Japan Aerospace Exploration Agency

About: Japan Aerospace Exploration Agency is a facility organization based out in Tokyo, Japan. It is known for research contribution in the topics: Galaxy & Telescope. The organization has 4327 authors who have published 12054 publications receiving 208330 citations.

Fe II Emission in 14 Low-Redshift Quasars: I - Observations

Abstract: We present the spectra of 14 quasars with a wide coverage of rest wavelengths from 1000 to 7300 A. The redshift ranges from z = 0.061 to 0.555 and the luminosity from M_{B} = -22.69 to -26.32. We describe the procedure of generating the template spectrum of Fe II line emission from the spectrum of a narrow-line Seyfert 1 galaxy I Zw 1 that covers two wavelength regions of 2200-3500 A and 4200-5600 A. Our template Fe II spectrum is semi-empirical in the sense that the synthetic spectrum calculated with the CLOUDY photoionization code is used to separate the Fe II emission from the Mg II line. The procedure of measuring the strengths of Fe II emission lines is twofold; (1) subtracting the continuum components by fitting models of the power-law and Balmer continua in the continuum windows which are relatively free from line emissions, and (2) fitting models of the Fe II emission based on the Fe II template to the continuum-subtracted spectra. From 14 quasars, we obtained the Fe II fluxes in five wavelength bands, the total flux of Balmer continuum, and the fluxes of Mg II, Halpha, and other emission lines, together with the full width at half maxima (FWHMs) of these lines. Regression analysis was performed by assuming a linear relation between any two of these quantities. Eight correlations were found with a confidence level higher than 99%. The fact that six of these eight are related to FWHM or M_{BH} may imply that M_{BH} is a fundamental quantity that controls Gamma or the spectral energy distribution (SED) of the incident continuum, which in turn controls the Fe II emission. Furthermore, it is worthy of noting that Fe II(O1)/Fe II(U1) is found to tightly correlate with Fe II(O1)/Mg II, but not with Fe II(U1)/Mg II.

Observations of Slow Electron Holes at a Magnetic Reconnection Site

Abstract: We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.

Investigating the nature of narrow-line Seyfert 1 galaxies with high-energy spectral complexity

Abstract: With the commissioning of XMM-Newton came the discovery of 2.5-10keV spectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). This high-energy complexity can be manifested as sharp, spectral drops or gradual curvature in the spectrum. Models which are normally considered are ionized reflection and partial covering. In this work, we define two samples of NLS1: a complex sample whose members exhibit high-energy complexity (C sample), and a general sample of NLS1 whose 2.5-10keV spectra do not strongly deviate from a simple power law (S sample). We than compare multiwavelength parameters of these two samples to determine if there are any distinguishing characteristics in the complex NLS1. Considering historical light curves of each object, we find that the C sample is representative of NLS1 in a low X-ray flux state, whereas the members of the S sample appear to be in a typical flux state. Moreover, from measurements of α ox with contemporaneous ultraviolet (UV)/X-ray data, we find that the C sample of NLS1 appear X-ray weaker at the time of the observation. For two NLS 1 in the C sample multi-epoch measurements of α ox are available and suggest that α ox approaches more normal values as the complexity between 2.5 and 10keV diminishes. This implies that a source could transit from one sample to the other as its X-ray flux varies. Secondly, there are indications that the C sample sources, on average, exhibit stronger optical Fe II emission, with the three most extreme (Fe II/Hβ > 1.8) Fe II emitters all displaying complexity in the 2.5-10 keV band. It is an intriguing possibility that we may be able to identify X-ray complex NLS 1 based on the extreme strength of the more easily observable optical Fe II emission. However, it is not clear if the possible connection between Fe II strength and spectral complexity is due to the Fe II producing mechanism or because strong Fe II emitters may exhibit the greatest variability and consequently more likely to be caught in an extreme (low) flux state. Based on the current analysis, we cannot straightforwardly dismiss absorption or reflection as the cause of the X-ray complexity; by considering the multiple UV/X-ray observations of 1H 0707-495 (a C sample member), we discuss a possible method of distinguishing the two models provided further UV/X-ray observations.

Jet spectral breaks in black hole X-ray binaries

Abstract: In X-ray binaries, compact jets are known to commonly radiate at radio to infrared frequencies, whereas at optical to γ-ray energies, the contribution of the jet is debated. The total luminosity, and hence power of the jet, is critically dependent on the position of the break in its spectrum, between optically thick (self-absorbed) and optically thin synchrotron emission. This break, or turnover, has been reported in just one black hole X-ray binary (BHXB) thus far, GX 339−4, and inferred via spectral fitting in two others, A0620−00 and Cyg X−1. Here, we collect a wealth of multi-wavelength data from the outbursts of BHXBs during hard X-ray states, in order to search for jet breaks as yet unidentified in their spectral energy distributions. In particular, we report the direct detection of the jet break in the spectrum of V404 Cyg during its 1989 outburst, at νb = (1.8 ± 0.3) × 1014 Hz (1.7 ± 0.2 μm). We increase the number of BHXBs with measured jet breaks from three to eight. Jet breaks are found at frequencies spanning more than two orders of magnitude, from νb = (4.5 ± 0.8) × 1012 Hz for XTE J1118+480 during its 2005 outburst, to νb > 4.7 × 1014 Hz for V4641 Sgr in outburst. A positive correlation between jet break frequency and luminosity is expected theoretically; νb∝L∼ 0.5ν, jet if other parameters are constant. With constraints on the jet break in a total of 12 BHXBs including two quiescent systems, we find a large range of jet break frequencies at similar luminosities and no obvious global relation (but such a relation cannot be ruled out for individual sources). We speculate that different magnetic field strengths and/or different radii of the acceleration zone in the inner regions of the jet are likely to be responsible for the observed scatter between sources. There is evidence that the high-energy cooling break in the jet spectrum shifts from UV energies at LX ∼ 10−8LEdd (implying the jet may dominate the X-ray emission in quiescence) to X-ray energies at ∼10−3LEdd. Finally, we find that the jet break luminosity scales as Lν, jet∝L0.56 ± 0.05X (very similar to the radio-X-ray correlation), and radio-faint BHXBs have fainter jet breaks. In quiescence the jet break luminosity exceeds the X-ray luminosity.