and v_Bsin i_B ⩽ 4.6 ± 0.1 km s⁻¹. These projected rotational velocities appear to be much lower than the synchronous values. We show that measurements of the apsidal motion of the system suffer from a degeneracy between orbital eccentricity and apsidal motion rate. We use our spectroscopically measured e = 0.164 ± 0.004 to break this degeneracy and measure $\dot{\omega }_{\rm {obs}}=0\fdg 133 \pm 0\fdg 010$ yr⁻¹. Subtracting the relativistic contribution of $\dot{\omega }_{\rm {GR}}=0\mbox{$.\!\!^\circ $}0963\,{\pm}\, 0\mbox{$.\!\!^\circ $}0002$ yr⁻¹ yields the contribution due to tidal torques: $\dot{\omega }_{\rm {cl}}=0\mbox{$.\!\!^\circ $}037\,{\pm}\, 0\mbox{$.\!\!^\circ $}010$ yr⁻¹. This value is much smaller than the rate predicted by stellar theory, 040–087 yr⁻¹. We interpret this as a misalignment between the orbital axis of the close binary and the rotational axes of its component stars, which also explains their apparently low rotational velocities. The observed and predicted apsidal motion rates could be brought into agreement if the stars were rotating three times faster than synchronous about axes perpendicular to the orbital axis. Measurement of the Rossiter–McLaughlin effect can be used to confirm this interpretation.

The D/H enrichment observed in Saturn's satellite Enceladus is remarkably similar to the values observed in the nearly-isotropic comets. Given the predicted strong variation of D/H with heliocentric distance in the solar nebula, this observation links the primordial source region of the nearly-isotropic comets with the formation location of Enceladus. That is, comets from the nearly-isotropic class were most likely fed into their current reservoir, the Oort cloud, from a source region near the formation location of Enceladus. Dynamical simulations of the formation of the Oort cloud indicate that Uranus and Neptune are, primarily, responsible for the delivery of material into the Oort cloud. In addition, Enceladus formed from material that condensed from the solar nebula near the location at which Saturn captured its gas envelope, most likely at or near Saturn's current location in the solar system. The coupling of these lines of evidence appears to require that Uranus and Neptune were, during the epoch of the formation of the Oort cloud, much closer to the current location of Saturn than they are currently. Such a configuration is consistent with the Nice model of the evolution of the outer solar system. Further measurements of the D/H enrichment in comets, particularly in ecliptic comets, will provide an excellent discriminator among various models of the formation of the outer solar system.

Recent studies have shown that massive galaxies in the distant universe are surprisingly compact, with typical sizes about a factor of three smaller than equally massive galaxies in the nearby universe. It has been suggested that these massive galaxies grow into systems resembling nearby galaxies through a series of minor mergers. In this model the size growth of galaxies is an inherently stochastic process, and the resulting size–luminosity relationship is expected to have considerable environmentally dependent scatter. To test whether minor mergers can explain the size growth in massive galaxies, we have closely examined the scatter in the size–luminosity relation of nearby elliptical galaxies using a large new database of accurate visual galaxy classifications. We demonstrate that this scatter is much smaller than has been previously assumed, and may even be so small as to challenge the plausibility of the merger-driven hierarchical models for the formation of massive ellipticals.

Short precession periods like the 164 day period of SS433 can be well determined by observations of timescales longer or much longer than the precession period. However, this does not work for sources with precession periods of millions of years. This Letter utilizes the particular morphologies of X-shaped sources, so that the three-dimensional kinematics of lobes can be obtained. Thus, for the first time, the million-year precession period of X-shaped sources by an observer on the Earth can be determined elegantly: 6.1 ± 1.5 Myr, 1.8 ± 0.5 Myr, and 3.2 ± 1.2 Myr for 3C52, 3C223.1, and 4C12.03, respectively. The result naturally explains the asymmetry displayed in the morphology of these sources, and the effect of propagation time on the diversity of morphologies is well demonstrated. The precession period may originate from long-term effects of a binary supermassive black hole system, which is a potential source of gravitational wave radiation.

Sw 1644+57/GRB 110328A is a remarkable cosmological X-ray outburst detected by the Swift satellite. Its early-time (t ≲ 0.1 days since the trigger) X-ray emission resembles some gamma-ray bursts (GRBs), e.g., GRB 090417B. But the late-time flaring X-ray plateau lasting >40 days renders it unique. We examine the possibilities that the outburst is a super-long GRB powered either by the fallback accretion onto a nascent black hole or by a millisecond pulsar, and find out that these two scenarios can address some but not all of the main observational features. We then focus on the model of tidal disruption of a (giant) star by a massive black hole. The mass of the tidal-disrupted star is estimated to be ≳a few solar masses. A simple/straightforward argument for a magnetic origin of the relativistic outflow is presented.

We present observations from the Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa, observed in 2010 May and September. Using two nights of drift scanning with PAPER's 60° FWHM beam we have made a map covering the entire sky below +10° declination with an effective center frequency of 145 MHz, a 70 MHz bandwidth, and a resolution of 26'. A 4800 deg² region of this large map with the lowest Galactic emission reaches an rms of 0.7 Jy. We establish an absolute flux scale using sources from the 160 MHz Culgoora catalog. Using the 408 MHz Molonglo Reference Catalog (MRC) as a finding survey, we identify counterparts to 480 sources in our maps and compare our fluxes to the MRC and to 332 sources in the Culgoora catalog. For both catalogs, the ratio of PAPER to catalog flux averages to 1, with a standard deviation of 50%. This measured variation is consistent with comparisons between independent catalogs observed at different bands. The PAPER data represent new 145 MHz flux measurements for a large number of sources in the band expected to encompass cosmic reionization and represents a significant step toward establishing a model for removing foregrounds to the reionization signal.

Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely ∼1 kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0−5408, gave a burst with an estimated isotropic energy >10⁴⁴ erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band- and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0 × 10⁴⁴d²₁ erg and 1.4 × 10⁴⁷d²₁ erg, respectively, where $d_\mathrm{1} = \frac{d_{\mathrm{0501}}}{1\,\mathrm{kpc}}$ and d₀₅₀₁ is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.

The merger of two neutron stars often results in a rapidly and differentially rotating hypermassive neutron star (HMNS). We show by numerical-relativity simulation that the magnetic-field profile around such HMNS is dynamically varied during its subsequent evolution, and as a result, electromagnetic radiation with a large luminosity ∼0.1B²R³Ω is emitted with baryons (B, R, and Ω are poloidal magnetic-field strength at stellar surface, stellar radius, and angular velocity of an HMNS). The predicted luminosity of electromagnetic radiation, which is primarily emitted along the magnetic-dipole direction, is ∼10⁴⁷(B/10¹³ G)²(R/10 km)³(Ω/10⁴ rad s⁻¹) erg s⁻¹, which is comparable to the luminosity of quasars.

Supermassive black holes (SMBHs) presumably grow through numerous mergers throughout cosmic time. During each merger, SMBH binaries are surrounded by a circumbinary accretion disk that imposes a significant (∼10⁴ G for a binary of 10⁸ M_☉) magnetic field. The motion of the binary through that field will convert the field energy to Poynting flux, with a luminosity ∼10⁴³ erg s⁻¹ (B/10⁴ G)²(M/10⁸ M_☉)², some of which may emerge as synchrotron emission at frequencies near 1 GHz where current and planned wide-field radio surveys will operate. We find that the short timescales of many mergers will limit their detectability with most planned blind surveys to <1 per year over the whole sky, independent of the details of the emission process and flux distribution. Including an optimistic estimate for the radio flux makes detection even less likely, with <0.1 mergers per year over the whole sky. However, wide-field radio instruments may be able to localize systems identified in advance of merger by gravitational waves. Further, radio surveys may be able to detect the weaker emission produced by the binary's motion as it is modulated by spin–orbit precession and inspiral well in advance of merger.