Detection Of Recombination Lines Research Articles

A Population III–Generated Dust Screen at z ∼ 16

The search for alternative cosmological models is largely motivated by the growing discordance between the predictions of ΛCDM and the ever-improving observations, such as the disparity in the value of H 0 measured at low and high redshifts. One model in particular, known as the R h = ct universe, has been highly successful in mitigating or removing all of the inconsistencies. In this picture, however, the anisotropies in the cosmic microwave background (CMB) would have emerged at a redshift z ∼ 16, rather than via fluctuations in the recombination zone at z ∼ 1080. We demonstrate here that a CMB created in the early universe, followed by scattering through a Population III–generated dust screen, is consistent with all of the current data. Indeed, the Planck measurements provide a hint of an ∼2%–4% frequency dependence in the CMB power spectrum, which would be naturally explained as a variation in the optical depth through the dust but not a Thomson scattering–dominated recombination environment. Upcoming measurements should be able to easily distinguish between these two scenarios, e.g., via the detection of recombination lines at z ∼ 1080, which would completely eliminate the dust-reprocessing idea.

N49: THE FIRST ROBUST DISCOVERY OF RECOMBINING PLASMA IN AN EXTRA GALACTIC SUPERNOVA REMNANT

Recent discoveries of recombining plasmas (RPs) in supernova remnants (SNRs) have dramatically changed our understanding of SNR evolution. To date, a dozen of RP SNRs have been identified in the Galaxy. Here we present Suzaku deep observations of four SNRs in the Large Magellanic Cloud (LMC), N49, N49B, N23, and DEM L71, for accurate determination of their plasma state. Our uniform analysis reveals that only N49 is in the recombining state among them, which is the first robust discovery of a RP from an extra-galactic SNR. Given that RPs have been identified only in core-collapse SNRs, our result strongly suggests a massive star origin of this SNR. On the other hand, no clear evidence for a RP is confirmed in N23, from which detection of recombination lines and continua was previously claimed. Comparing the physical properties of the RP SNRs identified so far, we find that all of them are categorized into the "mixed-morphology" class and interacting with surrounding molecular clouds. This might be a key to solve formation mechanisms of the RPs.

XMM-NewtonX-ray spectroscopy of the high-mass X-ray binary 4U 1700-37 at low flux

We present results of a monitoring campaign of the high-mass X-ray binary system 4U 1700−37/HD 153919, carried out with XMM-Newton in February 2001. The system was observed at four orbital phase intervals, covering 37% of one 3.41-day orbit. The lightcurve includes strong flares, commonly observed in this source. We focus on three epochs in which the data are not affected by photon pile up: the eclipse, the eclipse egress and a low-flux interval in the lightcurve around orbital phase φ ∼ 0.25. The high-energy part of the continuum is modelled as a direct plus a scattered component, each represented by a power law with identical photon index (α ∼ 1.4), but with different absorption columns. We show that during the low-flux interval the continuum is strongly reduced, probably due to a reduction of the accretion rate onto the compact object. A soft excess is detected in all spectra, consistent with either another continuum component originating in the outskirts of the system or a blend of emission lines. Many fluorescence emission lines from near-neutral species and discrete recombination lines from He- and H-like species are detected during eclipse and egress. The fluorescence Fe Kα line at 6.4 keV is very prominent; a second Kα line is detected at slightly higher energies (up to 6.7 keV) and a Kβ line at 7.1 keV. In the low-flux interval the Fe Kα line at 6.4 keV is strongly (factor ∼30) reduced in strength. In eclipse, the Fe Kβ/Kα ratio is consistent with a value of 0.13. In egress we initially measure a higher ratio, which can be explained by a shift in energy of the Fe K-edge to ∼7.15 keV, which is consistent with moderately ionised iron, rather than neutral iron, as expected for the stellar wind medium. The detection of recombination lines during eclipse indicates the presence of an extended ionised region surrounding the compact object. The observed increase in strength of some emission lines corresponding to higher values of the ionisation parameter ξ further substantiates this conclusion.

Detection of carbon recombination lines below 100 MHz towards the Galactic Centre and M16

La detection de raies de recombinaison du carbone en absorption en direction du Centre Galactique a 75 MHz et en direction de M16 a 68 MHz et 80 MHz est rapportee. En direction de M16, la raie a egalement ete detectee en emission a 325 MHz. Les largeurs des raies impliquent des densites d'electrons inferieures a 0.8 cm −3 dans les nuages absorbants

Microwave Observations of a Partially Ionized Interstellar Cloud

High resolution spectroscopy has enabled detection of recombination lines of excited hydrogen, carbon and elements of intermediate mass from a cool cloud in the direction of W3.