Swift and NuSTAR observations of GW170817: Detection of a blue kilonova.

With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counterpart of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (≈0.03 solar masses) wind-driven outflow with moderate electron fraction (Ye ≈ 0.27). Combined with the x-ray limits, we favor an observer viewing angle of ≈30° away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a γ-ray burst afterglow).

Supernovae. 44Ti gamma-ray emission lines from SN1987A reveal an asymmetric explosion.

In core-collapse supernovae, titanium-44 ((44)Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of (44)Ti produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

Galaxy evolution. Black hole feedback in the luminous quasar PDS 456.

The evolution of galaxies is connected to the growth of supermassive black holes in their centers. During the quasar phase, a huge luminosity is released as matter falls onto the black hole, and radiation-driven winds can transfer most of this energy back to the host galaxy. Over five different epochs, we detected the signatures of a nearly spherical stream of highly ionized gas in the broadband x-ray spectra of the luminous quasar PDS 456. This persistent wind is expelled at relativistic speeds from the inner accretion disk, and its wide aperture suggests an effective coupling with the ambient gas. The outflow's kinetic power larger than 10(46) ergs per second is enough to provide the feedback required by models of black hole and host galaxy coevolution.

An ultraluminous X-ray source powered by an accreting neutron star.

The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes. Their X-ray luminosities in the 0.5-10 kiloelectronvolt energy band range from 10(39) to 10(41) ergs per second. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 10(40) ergs per second), which require black hole masses of 50-100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3-30 kiloelectronvolt range of 4.9 × 10(39) ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 kiloelectronvolt range of 1.8 × 10(40) ergs per second. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

Active galaxies. A fast and long-lived outflow from the supermassive black hole in NGC 5548.

Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

Asymmetries in core-collapse supernovae from maps of radioactive 44Ti in Cassiopeia A.

Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive (44)Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. Cassiopeia A is a young, nearby, core-collapse remnant from which (44)Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed (44)Ti emission to estimated (56)Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the (44)Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the (44)Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.

A rapidly spinning supermassive black hole at the centre of NGC 1365.

Broad X-ray emission lines from neutral and partially ionized iron observed in active galaxies have been interpreted as fluorescence produced by the reflection of hard X-rays off the inner edge of an accretion disk. In this model, line broadening and distortion result from rapid rotation and relativistic effects near the black hole, the line shape being sensitive to its spin. Alternative models in which the distortions result from absorption by intervening structures provide an equally good description of the data, and there has been no general agreement on which is correct. Recent claims that the black hole (2 × 10(6) solar masses) at the centre of the galaxy NGC 1365 is rotating at close to its maximum possible speed rest on the assumption of relativistic reflection. Here we report X-ray observations of NGC 1365 that reveal the relativistic disk features through broadened Fe-line emission and an associated Compton scattering excess of 10-30 kiloelectronvolts. Using temporal and spectral analyses, we disentangle continuum changes due to time-variable absorption from reflection, which we find arises from a region within 2.5 gravitational radii of the rapidly spinning black hole. Absorption-dominated models that do not include relativistic disk reflection can be ruled out both statistically and on physical grounds.

A photometric redshift of z = 6.39 +/- 0.12 for GRB 050904.

Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to redshifts of z approximately 20, and therefore to be powerful probes of the early Universe. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.39 - 0.12 + 0.11 (refs 5-7). Subsequently, it was measured spectroscopically to be z = 6.29 +/- 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe.

The afterglow and elliptical host galaxy of the short gamma-ray burst GRB 050724.

Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two classes based on their duration and spectral hardness--the long-soft and the short-hard bursts. The discovery of afterglow emission from long GRBs was a watershed event, pinpointing their origin to star-forming galaxies, and hence the death of massive stars, and indicating an energy release of about 10(51) erg. While theoretical arguments suggest that short GRBs are produced in the coalescence of binary compact objects (neutron stars or black holes), the progenitors, energetics and environments of these events remain elusive despite recent localizations. Here we report the discovery of the first radio afterglow from the short burst GRB 050724, which unambiguously associates it with an elliptical galaxy at a redshift z = 0.257. We show that the burst is powered by the same relativistic fireball mechanism as long GRBs, with the ejecta possibly collimated in jets, but that the total energy release is 10-1,000 times smaller. More importantly, the nature of the host galaxy demonstrates that short GRBs arise from an old (> 1 Gyr) stellar population, strengthening earlier suggestions and providing support for coalescing compact object binaries as the progenitors.

The afterglow of GRB 050709 and the nature of the short-hard gamma-ray bursts.

The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.

The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003.

Past studies of cosmological gamma-ray bursts (GRBs) have been hampered by their extreme distances, resulting in faint afterglows. A nearby GRB could potentially shed much light on the origin of these events, but GRBs with a redshift z

Early optical emission from the gamma-ray burst of 4 October 2002.

Observations of the long-lived emission--or 'afterglow'--of long-duration gamma-ray bursts place them at cosmological distances, but the origin of these energetic explosions remains a mystery. Observations of optical emission contemporaneous with the burst of gamma-rays should provide insight into the details of the explosion, as well as into the structure of the surrounding environment. One bright optical flash was detected during a burst, but other efforts have produced negative results. Here we report the discovery of the optical counterpart of GRB021004 only 193 seconds after the event. The initial decline is unexpectedly slow and requires varying energy content in the gamma-ray burst blastwave over the course of the first hour. Further analysis of the X-ray and optical afterglow suggests additional energy variations over the first few days.

Optimization of graded multilayer designs for astronomical X-ray telescopes.

We developed a systematic method for optimizing the design of depth-graded multilayers for astronomical hard-x-ray and soft-gamma-ray telescopes based on the instrument's bandpass and the field of view. We apply these methods to the design of the conical-approximation Wolter I optics employed by the balloon-borne High Energy Focusing Telescope, using W/Si as the multilayer materials. In addition, we present optimized performance calculations of mirrors, using other material pairs that are capable of extending performance to photon energies above the W K-absorption edge (69.5 keV), including Pt/C, Ni/C, Cu/Si, and Mo/Si.

Immunoreactive fraction 1 leaf protein and dry matter content during wilting and ensiling of ryegrass and alfalfa.

In four experiments with ryegrass and alfalfa, cut herbage was wilted in the field and silage made in 1- or 200-L silos. Direct-cut (mean DM, 20.3%), low wilt (mean DM, 26.0%), medium wilt (mean DM, 36.2%) and high wilt (mean DM, 47.7%) herbages were used. Fraction 1, the most abundant leaf protein, was measured by crossed immunoelectrophoresis using rabbit anti-Fraction 1 serum. In two ryegrass and one alfalfa experiments in which weather conditions allowed rapid drying to high wilt herbage in 24 h, there was no significant loss of Fraction 1 protein. In the second alfalfa experiment, in which wilting was prolonged to 3 d by adverse weather, there was a 70% loss of Fraction 1. Ensiling proceeded normally in the four experiments, with rapid fall in pH and production of VFA, lactate, and NPN; the extent and rates of production were inversely related to DM content. In alfalfa and ryegrass, pH fell below the isoelectric point of Fraction 1 within 8 d. In each ryegrass experiment, a high proportion (58 to 100%) of Fraction 1 in medium and high wilt silages survived fermentation for 28 and 68 d, with lesser amounts in other silages. With alfalfa, however, almost all Fraction 1 protein was degraded at all DM concentrations during fermentation. Fiber-associated protein increased markedly with increases in DM during wilting, and these differences were present in the mature silage of both ryegrass and alfalfa. Digestibility studies with fistulated sheep showed that appreciable amounts of immunoreactive Fraction 1 protein in ryegrass silages were undegraded in the rumen.

The localization of somatostatin-like immunoreactivity in the alimentary tract of the sheep with observations on the effect of an infection with the parasite Haemonchus contortus.

Cells containing somatostatin immunoreactivity were localized in the alimentary tract of parasite-free sheep by indirect immunocytochemistry, using an antiserum raised to ovine somatostatin. Nerve fibres showing somatostatin-like immunoreactivity were identified in the oesophagus, reticulum wall and groove, rumen pillar and wall, omasum sulcus and abomasum. Varicose fibres were found in the myenteric plexuses of the duodenum, jejunum, ileum and colon. The greatest distribution of endocrine cells (99 cells mm-2) was found in the antrum of the abomasum with 47, 29, 12 and 6 cells mm-2 respectively in the fundus, the first part of the duodenum, mid-jejunum and ileum. Some of the parasite-free sheep which had never experienced infection with larvae of the abomasal nematode, Haemonchus contortus, were paired with similar sheep in an experiment to investigate the effect of parasitism on nitrogen metabolism in the small intestine. The protocol of this experiment required observations before and after parasite infection, with final observations 2 weeks after removal of the infection by treatment with an anthelmintic drug. The sheep were then killed and tissues taken from each paired animal. Tissues from the recently parasitized sheep showed increases of D cells in the fundus and antrum of the abomasum. At present it is not clear if these increases were related to parasitism, per se, or were the post-treatment indicators of healing and recovery from infection with parasite larvae.

The ontogeny of vasoactive intestinal polypeptide-like and substance P-like immunoreactivity in the digestive tract of the sheep.

Using the technique of indirect immunofluorescence cytochemistry, the development of structures showing vasoactive intestinal polypeptide-like (VIP-l.i.) and substance P-like (SP-l.i.) immunoreactivity was studied in the gut of the fetal sheep and of new-born lambs. The fetuses were obtained by hysterotomy at known stages of gestation. VIP-l.i. immunoreactivity was first detected at mid-gestation (70 d) in neuronal structures in the myenteric plexus of the oesophagus and the forestomachs. SP-l.i. immunoreactivity was detectable at 50 d of gestation in neuronal structures in the myenteric and submucous plexuses of the forestomachs and abomasum and in the myenteric plexus of the rectum. SP-l.i. immunoreactivity was also seen in open-type endocrine cells in the abomasal epithelium. Subsequently, VIP-l.i. staining progressively appeared caudally from the oesophagus and later cranially from the rectum. By birth the full adult staining pattern had developed in all regions except the colon. SP-l.i. was found to progress cranially and caudally from the forestomachs and abomasum and also cranially from the rectum and by birth the gut showed staining fully representative of the adult distribution. The SP-reactive endocrine cells appeared progressively along the intestine as the fetus developed and by birth were found predominantly in the small and large intestine with only a few in the abomasum.

Immunocytochemical localization of gastric inhibitory peptide and glucagon in the alimentary tract of ruminants.

Cells containing gastric inhibitory peptide (GIP) and glucagon immunoreactivity were localized in the alimentary tract of the adult sheep, young lamb, calf and goat kid by indirect immunocytochemistry, using antisera raised to the porcine peptides. GIP and glucagon were localized in two distinct cell populations. Cells containing immunoreactive GIP were confined to the mucosa of the duodenum, jejunum and ileum and were not observed in the forestomachs, abomasum, large intestine and pancreas. Cells containing immunoreactive glucagon were distributed widely throughout the alimentary tract but were most numerous in the pancreatic islets and the ileum. Neither GIP nor glucagon-containing cells were observed in the forestomachs. The distribution of the peptides was similar in adult and young animals. Both cell types appeared to possess an apical projection into the glandular lumen of the alimentary tract. Pre-absorption of the primary antisera with the appropriate peptide antigen abolished the staining.

The measurement of liver blood flow in conscious calves.

Observations were made following single I.V. injections or during continuous I.V. infusions of sulphobromophthalein (BSP) in three Jersey calves (3-5 months of age) which had an indwelling hepatic vein catheter, surgically implanted under general anaesthesia. Simultaneous sampling of blood from a peripheral (jugular) vein and an hepatic vein enabled calculations of hepatic plasma flow (E.H.P.F.) based on the Fick principle. Estimates of E.H.P.F. in nine single injection experiments gave a mean flow of 38.6 ml X min-1 X kg-1 compared to 32.6 ml X min-1 X kg-1 estimated in seven continuous infusion experiments. The over-all mean haematocrit in the three calves was 30.0% and the E.H.P.F. values are equivalent to hepatic blood flows of 55 and 47 ml X min-1 X kg-1 respectively. In thirteen out of fourteen experiments the plasma clearance of BSP in jugular vein blood after a single I.V. injection of 5 mg BSP X kg-1 body weight was best fitted by a double exponential model of distribution of BSP. Parameters from these exponentials were used to calculate E.H.P.F. by the method of Clarkson, Hardy-Smith & Richards (1976) and gave values of 11.3 ml X min-1 X kg-1, clearly indicating that the method cannot be applied in conscious calves.

Comparative rates of formation, in vivo, of 16-androstenes, testosterone and androstenedione in boar testis.

Three mature Large White boars were anaesthetized and received [7(n)-3H]pregnenolone by continuous infusion into right and left spermatic arteries for up to 180 min. Spermatic venous blood flow was measured by separate timed collections of completely diverted outflow from each testis and blood not sampled was returned to the peripheral circulation. The total radioactivity in plasma from each testis increased markedly during the first 60 min of infusion to reach a plateau from 80 to 180 min. Radiolabelling of 5 alpha-androst-16-en-3-one, 5 alpha-androst-16-en-3 beta-ol and -3 alpha-ol showed similar patterns with ratios of mean radioactivity of 5:3:1 respectively between 80 and 180 min. In comparison, the amounts of tritiated 4,16-androstadien-3-one formed were very small. The radiolabelling of testosterone and 4-androstenedione occurred more rapidly than that of the 16-androstenes and reached maxima by 30 min. However the amounts were only one-fifth (testosterone) and one-tenth (4-androstenedione) those of the combined quantities of tritiated 16-androstenes. Addition of human chorionic gonadotrophin (hCG) to the infusate to one testis in each animal (so that 5000 i.u. hCG were delivered in 15-20 min) produced no change in the outputs of radiolabelled steroids although radioimmunoassay of spermatic venous plasma in samples from the third experiment showed a transient increase in the concentration of 4-androstene-3,17-dione during the hCG infusion. It is suggested the lack of response to hCG could be produced by saturation and down regulation of binding sites by the very high local concentrations of hCG.

An improved model of the distribution and metabolism of progesterone and 20 alpha-dihydroprogesterone in sheep.

When [3H]progesterone is infused intravenously into ewes, blood 20 alpha-dihydroprogesterone (20 alpha-diHP) becomes labelled and the changes in [3H]20 alpha-diHP activity with time are clearly related to that of [3H]progesterone. Concentrations of 20 alpha-diHP in blood have now been estimated for these experiments. During the infusion, the specific radioactivity of 20 alpha-diHP at steady state was only 53% of the specific radioactivity of progesterone, indicating that 20 alpha-diHP was produced other than by C-20 reduction of secreted progesterone. The change in blood concentration of 20 alpha-diHP during pregnancy in ewes suggests that the placenta is its source. [3H]20 alpha-dihydroprogesterone was infused into pregnant ewes and the specific radioactivity of 20 alpha-diHP measured during and after infusion. Together with information from earlier experiments when [3H]progesterone was infused, there is now sufficient data to estimate, without constraint, the parameters of a four-pool model describing the distribution and metabolism of progesterone and 20 alpha-dyhydro-progesterone in sheep.