Waves & Packets
Jun. 23, 2012

Gamma-ray outbursts shed new light on pulsars
Waves and Packets
A team of researchers has developed a new method of detecting pulsars by using the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope with the sensitivity of a radio telescope. By combining a "wide area" approach of an all-sky telescope like the LAT with radio observations, the team has discovered five "millisecond" class pulsars. Their discoveries include one very unusual pulsar that is a new hybrid class of pulsar that features radio emissions that originate from low and high altitudes above the neutron star.

Matthew Kerr, the lead author on the current paper, told Waves and Packets, "The first pulsar detected in gamma rays was the Crab Nebula back in 1974 with the SAS-2 satellite. Before the launch of the Fermi-LAT, additional missions (primarily COS-B and CGRO on EGRET) brought this up to 6 pulsars known in high energy gamma rays. Fermi-LAT has let us find well over 100!"

The unusual pulsar that Kerr's team found, officially named PSR J0101–6422, has an unusual light curve (a plot of brightness vs time) that features a "sandwich" of two gamma-ray peaks with an intense radio peak in the center. "The pulses are locked in the sense that they always maintain the same separation in a light curve," says Kerr.

This work touches upon a complicated question for pulsars. That is, at what altitude above the neutron star's surface are the sources of the radio and gamma emissions? This is an area of active research, and it is especially complicated for millisecond pulsars. Kerr explains that by studying many hundreds of pulsars in the radio, it has been generally concluded that, for young pulsars (not the millisecond variety reported in the current paper, which are older pulsars) radio emission originates at relatively low altitudes.

For young pulsars, one can infer that gamma rays originate at high altitudes, (1) because they lag behind the radio pulses by an appropriate amount, governed essentially by light travel time, and (2) because astronomers do not see attenuation of gamma rays due to the very strong magnetic field present at the neutron star's surface.

It is not clear how well these arguments apply to millisecond pulsars, which — according to the leading theory — have accreted mass and thus have sped up. Where some millisecond pulsars seem to be very similar to young pulsars, others have quite different properties. For example, some pulsars are observed to have radio and gamma pulses arriving at the same time, indicating both come from high altitude.

Scott Ransom, an astronomer at NRAO and a co-author in the current paper, explains that the altitude of the emission sources are estimated based on the beam size observation and models based of the light cone geometry. Moreover, the wavelengths of the emissions can be a proxy for the magnetic field strength, which is of course position dependent. "The magnetic fields around pulsars are like giant synchrotrons, and are powerful enough to create new particles that lead to other cascade events. The field can even strip particles from the surface of the star."

Pulsars indeed are perhaps the most extraordinary physics laboratories in the universe. Their behavior covers fundamental questions in nuclear and condensed matter physics, as well as astrophysics.More

New study of superconductivity in iron pnictides provide strong hint of quantum critical point
Ars Technica
A new study of BaFe2(As1–xPx)2 reported in Science has found evidence of a quantum critical point: a place where the material's properties change radically due to quantum fluctuations rather than changes in temperature or pressure. While many physicists suspect the presence of a QCP in high-Tc superconductors, none have found unambiguous evidence for its existence. The current study is still not definitive, but the particular iron pnictide material the researchers used provides far cleaner data — and stronger hints that the QCP is actually there. The researchers found that at the optimal doping value, the depth at which a magnetic field can penetrate into the sample jumped sharply. While this behavior does not automatically mean there is a QCP, it is certainly suggestive and could explain other phenomena in iron-based superconductors. A side effect of a QCP is to divide the superconducting behavior into two regions, based again on doping. In one of these superconducting phases, both superconductivity and magnetism may be able to coexist, a phenomenon not seen in other materials. More

BaBar data hint at cracks in the standard model
Science and Technology Facilities Council
Recently analyzed data from BaBar, a high-energy physics experiment in the U.S., may suggest possible flaws in the Standard Model of particle physics. The data refers to a particle called the B-bar meson that decays into a D meson, an anti-neutrino and a tau lepton (³B to D-star-tau-nu²). This particular decay of a B meson should, theoretically, only happen in one in every 100 cases, but the new results from BaBar, reported in Physical Review Letters, show it is happening too often. While the level of certainty of the difference, or excess, (3.4 sigma in statistical language) is not enough to claim a break from the Standard Model, the results are a potential sign of something amiss and are likely to impact existing theories. Researchers also hope their colleagues in the Belle collaboration, which studies the same types of particle collisions, see something similar. The BaBar experiment, which collected data from 1999 to 2008, was designed to explore various mysteries of particle physics, including why the universe contains matter, but no antimatter. Researchers continue to apply BaBar data to a variety of questions in particle physics.More

The 1st detected signature of dark matter annihilation?
When dark matter particles collide and annihilate, they should produce a continuum of high-energy, gamma-ray photons plus excess emission at one or more specific energies (lines) related to the particle mass. If a high-energy gamma-ray emission line is seen from a place in the universe where there may be a high concentration of dark matter (e.g. tiny dwarf galaxies, galaxy clusters, or the center of our own galaxy), there would be tremendous implications for theory. A flurry of recent papers point to detection of a ~130 GeV gamma-ray emission line from near the Galactic center. If real, this could be the first detection of a signature of annihilating dark matter. More

Art and optics converge to preserve frescos: Reflected infrared light unlocks new details of renaissance paintings
Optical Society of American
When restoring damaged and faded works of art, artists often employ lasers and other sophisticated imaging techniques to study intricate details, analyze pigments and search for subtle defects not visible to the naked eye. To refine what can be seen during the restoration process even further, a team of Italian researchers has developed a Thermal Quasi-Reflectography system that can capture features not otherwise detectable with the naked eye or current imaging techniques. Detailed in the Optical Society's open-access journal Optics Express, the system shines a faint midinfrared light source onto the surface of the painting and records the light that is reflected back to a camera. Depending on their temperature, certain materials shine more brightly in one wavelength than in others. The method is nonintrusive enough that they were able to use it during normal museum hours without interruption. TQR may have applications beyond art preservation as in principle it should be able to differentiate surface materials and give good accounting of surface chemistry.More

Black holes as particle detectors
Vienna University of Technology
Axions, hypothetical particles with a very low mass, could be detected as they accumulate around black holes, according to a method presented in a paper published in Physical Review D. Previous work indicates that axions, if they exist, can circle a black hole, similar to electrons circling the nucleus of an atom. Axions are bosons, which means they can occupy the same quantum state at the same time. So axions can form bosonic-cloud around a black hole, which would attract more and more axions. This cloud is not necessarily stable. It could suddenly collapse which would make space and time vibrate and emit gravity waves, which could be measured. This new work shows theoretically what new insights such observations can give to astronomy and particle physics. But the actual observations will have to wait until at least 2016 when gravity wave detectors are expected to reach an accuracy at which gravity waves around black holes can be unambiguously detected.More

Plasmons spotted in graphene
Physics World
Two independent teams of physicists have been able to create and control surface plasmons in graphene for the first time. Their experimental approach, dubbed "plasmon interferometry" and reported via two back-to-back Nature papers, could be used to study a wide range of materials, including superconductors and topological insulators. As the plasmons interact so strongly with light, graphene could be used to create new optical devices. The two teams used sharp tips of an atomic force microscope to create the surface plasmon sea as conventional techniques of just shining infrared light on a surface to create and study plasmons do not work with graphene. The plasmon excitations set up standing wave patterns in the material, and the AFM tip can image them. The wavelength and amplitude of the plasmons could actually be controlled by changing a gate voltage, something that has not been demonstrated in metallic samples. Also in both experiments the physicists found that the wavelengths of the plasmons are much shorter than those created by shining infrared light on metals — confirming the idea that graphene plasmons concentrate electromagnetic energy into a much smaller region than metal plasmons.More

Tin-100 is a doubly magical
According to the shell model of nuclear physics, 50 is a "magic number" that gives rise to special properties. Tin-100, with 50 protons and 50 neutrons, is "doubly magic," making it particularly interesting for nuclear physicists. By shooting xenon-124 ions at a sheet of beryllium, an international team of physicists succeeded in creating tin-100 and measuring the half-life and decay energy of tin-100 and its decay products. Their experiments confirmed that tin-100 has the fastest beta decay of all atomic nuclei, as previously predicted by theoretical physicists. Moreover, the team was able to determine the largest Gamow–Teller strength so far measured in allowed nuclear beta decay, establishing the "superallowed" nature of this Gamow–Teller transition. The work is reported in Nature. More

UK urged to change pay model for scholarly journals
Physics World
The U.K. should lead the way in transforming scientific publishing from a "reader pays" model to an "author pays" model. That is the main conclusion of a 140-page report by an independent working group of academics, publishers, librarians and representatives from learned societies. In an author pays model, either research sponsors would have to allow publication costs, approximately $3,000 per paper, to be charged to the project, or the grantee would have to cover the cost as shift from subscription coverage to publication fee coverage. The transition in payee model has a fair degree of uncertainty, and is likely to create great upheaval in the competition for articles. Several academics have expressed a desire to curtail the high profits of commercial publishers, while others want to be sure to maintain the revenue streams provided by publications of professional societies. Then there are the questions of who pays complex cases of multi-institution, multinational collaborations, and cases of researchers at small schools that are able to make scholarly contributions despite having no research sponsorship. More

US National Institutes of Health releases 2 reports on postdoc development and diversity
National Postdoctoral Association
NIH should increase the proportion of postdoctoral researchers supported by training grants and fellowships and reduce the number supported by research project grants, without increasing the overall number of postdoctoral researchers. This was one of the recommendations sent to the NIH director in a recent advisory committee report. Amongst the other recommendations are measures to enrich and diversify postdoctoral training, and to accelerate pathways to independence. The workforce diversity report's recommendations focused on data collection and evaluation, mentoring/career preparation and retention, institutional support, research and intervention testing, and NIH diversity strategy and infrastructure. This particular report was spurred by a study published in Science last year, which found that after factors such as education and publication record are controlled for, black applicants are 10 percent less likely than white applicants to win NIH research funding. NIH supports research and training in medical physics as well as molecular and cellular biophysics through a variety of its institutes and funding mechanisms.More

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3x Senior Astronomers — SKA Africa
National Astrophysics and Space Science Program
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