Gamma-ray burst beaming: a universal configuration with a standard energy reservoir?

We consider a gamma-ray burst (GRB) model based on an anisotropic fireball with an axisymmetric power-law distribution of the energy per solid angle with index -k, and allow for the observer's viewing direction being at an arbitrary angle with respect to the jet axis. This model can reproduce the key features expected from the conventional on-axis uniform jet models, with the novelty that the achromatic break time in the broadband afterglow lightcurves corresponds to the epoch when the relativistic beaming angle is equal to the viewing angle rather than to the jet half opening angle. If all the GRB fireballs have such a similar energy distribution form with 1.5 < k < (or \sim) 2, GRBs may be modeled by a quasi-universal beaming configuration, and an approximately standard energy reservoir. The conclusion also holds for some other forms of angular energy distributions, such as the Gaussian function.Comment: Slightly expanded version accepted for publication in Ap

Probing the birth of fast rotating magnetars through high-energy neutrinos

We investigate the high-energy neutrino emission expected from newly born magnetars surrounded by their stellar ejecta. Protons might be accelerated up to 0.1-100 EeV energies possibly by, e.g., the wave dissipation in the winds, leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a few days after the birth of magnetars, making the characteristic soft-hard-soft behavior. Detections would be important as a clue to the formation mechanism of magnetars, although there are ambiguities coming from uncertainties of several parameters such as velocity of the ejecta. Non-detections would also lead to useful constraints on the scenario.Comment: 5 pages, 3 figures, accepted for publication in PR

High magnetic field pulsars and magnetars: a unified picture

We propose a unified picture of high magnetic field radio pulsars and magnetars by arguing that they are all rotating high-field neutron stars, but have different orientations of their magnetic axes with respective to their rotation axes. In strong magnetic fields where photon splitting suppresses pair creation near the surface, the high-field pulsars can have active inner accelerators while the anomalous X-ray pulsars cannot. This can account for the very different observed emission characteristics of the anomalous X-ray pulsar 1E 2259+586 and the high field radio pulsar PSR J1814-1744. A predicted consequence of this picture is that radio pulsars having surface magnetic field greater than about $2\times 10^{14}$ G should not exist.Comment: 5 pages, emulateapj style, accepted for publication in the ApJ Letter

Faint high-energy gamma-ray photon emission of GRB 081006A from Fermi observations

Since the launch of the Fermi gamma - ray Space Telescope on June 11, 2008, the LAT instrument has solidly detected more than 20 GRBs with high energy photon emission above 100 MeV. Using the matched filter technique, 3 more GRBs have also shown evidence of correlation with high energy photon emission as demonstrated by Akerlof et al. In this paper, we present another GRB unambiguously detected by the matched filter technique, GRB 081006A. This event is associated with more than 13 high energy photons above 100 MeV. The likelihood analysis code provided by the $Fermi$ Science Support Center (FSSC) generated an independent verification of this detection by comparison of the Test Statistics (TS) value with similar calculations for random LAT data fields. We have performed detailed temporal and spectral analysis of photons from 8 keV up to 0.8 GeV from the GBM and the LAT. The properties of GRB 081006A can be compared to the other two long duration GRBs detected at similar significance, GRB 080825C and GRB 090217A. We find that GRB 081006A is more similar to GRB 080825C with comparable appearances of late high energy photon emission. As demonstrated previously, there appears to be a surprising dearth of faint LAT GRBs, with only one additional GRB identified in a sample of 74 GRBs. In this unique period when both $Swift$ and $Fermi$ are operational, there is some urgency to explore this aspect of GRBs as fully as possible.Comment: ApJ, 745, 7

Dirac Fermion in Strongly-Bound Graphene Systems

It is highly desirable to integrate graphene into existing semiconductor technology, where the combined system is thermodynamically stable yet maintain a Dirac cone at the Fermi level. Firstprinciples calculations reveal that a certain transition metal (TM) intercalated graphene/SiC(0001), such as the strongly-bound graphene/intercalated-Mn/SiC, could be such a system. Different from free-standing graphene, the hybridization between graphene and Mn/SiC leads to the formation of a dispersive Dirac cone of primarily TM d characters. The corresponding Dirac spectrum is still isotropic, and the transport behavior is nearly identical to that of free-standing graphene for a bias as large as 0.6 V, except that the Fermi velocity is half that of graphene. A simple model Hamiltonian is developed to qualitatively account for the physics of the transfer of the Dirac cone from a dispersive system (e.g., graphene) to an originally non-dispersive system (e.g., TM).Comment: Apr 25th, 2012 submitte

Astrophysics: Most distant cosmic blast seen

The most distant -ray burst yet sighted is the earliest astronomical object ever observed in cosmic history. This ancient beacon offers a glimpse of the little-known cosmic dark ages.Comment: Published in Nature News & View

GCRT J1745-3009 as a Transient White Dwarf Pulsar

A transient radio source in the direction of the Galactic Center, GCRT J1745-3009, exhibited 5 peculiar consecutive outbursts at 0.33 GHz with a period of 77.13 minutes and a duration of ~10 minutes for each outburst. It has been claimed to be the prototype of a hitherto unknown class of transient radio sources. We interpret it as a transient white dwarf pulsar with a period of 77.13 minutes. The ~10-minute flaring duration corresponds to the epoch when the radio beam sweeps our line of sight. The bursting epoch corresponds to the episodes when stronger sunspot-like magnetic fields emerge into the white dwarf polar cap region during which the pair production condition is satisfied and the white dwarf behaves like a radio pulsar. It switches off as the pair production condition breaks down.Comment: minor changes, ApJL, in pres