Soft X-ray Bandpass Research Articles

Large-format X-Ray Reflection Grating Operated in an Echelle-like Mounting

Abstract We report on resolving power measurements of an X-ray reflection grating designed for use in an astronomical soft X-ray spectrograph. The grating was patterned via electron-beam lithography (EBL) to have fanned grooves to match the convergence of an illuminating beam. Grating measurements were conducted in an echelle-like mounting, which yields access to high diffraction orders in the soft X-ray bandpass (0.2–2.0 keV). By comparing the zeroth-order line-spread function to the telescope focus, we find evidence for minimal broadening (<1″) introduced by the figure of the grating. In addition, we fit for the spectral resolution (R = λ/Δλ) intrinsic to this grating using a Bayesian Markov Chain Monte Carlo approach. Using an ensemble fitting technique, we find that the grating resolution R exceeds 2200 (3σ lower bound). This current grating resolution meets the performance required for a notional soft X-ray grating spectroscopy mission measuring hot baryonic material in the extended halos of galaxies. Using ray-trace simulations, we identify a geometric aberration resulting from path length differences across the width of the grating as a limiting factor in assessing the resolution of these gratings and discuss methods for placing better constraints on the inherent resolution of X-ray astronomical reflection gratings fabricated using EBL.

Overview of the high-definition x-ray imager instrument on the Lynx x-ray surveyor

Four NASA Science and Technology Definition Teams have been convened in order to develop and study four mission concepts to be evaluated by the upcoming 2020 Decadal Survey. The Lynx x-ray surveyor mission is one of these four large missions. Lynx will couple fine angular resolution (<0.5 arcsec HPD) x-ray optics with large effective area (~2 m^2 at 1 keV), thus enabling exploration within a unique scientific parameter space. One of the primary soft x-ray imaging instruments being baselined for this mission concept is the high-definition x-ray imager, HDXI. This instrument would use a finely pixelated silicon sensor array to achieve fine angular resolution imaging over a wide field of view (~22 x 22 arcmin). Silicon sensors enable large-format/small-pixel devices, radiation tolerant designs, and high quantum efficiency across the entire soft x-ray bandpass. To fully exploit the large collecting area of Lynx (~30x Chandra), with negligible or minimal x-ray event pile-up, the HDXI will be capable of much faster frame rates than current x-ray imagers. We summarize the planned requirements, capabilities, and development status of the HDXI instrument, and associated papers in this special edition will provide further details on some specific detector options.

X-ray verification of an optically aligned off-plane grating module.

Off-plane x-ray reflection gratings are theoretically capable of achieving high resolution and high diffraction efficiencies over the soft x-ray bandpass, making them an ideal technology to implement on upcoming x-ray spectroscopy missions. To achieve high effective area, these gratings must be aligned into grating modules. X-ray testing was performed on an aligned grating module to assess the current optical alignment methods. Results indicate that the grating module achieved the desired alignment for an upcoming x-ray spectroscopy suborbital rocket payload with modest effective area and resolving power. These tests have also outlined a pathway towards achieving the stricter alignment tolerances of future x-ray spectrometer payloads, which require improvements in alignment metrology, grating fabrication, and testing techniques.

Doppler disc tomography applied to low-mass AGN spin

Doppler tomography can provide a powerful means of determining black hole spin when our view to the central regions are revealed and obscured by optically thick orbiting material, and can provide an independent estimate that does not suffer as many degeneracies as traditional methods. For low mass AGN, time-dependent obscuration is expected to leave a signature in the changing spectrum of the disc emission which extends into the soft X-ray bandpass. We create a spectral model incorporating Doppler tomography and apply it to the case of the low mass (8 $\times$ 10$^{5}$ M$_{\odot}$) AGN, RX J1301.9+2747 which shows unusual timing properties in the form of short-lived flares that we argue are best explained by the orbit of a window through an optically thick wind. Modelling the phase-resolved spectrum over the course of the highest data quality flare indicates a very low spin even when we relax our constraints. This is the lowest mass AGN for which a spin has been measured and the first via this technique. We note that, as the mass and spin are very low, this appears to favour supermassive black hole (SMBH) growth by chaotic rather than constant accretion.

A new way to measure supermassive black hole spin in accretion disc-dominated active galaxies

We show that disc continuum fitting can be used to constrain black hole spin in a subclass of Narrow Line Seyfert 1 (NLS1) AGN as their low mass and high mass accretion rate means that the disc peaks at energies just below the soft X-ray bandpass. We apply the technique to the NLS1 PG1244+026, where the optical/UV/X-ray spectrum is consistent with being dominated by a standard disc component. This gives a best estimate for black hole spin which is low, with a firm upper limit of $a_*<0.86$. This contrasts with the recent X-ray determinations of (close to) maximal black hole spin in other NLS1 based on relativistic smearing of the iron profile. While our data on PG1244+026 does not have sufficient statistics at high energy to give a good measure of black hole spin from the iron line profile, cosmological simulations predict that black holes with similar masses have similar growth histories and so should have similar spins. This suggests that there is a problem either in our understanding of disc spectra, or/and X-ray reflection or/and the evolution of black hole spin.

A new method of soft X-ray transmission band-pass

Based on microchannel plate (MCP) X-ray optics, a transmission soft X-ray band-pass approach is presented. X-ray transmission band-pass characteristics are given through three structures of MCP channel. Calibration results from a square hole MCP and filter on Beijing Synchrotron Radiation Facility show that MCP transmission spectrum is of a wide range of band-pass options and high efficiency, and can achieve multi-point design of 100 eV bandwidth at lower than 1 keV with different filters.

Intrinsic disc emission and the soft X-ray excess in active galactic nuclei

(Abridged) Narrow Line Seyfert 1 (NLS1) galaxies have low mass black holes and mass accretion rates close to (or exceeding) Eddington, so a standard blackbody accretion disc should peak in the EUV. However, the lack of true absorption opacity in the disc means that the emission is better approximated by a colour temperature corrected blackbody, and this colour temperature correction is large enough ($\sim 2.4$) that the bare disc emission from a zero spin black hole can extend into the soft X-ray bandpass. Part of the soft X-ray excess seen in these objects must be intrinsic emission from the disc unless the vertical structure is very different to that predicted. However, the soft excess is much broader than predicted by a bare disc spectrum, indicating some Compton upscattering by cool, optically thick material. We associate this with the disc itself, so it must ultimately be powered by mass accretion. We build an energetically self consistent model assuming that the emission thermalises at large radii, but that at smaller radii the gravitational energy is split between powering optically thick Comptonised disc emission (forming the soft X-ray excess) and an optically thin corona above the disc (forming the tail to higher energies). We show examples of this model fit to the extreme NLS1 REJ1034+396, and to the much lower Eddington fraction Broad Line Seyfert 1 PG1048+231. We use these to guide our fits and interpretations of three template spectra made from co-adding multiple sources to track out a sequence of AGN spectra as a function of $L/L_{Edd}$. The new model is publically available within the {\sc xspec} spectral fitting package.

The Seyfert AGN RX J0136.9–3510 and the spectral state of super Eddington accretion flows

Abstract We have carried out a survey of long 50 ks XMM–Newton observations of a sample of bright, variable active galactic nuclei (AGN). We found a distinctive energy dependence of the variability in RX J0136.9−3510 where the fractional variability increases from 0.3 to 2 keV, and then remains constant. This is in sharp contrast to other AGN where the X-ray variability is either flat or falling with energy, sometimes with a peak at ∼2 keV superimposed on the overall trend. Intriguingly, these unusual characteristics of the variability are shared by one other AGN, namely RE J1034+396, which is so far unique showing a significant X-ray quasi-periodic oscillation (QPO). In addition, the broad-band spectrum of RX J0136.9−3510 is also remarkably similar to that of RE J1034+396, being dominated by a huge soft excess in the Extreme-UV (EUV) to soft X-ray bandpass. The bolometric luminosity of RX J0136.9−3510 gives an Eddington ratio of about 2.7 for a black hole mass (from the H beta line width) of 7.9 × 107 M⊙. This mass is about a factor of 50 higher than that of RE J1034+396, making any QPO undetectable in this length of observation. None the less, its X-ray spectral and variability similarities suggest that RE J1034+396 is simply the closest representative of a new class of AGN spectra, representing the most extreme mass accretion rates.

Evidence Against Broad Absorption Lines in the X‐Ray–bright Quasar PG 1416−129

Recent results from the ROSAT All-Sky Survey and from deep ROSAT pointings reveal that broad absorption line quasars (BALQSOs) are weak in the soft X-ray bandpass (αox > 1.8) in comparison to QSOs with normal OUV spectra ( = 1.4). One glaring exception appeared to be the nearby BALQSO PG 1416-129, which is a bright ROSAT source showing no evidence for intrinsic soft X-ray absorption. We present here our new HST Faint Object Spectrograph (FOS) spectrum of PG 1416-129, in which we find no evidence for BALs. We show that the features resulting in the original BAL classification, based on IUE spectra, were probably spurious. On the basis of UV, X-ray, and optical evidence, we conclude that PG 1416-129 is not now, and has never been, a BALQSO. Our result suggests that weak soft X-ray emission is a defining characteristic of true BALQSOs. If BALQSOs indeed harbor normal intrinsic spectral energy distributions, their observed soft X-ray weakness is most likely the result of absorption. The ubiquitous occurrence of weak soft X-ray emission with UV absorption (BALs) thus suggests absorbers in each energy regime that are physically associated, if not identical.

Broad Absorption Line Quasars Observed by the ROSAT PSPC

view Abstract Citations (143) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Broad Absorption Line Quasars Observed by the ROSAT PSPC Green, Paul J. ; Mathur, Smita Abstract Recent results from the ROSAT All-Sky Survey have shown that broad absorption line (BAL) QSOs are either highly absorbed or underluminous in the soft X-ray bandpass. Here we extend this work by analyzing all known bona fide BAL QSOs observed within the inner 20' of the ROSAT Position Sensitive Proportional Counter. This sample includes both targeted and serendipitous exposures ranging from 8 to 75 ks. Despite these deep exposures, most of the BAL QSOs are undetected and have unusually weak X- ray emission, as evidenced by large optical-to-X-ray slopes α_OX_. Large values of α_OX_ (~>1.8) may prove to be a defining characteristic of BAL QSOs. We predict that samples of QSO candidates with large α_OX_ will yield a higher percentage of BAL QSOs, particularly at low redshift. As a corollary, X-ray-selected QSO samples should yield fewer BAL QSOs. The optical/UV emission line spectra of BAL and non-BAL QSOs are quite similar, suggesting that their intrinsic spectral energy distributions are similar as well. Absorption thus seems the likely reason for the X- ray-quiet nature of BAL QSOs. To constrain the total absorbing column of the BAL clouds, we compare our measured soft X-ray fluxes or upper limits with those expected from normal radio-quiet QSOs of comparable optical continuum magnitude and redshift. From sensitive X-ray observations, we derive column densities of ~> 2 x 10^22^ cm^-2^ for intrinsic cold absorbers of solar metallicity. These new results suggest columns at least an order of magnitude larger than the columns previously estimated from optical/UV spectra alone. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177178 arXiv: arXiv:astro-ph/9512032 Bibcode: 1996ApJ...462..637G Keywords: GALAXIES: ACTIVE; GALAXIES: QUASARS: ABSORPTION LINES; X-RAYS: GALAXIES; Astrophysics E-Print: 10 pages, no figures, AAS latex (aaspptwo.sty), to be published in ApJ Vol. 462, May 20 1996 full text sources arXiv | ADS | data products SIMBAD (17) NED (12) HEASARC (1)

Tin–polyimide and indium–polyimide thin-film composites as soft x-ray bandpass filters

A tin-polyimide and an indium-polyimide soft x-ray bandpass filter were fabricated with thicknesses of 1400 and 1750 A for the metal and polyimide components, respectively. The transmission of each filter was measured at the Stanford Synchrotron Radiation Laboratory. The transmission of the tin-polyimide filter was found to be ~40% for radiation with wavelengths between 60 and 80 A. The transmission of the indium-polyimide filter was greater than 40% between 70 and 90 A. The indium was ~5% more transmissive than the tin and attained a maximum transmission of ~48% at 76 A. Such filters have potential applications to soft x-ray telescopes that operate in this region. They might also be of interest to investigators who work with x-ray microscopes that image live biological specimens in the 23-44-A water window.