118614871
THE LIKELY ORBITAL PERIOD OF THE ULTRACOMPACT LOW-MASS X-RAY BINARY 2S 0918-549
We report the discovery of the likely orbital period of the ultracompact low-mass X-ray binary (LMXB) 2S 0918-549. Using time-resolved optical photometry carried out with the 8 m Gemini South Telescope, we obtained a 2.4 hr long, Sloan r' light curve of 2S 0918-549 and found a periodic, sinusoidal modulation at 17.4 +/- 0.1 minutes with a semiamplitude of 0.015 +/- 0.002 mag, which we identify as the binary period. In addition to 4U 0513-40 in the globular cluster NGC 1851 and the Galactic disk source 4U 1543-624, 2S 0918-549 is the third member of the ultracompact LMXBs that have orbital periods around 18 minutes. Our result verifies the suggestion that 2S 0918-549 is an ultracompact binary based on its X-ray and optical spectroscopic properties. Given that the donor in 2S 0918-549 has been suggested to be either a C-O or He white dwarf, its likely mass and radius are around 0.024-0.029 M-circle dot and 0.03-0.032 R-circle dot, respectively, for the former case and 0.034-0.039 M-circle dot and 0.033-0.035 R-circle dot for the latter case. If the optical modulation arises from X-ray heating of the mass donor, its sinusoidal shape suggests that the binary has a low inclination angle, probably around 10 degrees.
14090535
An Accurate Determination of the Optical Periodic Modulation in the X-Ray Binary SAX J1808.4-3658
We report on optical imaging of the X-ray binary SAX J1808.4 – 3658 with the 8 m Gemini South Telescope. The binary, containing an accretion-powered millisecond pulsar, appears to have a large periodic modulation in its quiescent optical emission. In order to clarify the origin of this modulation, we obtained three time-resolved r'-band light curves (LCs) of the source over five days. The LCs can be described by a sinusoid, and the long time-span between them allows us to determine optical period P = 7251.9 s and phase 0.671 at MJD 54599.0 (TDB; phase 0.0 corresponds to the ascending node of the pulsar orbit), with uncertainties of 2.8 s and 0.008 (90% confidence), respectively. This periodicity is highly consistent with the X-ray orbital ephemeris. By considering this consistency and the sinusoidal shape of the LCs, we rule out the possibility of the modulation arising from the accretion disk. Our study supports the previous suggestion that the X-ray pulsar becomes rotationally powered in quiescence, with its energy output irradiating the companion star, causing the optical modulation. While it has also been suggested that the accretion disk would be evaporated by the pulsar, we argue that the disk exists and gives rise to the persistent optical emission. The existence of the disk can be verified by long-term, multiwavelength optical monitoring of the source in quiescence, as an increasing flux and spectral changes from the source would be expected based on the standard disk-instability model.
303237
Discovery of Pulsations in the X-Ray Transient 4U 1901+03
We describe observations of the 2003 outburst of the hard-spectrum X-ray transient 4U 1901+03 with the Rossi X-Ray Timing Explorer (RXTE). The outburst was first detected in 2003 February by the All-Sky Monitor and reached a peak 2.5-25 keV flux of 8 × 10-9 ergs cm-2 s-1 (around 240 mcrab). The only other known outburst occurred 32.2 yr earlier, likely the longest currently known recurrence time for any X-ray transient. Proportional Counter Array (PCA) observations over the 5 month duration of the 2003 outburst revealed a 2.763 s pulsar in a 22.58 days orbit. The detection of pulsations down to a flux of 3 × 10-11 ergs cm-2 s-1 (2.5-25 keV), along with the inferred long-term accretion rate of 8.1 × 10-11 M☉ yr-1 (assuming a distance of 10 kpc), suggests that the surface magnetic field strength is below ~5 × 1011 G. The corresponding cyclotron energy is thus below 4 keV, consistent with the nondetection of resonance features at high energies. Although we could not unambiguously identify the optical counterpart, the lack of a bright IR candidate within the 1' RXTE error circle rules out a supergiant mass donor. The neutron star in 4U 1901+03 probably accretes from the wind of a main-sequence OB star, like most other high-mass binary X-ray pulsars. The almost circular orbit (e = 0.036) confirms the system's membership in a growing class of wide, low-eccentricity systems in which the neutron stars may have received much smaller kicks as a result of their natal supernova explosions.
119218814
Infrared Observations of the Millisecond Pulsar Binary J1023+0038: Evidence for the Short-term Nature of Its Interacting Phase in 2000-2001
We report our multi-band infrared (IR) imaging of the transitional millisecond pulsar system J1023+0038, a rare pulsar binary known to have an accretion disk in 2000-2001. The observations were carried out with ground-based and space telescopes from near-IR to far-IRwavelengths. We detected the source in near-IR JH bands and Spitzer 3.6 and 4.5 mu m mid-IR channels. Combined with the previously reported optical spectrum of the source, the IR emission is found to arise from the companion star, with no excess emission detected in the wavelength range. Because our near-IR fluxes are nearly equal to those obtained by the 2MASS all-sky survey in 2000 February, the result indicates that the binary did not contain the accretion disk at the time, whose existence would have raised the near-IR fluxes to twice larger values. Our observations have thus established the short-term nature of the interacting phase seen in 2000-2001: the accretion disk existed for at most 2.5 yr. The binary was not detected by the WISE all-sky survey carried out in 2010 at its 12 and 22 mu m bands and our Herschel far-IR imaging at 70 and 160 mu m. Depending on the assumed properties of the dust, the resulting flux upper limits provide a constraint of <3 x 10(22)-3 x 10(25) g on the mass of the dust grains that possibly exist as the remnants of the previously seen accretion disk.
18351437
Search for the Optical Counterparts of Southern Anomalous X-Ray Pulsars and Radio-Quiet Neutron Stars in Young Supernova Remnants
We report on our search for the optical counterparts of the Southern Hemisphere anomalous X-ray pulsar 1E1048.1-5937 and the radio-quiet neutron stars in supernova remnants Puppis A, RCW 103, and PKS 1209-52. The observations were carried out with the new MIT/CfA MagIC camera on the Magellan-I 6.5 m telescope in Chile. We present deep multiband optical images of the X-ray error circles for each of these targets and discuss the resulting candidates and limits.
119069538
Search for gamma-ray emission from four accreting millisecond pulsars with Fermi/LAT
We report our search for -ray emission in the energy range from 100 MeV to 300 GeV from four Accreting Millisecond Pulsars (AMPs), SAX J1808.4 3658, IGR J00291+5934, XTE J1814 338, and XTE J0929 314. The data are from four-year observations carried out by Large Area Telescope (LAT) onboard the Fermi -ray Space Telescope. The AMPs were not detected, and their -ray luminosity upper limits we obtain are 5.1 × 10 33 ergs s −1 for SAX J1808.4 3658, 2.1 × 10 33 ergs s −1 for IGR J00291+5934, 1.2 × 10 34 ergs s −1 for XTE J1814 338, and 2.2 × 10 33 ergs s −1 for XTE J0929 314. We compare our results with -ray irradiation luminosities required for producing optical modulations seen from the companions in the AMPs, which has been suggested by Takata et al. (2012), and our upper limits have excluded -ray emission as the heating source in these systems except XTE J0929 314, the upper limit of which is not deep enough. Our results also do not support the model proposed by Takata et al. (2012) that relatively strong -ray emission could arise from the outer gap of a high-mass neutron star controlled by the photon-photon pair-creation for the AMPs. Two AMPs, SAX J1808.4 3658 and IGR J00291+5934, have the measurements of their spin-down rates, and we derive the upper limits of their -ray conversion efficiencies, which are 57% and 3%, respectively. We discuss the implications to the AMP systems by comparing the efficiency upper limit values with that of 20 -ray millisecond pulsars (MSP) detected by Fermi and the newly discovered transitional MSP binary J1023+0038. Subject headings: pulsars: general – stars: neutron – binaries: close – gamma rays: stars
118521941
Relativistic quantum effects of Dirac particles simulated by ultracold atoms
Quantum simulation is a powerful tool to study a variety of problems in physics, ranging from high-energy physics to condensed-matter physics. In this article, we review the recent theoretical and experimental progress in quantum simulation of Dirac equation with tunable parameters by using ultracold neutral atoms trapped in optical lattices or subject to light-induced synthetic gauge fields. The effective theories for the quasiparticles become relativistic under certain conditions in these systems, making them ideal platforms for studying the exotic relativistic effects. We focus on the realization of one, two, and three dimensional Dirac equations as well as the detection of some relativistic effects, including particularly the well-known Zitterbewegung effect and Klein tunneling. The realization of quantum anomalous Hall effects is also briefly discussed.
283978
In-flight performance and calibration of the Infrared Array Camera (IRAC) for the Spitzer Space Telescope
The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.
124533627
INTRINSIC LOOP REGULARIZATION AND RENORMALIZATION IN PHI(4) FIELD-THEORY
We find that there exist certain intrinsic relations between the divergent diagrams and the convergent ones at the same loop order in some renormalizable quantum field theories. Whereupon we propose a new method for regularization and renormalization of those divergent diagrams. We name it the intrinsic loop regularization. In this paper, we take the renormalized 4 theory up to the second order of the coupling constant as an example to present this method.
119266949
MULTIBAND STUDIES OF THE OPTICAL PERIODIC MODULATION IN THE X-RAY BINARY SAX J1808.4–3658 DURING ITS QUIESCENCE AND 2008 OUTBURST
We report on time-resolved optical imaging of the X-ray binary SAX J1808.4-3658 during its quiescent state and 2008 outburst. The binary, containing an accretion-powered millisecond pulsar, has a large sinusoidal-like modulation in its quiescent optical emission. We employ a Markov chain Monte Carlo technique to fit our multi-band light curve data in quiescence with an irradiated star model, and derive a tight constraint of 50(-5)(+6) deg on the inclination angle i of the binary system. The pulsar and its companion are constrained to have masses of 0.97(-0.22)(+0.31) M-circle dot and 0.04(-0.01)(+0.02) M-circle dot (both 1 sigma ranges), respectively. The dependence of these results on the measurements of the companion's projected radial velocity is discussed. We also find that the accretion disk had nearly constant optical fluxes over a similar to 500 day period in the quiescent state our data covered, but started brightening 1.5 months before the 2008 outburst. Variations in modulation during the outburst were detected in our four observations made 7-12 days after the start of the outburst, and a sinusoidal-like modulation with 0.2 mag amplitude changed to have a smaller amplitude of 0.1 mag. The modulation variations are discussed. We estimate the albedo of the companion during its quiescence and the outburst, which was approximately 0 and 0.8 (for isotropic emission), respectively. This large difference probably provides additional evidence that the neutron star in the binary turns on as a radio pulsar in quiescence.
1162741
Low-Mass X-Ray Binary as the Progenitor of PSR J1713 + 0747
We have calculated the evolution of low-mass X-ray binaries that leads to the formation of the binary radio pulsars like PSR J1713+0747. We show that the mass transfer is most likely to be nonconservative, due to unstable disk accretion, to account for the mass of PSR J1713+0747, which is close to its initial value. We assume that part of the lost material from the binary may form a circumbinary disk, and find that it can significantly influence the mass transfer processes. We briefly discuss the implications of the circumbinary disks on the evolution of low-mass X-ray binaries and the formation of low-mass binary pulsars.