599 research outputs found
Bright broad-band afterglows of gravitational wave bursts from mergers of binary neutron stars
If double neutron star mergers leave behind a massive magnetar rather than a
black hole, a bright early afterglow can follow the gravitational wave burst
(GWB) even if there is no short gamma-ray burst (SGRB) - GWB association or
there is an association but the SGRB does not beam towards earth. Besides
directly dissipating the proto-magnetar wind as suggested by Zhang, we here
suggest that the magnetar wind could push the ejecta launched during the merger
process, and under certain conditions, would reach a relativistic speed. Such a
magnetar-powered ejecta, when interacting with the ambient medium, would
develop a bright broad-band afterglow due to synchrotron radiation. We study
this physical scenario in detail, and present the predicted X-ray, optical and
radio light curves for a range of magnetar and ejecta parameters. We show that
the X-ray and optical lightcurves usually peak around the magnetar spindown
time scale (10^3-10^5s), reaching brightness readily detectable by wide-field
X-ray and optical telescopes, and remain detectable for an extended period. The
radio afterglow peaks later, but is much brighter than the case without a
magnetar energy injection. Therefore, such bright broad-band afterglows, if
detected and combined with GWBs in the future, would be a probe of massive
millisecond magnetars and stiff equation-of-state for nuclear matter.Comment: ApJ, in pres
A double neutron star merger origin for the cosmological relativistic fading source PTF11agg?
The Palomar Transient Factory (PTF) team recently reported the discovery of a
rapidly fading optical transient source, PTF11agg. A long-lived scintillating
radio counterpart was identified, but the search for a high energy counterpart
showed negative results. The PTF team speculated that PTF11agg may represent a
new class of relativistic outbursts. Here we suggest that a neutron star
(NS)-NS merger system with a supra-massive magnetar central engine could be a
possible source to power such a transient, if our line of sight is not on the
jet axis direction of the system. These systems are also top candidates for
gravitational wave sources to be detected in the advanced LIGO/Virgo era. We
find that the PTF11agg data could be explained well with such a model,
suggesting that at least some gravitational wave bursts due to NS-NS mergers
may be associated with such a bright electromagnetic counterpart without a
\gamma-ray trigger.Comment: Accepted for publication in ApJ Letter
Edge States at the Interface between Monolayer and Bilayer Graphene
The electronic property of monolayer-bilayer hybrid graphene with a zigzag
interface is studied by both the Dirac equation and numerical calculation.
There are two types of zigzag interface stacks. The dispersion and local
density of states behave quit differently along the interface at the Fermi
energy due to the different locations of the edge state. We hope our study can
give some insights in the understanding of the transport and STM experiments.Comment: 8 pages, 8 figure
Comparison of five methods for genomic breeding value estimation for the common dataset of the 15th QTL-MAS Workshop
GRB 080503 LATE AFTERGLOW RE-BRIGHTENING: SIGNATURE OF A MAGNETAR-POWERED MERGER-NOVA
ABSTRACT GRB 080503 is a short gamma-ray burst (GRB) detected by Swift and has been classified as a GRB originating from a compact star merger. The soft extended emission and the simultaneous late re-brightening in both the X-ray and optical afterglow light curves raise interesting questions regarding its physical origin. We show that the broadband data of GRB 080503 can be well explained within the framework of the double neutron star merger model, provided that the merger remnant is a rapidly rotating massive neutron star with an extremely high magnetic field (i.e., a millisecond magnetar). We show that the late optical re-brightening is consistent with the emission from a magnetar-powered "merger-nova." This adds one more case to the growing sample of merger-novae associated with short GRBs. The soft extended emission and the late X-ray excess emission are well connected through a magnetar dipole spin-down luminosity evolution function, suggesting that direct magnetic dissipation is the mechanism to produce these X-rays. The X-ray emission initially leaks from a hole in the merger ejecta pierced by the short GRB jet. The hole subsequently closes after the magnetar spins down and the magnetic pressure drops below ram pressure. The X-ray photons are then trapped behind the merger-nova ejecta until the ejecta becomes optically thin at a later time. This explains the essentially simultaneous re-brightening in both the optical and X-ray light curves. Within this model, future gravitational-wave sources could be associated with a bright X-ray counterpart along with the merger-nova, even if the short GRB jet beams away from Earth
Spin-Neutral Tunneling Anomalous Hall Effect
Anomalous Hall effect (AHE) is a fundamental spin-dependent transport property that is widely used in spintronics. It is generally expected that currents carrying net spin polarization are required to drive the AHE. Here we demonstrate that, in contrast to this common expectation, a spin-neutral tunneling AHE (TAHE), i.e. a TAHE driven by spin-neutral currents, can be realized in an antiferromagnetic (AFM) tunnel junction where an AFM electrode with a non-spin-degenerate Fermi surface and a normal metal electrode are separated by a non-magnetic barrier with strong spin-orbit coupling (SOC). The symmetry mismatch between the AFM electrode and the SOC barrier results in an asymmetric spin-dependent momentum filtering of the spin-neutral longitudinal current generating the transverse Hall current in each electrode. We predict a sizable spin-neutral TAHE in an AFM tunnel junction with a RuO2-type AFM electrode and a SnTe-type SOC barrier and show that the Hall currents are reversible by the Néel vector switching. With the Hall angle being comparable to that in conventional AHE bulk materials, the predicted spin-neutral TAHE can be used for the Néel vector detection in antiferromagnetic spintronics
Néel Spin Currents in Antiferromagnets
Ferromagnets are known to support spin-polarized currents that control various spin-dependent transport phenomena useful for spintronics. On the contrary, fully compensated antiferromagnets are expected to support only globally spin-neutral currents. Here, we demonstrate that these globally spin-neutral currents can represent the Néel spin currents, i.e., staggered spin currents flowing through different magnetic sublattices. The Néel spin currents emerge in antiferromagnets with strong intrasublattice coupling (hopping) and drive the spin-dependent transport phenomena such as tunneling magnetoresistance (TMR) and spin-transfer torque (STT) in antiferromagnetic tunnel junctions (AFMTJs). Using RuO2 and Fe4GeTe2 as representative antiferromagnets, we predict that the Néel spin currents with a strong staggered spin polarization produce a sizable fieldlike STT capable of the deterministic switching of the Néel vector in the associated AFMTJs. Our work uncovers the previously unexplored potential of fully compensated antiferromagnets and paves a new route to realize the efficient writing and reading of information for antiferromagnetic spintronics
Prediction of Giant Tunneling Magnetoresistance in RuO/TiO/RuO (110) Antiferromagnetic Tunnel Junctions
Using first-principles quantum-transport calculations, we investigate
spin-dependent electronic and transport properties of antiferromagnetic tunnel
junctions (AFMTJs) that consist of (110)-oriented antiferromagnetic (AFM) metal
RuO electrodes and an insulating TiO tunneling barrier. We predict
the emergence of a giant tunneling magnetoresistance (TMR) effect in a wide
energy window, a series of barrier layer thicknesses, and different interface
terminations, indicating the robustness of this effect. We show that the
predicted TMR cannot be explained in terms of the global transport
spin-polarization of RuO (110) but is well understood based on matching
the momentum-dependent spin-polarized conduction channels of the two RuO
(110) electrodes. We predict oscillations of TMR with increasing barrier
thickness, indicating a non-negligible contribution from the perfectly
epitaxial interfaces. Our work helps the understanding of the physics of TMR in
AFMTJs and aids in realizing efficient AFM spintronic devices
- …