News Article | March 1, 2017
We used all the available XMM-Newton data, both from our recent observing campaign (Principal Investigator A.C.F.) and from the archive. The EPIC-pn data are reduced using XMM-Newton’s Science Analysis System (SAS) version 15.0.0 EPPROC (https://www.cosmos.esa.int/web/xmm-newton/download-and-install-sas) tool. The EPIC observations were made in large-window mode. We extracted source counts from a 30″-diameter circular region centred on the source coordinates, and background counts from a circular region about 60″ in diameter nearby on the same chip, avoiding contaminating sources, chip edges, and the region where the internal background due to copper is high, and filter the data for background flares. We created separate stacked spectra of the archival and new data using the ADDSPEC ftool (available as part of NASA’s high-energy astrophysics software, HEASOFT; http://heasarc.nasa.gov/lheasoft/). We extracted full band (0.3–10 keV) lightcurves for each spectrum, shown in Extended Data Fig. 1, and divided the lightcurve into low-, medium- and high-flux intervals such that each flux band contained the same total number of counts (thus the low-flux intervals are much longer than the high-flux intervals). We then extracted spectra corresponding to each flux level from each observation, and combined them using ADDSPEC. We binned all the EPIC-pn spectra to achieve a signal-to-noise ratio of 6, after background subtraction, and to oversample the spectral resolution by a factor of 3. The RGS camera consists of two similar detectors, which have high effective area and high spectral resolution between 7 Å and 38 Å. The second-order spectra cover the wavelength range 7–18 Å and provide double the spectral resolution. We corrected for contamination from soft-proton flares following the XMM-SAS standard procedures. For each exposure, we extracted the first- and second-order RGS spectra in a cross-dispersion region of 1′ width, centred on IRAS sky coordinates. We extracted background spectra by selecting photons beyond 98% of the source point spread function. The background spectra were consistent with those from blank field observations. Using the SAS task RGSCOMBINE, we stacked all RGS 1 and 2 spectra, obtaining two high-quality spectra for both the first and the second order with a total, clean exposure of 1.529 Ms each. We grouped the RGS spectra in channels equal to one-third of the point spread function, and use C-statistics, because it provides optimal spectral binning and avoids over-sampling. RGS spectral fitting is performed using the SPEX package (https://www.sron.nl/astrophysics-spex), with contributions from XSPEC, in particular for reflection models. Flux-resolved spectra are extracted using the same good-time-interval files as used for the EPIC-pn analysis. The NuSTAR data were reduced using the NuSTAR data analysis software (NuSTARDAS) version 1.6.0 and CALDB version 20160731. We extracted source counts from a 30″-diameter circular region, centred on the source, and background counts from a large circular region on the same chip. We combined all the NuSTAR data into a single spectrum, given that the count rate is very low due to the extremely soft spectrum, and binned to achieve a signal-to-noise ratio of 6 and oversampling of 3. In the high-flux intervals, the source flux is above the nominal EPIC-pn large-window-mode pile-up limit of 3 counts s−1 (ref. 23), reaching about 9 counts s−1 at times. This risks distorting the spectrum and potentially affecting the detection of the ultrafast outflow. However, the count rate of IRAS 13224−3809 is dominated by photons from below 1 keV (the count rate from 0.5 keV to 1 keV is an order of magnitude higher than the count rate from 2 keV to 3 keV), because it is an extremely soft source. This means that the effects of pile-up are strongest below 2–3 keV. We tested this by extracting the same high-flux spectrum using an annular region, instead of a circle, with an excised core of 7″, which encircles the central four piled-up pixels. Above 2 keV, we found no difference in spectral shape between the two spectra, so we conclude that our analysis (restricted to E > 3 keV) is robust to this effect. The absorption feature is still present in both the mean spectrum and the low-flux spectrum when an annular extraction region is used. We also repeated this test using only single events, and again found no difference. The low-flux spectrum and the RGS spectra are not affected by pile-up. One potential cause of a false detection of an ultrafast outflow around 8 keV is the complex of emission lines, dominated by Cu Kα, in the instrumental background26. Over-subtracting these features would result in an artificial absorption feature at the corresponding energy, which would depend on the source to background flux ratio, giving an anticorrelation between the equivalent width of the line and the source flux. The copper background is only high in the outer regions of the detector, outside the central 300″, leaving a central ‘hole’ where contamination is minimal. We were careful to avoid the region where the copper background is high when selecting background regions, which should prevent contamination (see Extended Data Fig. 2). The easiest way to show that the ultrafast-outflow line is not an artefact of background over-subtraction is simply to not subtract the background and check the line remains. Although this is not always optimal (it may remove genuine but weak lines, or introduce new features), strong absorption features should remain in the spectrum. In Extended Data Fig. 3, we show the low-flux spectrum with no background subtraction, fitted with a power law. The iron line is weaker, owing to the additional high-energy contribution from the background, but the ultrafast-outflow line is clearly still present. If the observed line were produced by over-subtraction of the background, the (negative) flux of the line should be constant, the equivalent of an additional constant (positive) line in the background. This is trivial to test, by measuring the strength of an additive line with flux, rather than the multiplicative line we use elsewhere. We find clear variability, and an anti-correlation between the line flux and source flux (Fig. 3, inset), which is impossible if the line is a background feature. Finally, we note that the lines seen in the RGS spectrum are independent of this effect. We conclude that the line is genuine, and produced by absorption in the AGN spectrum. The potential secondary feature at about 8.7 keV (observer’s frame, 9.2-keV source frame) is coincidental with the Zn Kα line, and appears as an emission feature when the background is not subtracted. We cannot therefore robustly determine whether it is a genuine spectral feature, a statistical fluctuation, or due to the background. We fitted the stacked 2016 EPIC-pn spectrum in the range 3–10 keV (outside the band where pileup effects are present, and where the spectrum is relatively simple and unambiguous), and the stacked NuSTAR spectrum in the range 3–40 keV. We modelled the spectrum with the RELXILL relativistic reflection model27. The relativistic blurring parameters are consistent with those found by previous authors10 (see Extended Data Table 1), but a strong absorption feature remains at around 8.6 keV. When we included an additional Gaussian absorption line (modelled with GABS, with σ fixed at 0.1 keV), the fit improved by Δχ2 = 26, for two additional free parameters (degrees of freedom). Parameters for both these models are given in Extended Data Table 1. We also tested allowing σ to vary, but we found no significant difference in the fit statistic and no impact on the other fitting parameters. There are some differences between this result and those found by previous authors, which probably stem from the different energy range used. In particular, the photon index, the high-energy cut-off, and the iron abundance are different. The continuum parameters are not of great importance to this work, so long as the continuum is adequately described. The steeper Γ value in archival results (about 2.7; ref. 14) is probably due to the inclusion of the soft excess, which past authors10, 14 have fitted with a two-component reflection model. This requires a steep power law to produce enough soft photons to fit the soft excess. This model is not unique, because the soft excess generally has limited spectral features owing to the lower resolution of the EPIC-pn at these energies, and other factors, such as density of the disk, may alter the parameters from such a fit28. A visual comparison of the archival data and the new data (Extended Data Fig. 4a) does not show any major changes in the structure of the iron line or ultrafast-outflow absorption. Similarly, the iron abundance is largely determined by the relative strengths of the iron line and soft excess or Compton hump. Given the steep power law in the dual-reflection model, a high iron abundance is required to produce enough flux in the iron line. This is not required here, as we did not fit the soft excess and the Compton hump is only weakly constrained. This is important, as the iron abundance is potentially degenerate with the strength of the 8.6-keV absorption feature: an increased iron abundance produces a larger iron absorption edge in the reflection spectrum. We can be confident that this is not having a significant effect on our results, because the iron abundance is free to vary in all our fits, including the fits without the absorption modelled, and the feature still remains. We have explicitly searched for degeneracies using a Markov Chain Monte Carlo, and find no degeneracy between the strength of the line and the iron abundance. Following on from this, we performed a blind line scan over the 6–10-keV band, stepping an unresolved Gaussian line (σ = 0.01, allowed to be positive or negative) across the energy band, varying the normalization, and recording the Δχ2 at each point on this grid (Fig. 1a). We use the same underlying RELXILL model, allowing the same parameters to vary. We calculate the significance of this by taking the probability of the maximum Δχ2 for two additional free parameters, and correcting by the number of trials (that is, the number of resolution elements from 6.7 keV to 10 keV). This gives a final chance probability of 1.5 × 10−5, which corresponds to a 4.3σ detection. No other features are significant above about 1σ. We also fitted the absorption with a series of physical models—WARMABS in XSPEC (shown in Extended Data Fig. 4b), which uses grids of XSTAR photoionization models, and XABS and PION in SPEX. The three models give consistent results, with a degeneracy between two possible solutions with outflow velocities of v = 0.210 ± 0.009 and v = 0.244 ± 0.09, corresponding to Fe xxv and Fe xxvi. These solutions have different column densities and ionizations, which are summarized in Extended Data Table 2. The velocity broadening is not strongly constrained, but does not appear to affect any of the other wind parameters. We test this by fixing the broadening to lower and higher values, and find no change in the column density, velocity or ionization of the fit. The RGS spectrum is complex, showing several broad emission-like features at 15 Å and 18 Å. This spectrometer is the most sensitive to narrow (≲,000 Å) features, but higher effective area and broader energy range EPIC detectors are more efficient for determining the spectral continuum. We therefore performed an independent analysis of the RGS spectra using either a phenomenological spline continuum model fitted to the RGS spectrum or the physical reflection model provided by the best-fit reflection (RELXILL) model of the EPIC-pn stacked spectrum. When fitting the RGS spectrum, the spline is corrected for redshift and Galactic interstellar-medium absorption. We search for features in the RGS spectrum following an advanced procedure18. We include a Gaussian spanning the wavelength range 7–38 Å in increments of 0.05 Å, and assume a linewidth of 1,000 km s−1 (comparable to the RGS resolution). This broadening will also tend to strengthen the detection of any warm-absorber and ultrafast-outflow lines with respect to interstellar absorption lines, since the latter are typically narrower29 (≤200 km s−1). We take into account the absorption edges of neutral neon (14.3 Å), iron (17.5 Å), and oxygen (23.0 Å), but we exclude the corresponding 1s–2p absorption lines in order to detect and compare any spectral feature intrinsic to IRAS 13224−3809 or to the interstellar medium. The strongest non-Galactic absorption feature detected is a broad depression around 16 Å, which is also clear in the RGS stacked spectrum (see Extended Data Fig. 5). The other two putative, weaker, absorption-like features appear at 10 Å and 13 Å. Interestingly, the photoionization model of the EPIC spectrum predicts three broad (about 1,500 km s−1) ultrafast-outflow absorption lines that match the three RGS absorption features. We have tested different linewidths (from 100 km s−1 to 5,000 km s−1) without finding a major effect on their detection. The significance of the rest-frame absorption lines of Galactic O vii and O viii instead increase up to 5σ for narrower widths (<200 km s−1), confirming the results obtained with the grating spectra of the brightest X-ray binaries29. A full description of the RGS spectral modelling and the corresponding flux-resolved high-resolution X-ray spectroscopy will be discussed in a forthcoming paper. Here we provide the main result obtained with the overall spectrum and a first interpretation of the wind variability. We modelled the RGS stacked spectrum with both a spline and a reflection continuum in order to constrain the characteristics of the ultrafast outflow. The interstellar medium was modelled following the detailed multi-phase gas model constrained with the low-mass X-ray binaries29. We modelled the ultrafast-outflow absorption features in the RGS spectrum with an outflowing gas in photoionization equilibrium (XABS model in SPEX 3.02). The best fit of the RGS stacked spectrum provides the column density N = 9.5 ± 0.5 × 1022 cm−2 (90% error) the ionization parameter logξ = 4.0 ± 0.1 erg cm s−1 and the linewidth σ = 2,000 ± 1,000 km s−1. The RGS velocity shift v = −0.231c ± 0.007c fits between the EPIC Fe xxv (−0.244c ± 0.009c) and the Fe xxvi (−0.210c ± 0.009c) solutions, and does not fully constrain which solution is most likely, but slightly prefers the Fe xxv (−0.244c) solution, which is consistent within the 90% confidence level. We investigate a combined fit to both EPIC-pn and RGS spectra, fitting with the same absorption model but different continuum models for each spectrum (the physical reflection model for the EPIC-pn, and a spline for the RGS). We also include a photoionized emission component, modelled with the XSPEC PHOTEMIS model. The soft and hard absorption features are consistent with being from the same absorber (freeing the parameters between the two results in an improvement to the fit of only Δχ2 = 3, for four additional free parameters). The joint fit clearly prefers the Fe xxv solution, with final best-fit parameters of v = 0.236c ± 0.006c, σ = 4,000 ± 1,000, logξ = 4.14 ± 0.13 and . The increased broadening with respect to the individual spectrum fits may be due to a small offset between the EPIC-pn and RGS spectra, which could be caused by gain shift in the EPIC-pn. However, it is consistent at the 90% level with that found from the RGS alone. The inclusion of the emission component improves the fit significantly (Δχ2 = 21, for two additional free parameters), accounting for the residuals at about 8.3 keV and other possible features. The velocity of this component is 0.213c ± 0.015c, and the luminosity is (1.1 ± 0.5) × 1041 erg s−1. If this component is genuine, it is made up of scattered emission from the wind, and can in principle be used to determine the wind geometry. However, it is likely that much of the P Cygni profile, including any redshifted emission, is obscured by the relativistic iron line, which is very strong in this source. One possible approach to take here would be to search for the emission component of the P Cygni profile in the lag spectra, as the reverberation timescale should be much longer than for the relativistic reflection component, owing to the greater distance from the source. We also fitted the three flux-resolved spectra, tying parameters we expect to be constant (such as a and i) between the different spectra. The model parameters are consistent with those given in Extended Data Table 1, with the reflection fraction inversely proportional to flux. We performed the same line scan over these spectra simultaneously, stepping the line across in energy then recording the Δχ2 for each spectrum individually. The line is only significantly detected in the low flux spectrum, with a maximum Δχ2 of 59.7, for two additional free parameters. This gives a corrected probability of 1.96 × 10−12, and a significance of 7.0σ. We also check the robustness of the low-flux line detection using a Monte Carlo test. We draw parameters from a Markov chain Monte Carlo, used to evaluate the errors and degeneracies in the best-fit parameters, and use them to simulate 10,000 fake spectra. We then fitted these spectra using the same procedure. None of the simulated spectra have higher significance features, in either emission or absorption, setting a lower limit of P > 99.99% on the significance. Given the expected fraction of 4.6 × 10−12, it is not feasible to test sufficient spectra to establish the true significance using this method. We performed a similar analysis with ten flux-resolved spectra, again with the same number of counts in each. We fitted the spectra simultaneously, using RELXILL and a Gaussian absorption line, allowing the reflection fraction, power-law index, and normalizations of the reflection and Gaussian components to vary between each spectrum. This gives a reasonable fit (χ2/d.o.f. = 966/857 = 1.13, where d.o.f. is degrees of freedom). We then recorded the equivalent width and flux of the absorption line in each spectrum, and the 3–10-keV flux. These are plotted against each other in Fig. 3, showing a strong correlation. We used Bayesian regression to perform a linear fit, which incorporates the upper limits, and draw samples from the posterior distribution to calculate the uncertainty. We calculated the probability of a stronger correlation being found from a constant absorption feature by simulating 10,000 sets of points with the same errors, assuming that the line strength is constant in each case, and performing the same analysis. In no case did we find a stronger correlation. We performed high-resolution flux-resolved X-ray spectroscopy with the RGS data, consistent with that performed with EPIC: we extracted RGS 1 and 2 first- and second-order spectra with the good time intervals defined according to the EPIC flux prescriptions. We stacked the RGS 1 and 2 spectra for each flux range, obtaining three high-quality RGS spectra with comparable statistics. As previously seen for the overall stacked spectrum, there are some non-interstellar absorption-like features (at 9.5 Å, 13 Å and 16 Å) which show evidence of variability, being both stronger and possibly bluer in the low-flux spectrum. To probe the strength of the features in each spectrum, we applied the same technique used for the stacked spectrum by fitting a Gaussian over the wavelength range 7–38 Å in increments of 0.05 Å. In Fig. 2, we show the significance of the spectral features obtained adopting the (RGS fitted) spline continuum. The three broad features were still detected at 9.5 Å, 13.0 Å and 16 Å in the low-flux spectrum. They have less significance or are undetected in the higher-flux spectra with possible evidence of slight velocity change. Their wavelengths match with the strongest lines predicted by the 0.24c ultrafast outflow model in the RGS energy band: 10.0 ± 0.5 Å (Ne x + Fe xviii–Fe xxii blend), 13.2 ± 0.5 Å (O viii Kβ + Fe xviii) and 15.8 ± 0.5 Å (O viii Kα). The strength of the absorption lines anti-correlate with the flux in agreement with the EPIC result and therefore provides strong evidence in favour of a connection between the EPIC and RGS absorbers as being part of the same extreme wind. We computed the confidence level of the three main absorption lines in the low-flux spectrum, where they are significantly detected as in EPIC. Accounting for the number of trials due to bins of 0.05 Å and an outflow-velocity range from 0c to 0.3c, we obtain 2.1σ, 2.9σ and 3.4σ for the 9.5-Å, 13-Å and 16-Å absorption lines, respectively, which—since they have the same velocity shift—gives a cumulative 5.1σ detection. We can estimate the mass outflow rate by combining the velocity and column densities3, and the mass30 of 6 × 106M (estimated using the empirical reverberation relation31): where Ω is the solid angle of the wind and R is the radius of the wind. We cannot be confident of the value of Ω, as the emission from the P Cygni profile, if there is any, is obscured by the blue horn of the iron line, which is extremely strong in this source. However, given that the absorption line is found in the stacked archival data (most of which is from 2011), this implies that the feature has been present and roughly constant (as a function of flux) for at least 5 years, which would argue for a reasonably large covering fraction, otherwise any clump along the line of sight would probably have moved away. Similarly, we do not know the radius of the wind. However, we know that it must be variable on timescales ≲5 ks, which corresponds to 170 gravitational radii (R ). Assuming a radius of 100R , we find the accretion rate = 2 × 1023 × Ω g s−1 (0.03ΩM year−1) for Fe xxv, while the Eddington accretion rate for a black hole of this mass is 2.7 × 1024 g s−1, assuming an efficiency of 0.3 for near-maximal spin. In either case, a large fraction of the matter accreted by the disk is lost to the wind, possibly implying super-Eddington accretion at large radii (beyond R ). We can then calculate the power in the wind: For Ω = 2π, this gives a power of 4% of the Eddington luminosity L , implying that a non-negligible fraction of the accretion power must be lost into the wind. For the same assumed covering fraction, the power of the quasar PDS 456 is 15% of the Eddington luminosity3. The prevailing interpretation for highly blueshifted absorption features in the X-ray spectra of AGNs is that they are due to outflowing gas. However, it is possible that some of these features may instead be due to absorption by a diffuse absorbing surface layer on the approaching side of the accretion disk, which naturally gives relativistic velocities32. The absorption line then appears in the reflection component. Aberration means that the blue side is brighter than the red side. For a disk inclination of 60° the absorption layer needs to extend from about 5R to 10R to give an observed line at 8.2 keV. If the brighter parts of the light curve are associated with the corona rising above 10R , then reduced light bending and irradiation of the inner disk weakens both the reflection component and the absorption, consistent with observation. It is also possible that the variability is produced by a geometric effect. Previous authors have suggested that the relatively constant spectrum of the relativistic reflection component can be produced by changes in the height or extent of the X-ray corona above the disk33, and the covering fraction of a wind at a small angle to the disk could similarly depend on the size or position of the compact X-ray source. All the code used for the data reduction is available from the respective websites. XSPEC and SPEX are freely available online. Code used for generating figures, calculating flux-resolved extraction intervals, and calculating line significance, is available upon request to M.L.P. All data used in this work is publicly available. The XMM-Newton observations can be accessed from the XMM-Newton science archive (http://nxsa.esac.esa.int/nxsa-web/) and the NuSTAR data from the HEASARC archive (http://heasarc.gsfc.nasa.gov/docs/archive.html). Figure data are available from the authors.
News Article | March 3, 2017
Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World's team of editors and reporters A new high-resolution map of dark matter – an invisible substance that appears to have a profound gravitational effect on galaxies and other large-scale structures in the cosmos – has been produced by an international team of astronomers using the Hubble Space Telescope. The map focuses on three galaxy clusters that act as cosmic telescopes by magnifying images of the more distant universe through gravitational lensing. The degree to which this magnification occurs gives an extremely precise measurement of the dark matter within the clusters. "We have mapped all of the clumps of dark matter that the data permit us to detect, and have produced the most detailed topological map of the dark-matter landscape to date," explains Priyamvada Natarajan of Yale University in the US, who led the team. An important feature of the map is that it is in close agreement with computer simulations of how cold dark matter (CDM) – a popular theoretical description of dark matter – is expected to be distributed within the galaxy clusters. The map is described in the Monthly Notices of the Royal Astronomical Society. A hard-to-detect pigment in melanoma skin cancer can be imaged using a laser-based technique. A team at Massachusetts General Hospital's Wellman Center for Photomedicine in the US has used a form of Raman spectroscopy to identify the pheomelanin molecule. Melanoma is the deadliest form of skin cancer and fair skin has a higher probability of developing the hard-to-detect variation of the disease called amelanotic melanoma. This is linked to the fact that fair skin contains a higher concentration of pheomelanin – a pigment, or melanin, within the skin. While the black-brown pigment found in most melanomas is easily observed, pheomelanin is essentially invisible. To detect the pigment, the team, led by Conor Evans, turned to a form of Raman spectroscopy called coherent anti-Stokes Raman Scattering (CARS) microscopy. Raman spectroscopy is a well-known technique that uses lasers to measure the unique chemical vibrations within molecules and hence identify them. CARS microscopy meanwhile, is a high-resolution imaging technique. It focuses two lasers on a sample and "tunes" the energy difference to specific molecular vibrations. This means a high-resolution image can be generated. Using CARS, the researchers successfully imaged the usually invisible pheomelanin by looking for its unique chemical structure. The method could be incorporated into a brand-new tool for early cancer diagnosis. The work will be presented at the OSA Biophotonics Congress: Optics in the Life Sciences meeting on 2–5 April in San Diego, US. It has also been described in Scientific Reports. A connection between the sudden outflows of gas from a supermassive black hole and X-ray bursts has been made by astronomers using two space telescopes – NASA's NuSTAR and the European Space Agency's XMM-Newton. Gas outflows are common features of supermassive black holes, which sit at the centre of large galaxies. These objects ingest vast amounts of material and the dynamics of this accretion process can lead to the ejection of gas in a burp-like ultrafast wind. The team trained the instruments on an outflow from the black hole at the centre of galaxy IRAS 13224-3809 and observed that the temperature of an outflow was changing much more rapidly than had previously been seen in other events – on a timescale of less than 1 h. According to team member Erin Kara of the University of Maryland, these fluctuations provide important clues about where the outflow was created. "Because we saw such rapid variability in the winds, we know that the emission is coming from very close to the black hole itself, and because we observed that the wind was also changing on rapid timescales, it must also be coming from very close to the black hole." The observations were made over several days and revealed that the temperature fluctuations were a response to changes in the intensity of X-rays emitted by the black hole. This information could provide important clues about where the X-rays and outflows are produced. The research is described in Nature.
News Article | November 24, 2016
One of the open questions in astrochemistry is how complex organic and prebiotic molecules are formed. Aims. Our aim is to start the process of compiling an inventory of oxygen-bearing complex organic molecules toward the solar-type Class 0 protostellar binary IRAS16293-2422 from an unbiased spectral survey with ALMA (PILS). Here we focus on the new detections of ethylene oxide (c-C2H4O), acetone (CH3COCH3), and propanal (C2H5CHO). Methods. With ALMA, we surveyed the spectral range from 329 to 363 GHz at 0.5" (60 AU diameter) resolution. Using a simple model for the molecular emission in LTE, the excitation temperatures and column densities of each species were constrained. Results. We successfully detect propanal (44 lines), ethylene oxide (20 lines) and acetone (186 lines) toward one component of the protostellar binary, IRAS16293B. The high resolution maps demonstrate that the emission for all investigated species originates from the compact central region close to the protostar. This, along with a derived common excitation temperature of ∼ 125 K, is consistent with a coexistence of these molecules in the same gas. Conclusions. The observations mark the first detections of acetone, propanal and ethylene oxide toward a low-mass protostar. The relative abundance ratios of the two sets of isomers (CH3COCH3/C2H5CHO ∼ 8 and CH3CHO/c-C2H4O ∼ 12) are comparable to previous observations toward high-mass protostars. The majority of observed abundance ratios from these results as well as those measured toward high-mass protostars are up to an order of magnitude above the predictions from chemical models. This may reflect either missing reactions or uncertain rates in the chemical networks. The physical conditions, such as temperatures or densities, used in the models, may not be applicable to solar-type protostars either. The ALMA-PILS survey: First detections of ethylene oxide, acetone and propanal toward the low-mass protostar IRAS 16293-2422 J. M. Lykke, A. Coutens, J. K. Jørgensen, M. H. D. van der Wiel, R. T. Garrod, H. S. P. Müller, P. Bjerkeli, T. L. Bourke, H. Calcutt, M. N. Drozdovskaya, C. Favre, E. C. Fayolle, S. K. Jacobsen, K. I. Öberg, M. V. Persson, E. F. van Dishoeck, S. F. Wampfler (Submitted on 22 Nov 2016) Comments: Accepted in A&A Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA) DOI: 10.1051/0004-6361/201629180 Cite as: arXiv:1611.07314 [astro-ph.SR] (or arXiv:1611.07314v1 [astro-ph.SR] for this version) Submission history From: Audrey Coutens [v1] Tue, 22 Nov 2016 14:24:59 GMT (5612kb,D) https://arxiv.org/abs/1611.07314
News Article | March 1, 2017
Gas outflows are common features of active supermassive black holes that reside in the center of large galaxies. Millions to billions of times the mass of the Sun, these black holes feed on the large disks of gas that swirl around them. Occasionally the black holes eat too much and burp out an ultra-fast wind, or outflow. These winds may have a strong influence on regulating the growth of the host galaxy by clearing the surrounding gas away and suppressing star formation. Scientists have now made the most detailed observation yet of such an outflow, coming from an active galaxy named IRAS 13224-3809. The outflow's temperature changed on time scales of less than an hour, which is hundreds of times faster than ever seen before. The rapid fluctuations in the outflow's temperature indicated that the outflow was responding to X-ray emissions from the accretion disk, a dense zone of gas and other materials that surrounds the black hole. The new observations are published in the journal Nature on March 2, 2017. "Although we have seen these outflows before, this observation was the first time we were able to see the launching of the gases being connected with changes in the luminosity of black holes," said Erin Kara, a postdoctoral researcher in astronomy at the University of Maryland and a co-author of the study. Scientists made these measurements using two space telescopes, NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) telescope and the European Space Agency's (ESA) XMM-Newton. To capture the variability of these signals, scientists focused the XMM-Newton on the black hole for 17 days in a row, and observed the black hole with NuSTAR for six days. To measure the temperatures of these winds, scientists studied X-rays coming from the edge of the black hole. As they travel towards Earth, these X-rays pass through the outflows. Elements such as iron or magnesium present in the outflows can absorb specific parts of the X-ray spectrum, creating signature "dips" in the X-ray signal. By observing these dips, called absorption features, astronomers can learn what elements exist in the wind. The team noticed that the absorption features disappeared and reappeared in the span of a few hours. The researchers concluded that the X-rays were heating up the winds to millions of degrees Celsius, at which point the winds became incapable of absorbing any more X-rays. The observations that the outflows appear to be linked with X-rays, and that both are so highly variable, provide possible clues for locating where exactly the X-rays and outflows originate. "The radiating gas flows into black holes are most variable at their centers," Kara said. "Because we saw such rapid variability in the winds, we know that the emission is coming from very close to the black hole itself, and because we observed that the wind was also changing on rapid time scales, it must also be coming from very close to the black hole." To further study galaxy formation and black holes, Chris Reynolds, a professor of astronomy at UMD and a co-PI on the project, noted the need for more detailed data and observations. "We need to observe this black hole with better and more spectrometers, so we can get more details about these outflows," Reynolds said. "For instance, we don't know whether the outflow is composed of one or multiple sheets of gas. And we need to observe on multiple bands in addition to X-rays--that would allow us to detect molecular gases, and colder gases, that can be driven by these high-energy outflows. All that information will be crucial to understanding how these outflows are connected to galaxy formation." This research was supported by NASA, the European Space Agency, the European Research Council (Award No. 340492), the European Union Seventh Framework Programme (Award No. n.312789, StrongGravity), and the United Kingdom Science and Technology Facilities Council. The content of this article does not necessarily reflect the views of these organizations. The research paper, "Relativistically outflowing gas responds to the inner accretion disk of a black hole," Michael Parker, Ciro Pinto, Andrew Fabian, Anne Lohfink, Douglas Buisson, William Alston, Erin Kara, Edward Cackett, Chia-Ying Chiang, Thomas Dauser, Barbara De Marco, Luigi Gallo, Javier Garcia, Fiona Harrison, Ashley King, Matthew Middleton, Jon Miller, Giovanni Miniutti, Christopher Reynolds, Phil Uttley, Ranjan Vasudevan, Dominic Walton, Daniel Wilkins and Abderahmen Zoghbi, was published in the journal Nature on March 2, 2017. Media Relations Contact: Irene Ying, 301-405-5204, firstname.lastname@example.org University of Maryland College of Computer, Mathematical, and Natural Sciences 2300 Symons Hall College Park, MD 20742 http://www. @UMDscience About the College of Computer, Mathematical, and Natural Sciences The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 7,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $150 million.
News Article | August 29, 2016
Researchers initially classified the star as elderly, perhaps a red supergiant. But a new study by a NASA-led team of researchers suggests that the object, labeled IRAS 19312+1950, might be something quite different - a protostar, a star still in the making. "Astronomers recognized this object as noteworthy around the year 2000 and have been trying ever since to decide how far along its development is," said Martin Cordiner, an astrochemist working at NASA's Goddard Space Flight Center in Greenbelt, Maryland. He is the lead author of a paper in the Astrophysical Journal describing the team's findings, from observations made using NASA's Spitzer Space Telescope and ESA's Herschel Space Observatory. Located more than 12,000 light-years from Earth, the object first stood out as peculiar when it was observed at particular radio frequencies. Several teams of astronomers studied it using ground-based telescopes and concluded that it is an oxygen-rich star about 10 times as massive as the sun. The question was: What kind of star? Some researchers favor the idea that the star is evolved - past the peak of its life cycle and on the decline. For most of their lives, stars obtain their energy by fusing hydrogen in their cores, as the sun does now. But older stars have used up most of their hydrogen and must rely on heavier fuels that don't last as long, leading to rapid deterioration. Two early clues - intense radio sources called masers - suggested the star was old. In astronomy, masers occur when the molecules in certain kinds of gases get revved up and emit a lot of radiation over a very limited range of frequencies. The result is a powerful radio beacon - the microwave equivalent of a laser. One maser observed with IRAS 19312+1950 is almost exclusively associated with late-stage stars. This is the silicon oxide maser, produced by molecules made of one silicon atom and one oxygen atom. Researchers don't know why this maser is nearly always restricted to elderly stars, but of thousands of known silicon oxide masers, only a few exceptions to this rule have been noted. Also spotted with the star was a hydroxyl maser, produced by molecules comprised of one oxygen atom and one hydrogen atom. Hydroxyl masers can occur in various kinds of astronomical objects, but when one occurs with an elderly star, the radio signal has a distinctive pattern - it's especially strong at a frequency of 1612 megahertz. That's the pattern researchers found in this case. Even so, the object didn't entirely fit with evolved stars. Especially puzzling was the smorgasbord of chemicals found in the large cloud of material surrounding the star. A chemical-rich cloud like this is typical of the regions where new stars are born, but no such stellar nursery had been identified near this star. Scientists initially proposed that the object was an old star surrounded by a surprising cloud typical of the kind that usually accompanies young stars. Another idea was that the observations might somehow be capturing two objects: a very old star and an embryonic cloud of star-making material in the same field. Cordiner and his colleagues began to reconsider the object, conducting observations using ESA's Herschel Space Observatory and analyzing data gathered earlier with NASA's Spitzer Space Telescope. Both telescopes operate at infrared wavelengths, which gave the team new insight into the gases, dust and ices in the cloud surrounding the star. The additional information leads Cordiner and colleagues to think the star is in a very early stage of formation. The object is much brighter than it first appeared, they say, emitting about 20,000 times the energy of our sun. The team found large quantities of ices made from water and carbon dioxide in the cloud around the object. These ices are located on dust grains relatively close to the star, and all this dust and ice blocks out starlight making the star seem dimmer than it really is. In addition, the dense cloud around the object appears to be collapsing, which happens when a growing star pulls in material. In contrast, the material around an evolved star is expanding and is in the process of escaping to the interstellar medium. The entire envelope of material has an estimated mass of 500 to 700 suns, which is much more than could have been produced by an elderly or dying star. "We think the star is probably in an embryonic stage, getting near the end of its accretion stage - the period when it pulls in new material to fuel its growth," said Cordiner. Also supporting the idea of a young star are the very fast wind speeds measured in two jets of gas streaming away from opposite poles of the star. Such jets of material, known as a bipolar outflow, can be seen emanating from young or old stars. However, fast, narrowly focused jets are rarely observed in evolved stars. In this case, the team measured winds at the breakneck speed of at least 200,000 miles per hour (90 kilometers per second) - a common characteristic of a protostar. Still, the researchers acknowledge that the object is not a typical protostar. For reasons they can't explain yet, the star has spectacular features of both a very young and a very old star. "No matter how one looks at this object, it's fascinating, and it has something new to tell us about the life cycles of stars," said Steven Charnley, a Goddard astrochemist and co-author of the paper. NASA's Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission, whose science operations are conducted at the Spitzer Science Center. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Herschel is an ESA space observatory with science instruments provided by European-led principal investigator consortia and with important participation from NASA. More information: On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation? M. A. Cordiner et al., 2016 Sep. 1, Astrophysical Journal iopscience.iop.org/article/10.3847/0004-637X/828/1/51 , On Arxiv: arxiv.org/abs/1607.00432
News Article | March 1, 2017
An artist impression illustrating a supermassive black hole with X-ray emission emanating from its inner region (pink) and ultrafast winds streaming from the surrounding disk (purple). Credit: The European Space Agency (ESA) Gas outflows are common features of active supermassive black holes that reside in the center of large galaxies. Millions to billions of times the mass of the Sun, these black holes feed on the large disks of gas that swirl around them. Occasionally the black holes eat too much and burp out an ultra-fast wind, or outflow. These winds may have a strong influence on regulating the growth of the host galaxy by clearing the surrounding gas away and suppressing star formation. Scientists have now made the most detailed observation yet of such an outflow, coming from an active galaxy named IRAS 13224-3809. The outflow's temperature changed on time scales of less than an hour, which is hundreds of times faster than ever seen before. The rapid fluctuations in the outflow's temperature indicated that the outflow was responding to X-ray emissions from the accretion disk, a dense zone of gas and other materials that surrounds the black hole. The new observations are published in the journal Nature on March 2, 2017. "Although we have seen these outflows before, this observation was the first time we were able to see the launching of the gases being connected with changes in the luminosity of black holes," said Erin Kara, a postdoctoral researcher in astronomy at the University of Maryland and a co-author of the study. Scientists made these measurements using two space telescopes, NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) telescope and the European Space Agency's (ESA) XMM-Newton. To capture the variability of these signals, scientists focused the XMM-Newton on the black hole for 17 days in a row, and observed the black hole with NuSTAR for six days. To measure the temperatures of these winds, scientists studied X-rays coming from the edge of the black hole. As they travel towards Earth, these X-rays pass through the outflows. Elements such as iron or magnesium present in the outflows can absorb specific parts of the X-ray spectrum, creating signature "dips" in the X-ray signal. By observing these dips, called absorption features, astronomers can learn what elements exist in the wind. The team noticed that the absorption features disappeared and reappeared in the span of a few hours. The researchers concluded that the X-rays were heating up the winds to millions of degrees Celsius, at which point the winds became incapable of absorbing any more X-rays. The observations that the outflows appear to be linked with X-rays, and that both are so highly variable, provide possible clues for locating where exactly the X-rays and outflows originate. "The radiating gas flows into black holes are most variable at their centers," Kara said. "Because we saw such rapid variability in the winds, we know that the emission is coming from very close to the black hole itself, and because we observed that the wind was also changing on rapid time scales, it must also be coming from very close to the black hole." To further study galaxy formation and black holes, Chris Reynolds, a professor of astronomy at UMD and a co-PI on the project, noted the need for more detailed data and observations. "We need to observe this black hole with better and more spectrometers, so we can get more details about these outflows," Reynolds said. "For instance, we don't know whether the outflow is composed of one or multiple sheets of gas. And we need to observe on multiple bands in addition to X-rays—that would allow us to detect molecular gases, and colder gases, that can be driven by these high-energy outflows. All that information will be crucial to understanding how these outflows are connected to galaxy formation." More information: The response of relativistic outflowing gas to the inner accretion disk of a black hole, Nature, nature.com/articles/doi:10.1038/nature21385
News Article | March 3, 2017
A team of scientists detected temperature swings in ultrafast “burps” of hot winds emitted by a black hole's accretion disk. These outflows could be responsible for preventing the birth of stars. Black holes, as we all know, are voracious eaters. These objects are so dense that nothing, not even light, can escape once ensnared by their immense gravitational pull. Occasionally, though, young and overeager black holes gobble down so much material so fast that they produce ultrafast “burps” of hot winds. Observations now conducted using NASA’s NuSTAR and the European Space Agency’s XMM-Newton telescopes indicate that these outflows, which can travel at nearly a quarter of the speed of light, could be suppressing the birth of stars in galaxies. Although it has previously been suggested that black hole-driven jets and winds can inhibit star formation, this is the first time the temperature swings of these outflows has been measured and their interactions with a black hole’s radiation studied. “We know that supermassive black holes affect the environment of their host galaxies, and powerful winds arising from near the black hole may be one means for them to do so,” NuSTAR principal investigator Fiona Harrison, a professor of physics at the California Institute of Technology, said in a statement released Wednesday. “The rapid variability, observed for the first time, is providing clues as to how these winds form and how much energy they may carry out into the galaxy.” For the purpose of this study, which was published in the March 2 issue of the journal Nature, the researchers trained their telescopes on IRAS 13224-3809 — an active galaxy located in the constellation Centaurus. This revealed that the ultrafast outflows emanating from the vicinity of the supermassive black hole at the galaxy’s center were heating up and cooling down in a span of just a few hours — hundreds of times faster than ever seen before. This, the researchers said, was an indication that the outflows were responding to X-ray emissions from the accretion disk, which is an orbiting disk of dust, gas and debris that surrounds active black holes. The X-rays were heating up the winds to millions of degrees, pushing them past a point where they become incapable of absorbing any more X-rays. These high-speed winds, in turn, could be responsible for suppressing star formation — a process that occurs at a temperature of roughly 10 Kelvin (-442 degrees Fahrenheit), at which point clouds of gas and dust cool down enough to condense. However, further observations would be needed to better understand the role these winds play in regulating the environment within their host galaxies. “We need to observe this black hole with better and more spectrometers, so we can get more details about these outflows,” study co-author Christopher Reynolds, a professor of astronomy at the University of Maryland, said in a statement. “For instance, we don't know whether the outflow is composed of one or multiple sheets of gas. And we need to observe on multiple bands in addition to X-rays — that would allow us to detect molecular gases, and colder gases, that can be driven by these high-energy outflows.”
News Article | March 9, 2016
Some stars may host multiple generations of planets, a dazzling new photo suggests. The newly released image, which was captured by the Very Large Telescope Interferometer (VLTI) in Chile, shows a dusty disk around an old double star called IRAS 08544-4431, which lies about 4,000 light-years from Earth in the southern constellation of Vela (The Sails). Scientists created this video look at the dust-shrouded star to showcase the discovery. This disk is very similar to the planet-forming structures commonly observed around young stars. While it's not clear whether planets actually do take shape around older stars, the new photo — the sharpest ever taken of such a disk around a mature star — hints that this is a possibility, researchers said. [The Strangest Alien Planets (Gallery)] "Our observations and modeling open a new window to study the physics of these disks, as well as stellar evolution in double stars," study co-author Hans Van Winckel, of the Instituut voor Sterrenkunde in Belgium, said in a statement. "For the first time, the complex interactions between close binary systems and their dusty environments can now be resolved in space and time." The scientists used several VLTI telescopes, an associated instrument called the Precision Integrated-Optics Near-infrared Imaging ExpeRiment (PIONIER) and a new high-speed infrared detector to take the photo. "We obtained an image of stunning sharpness — equivalent to what a telescope with a diameter of 150 meters [490 feet] would see," study team member Jacques Kluska, of Exeter University in England, said in the same statement. "The resolution is so high that, for comparison, we could determine the size and shape of a 1-euro coin seen from a distance of 2,000 kilometers [1,240 miles]." The IRAS 08544-4431 system consists of an old red giant star, as well a nearby, younger, "normal" star. The dust that comprises the newly imaged disk was expelled by the red giant, researchers said. "We were also surprised to find a fainter glow that is probably coming from a small accretion disk around the companion star," said study lead author Michael Hillen, also of the Instituut voor Sterrenkunde. "We knew the star was double, but weren't expecting to see the companion directly," Hillen added. "It is really thanks to the jump in performance now provided by the new detector in PIONIER, that we are able to view the very inner regions of this distant system." Hillen and his colleagues are publishing their results in the journal Astronomy & Astrophysics. The VLTI is located at the European Southern Observatory's Paranal Observatory in northern Chile. Follow Elizabeth Howell @howellspace, or Space.com @Spacedotcom. We're also on Facebook and Google+. Original article on Space.com. Copyright 2016 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
News Article | November 8, 2016
CHICAGO--(BUSINESS WIRE)--$NTRS #IRAS--Northern Trust Universe data today revealed the third quarter of 2016 marked the fourth consecutive quarterly gain for plan sponsors.
News Article | March 1, 2017
Scientists have made the most detailed observation yet of a black hole outflow, from the active galaxy IRAS 13224-3809. The outflow's temperature changed on time scales of less than an hour -- hundreds of times faster than ever seen before. The rapid fluctuations in the outflow's temperature also indicated that the outflow was responding to X-ray emissions from the accretion disk, a dense zone of gas and other materials that surrounds the black hole.