Broad Absorption Features Research Articles

A Ground Plane Artifact that Induces an Absorption Profile in Averaged Spectra from Global 21 cm Measurements, with Possible Application to EDGES

Abstract Most of the current Global 21 cm experiments include ground screens that help moderate effects from the Earth. In this paper, we report on a possible systematic artifact within the ground plane that may produce broad absorption features in the spectra observed by these experiments. Using analytical approximations and numerical modeling, the origin of the artifact and its impact on the sky-averaged spectrum are described. The publicly released EDGES data set, from which a 78 MHz absorption feature was recently suggested, is used to probe for the potential presence of ground plane resonances. While the lack of a noise level for the EDGES spectrum makes traditional goodness-of-fit statistics unattainable, the rms residual can be used to assess the relative goodness of fits performed under similar circumstances. The fit to the EDGES spectrum using a model with a simple two-term foreground and three cavity-mode resonances is compared to a fit to the same spectrum with a model used by the EDGES team consisting of a five-term foreground and a flattened-Gaussian signal. The fits with the physically motivated resonance and empirical flattened-Gaussian models have rms residuals of 20.8 mK (11 parameters) and 24.5 mK (9 parameters), respectively, allowing us to conclude that ground plane resonances constitute another plausible explanation for the EDGES data.

Spectroscopy of corannulene cations in helium nanodroplets.

Helium tagging in action spectroscopy is an efficient method for measuring the absorption spectra of complex molecular ions with minimal perturbations to the gas phase spectra. We have used superfluid helium nanodroplets doped with corannulene to prepare cations of these molecules complexed with different numbers of He atoms. In total we identify 13 different absorption bands from corannulene cations between 5500 Å and 6000 Å. The He atoms cause a small, chemically induced redshift of the band positions of the corannulene ion. By studying this effect as a function of the number of solvating atoms we are able to identify the formation of solvation structures that are not visible in the mass spectrum. The solvation features detected using action spectroscopy agree very well with the results of atomistic modeling based on path-integral molecular dynamics simulations. By additionally doping our He droplets with D2, we produce protonated corannulene ions. The absorption spectrum of these ions differs significantly from the case of the radical cations as the numerous narrow bands are replaced by a broad absorption feature that spans nearly 2000 Å in width.

Extracting diffuse interstellar bands from cool star spectra: tracing Galactic ISM structures, kinematics, and properties

Diffuse interstellar bands (DIBs) are broad and weak absorption features that appear in spectra recorded towards stars that lie behind interstellar (IS) clouds. They are known as a long-standing challenge in astronomical spectroscopy because of their unknown carriers. However, they are also a potential IS tracers, in particular to probe distant clouds because they are not easily saturated. We devised automated DIB-fitting methods appropriate for cool star spectra and multiple IS components. The data were fitted with a combination of a synthetic stellar spectrum, a synthetic telluric transmission, and empirical DIB profiles. The initial number of DIB components and their radial velocity were guided by HI 21 cm emission spectrum, or, when available in the spectral range, IS neutral sodium (NaI) absorption lines. For NaI, radial velocities of IS NaI lines and DIBs were maintained linked during a global simultaneous fit. Using the tools, we have analyzed Gaia-ESO Survey (GES) spectra of stars that probe between 2-10 kpc long line-of-sight (LOS) in few different regions of the Milky Way (fields). For all fields, the DIB strength and target extinction are well correlated. We show that, toward distance-distributed target stars, DIBs can be used to locate dense clouds in the Galaxy (i.e., Galactic arm) and probe a LOS kinematical structure. In addition, we have devised the DIB-DIB global fit to study the relation between DIBs and can be a potential tool to trace interstellar environmental conditions.

The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole?

Wide-field optical surveys have begun to uncover large samples of fast (t_rise < 5d), luminous (M_peak < -18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT2018cow (ATLAS18qqn), the first fast-luminous optical transient to be found in real time at low redshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3-8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R<10^14 cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.

The complex evolution of the X-ray binary transient MAXI J1807+132 along the decay of its discovery outburst

MAXI J1807+132 is an X-ray transient discovered during the decay of an outburst in 2017. We present optical and X-ray monitoring of the source over more than 125 days, from outburst to quiescence. The outburst decay is characterized by the presence of several re-flares with a quasi-periodic recurrence time of $\sim 6.5$ days. We detect broad H and He emission lines during outburst, characteristic of transient low mass X-ray binaries. These emission lines show strong variability from epoch to epoch and, in particular, during the early stages are found embedded into deep and very broad absorption features. The quiescent spectrum shows H$\alpha$ in emission and no obvious signatures of the donor star. XMM-Newton and Swift spectra can be fitted with standard X-ray models for accreting black-holes and neutron stars, although the obtained spectral parameters favour the latter scenario. Conversely, other observables such as the optical/X-ray flux ratio, the likely systemic velocity ($\gamma \sim -150$ km s$^{-1}$) and the re-flares recurrence time suggest a black hole nature. We discuss all the above possibilities with emphasis on the strong similarities of MAXI J1807+132 with short orbital period systems.

Diffuse interstellar bands in the H II region M17

Context. Diffuse interstellar bands (DIBs) are broad absorption features measured in sightlines probing the diffuse interstellar medium. Although large carbon-bearing molecules have been proposed as the carriers producing DIBs, their identity remains unknown. DIBs make an important contribution to the extinction curve; the sightline to the young massive star-forming region M17 shows anomalous extinction in the sense that the total-to-selective extinction parameter (RV) differs significantly from the average Galactic value and may reach values RV &gt; 4. Anomalous DIBs have been reported in the sightline towards Herschel 36 (RV = 5.5), in the massive star-forming region M8. Higher values of RV have been associated with a relatively higher fraction of large dust grains in the line of sight. Aims. Given the high RV values, we investigate whether the DIBs in sightlines towards young OB stars in M17 show a peculiar behaviour. Methods. We measure the properties of the most prominent DIBs in M17 and study these as a function of E(B–V) and RV. We also analyse the gaseous and dust components contributing to the interstellar extinction. Results. The DIB strengths in M17 concur with the observed relations between DIB equivalent width and reddening E(B–V) in Galactic sightlines. For several DIBs we discover a linear relation between the normalised DIB strength EW/AV and RV−1. These trends suggest two groups of DIBs: (i) a group of ten moderately strong DIBs that show a sensitivity to changes in RV that is modest and proportional to DIB strength, and (ii) a group of four very strong DIBs that react sensitively and to a similar degree to changes in RV, but in a way that does not appear to depend on DIB strength. Conclusions. DIB behaviour as a function of reddening is not peculiar in sightlines to M17. Also, we do not detect anomalous DIB profiles like those seen in Herschel 36. DIBs are stronger, per unit visual extinction, in sightlines characterised by a lower value of RV, i.e. those sightlines that contain a relatively large fraction of small dust particles. New relations between extinction normalised DIB strengths, EW/AV, and RV support the idea that DIB carriers and interstellar dust are intimately connected. Furthermore, given the distinct behaviour of two groups of DIBs, different types of carriers do not necessarily relate to the dust grains in a similar way.

Conjugated polymer donor with alkylthio-thiophene π-bridge for efficient polymer solar cells

Abstract A new conjugated polymer donor with alkylthio-substituted thiophene as π-bridge (namely PBZ-TS) is developed to further exploit the capability of alkylthio chains in designing high-performance donor materials. PBZ-TS possesses a broad absorption feature, a low-lying HOMO level, and high crystallinity. The polymer solar cell devices based on PBZ-TS:m-ITIC demonstrate high open-circuit voltage (Voc) of 0.93 V. Especially, relative to the PBZ-TS:m-ITIC (1:1, w/w) based binary device, an enhanced power conversion efficiency (PCE) of 8.66% is achieved from the PBZ-TS:m-ITIC:PC71BM (1:0.6:0.4, w/w) based ternary device resulting from the suppressed carrier recombination of binary blends. The results demonstrate that using alkylthio-substituted thiophene as π-bridge is an effective strategy to down-shift HOMO level and increase Voc of the polymer donor materials for PSCs.

Linking Infrared Spectra of Laboratory Iron Gall Inks Based on Traditional Recipes with their Material Components.

The question for discriminating iron gall inks is addressed by correlating their infrared (IR) spectra in liquid and dried states with the materials used in their formulations and considering their possible interactions. A series of laboratory inks were prepared according to historic recipes, mainly found in 19th-century documents, and were accordingly studied using Fourier transform infrared (FT-IR) spectroscopy. All ink formulations were based on Aleppo galls, ferrous sulfate, and gum arabic at variable proportions, with various added components, such as alum, vinegar, glycerol, sugar, silver nitrate, cloves, and white wine. Ingredients of the corresponding inks were recognized by means of their IR fingerprints in both their liquid and dried states, respectively. Although a few inks of distinct formulations showed discernible differences in their spectra, the majority showed quite similar absorptions. Principal component analysis and discriminant analysis were employed to successfully discriminate inks, based on their IR peaks. Spectra recorded in the liquid state, despite their broad absorption features, led to satisfactory discrimination of certain types of inks as most of their ingredients are reflected in their IR peaks. Spectra from dried inks contained similar information, which equally worked in a sufficient discriminatory way. Key IR peaks in the recorded spectra of inks made with the addition of special ingredients, such as vinegar, wine, alum, glycerol, and sugar, as well as those prepared with specific tannin-enhancing procedures, such as gall boiling, were located and used in the discrimination basis.

NIR reflectance spectroscopy of hydrated and anhydrous sodium carbonates at different temperatures

Recent space-based observations have revealed or suggested the existence of various types of carbonate salts in several Solar System bodies, such as Mars, Ceres, Enceladus, and Europa. Natrite is the main component of the crater Occator's faculae observed in detail by the Dawn spacecraft on the dwarf planet Ceres. Sodium carbonates are thought to form as precipitates in brines, originating in aqueous environments in the subsurface of Ceres and icy bodies. Here we report about near-infrared (0.8–4.2 μm) reflectance spectroscopic investigations on three compounds, namely natrite (anhydrous Na2CO3), monohydrated sodium carbonate (Na2CO3•H2O, thermonatrite) and decahydrate sodium carbonate (Na2CO3•10H2O, natron). Spectral measurements have been carried out in the overall temperature range 93–279 K, representative of planetary surfaces. The analysis of diagnostic spectral signatures shows different temperature-dependent trends for several band parameters, as well as different behavior as a function of the grain size for a given temperature. While spectra of natrite are characterized by several CO3 absorptions, broad and strong absorption features due to H2O dominate the spectra of heavily hydrated natron. The intermediate sample (monohydrated) shows multiple bands due to the overlap of CO3 and H2O vibrational modes. Our temperature-dependent laboratory spectra are compared with Dawn-VIR spectra of Ceres and with Galileo-NIMS spectra of Europa.

Ultraviolet photodissociation dynamics of 1-pentyl radical

The ultraviolet (UV) photodissociation of jet-cooled 1-pentyl radical is investigated in the wavelength region of 236−254 nm using the high-n Rydberg-atom time-of-flight (HRTOF) technique. The H-atom photofragment yield spectrum of the 1-pentyl radical shows a broad UV absorption feature peaking near 245 nm, similar to the 2pz →3s absorption bands of ethyl and n-propyl. The center-of-mass translational energy distribution, P (ET), of the H+C5H10 product channel is bimodal, with a slow peak at ~5 kcal/mol and a fast peak at ~50 kcal/mol. The fraction of the average translational energy release in the total available energy, ⟨fT⟩, is 0.30, with those of the slow and fast components being 0.13 and 0.58, respectively. The slow component has an isotropic product angular distribution, while the fast component is anisotropic with an anisotropy parameter ~0.4. The bimodal translational energy and angular distributions of the H+C5H10 products indicate two H-atom elimination channels in the photodissociation of 1-pentyl: (i) a direct, prompt dissociation from the electronic excited state and/or the repulsive part of the ground electronic state potential energy surface; and (ii) a unimolecular dissociation of internally hot radical in the ground electronic state after internal conversion from the electronic excited state.

Implications of a prereionization 21-cm absorption signal for fuzzy dark matter

The EDGES experiment recently announced evidence for a broad absorption feature in the sky-averaged radio spectrum around 78 MHz, as may result from absorption in the 21 cm line by neutral hydrogen at z~15-20. If confirmed, one implication is that the spin temperature of the 21 cm line is coupled to the gas temperature by z=20. The known mechanism for accomplishing this is the Wouthuysen-Field effect, whereby Lyman-alpha photons scatter in the intergalactic medium (IGM) and impact the hyperfine level populations. This suggests that early star formation had already produced a copious Lyman-alpha background by z=20, and strongly constrains models in which the linear matter power spectrum is suppressed on small-scales, since halo and star formation are delayed in such scenarios. Here we consider the case that the dark matter consists of ultra-light axions with macroscopic de Broglie wavelengths (fuzzy dark matter, FDM). We assume that star formation tracks halo formation and adopt two simple models from the current literature for the halo mass function in FDM. We further suppose that the fraction of halo baryons which form stars is less than a conservative upper limit of $f_\star \leq 0.05$, and that ~10^4 Lyman-alpha to Lyman-limit photons are produced per stellar baryon. We find that the requirement that the 21 cm spin temperature is coupled to the gas temperature by $z=20$ places a lower-limit on the FDM particle mass of $m_a \geq 5 \times 10^{-21} {\rm eV}$. The constraint is insensitive to the precise minimum mass of halos where stars form. As the global 21 cm measurements are refined, the coupling redshift could change and we quantify how the FDM constraint would be modified. A rough translation of the FDM mass bound to a thermal relic warm dark matter (WDM) mass bound is also provided.

Far-UV HST Spectroscopy of an Unusual Hydrogen-poor Superluminous Supernova: SN2017egm

Abstract SN2017egm is the closest (z = 0.03) H-poor superluminous supernova (SLSN-I) detected to date, and a rare example of an SLSN-I in a massive, metal-rich galaxy. We present the HST UV and optical spectra covering 1000–5500 Å, taken at +3 day relative to the peak. Our data reveal two absorption systems at redshifts matching the host galaxy NGC 3191 (z = 0.0307) and its companion galaxy (z = 0.0299) 73″ apart. Weakly damped Lyα absorption lines are detected at these two redshifts, with H i column densities of (3.0 ± 0.8) × 1019 and (3.7 ± 0.9) × 1019 cm−2, respectively. This is an order of magnitude smaller than the H i column densities in the disks of nearby galaxies (&gt;1010 M ⊙) and suggests that SN2017egm is on the near side of NGC 3191 and has a low host extinction (E(B − V) ∼ 0.007). Using unsaturated metal absorption lines, we find that the host of SN2017egm probably has a solar or higher metallicity and is unlikely to be a dwarf companion to NGC 3191. Comparison of early-time UV spectra of SN2017egm, Gaia16apd, iPTF13ajg, and PTF12dam finds that the continuum at λ &gt; 2800 Å is well fit by a blackbody, whereas the continuum at λ &lt; 2800 Å is considerably below the model. The degree of UV suppression varies from source to source, with the 1400–2800 Å continuum flux ratio of 1.5 for Gaia16apd and 0.4 for iPTF13ajg. This cannot be explained by the differences in magnetar power or blackbody temperature. Finally, the UV spectra reveal a common set of seven broad absorption features and their equivalent widths are similar (within a factor of 2) among the four events.

A New Method for Quantifying SWCNT Dispersion Quality from Absorption Spectra

Individualization of single-walled carbon nanotubes (SWCNTs) in aqueous surfactant dispersions can vary greatly. We will present a new method for quantitatively assessing dispersion quality based on simple absorption spectra. In this method, the visible and short-wave infrared portions of a sample’s absorption spectrum are modeled as a superposition of two components. One component (labeled “S”) has sharp resonant features and is associated with the subpopulation of SWCNTs that are suspended as individuals or very small aggregates; the other (labeled “B”) has broad absorption features and is associated with stably dispersed materials such as carbonaceous impurities, imperfect nanotubes, and larger aggregates. Using absorption spectra from samples in various stages of purification by centrifugation or magnetic processing, we apply the method of multivariate curve resolution to extract the S and B component spectra and determine their relative contributions in samples of interest. The ratio of S to B content then provides a simple index of dispersion quality. We illustrate this new characterization method with measurements on both shear-dispersed and tip-sonicated SWCNT samples purified by three different processes: centrifugation, ultracentrifugation, and magnetic purification. We determine the dispersion efficiency of each sample preparation and find results that correlate well with those of established analytical techniques. In addition, we have further characterized the effects of these purification processes on the SWCNT length distribution (using the diffusion-based LAND method) and on SWCNT emissive properties (through variance spectroscopy). We believe that our new absorption-based method provides a practical tool for quickly assessing the dispersion quality of SWCNT samples.

Correlation between diffuse interstellar bands (DIBs) and interstellar extinction using data from Bosscha Compact Spectrograph

A longstanding challenge in astronomical spectroscopy is to uncover the carriers of diffuse interstellar bands (DIBs). They are broad absorption features due to the interstellar matter (ISM). They are seen in stellar spectra of background stars or other astronomical objects. Although we do not know utterly the carriers of the DIBs, they can be a promising tracer of the ISM. One of the interesting properties is their correlations with the interstellar (IS) extinction. For each band, the correlation has considerable dispersion and differences that possibly due to the IS physical conditions. Some DIBs are sensitive to the stellar radiation field, and some are not. To study the effect, we measured the DIB observed in Be/B stars spectra. The stars were observed by using Bosscha Compact Spectrograph at the Bosscha Observatory, Lembang, Indonesia. We performed an automated fitting of a combination of a smooth stellar continuum, the DIB profile, and a synthetic telluric transmission to the spectrum. The DIB measurements were compared to the general DIBs-extinction relationship. The correlation is found to be in good agreement with previous determinations.

2004 EW95: A Phyllosilicate-bearing Carbonaceous Asteroid in the Kuiper Belt

Abstract Models of the Solar System’s dynamical evolution predict the dispersal of primitive planetesimals from their formative regions among the gas-giant planets due to the early phases of planetary migration. Consequently, carbonaceous objects were scattered both into the outer asteroid belt and out to the Kuiper Belt. These models predict that the Kuiper Belt should contain a small fraction of objects with carbonaceous surfaces, though to date, all reported visible reflectance spectra of small Kuiper Belt Objects (KBOs) are linear and featureless. We report the unusual reflectance spectrum of a small KBO, (120216) 2004 EW95, exhibiting a large drop in its near-UV reflectance and a broad shallow optical absorption feature centered at ∼700 nm, which is detected at greater than 4σ significance. These features, confirmed through multiple epochs of spectral photometry and spectroscopy, have respectively been associated with ferric oxides and phyllosilicates. The spectrum bears striking resemblance to those of some C-type asteroids, suggesting that 2004 EW95 may share a common origin with those objects. 2004 EW95 orbits the Sun in a stable mean motion resonance with Neptune, at relatively high eccentricity and inclination, suggesting it may have been emplaced there by some past dynamical instability. These results appear consistent with the aforementioned model predictions and are the first to show a reliably confirmed detection of silicate material on a small KBO.

Discovery of an Ultraviolet Counterpart to an Ultrafast X-Ray Outflow in the Quasar PG 1211+143

Abstract We observed the quasar PG 1211+143 using the Cosmic Origins Spectrograph on the Hubble Space Telescope in 2015 April as part of a joint campaign with the Chandra X-ray Observatory and the Jansky Very Large Array. Our ultraviolet spectra cover the wavelength range 912–2100 Å. We find a broad absorption feature ( ) at an observed wavelength of 1240 Å. Interpreting this as H i Lyα, in the rest frame of PG 1211+143 (z = 0.0809), this corresponds to an outflow velocity of −16,980 (outflow redshift ), matching the moderate ionization X-ray absorption system detected in our Chandra observation and reported previously by Pounds et al. With a minimum H i column density of , and no absorption in other UV resonance lines, this Lyα absorber is consistent with arising in the same ultrafast outflow as the X-ray absorbing gas. The Lyα feature is weak or absent in archival ultraviolet spectra of PG 1211+143, strongly suggesting that this absorption is transient, and intrinsic to PG 1211+143. Such a simultaneous detection in two independent wavebands for the first time gives strong confirmation of the reality of an ultrafast outflow in an active galactic nucleus.

SN2012ab: a peculiar Type IIn supernova with aspherical circumstellar material

We present photometry, spectra, and spectropolarimetry of supernova (SN) 2012ab, mostly obtained over the course of $\sim 300$ days after discovery. SN 2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN 1998S, its spectral evolution does not. We see indications of CSM interaction in the strong intermediate-width emission features, the high luminosity (peak at absolute magnitude $M=-19.5$), and the lack of broad absorption features in the spectrum. The H$\alpha$ emission undergoes a peculiar transition. At early times it shows a broad blue emission wing out to $-14{,}000$ km $\mathrm{s^{-1}}$ and a truncated red wing. Then at late times ($>$ 100$\,$days) it shows a truncated blue wing and a very broad red emission wing out to roughly $+20{,}000$ km $\mathrm{s^{-1}}$. This late-time broad red wing probably arises in the reverse shock. Spectra also show an asymmetric intermediate-width H$\alpha$ component with stronger emission on the red side at late times. The evolution of the asymmetric profiles requires a density structure in the distant CSM that is highly aspherical. Our spectropolarimetric data also suggest asphericity with a strong continuum polarization of $\sim 1-3$% and depolarization in the H$\alpha$ line, indicating asphericity in the CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss rate of $\dot{M} = 0.050\, {\rm M}_{\odot}\,\mathrm{yr^{-1}}$ for $v_{\rm pre} = 100$$\,$km$\,$$\mathrm{s^{-1}}$ extending back at least 75$\,$yr prior to the SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest that the progenitor was an eccentric binary system undergoing eruptive mass loss.

Redshift determination of the BL Lac object 3C 66A by the detection of its host galaxy cluster at z = 0.340 ★

The BL Lac object 3C66A is one of the most luminous extragalactic sources at TeV $\gamma$-rays (VHE, i.e. $E >100$ GeV). Since TeV $\gamma$-ray radiation is absorbed by the extragalactic background light (EBL), it is crucial to know the redshift of the source in order to reconstruct its original spectral energy distribution, as well as to constrain EBL models. However, the optical spectrum of this BL\,Lac is almost featureless, so a direct measurement of $z$ is very difficult; in fact, the published redshift value for this source ($z=0.444$) has been strongly questioned. Based on EBL absorption arguments, several constraints to its redshift, in the range $0.096 < z < 0.5$, were proposed. Since these AGNs are hosted, typically, in early type galaxies that are members of groups or clusters, we have analysed spectro-photometrically the environment of 3C66A, with the goal of finding the galaxy group hosting this blazar. This study was made using optical images of a $5.5 \times 5.5$\,arcmin$^{2}$ field centred on the blazar, and spectra of 24 sources obtained with Gemini/GMOS-N multi-object spectroscopy. We found spectroscopic evidence of two galaxy groups along the blazar's line of sight: one at $z \simeq 0.020$ and a second one at $z \simeq 0.340$. The first one is consistent with a known foreground structure, while the second group here presented has six spectroscopically confirmed members. Their location along a red sequence in the colour-magnitude diagram allows us to identify 34 additional candidate members of the more distant group. The blazar's spectrum shows broad absorption features that we identify as arising in the intergalactic medium, thus allowing us to tentatively set a redshift lower limit at $z_{3C66A} \ge 0.33$. As a consequence, we propose that 3C66A is hosted in a galaxy that belongs to a cluster at $z=0.340$.

The active nucleus of the ULIRG IRAS F00183–7111 viewed byNuSTAR

We present an X-ray study of the ultra-luminous infrared galaxy IRAS F00183-7111 (z=0.327), using data obtained from NuSTAR, Chandra X-ray Observatory, Suzaku and XMM-Newton. The Chandra imaging shows that a point-like X-ray source is located at the nucleus of the galaxy at energies above 2 keV. However, the point source resolves into diffuse emission at lower energies, extending to the east, where the extranuclear [O III] emission, presumably induced by a galactic-scale outflow, is present. The nuclear source is detected by NuSTAR up to the rest-frame 30 keV. The strong, high-ionization Fe K line, first seen by XMM-Newton, and subsequently by Suzaku and Chandra, is not detected in the NuSTAR data. The line flux appears to have been declining continuously between 2003 and 2016, while the continuum emission remained stable to within 30%. The X-ray continuum below 10 keV is characterised by a hard spectrum caused by cold absorption of nH ~1e23 cm-2, compatible to that of the silicate absorption at 9.7 micron, and a broad absorption feature around 8 keV which we attribute to a high-ionization Fe K absorption edge. The latter is best described by a blueshifted, high-ionization (log xi ~3) absorber. No extra hard component, which would arise from a Compton-thick source, is seen in the NuSTAR data. While a pure reflection scenario (with a totally hidden central source) is viable, direct emission from the central source of L(2-10 keV) = 2e44 erg/s, behind layers of cold and hot absorbing gas may be an alternative explanation. In this case, the relative X-ray quietness (Lx/L_AGN ~6e-3), the high-ionization Fe line, strong outflows inferred from various observations, and other similarities to the well-studied ULIRG/QSO Mrk 231 point that the central source in this ULIRG might be accreting close to the Eddington limit.

Accurate spectroscopic redshift of the multiply lensed quasar PSOJ0147 from the Pan-STARRS survey

Context: The gravitational lensing time delay method provides a one-step determination of the Hubble constant (H0) with an uncertainty level on par with the cosmic distance ladder method. However, to further investigate the nature of the dark energy, a H0 estimate down to 1% level is greatly needed. This requires dozens of strongly lensed quasars that are yet to be delivered by ongoing and forthcoming all-sky surveys. Aims: In this work we aim to determine the spectroscopic redshift of PSOJ0147, the first strongly lensed quasar candidate found in the Pan-STARRS survey. The main goal of our work is to derive an accurate redshift estimate of the background quasar for cosmography. Methods: To obtain timely spectroscopically follow-up, we took advantage of the fast-track service programme that is carried out by the Nordic Optical Telescope. Using a grism covering 3200 - 9600 A, we identified prominent emission line features, such as Ly-alpha, N V, O I, C II, Si IV, C IV, and [C III] in the spectra of the background quasar of the PSOJ0147 lens system. This enables us to determine accurately the redshift of the background quasar. Results: The spectrum of the background quasar exhibits prominent absorption features bluewards of the strong emission lines, such as Ly-alpha, N V, and C IV. These blue absorption lines indicate that the background source is a broad absorption line (BAL) quasar. Unfortunately, the BAL features hamper an accurate determination of redshift using the above-mentioned strong emission lines. Nevertheless, we are able to determine a redshift of 2.341+/-0.001 from three of the four lensed quasar images with the clean forbidden line [C III]. In addition, we also derive a maximum outflow velocity of ~ 9800 km/s with the broad absorption features bluewards of the C IV emission line. This value of maximum outflow velocity is in good agreement with other BAL quasars.