We analyzed continuous Monitor of All-sky X-ray Image/Gas Slit Camera (MAXI/GSC) data of the X-ray binary pulsar 4U 1626−67 from 2009 October to 2013 September, and determined the pulse period and ...the pulse-period derivative for every 60-d interval by the epoch folding method. The obtained periods are consistent with those provided by the Fermi/Gamma-ray Burst Monitor pulsar project. In all the 60-d intervals, the pulsar was observed to spin up, with the spin-up rate positively correlated with the 2–20 keV flux. We applied the accretion torque model proposed by Ghosh and Lamb (1979, ApJ, 234, 296) to the MAXI/GSC data, as well as the past data including both spin-up and spin-down phases. The “Ghosh & Lamb” relation was confirmed to successfully explain the observed relation between the spin-up/down rate and the flux. By comparing the model-predicted luminosity with the observed flux, the source distance was constrained as 5–13 kpc, which is consistent with that found by Chakrabarty (1998, ApJ, 492, 342). Conversely, if the source distance is assumed, the data can constrain the mass and radius of the neutron star, because the Ghosh & Lamb model depends on these parameters. We attempted this idea, and found that an assumed distance of, e.g., 10 kpc gives a mass in the range of 1.81–1.90 solar mass, and a radius of 11.4–11.5 km, although these results are still subject to considerable systematic uncertainties, other than distance.
Abstract
The accretion-induced pulse period changes of the Be/X-ray binary pulsar X Persei were investigated over the period of 1996 January to 2017 September. This study utilized the monitoring data ...acquired with the RXTE All-Sky Monitor in 1.5–12 keV and the MAXI Gas-Slit Camera in 2–20 keV. The source intensity changed by a factor of 5–6 over this period. The pulsar was spinning down for 1996–2003, and has been spinning up since 2003, as already reported. The spin-up/down rate and the 3–12 keV flux, determined every 250 d, showed a clear negative correlation, which can be successfully explained by the accretion torque model proposed by Ghosh and Lamb (1979, ApJ, 234, 296). When the mass, radius, and distance of the neutron star were allowed to vary over a range of 1.0–2.4 solar masses, 9.5–15 km, and 0.77–0.85 kpc, respectively, the magnetic field strength of B = (4–25) × 1013 G gave the best fits to the observations. In contrast, the observed results cannot be explained by the values of B ∼ 1012 G previously suggested for X Persei, as long as the mass, radius, and distance are required to take reasonable values. Assuming a distance of 0.81 ± 0.04 kpc as indicated by optical astrometry, the mass of the neutron star is estimated as M = 2.03 ± 0.17 solar masses.
Possible regular phenomena in EXO 2030+375 Laplace, Eva; Mihara, Tatehiro; Moritani, Yuki ...
Astronomy and astrophysics (Berlin),
2017, 2017-1-00, 20170101, Letnik:
597
Journal Article
Recenzirano
Odprti dostop
In the last 10 yr, since its last giant outburst in 2006, regular X-ray outbursts (type I) were detected every periastron passage in the Be X-ray binary EXO 2030+375. Recently, however, it was ...reported that the source started to show a peculiar behavior: its X-ray flux decreased significantly and type I outbursts were missed in several cases. At the same time, the spin frequency of the neutron star, which had been increasing steadily since the end of the 2006 giant outburst, reached a plateau. Very recent observations indicate that the source is now starting to spin down. These observed phenomena have a striking similarity with those which took place 21 yr ago, just before the source displayed a sudden orbital phase shift of the outburst peak (1995). This historical event occurred at the time exactly between the two giant outbursts (1985 and 2006). These phenomena suggest the system to have an underlying periodicity of 10.5 yr between orbital phase shifts and/or giant outbursts. The suggested periodicity may reflect some long-period dynamics in the circumstellar disk of the Be star, due, e.g., to the Kozai-Lidov effect. A model generating such a periodic change of the Be disk, namely Kozai-Lidov oscillations in the Be disk, is discussed. If this behavior is really periodical, another phase shift of the X-ray outburst peak is predicted to occur around 2016 December.
Abstract
A neural probe with six micro-light-emitting diodes (MicroLEDs) and 15 neural electrodes was fabricated for optogenetic application. Local field potentials, which provide information about ...the neural activity, were successfully recorded using the neural probe, indicating the effectiveness of the neural electrodes. The MicroLEDs on the probe exhibited highly consistent current–voltage characteristics and sufficient light output of 20 mW mm
−2
at 1 mA to manipulate neural activity. The light distribution in brain tissue was simulated to estimate the optical stimulation area and a number of optically stimulated neurons. The increase in LED temperature, i.e. Δ
T
, was investigated because high temperatures can damage brain tissue. A curve illustrating the relationship between Δ
T
and the wall-plug efficiency was derived. The wall-plug efficiency was increased 1.8 times by installing an Ag mirror on the back of a MicroLED. These results suggest that the MicroLED neural probe would significantly contribute to the development of neuroscience research-purposed optogenetic technology.
Various transient phenomena on a timescale ranging from seconds to days appear at unexpected sky positions in X-rays. MAXI, Monitor of All-sky X-ray Image, on the International Space Station has been ...monitoring about 95% of the sky a day and has detected transient objects since 2009 August. Here, we describe quasi-real-time data processing systems of MAXI and a subsequent nova-alert system to find transient objects, and present the capabilities for the nova-alert system to detect transient events with excess fluxes from ≳80 mCrab in a single scan transit to ≳8 mCrab for 4 d, and to send prompt alert information to the world in less than 30 s after the onboard detection of a burst, making the best use of the International Space Station (ISS) real-time network. We also report on highlights of scientific results obtained with the system until the end of the first extended mission phase, 2015 March. Including 15 X-ray novae solely or independently discovered, we have reported on 177 transient phenomena, such as X-ray bursts, outbursts, and state transitions of X-ray binaries and X-ray flares from active stars and blazars, via the Astronomer's Telegram, and on 63 burst phenomena of other types via the Gamma-ray Coordinates Network. We summarize the results of these transient sources and phenomena focusing on the detections with the nova-alert system, and some new transients yet unpublished or requiring attention.
US eBook market was 1352 Billion yen in 2010. It was twice the eBook market in Japan. Japanese eBook market was led by mobile eComics, and expanded between 2004 and 2007. US eBook market was led by ...Amazon Kindle and iPad, and expanded between 2008 and 2010. US vertically integrated model player presented a clear benefit for users. Then, US market surpassed Japanese market.
We present a catalog of high Galactic-latitude (b > 10degrees) X-ray sources detected in the first 37 months of data of the Monitor of All-sky X-ray Image/Gas Slit Camera (MAXI/GSC). To achieve the ...best sensitivity, we develop a background model of the GSC that well reproduces the data based on the detailed on-board calibration. Source detection is performed through image fits with a Poisson likelihood algorithm. The catalog contains 500 objects detected with significances of s sub(D,4-10 keV) > or =, slanted 7 in the 4-10 keV band. The limiting sensitivity is approximate7.5 x 10 super(-12) erg cm super(-2) s super(-1) (approximate0.6 mCrab) in the 4-10 keV band for 50% of the survey area, which is the highest ever achieved in an all-sky survey mission covering this energy band. We summarize the statistical properties of the catalog and results from cross matching with the Swift/BAT 70 month catalog, the meta-catalog of X-ray detected clusters of galaxies, and the MAXI/GSC 7 month catalog. Our catalog lists the source name (2MAXI), position and its error, detection significances and fluxes in the 4-10 keV and 3-4 keV bands, the hardness ratio, and the basic information of the likely counterpart available for 296 sources.
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