Table of contents

We present observational evidence for the oscillating two stream instability (OTSI) and spatial collapse of Langmuir waves in the source region of a solar type III radio burst. High time resolution observations from the STEREO A spacecraft show that Langmuir waves excited by the electron beam occur as isolated field structures with short durations ∼3.2 ms and with high intensities exceeding the strong turbulence thresholds. These short duration events are identified as the envelope solitons which have collapsed to spatial scales of a few hundred Debye lengths. The spectra of these wave packets contain an intense peak and two sidebands, corresponding to beam-resonant Langmuir waves, and down-shifted and up-shifted daughter Langmuir waves, respectively, and low-frequency enhancements below a few hundred Hz. The frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI. The observed high intensities, short scale lengths, sideband spectral structures, and low-frequency enhancements strongly suggest that the OTSI and spatial collapse of Langmuir waves probably control the nonlinear beam–plasma interactions in type III radio bursts.

Simulations have shown that a diverse range of extrasolar terrestrial planet bulk compositions are likely to exist based on the observed variations in host star elemental abundances. Based on recent studies, it is expected that a significant proportion of host stars may have Mg/Si ratios below 1. Here we examine this previously neglected group of systems. Planets simulated as forming within these systems are found to be Mg-depleted (compared to Earth), consisting of silicate species such as pyroxene and various feldspars. Planetary carbon abundances also vary in accordance with the host star C/O ratio. The predicted abundances are in keeping with observations of polluted white dwarfs, lending validity to this approach. Further studies are required to determine the full planetary impacts of the bulk compositions predicted here.

The Fermi γ-ray Space Telescope has revolutionized our knowledge of the γ-ray pulsar population, leading to the discovery of almost 100 γ-ray pulsars and dozens of γ-ray millisecond pulsars (MSPs). Although the outer-gap model predicts different sites of emission for the radio and γ-ray pulsars, until now all of the known γ-ray MSPs have been visible in the radio. Here we report the discovery of a "radio-quiet" γ-ray-emitting MSP candidate by using Fermi, Chandra, Swift, and optical observations. The X-ray and γ-ray properties of the source are consistent with known γ-ray pulsars. We also found a 4.63 hr orbital period in optical and X-ray data. We suggest that the source is a black widow-like MSP with a ∼0.1 M_☉ late-type companion star. Based on the profile of the optical and X-ray light curves, the companion star is believed to be heated by the pulsar while the X-ray emissions originate from pulsar magnetosphere and/or from intrabinary shock. No radio detection of the source has been reported yet, and although no γ-ray/radio pulsation has been found we estimate that the spin period of the MSP is ∼3–5 ms based on the inferred γ-ray luminosity.

We report the discovery of 8.5σ high-frequency quasi-periodic oscillations (HFQPOs) at 66 Hz in the Rossi X-ray Timing Explorer data of the black hole candidate IGR J17091−3624, a system whose X-ray properties are very similar to those of microquasar GRS 1915+105. The centroid frequency of the strongest peak is ∼66 Hz, its quality factor above five, and its rms is between 4% and 10%. We found a possible additional peak at 164 Hz when selecting a subset of the data; however, at the 4.5σ level we consider this detection marginal. These QPOs have hard spectrum and are stronger in observations performed between 2011 September and October, during which IGR J17091−3624 displayed for the first time light curves that resemble those of the γ variability class in GRS 1915+105. We find that the 66 Hz QPO is also present in previous observations (4.5σ), but only when averaging ∼235 ks of relatively high count rate data. The fact that the HFQPOs frequency in IGR J17091−3624 matches surprisingly well with that seen in GRS 1915+105 raises questions on the mass scaling of QPOs frequency in these two systems. We discuss some possible interpretations; however, they all strongly depend on the distance and mass of IGR J17091−3624, both completely unconstrained today.

We present the discovery of PTF 10vgv, a Type Ic supernova (SN) detected by the Palomar Transient Factory, using the Palomar 48 inch telescope (P48). R-band observations of the PTF 10vgv field with P48 probe the SN emission from its very early phases (about two weeks before R-band maximum) and set limits on its flux in the week prior to the discovery. Our sensitive upper limits and early detections constrain the post-shock-breakout luminosity of this event. Via comparison to numerical (analytical) models, we derive an upper-limit of R ≲ 4.5 R_☉ (R ≲ 1 R_☉) on the radius of the progenitor star, a direct indication in favor of a compact Wolf–Rayet star. Applying a similar analysis to the historical observations of SN 1994I yields R ≲ 1/4 R_☉ for the progenitor radius of this SN.

We report the detection of carbon monoxide (CO) emission from the young supernova remnant Cassiopeia A (Cas A) at wavelengths corresponding to the fundamental vibrational mode at 4.65 μm. We obtained AKARI Infrared Camera spectra toward four positions which unambiguously reveal the broad characteristic CO ro-vibrational band profile. The observed positions include unshocked ejecta at the center, indicating that CO molecules form in the ejecta at an early phase. We extracted a dozen spectra across Cas A along the long 1' slits and compared these to simple CO emission models in local thermodynamic equilibrium to obtain first-order estimates of the excitation temperatures and CO masses involved. Our observations suggest that significant amounts of carbon may have been locked up in CO since the explosion 330 years ago. Surprisingly, CO has not been efficiently destroyed by reactions with ionized He or the energetic electrons created by the decay of the radiative nuclei. Our CO detection thus implies that less carbon is available to form carbonaceous dust in supernovae than is currently thought and that molecular gas could lock up a significant amount of heavy elements in supernova ejecta.

We have used the Australia Telescope Compact Array to measure the absorption from the 2₀ → 3₋₁E 12.2 GHz transition of methanol toward the z = 0.89 lensing galaxy in the PKS B1830−211 gravitational lens system. Comparison of the velocity of the main absorption feature with the published absorption spectrum from the 1₀ → 2₋₁E transition of methanol shows that they differ by −0.6 ± 1.6 km s⁻¹. We can use these observations to constrain the changes in the proton-to-electron mass ratio μ from z = 0.89 to the present to 0.8 ± 2.1 × 10⁻⁷. This result is consistent, and of similar precision to recent observations at z = 0.68 achieved through comparison of a variety of rotational and inversion transitions, and approximately a factor of two better than previous constraints obtained in this source. Future more sensitive observations that incorporate additional rotational methanol transitions offer the prospect of improving current results by a factor of 5–10.

Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, BD +17 3248, HD 108317, and HD 128279. Tellurium (Te, Z = 52) is found at the second r-process peak (A ≈ 130) associated with the N = 82 neutron shell closure, and it has not been detected previously in Galactic halo stars. The derived tellurium abundances match the scaled solar system r-process distribution within the uncertainties, confirming the predicted second peak r-process residuals. These results suggest that tellurium is predominantly produced in the main component of the r-process, along with the rare earth elements.

We report the discovery of a z_phot = 6.18^+0.05_{− 0.07} (95% confidence level) dwarf galaxy, lensed into four images by the galaxy cluster MACS J0329.6-0211 (z_l = 0.45). The galaxy is observed as a high-redshift dropout in HST/ACS/WFC3 CLASH and Spitzer/IRAC imaging. Its redshift is securely determined due to a clear detection of the Lyman break in the 18-band photometry, making this galaxy one of the highest-redshift multiply lensed objects known to date with an observed magnitude of F125W =24.00 ± 0.04 AB mag for its most magnified image. We also present the first strong-lensing analysis of this cluster uncovering 15 additional multiply imaged candidates of five lower-redshift sources spanning the range z_s ≃ 2–4. The mass model independently supports the high photometric redshift and reveals magnifications of 11.6^+8.9_{− 4.1}, 17.6^+6.2_{− 3.9}, 3.9^+3.0_{− 1.7}, and 3.7^+1.3_{− 0.2}, respectively, for the four images of the high-redshift galaxy. By delensing the most magnified image we construct an image of the source with a physical resolution of ∼200 pc when the universe was ∼0.9 Gyr old, where the z ≃ 6.2 galaxy occupies a source-plane area of approximately 2.2 kpc². Modeling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of ${\sim}10^{9} \,\mathcal {M}_{\odot }$, subsolar metallicity (Z/Z_☉ ∼ 0.5), low dust content (A_V ∼ 0.1 mag), a demagnified star formation rate (SFR) of ${\sim}3.2 \,\mathcal {M}_{\odot }$ yr⁻¹, and a specific SFR of ∼3.4 Gyr⁻¹, all consistent with the properties of local dwarf galaxies.

One of the most important questions regarding the progenitor systems of Type Ia supernovae (SNe Ia) is whether mergers of two white dwarfs can lead to explosions that reproduce observations of normal events. Here we present a fully three-dimensional simulation of a violent merger of two carbon–oxygen white dwarfs with masses of 0.9 M_☉ and 1.1 M_☉ combining very high resolution and exact initial conditions. A well-tested combination of codes is used to study the system. We start with the dynamical inspiral phase and follow the subsequent thermonuclear explosion under the plausible assumption that a detonation forms in the process of merging. We then perform detailed nucleosynthesis calculations and radiative transfer simulations to predict synthetic observables from the homologously expanding supernova ejecta. We find that synthetic color light curves of our merger, which produces about 0.62 M_☉ of ⁵⁶Ni, show good agreement with those observed for normal SNe Ia in all wave bands from U to K. Line velocities in synthetic spectra around maximum light also agree well with observations. We conclude that violent mergers of massive white dwarfs can closely resemble normal SNe Ia. Therefore, depending on the number of such massive systems available these mergers may contribute at least a small fraction to the observed population of normal SNe Ia.

We present XMM-Newton spectra of the Seyfert 2 Galaxy IRAS 00521-7054. A strong feature at ∼6 keV (observer's frame) can be formally fitted with a strong (EW = 1.3 ± 0.3 keV in the rest frame) and broad Fe Kα line, extending down to 3 keV. The underlying X-ray continuum could be fitted with an absorbed power law (with Γ = 1.8 ± 0.2 and N_H = 5.9^+0.6_−0.7 × 10²² cm⁻²) plus a soft component. If due to relativistically smeared reflection by an X-ray illuminated accretion disk, the spin of the supermassive black hole (SMBH) is constrained to be 0.97^+0.03_−0.13 (errors at 90% confidence level for one interesting parameter), and the accretion system is viewed at an inclination angle of 37° ± 4°. This would be the first type 2 active galactic nucleus reported with strong red Fe Kα wing detected which demands a fast rotating SMBH. The unusually large EW would suggest that the light bending effect is strong in this source. Alternatively, the spectra could be fitted by a dual-absorber model (though with a global χ² higher by ∼6 for 283 dof) with N_H1 = 7.0 ± 0.8 × 10²² cm⁻² covering 100% of the X-ray source, and N_H2 = 21.7^+5.6_−5.4 × 10²² cm⁻² covering 71%, which does not require an extra broad Fe Kα line.

We report a correspondence between giant, polarized microwave structures emerging north from the Galactic plane near the Galactic center and a number of GeV gamma-ray features, including the eastern edge of the recently discovered northern Fermi Bubble. The polarized microwave features also correspond to structures seen in the all-sky 408 MHz total intensity data, including the Galactic center Spur. The magnetic field structure revealed by the Wilkinson Microwave Anisotropy Probe polarization data at 23 GHz suggests that neither the emission coincident with the Bubble edge nor the Galactic center Spur are likely to be features of the local interstellar medium. On the basis of the observed morphological correspondences, similar inferred spectra, and the similar energetics of all sources, we suggest a direct connection between the Galactic center Spur and the northern Fermi Bubble.

We present Hubble Space Telescope and simultaneous Swift X-ray Telescope observations of the strongest candidate intermediate-mass black hole (IMBH) ESO 243-49 HLX-1. Fitting the spectral energy distribution from X-ray to near-infrared wavelengths showed that the broadband spectrum is not consistent with simple and irradiated disk models, but is well described by a model comprised of an irradiated accretion disk plus a ∼10⁶ M_☉ stellar population. The age of the population cannot be uniquely constrained, with both young and old stellar populations allowed. However, the old solution requires excessive disk reprocessing and an extremely small disk, so we favor the young solution (∼13 Myr). In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy suggest that a gas-rich minor merger may have taken place less than ∼200 Myr ago. Such a merger event would explain the presence of the IMBH and the young stellar population.

We report the observation in the GeV band of the blazar 1ES 0229+200, which over recent years has become one of the primary sources used to put constraints on the extragalactic background light (EBL) and extragalactic magnetic field (EGMF). We derive constraints on both the EBL and EGMF from the combined Fermi–HESS data set taking into account the direct and cascade components of the source spectrum. We show that the limit on the EBL depends on the EGMF strength and vice versa. In particular, an EBL density twice as high as that derived by Franceschini et al. in 2008 is allowed if the EGMF is strong enough. On the other hand, an EGMF strength as low as 6 × 10⁻¹⁸ G is allowed if the EBL density is at the level of the lower bound from the direct source counts. We present the combined EBL and EGMF limits as an exclusion plot in two-dimensional parameter space: EGMF strength versus EBL density.

We study a sample of 39 massive early-type lens galaxies at redshift z ≲ 0.3 to determine the slope of the average dark-matter density profile in the innermost regions. We keep the strong-lensing and stellar population synthesis modeling as simple as possible to measure the galaxy total and luminous masses. By rescaling the values of the Einstein radius and dark-matter projected mass with the values of the luminous effective radius and mass, we combine all the data of the galaxies in the sample. We find that between 0.3 and 0.9 times the value of the effective radius the average logarithmic slope of the dark-matter projected density profile is −1.0 ± 0.2 (i.e., approximately isothermal) or −0.7 ± 0.5 (i.e., shallower than isothermal), if, respectively, a constant Chabrier or heavier, Salpeter-like stellar initial mass function is adopted. These results provide positive evidence of the influence of the baryonic component on the contraction of the galaxy dark-matter halos, compared to the predictions of dark-matter-only cosmological simulations, and open a new way to test models of structure formation and evolution within the standard ΛCDM cosmological scenario.

Using deep narrowband and broadband imaging, we identify 401 z ≈ 0.40 and 249 z ≈ 0.49 Hα line-emitting galaxies in the Subaru Deep Field. Compared to other Hα surveys at similar redshifts, our samples are unique since they probe lower Hα luminosities, are augmented with multi-wavelength (rest-frame 1000 Å–1.5 μm) coverage, and a large fraction (20%) of our samples has already been spectroscopically confirmed. Our spectra allow us to measure the Balmer decrement for nearly 60 galaxies with Hβ detected above 5σ. The Balmer decrements indicate an average extinction of A(Hα) = 0.7^+1.4_−0.7 mag. We find that the Balmer decrement systematically increases with higher Hα luminosities and with larger stellar masses, in agreement with previous studies with sparser samples. We find that the star formation rates (SFRs) estimated from modeling the spectral energy distribution (SED) are reliable—we derived an "intrinsic" Hα luminosity which is then reddened assuming the color excess from SED modeling. The SED-predicted Hα luminosity agrees with Hα narrowband measurements over 3 dex (rms of 0.25 dex). We then use the SED SFRs to test different statistically based dust corrections for Hα and find that adopting 1 mag of extinction is inappropriate: galaxies with lower luminosities are less reddened. We find that the luminosity-dependent dust correction of Hopkins et al. yields consistent results over 3 dex (rms of 0.3 dex). Our comparisons are only possible by assuming that stellar reddening is roughly half of nebular reddening. The strong correspondence argues that with SED modeling, we can derive reliable intrinsic SFRs even in the absence of Hα measurements at z ∼ 0.5.

Type IIn and related supernovae show evidence for an interaction with a dense circumstellar medium that produces most of the supernova luminosity. X-ray emission from shock heated gas is crucial for the energetics of the interaction and can provide diagnostics on the shock interaction. Provided that the shock is at an optical depth τ_w ≲ c/v_s in the wind, where c is the speed of light and v_s is the shock velocity, a viscous shock is expected that heats the gas to a high temperature. For τ_w ≳ 1, the shock wave is in the cooling regime; inverse Compton cooling dominates bremsstrahlung at higher densities and shock velocities. Although τ_w ≳ 1, the optical depth through the emission zone is ≲ 1 so that inverse Compton effects do not give rise to significant X-ray emission. The electrons may not reach energy equipartition with the protons at higher shock velocities. As X-rays move out through the cool wind, the higher energy photons are lost to Compton degradation. If bremsstrahlung dominates the cooling and Compton losses are small, the energetic radiation can completely photoionize the preshock gas. However, inverse Compton cooling in the hot region and Compton degradation in the wind reduce the ionizing flux, so that complete photoionization is not obtained and photoabsorption by the wind further reduces the escaping X-ray flux. We conjecture that the combination of these effects led to the low observed X-ray flux from the optically luminous SN 2006gy.