As the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory enters its seventeenth year of operation on orbit, it continues to perform well and produce spectacular scientific results. The response of ACIS has evolved over the lifetime of the observatory due to radiation damage, molecular contamination and aging of the spacecraft in general. Here we present highlights from the instrument team's monitoring program and our expectations for the future of ACIS. The ACIS calibration source produces multiple line energies and fully illuminates the entire focal plane which has greatly facilitated the measurement of charge transfer inefficiency and absorption from contamination. While the radioactive decay of the source has decreased its utility, it continues to provide valuable data on the health of the instrument. Performance changes on ACIS continue to be manageable, and do not indicate any limitations on ACIS lifetime.
Galactic star-forming complexes are multi-generational, hosting collapsed objects and SNRs as well as young stars, but it takes wide fields to see this big picture. Our ACIS Extract software can accommodate wide-field ACIS mosaics mined from the Chandra archive. It naturally handles overlapping ACIS imaging observations with both ACIS-I and ACIS-S configurations and arbitrary aimpoints. Off-axis CCDs can be included to maximize mosaic fields of view. Overlapping observations are astrometrically aligned with each other using common X-ray point sources. When a point source is observed multiple times with a range of off-axis angles, the code automatically includes/excludes observations to maximize signal-to-noise. Point sources can be masked and remaining emission adaptively smoothed to reveal diffuse X-ray structures from massive star feedback. These tools yield a more global picture of star formation and evolution and show that Chandra contributes significantly to the star formation story being constructed by Herschel, Spitzer, and WISE.
The second major release of the Chandra Source Catalog (CSC 2.0) is nearing completion. The final catalog will be made available to the user community later this year, and an interim list of detections is available now. Release 2.0 will roughly triple the size of the original catalog released in 2009 to an estimated 350,000 detections. CSC 2.0 improves on the first catalog by stacking subsets of overlapping observations to enable detection of fainter sources. A permissive compact source detection algorithm, combined with application of a Sherpa-based maximum-likelihood estimator to evaluate the reality of candidate detections, enables point detections down to ~5 net counts on-axis for exposures shorter than ~15ks. In addition to point sources, CSC 2.0 includes regions of extended emission detected using a Voronoi tessellation algorithm. Release 2.0 provides a detailed set of properties for each detected X-ray source, including the source position and associated position error ellipse, source extent, multi-band aperture photometry probability density functions computed using an improved Bayesian algorithm, spectral fits using several source models, hardness ratios, and intra- and inter-observation temporal variability measures. All numerical measures have associated two-sided confidence intervals. In addition to tabular data, the catalog provides FITS data products that are immediately suitable for further user analysis, including per-field and per-source images, photon event lists, responses, spectra, light curves, and extended source polygons. We provide an update on the status of the ongoing release 2.0 production run, and discuss plans for future Chandra Source Catalog releases and enhancements that may be incorporated in those releases.
While ultraluminous supersoft X-ray sources (ULSs) bear features for intermediate mass black holes or very massive white dwarfs possibly close to Chandrasekhar mass limit, our recent discovery of processing relativistic baryonic jets from a prototype ULS in M81 (Liu et al. 2015, Nature, 528, 508) demonstrates that they are not IMBHs or WDs, but black holes accreting at super-Eddington rates. This discovery strengthens the recent ideas that ULXs are stellar black holes with supercritical accretion, and provides a vivid manifestation of what happens when a black hole devours too much, that is, it will generate thick disk winds and fire out sub-relativistic baryonic jets along the funnel as predicted by recent numerical simulations.
For almost two decades the Chandra X-ray Observatory has elucidated the high energy environments of magnetically active, pre-main sequence (pre-MS) stars. With the growing number of confirmed exoplanets, it is increasingly important to understand exoplanet birthplaces and, in particular, whether and how pre-MS stellar X-rays influence circumstellar disk heating, ionization and evaporation. X-ray observations alone can characterize high energy stellar radiation fields and plasma properties but simultaneous multiwavelength X-ray/optical observations are necessary to differentiate the multitude of astrophysical processes thought to be responsible for hour- to day-long variable emission from pre-MS stars. We present preliminary results of one such simultaneous multiwavelength and multi-epoch campaign to study the circumstellar environments of the nearby (<150 pc) pre-MS transitional disk sources T Cha and RY Lup. Both systems are highly inclined (i.e., viewed nearly edge-on) and present unique opportunities to probe star-disk interactions during late-stage circumstellar disk evolution. Based on simultaneous Chandra grating X-ray spectroscopy and Siding Spring Observatory (SSO) optical spectroscopy, we find a correlation between X-ray and optical extinction in T Cha resulting from variable photospheric obscuration from a circumstellar disk warp/clump and we detect an order of magnitude X-ray flare in RY Lup. We investigate potential accretion signatures and we infer the X-ray spectrum absorbed by the gaseous disks surrounding both of these late-stage, and potentially planet-forming, pre-MS stars.
We present a comprehensive timing analysis of two RXTE observations of the microquasar GRS~1915+105 during the heartbeat state. The phase-frequency-power map shows that when the quasi-periodic oscillation disappears its sub-harmonic is still present. In the slow rise phase, most of the aperiodic variability is produced in the corona, the phase lag is soft at low- and high-frequencies (the time lag, τ, is up to ~20 ms), the low- and high-frequency aperiodic variabilities from the disk are produced at the same radii, suggesting that the aperiodic variability in the corona is initiative and drives the aperiodic variability from the disk. In the rise phase of the pulse, the low-frequency aperiodic variabilities from the disk and corona are both significant while most of the high-frequency aperiodic variability is still produced in the corona, part or all of the low-frequency aperiodic variability from the disk is produced at smaller radii while the high-frequency aperiodic variability from the disk is produced at larger radii, the phase lag is hard at low-frequency (τ is up to ~50 ms) and is soft at high-frequency (τ is several ms), suggesting that the low-frequency aperiodic variability at smaller radii of the disk is initiative and drives the low-frequency aperiodic variability in the corona while the high-frequency aperiodic variability at larger radii of the disk is still driven by the high-frequency aperiodic variability from the corona. These timing results are consistent with the spectral results presented by Neilsen et al. which indicated that the slow rise phase corresponds to a local Eddington limit and the rise phase of the pulse corresponds to a radiation pressure instability in the disk.
We present a new analysis of the complex hard X-ray spectrum of the Seyfert 1.5 galaxy NGC 4151, using simultaneous Ultraviolet (UV) / X-Ray observations taken with Hubble STIS Echelle and Chandra HETG in 2014. Past observations show high variability in the continuum flux in the X-ray and UV, and the most recent observations were found in very low fluxes. The intrinsic continuum in the lower flux state epochs is more heavily absorbed than in the higher flux state ones, but overall they seem to present very similar spectral shape. We propose a model consisting of a broken powerlaw, neutral reflection and dual absorption components: X-High and D+Ea, as defined in Kraemer et. al (2005). The absorbers span a range in radial distances, and the transmitted continuum of X-High serves as a filter for the incident radiation on D+Ea. Our preliminary fittings for the 2014 observation suggested a substantial increase in the column density of D+Ea, corroborating with previous results for the 2000 Chandra data presented by Kraemer et. al (2005). However, by comparing 2014 and 2000 datasets, we rule out the possibility of a big column density, and our new model suggests an additional absorption feature, covering the reflection component. This absorption component is only evident in low flux states when the reflection component becomes more dominant. Our model results agree with both low flux state and high flux state epochs, and the changes in absorption appear to be principally due to the changes in ionization state/opacity of the individual components rather than changes in column density.
Chandra's sub-arcsecond angular resolution offers unprecedented opportunities for detailed studies of accretion phenomena in interacting binaries at X-ray wavelengths, where the signatures of accretion processes are very prominent. Long-term study of interacting binaries using the highest available spatial resolution at X-ray wavelengths is a key to understanding the mass transfer and accretion processes in these evolving dynamic systems.Among the interacting binaries, Symbiotic Systems are of a particular astrophysical interest, since they have been invoked as a potential progenitors of asymmetric Planetary Nebulae, and of at least a fraction of SN Type Ia - key cosmological distance indicators. These systems provide a great target for studying accretion processes, jets, and outburst in interacting binaries with a focused wind mass accretion, on time scales from days to decades.Several nearby system have been observed with Chandra allowing for the first time mapping of the the inter-binary and circum-binary X-ray environments, at unprecedented resolution reaching 0.1". High-angular resolution imaging and spectroscopy have shown dramatic changes in the spatial and spectral distribution of the emission in these systems on time scales of years. These include significant variability of the accretion rate on the white dwarf companion, and powerful outbursts, jets, and outflows.However, there are many aspects of the accretion processes in these interacting binaries, and of wind accretion processes in particular, that are not yet understood. Given the observed dynamic evolution and variability of Symbiotic Systems on time scales of years, it is of a great importance to explore and characterize their long-term dynamic evolution and identify the mechanisms causing this activity.I will highlight results from snapshot-type Chandra observations of several nearby Symbiotic Systems (including of Mira AB, CH Cyg, RT Cru and R Aqr), and describe the scientific objectives and goals for Chandra observations in the next decade.I will also emphasize the need for detailed characterization of the Chandra PSF at a sub-arcsecond scale, and including modeling of artifacts which are currently significantly impacting the results from the highest spatial resolution studies of sub-arcsecond structures in sources ranging from stellar systems to AGN nuclear regions.
Massive star-forming regions (MSFRs) are formed by supersonic flows compressing gas into dense clumps in massive molecular filaments. Seen in absorption against the bright IR background of the Galactic plane, these "Infrared Dark Clouds" (IRDCs) may be the birthplaces of all stars. By sampling evolutionary sequences and the two distinct morphologies of IRDCs, Chandra will bring new insight into how, when, and where molecular clumps form MSFRs, when X-ray emission turns on in massive star birth, and the star formation history (and future) of giant molecular clouds. Chandra should study the most prominent and iconic IRDCs in the nearby Galaxy, objects so fundamental to our understanding of star formation and Galactic structure that Goodman14 dubbed them "The Bones of the Milky Way."
The X-ray absorption near-edge structure (XANES) spectra can reveal the chemical state of elements which are present in the dust grains. In the X-ray band it is possible to measure the absorption feature of iron, magnesium and silicon, among others. We focus here on iron which is heavily depleted (around 98%) and it is not certain yet in which form this element is locked up in dust. We performed synchrotron measurements (done at the synchrotron facility ESRF in Grenoble, France) of interstellar dust analogues. Here we show the characterisation of the absorption iron K-edge (at 7.1 keV) for a set of 7 different compounds: silicates with different Mg:Fe ratio and iron sulfides. These measurements provide a comparison sample for the astronomical observations.
Luminous X-ray Galactic sources can be used to illuminate several sight-lines to probe the intervening dust in the interstellar matter. We show through simulations how present and future instruments can reveal the nature of dust in dense environments through the study of high-energy absorption edges.
Galaxy clusters are important objects for studying the physics of the intracluster medium (ICM), galaxy formation and evolution, and cosmological parameters. Clusters containing wide-angle tail (WAT) radio sources are particularly valuable for studies of the interaction between these sources and the surrounding ICM. These sources are thought to form when the ram pressure from the ICM caused by the relative motion between the host radio galaxy and the cluster bends the radio lobes into a distinct wide-angle morphology. We present first results from the analysis of a Chandra observation of the nearby WAT hosting galaxy cluster Abell 623. A clear decrement in X-ray emission is coincident with the southern radio lobe, consistent with being a cavity carved out by the radio source. We present profiles of surface brightness, temperature, density, and pressure. We analyze our data for evidence of shocks and cold fronts. Based on the X-ray pressure in the vicinity of the radio lobes and assumptions about the content of the lobes, we estimate the relative ICM velocity required to bend the lobes into the observed angle. Since ICM velocities are very difficult to measure directly, future Chandra observations of such systems will be important probes of the dynamics of the ICM.
As an AGN flickers, the ionization state of its surrounding gas becomes out of equilibrium. We show that the observation of this non-equilibrium can be used to explore the flickering history. Specifically, we study the X-ray spectral evolution of the recombining hot plasma in a galactic spheroid, based on a simply switch-off model of a recent AGN. This model gives a satisfactory fit to the XMM-Newton RGS spectrum of the M31 bulge, especially its OVII forbidden line. Approximate solar or super-solar metal abundances are obtained from the fit, in contrast to the substantially sub-solar values obtained from the previous collisional ionization equilibrium spectral model. Most interestingly, our AGN switch-off modeling suggests that the nucleus, while currently quiescent, had a characteristic luminosity of ~1043.5 erg s-1, about 4×105 yrs ago.
The Chandra Data Archive (CDA) has been tracking publications based on Chandra observations in journals and on-line conference proceedings throughout the mission. Chandra users have predicted Chandra findings, plead for additional Chandra observations; and announced the imminent arrival of new data. They have compiled more than 40 catalogs and surveys; they have presented theoretical work to help understand Chandra findings; and they have combined Chandra data with data from all parts of the spectra in an attempt to understand the universe. In this poster we will present the diversity of publications we have examined and highlight some of the exciting science accomplished with Chandra and show how the bibliography can be used as an invaluable research tool.
This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center. It depends critically on the services provided by the ADS.
As data repositories gained prominence while "Big Data" became a household term in the scientific (and political) world, curators and users became concerned about the stability, persistence, and general trustworthiness of those repositories. Within the context of the Smithsonian Institution's digitization effort the subject was first discussed some ten years ago in reference to the Trusted Repository Audit Checklist (TRAC) used by the Center for Research Libraries (CRL). The effort required for such certification was considerable and a reason why take-up was very limited. However, later this year the Research Data Alliance (RDA) is expected to issue a recommendation to adopt a certification process worked out in collaboration with Data Seal of Approval (DSA; social sciences) and World Data System (ICSU-WDS; physical sciences) that requires a very reduced level of effort and can be carried out entirely internally. CDS in Strasbourg has reported the process to be quite feasible and very helpful to their operations. We have no doubt that within the next ten years some form of trustworthiness certification is going to be standard for all major data repositories and may well be required by funding agencies. The Chandra Data Archive Operations team hopes to get ahead of the curve and execute such an internal audit which we trust will be beneficial for our users and help us to improve our services. The Catalogue of Common Procedures developed by the DSA-WDS Partnership Working Group on Repository Audit and Certification, a Working Group of the RDA, lists 16 common criteria covering three areas: organizational infrastructure, digital object management, and technology. These form a solid basis for an assessment of the robustness, trustworthiness, and sustainability of the Chandra Data Archive - which will remain the bedrock of Chandra science for the next decade and beyond. This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.
The Chandra Data Archive is instrumental in maximizing the scientific output of the Chandra X-ray Observatory by providing support to the astronomical community for the access to Chandra data through a comprehensive set of interfaces. These interfaces provide powerful, user-friendly and flexible methods to search, inspect and retrieve all public Chandra data. Chaser, the centerpiece of the Chandra archive ecosystem, is a versatile query engine with an intuitive graphical interface that makes possible to build complex queries based on constraints involving position in the sky, proposal information and instrumental parameters. Two other specialized interfaces are offered to search for and retrieve Chandra data: the Bibliography Search, which searches the CDA archive and the Chandra-related astronomical literature based on both spatial and bibliographic criteria, and the Footprint Service, that allows to browse and visualize the footprints of spatially selected Chandra observations. The Chandra Archive also provides access to the Chandra Source Catalog, the most comprehensive catalog of sources detected in public Chandra observations, through the CSCView stand-alone application and, in alternative, through a command-line interface that harnesses the syntax and capabilities of the Astronomical Data Query Language and the VO-compliant cone search service. The Chandra Archive also offers additional specialized interfaces that provide the astronomical community with the access to Chandra aggregated datasets and the processing status of the archived data, or to submit request for custom access to the data. Moreover, since the start of the mission, the technology used to build the graphical user interfaces and the expectation of the users' community have dramatically advanced. In this poster, we will review the interfaces and tools offered by the Chandra Data Archive and will present the latest updates that the Chandra Archive has implemented in order to keep up with the progress of technology and users' community needs.
This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center. It depends critically on the services provided by the ADS.
In addition to the archiving and distribution of Chandra data produced by the CXC's Standard Data Processing, the Chandra Data Archive (CDA) provides a service that collects and distributes contributed data products and datasets. In particular, processed images or other pertinent datasets that are essential parts of Chandra papers. For these products, the CDA can serve as a permanent storage and distribution source. Among the items we currently provide are galaxy cluster images, galaxy cluster contour files, and pre-packaged datasets of the Chandra Deep Fields. In the near future, we will be providing images, datasets, and products from the Chandra Galaxy Atlas.
In this poster, we will discuss how these products are presented and made available. We will also demonstrate how we can help you contribute your own high-level science products, allow them to be properly cited and achieve a wider exposure of, and receive credit for, your work in the astronomical community.
This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.
Here I will present some preliminary results of our analysis of the Chandra observations of the diffuse X-ray emission from the extended lobes in Pictor A radio galaxy. All the available Chandra data for the target, consisting of multiple pointings spanning over 15 years and amounting to the total exposure time of 464 ks, have been included in the analysis. All the point and compact sources in the field - both unrelated background/foreground objects, as well as the unresolved core, the jets, and the hotspots of Pictor A - were removed, and the radio contours were superimposed on the Chandra image to define the edges of the lobes. This allowed us to calculate the ratio of the X-ray to radio (both total and polarised) fluxes of the non-thermal diffuse emission, as a function of the position within the lobes (following Hardcastle et al. 2016). Our main goal is an in-depth statistical analysis of the resulting distribution, offering a unique insight into the lobes magnetic field structure.
In stars like our Sun, magnetic fields power star spots, flares and coronal mass ejections, chromospheric and coronal emission from the ultraviolet to X-rays, and stellar winds that control rotation spin-down. Stellar magnetism is central to issues as diverse as the evolution of close binary stars and the space weather conditions faced by exoplanet atmospheres. The dynamo responsible depends on stellar rotation through the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer between the radiative core and the convective envelope known as the tachocline. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different. Here we report Chandra observations of four fully convective stars whose X-ray emission correlates with their rotation periods exactly as it does in Sun-like stars, implying that fully convective stars also operate a Solar-type dynamo. The lack of a tachocline in fully convective stars suggests it is not a critical ingredient in the Solar dynamo and favours models where the dynamo is seated throughout the convection zone. A future Chandra survey of slowly-rotating M dwarfs will confirm this fundamental revision of magnetic dynamo theory.
High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in Classical T Tauri stars (CTTS). In particular the accretion-shock region, where the accreting material is shocked and heated to temperatures of a few million degrees, can be probed by X-ray spectroscopy.
MHD models predict that this hot post-shock plasma should have an inward bulk motion, with v~100 km/s, with respect to the surrounding stellar atmosphere. To test this prediction we analyzed the deep Chandra/HETG observation of the CTTS TW Hya. Because of the high S/N ratio and high spectral resolution, this dataset should allow us to check whether or not a Doppler shift is present, constraining definitively the nature of this X-ray emitting plasma component in CTTS. To check the absolute wavelength calibration of the Chandra gratings, and to check whether or not bulk motions with respect to the photosphere are observed in coronal plasma, we also analyzed a selected sample of Chandra/HETG spectra of non-accreting low-mass active stars.
We found that the soft part of the X-ray spectrum of TW Hya is red-shifted by ~30-40 km/s with respect to the known radial velocity of the stellar photosphere. Conversely no X-ray Doppler shift is observed in the X-ray emission of non-accreting active stars. The evidence that the X-ray emitting plasma on TW Hya is moving inward with respect to the stellar surface definitively confirms that it originates in the post-shock region, at the base of the accretion stream, and not in coronal structures.
The observed radial velocity indicates that the base of the accretion stream on TW Hya is located at low latitudes on the stellar surface. Moreover this velocity is very similar to the velocity of the narrow component of the C IV resonance doublet at 1550 Å (Ardila et al. 2013), suggesting that the inspected X-ray and UV lines could originate from the same region.
Line-driven winds from early type stars are structured, with small, overdense clumps embedded in tenuous hot gas. High mass X-ray binaries (HMXBs), systems where a neutron star or a black hole accretes from the line-driven stellar wind of an O/B-type companion, are ideal for studying such winds: the wind drives the accretion onto the compact object and thus the X-ray production. The radiation from close to the compact object is quasi-pointlike and effectively X-rays the wind.
The structured nature of these winds results in absorption variability on short timescales: current instruments can resolve significant changes on timescales of kiloseconds and below in bright sources such as Cygnus X-1 and Vela X-1. We show that time resolved high-resolution spectroscopy can reveal the structure of the winds, including the temperature gradient of the clumps when using the newest EBIT-based reference values for low ionization lines of Si and S. We further introduce our newly Bayesian hierarchical inference model for lines in high resolution data, ShiftyLines, and show how it enables us to reliably constrain line shifts and thus the dynamics of the wind components.
The pre-main-sequence stars in IC 348, because of their age of 3 Myr, are key objects to study for understanding the evolution of high energy processes as low mass stars evolve toward the main sequence. Furthermore, because IC 348 is nearby (310 pc) and compact (200-400 members within a radius of 10 arcmin), HETGS can spatially resolve and obtain high signal-to-noise ratio spectra of multiple sources in a single pointing, making this project an extremely efficient use of Chandra. A comparison of the IC 348 data to more extreme cases, like the Orion Nebula Cluster, which is comparable in age but contains high mass stars that are absent in IC 348, will reveal the importance of different high energy processes in the early phases of stellar evolution. Here we give a preview of our Chandra/HETG Large Project, showing spectra and light curves of several sources for 300 ks out of the final 500 ks exposure. We will characterize the temperatures and column densities from the X-ray spectra and relate to accretion and coronal signatures.
Cataclysmic variables (CVs), in which a white dwarf accretes from a Roche-lobe filling mass donor on or near the main sequence, are an important minority population of X-ray sources throughout the X-ray band. Observations of CVs show that there are still much we do not yet know about the physics of accretion disks, particularly at low accretion rate, and some of the key clues come from X-ray observations. There is also an emerging consensus that CVs are a major contributor to the apparently diffuse X-ray emission from the Galactic bulge and ridge. Past X-ray studies of CVs have been biased towards magnetic CVs, which are relatively common and relatively X-ray luminous (1031--1033 ergs s-1). However, the majority of CVs are non-magnetic, and those with low (1029 erg s-1) X-ray luminosities may be the most numerous. On the other end of the extreme, there may be a rare subpopulation of CVs with high X-ray luminosities (~1034 erg s-1). They are sufficiently rare to be found several kpc away, often in crowded field. I will present selected recent results on both the ordinary and extraordinary CVs and consider ways in which future Chandra observations can advance the field.
The Interactive Spectral Interpretation System (ISIS; Houck & Denicola 2000) is a highly flexible, scriptable, and extensible data analysis system. Originally primarily developed as a tool for Chandra High Energy Transmission Gratings (HETG) data analysis, providing the underlying core of the Transmission Gratings Catalog (TGCat), it has grown beyond its initial use to effectively become a general purpose analysis system. ISIS is essentially a superset of XSPEC, having access to all XSPEC models including user local models, as well as analogs of all core XSPEC functionality. However, ISIS also has a wide range of tools developed for multi-wavelength spectroscopy, timing analysis, data simulation, as well as further development for high resolution spectroscopy. Furthermore, ISIS has extremely well-developed tools for "transparent" user parallelization of scripts and custom codes. In this poster, we highlight some recent tools that we have developed for ISIS. This includes a parallelized Markov Chain Monte Carlo (MCMC) code, based upon the Goodman-Weare method, sophisticated interfaces to plasma codes allowing users access to the underlying atomic physics information, and a new module under development to provide "simple" descriptions of high resolution spectroscopic data that are more sophisticated that simply adding successive gaussians to a fit model, but far less involved than a full plasma-code description. The latter is being designed for simple, preliminary assessments of high resolution spectroscopic data, prior to detailed analysis with more sophisticated, and typically much slower running, code.
We survey the Si K edge properties of several bright low-mass X-ray binaries in the Chandra archive and characterize the edge properties using the high energy transmission grating spectrometer. The Si K edge shows distinct structure which is modeled with most recent X-ray extinction dust models. One of the discoveries of this survey was that the edge is subject to various physical effects relating to atomic, ionized atomic and silicate dust signatures. The fact that we are able to resolve atomic as well as a silicate edge contributions allows us to directly measure the silicon dust to gas ratio. We present results of several sources in which we can resolve the contributing edge contributions and make predictions of how much silicon is local to the X-rays sources but also how much of the silicon is depleted in dust in the interstellar medium.
Massive stars produce X-ray emission in their winds, presumably due either to clumps or to co-rotating interaction regions (CIRs). The exact physical processes related to the X-ray emission is not fully understood. In the UV, Discrete Absorption Components (DACs) seen in UV P-Cygni are the recognized signature of these structures but there has been no evidence that X-ray emission in massive stars is directly related to UV DACs. We use an archival HETG Chandra spectrum of zeta Pup, an O4 If star, to create time-sliced spectra and study variability. The variability pattern is compared to models of CIRs and of clumpy winds.
Arcus is a NASA/MIDEX mission under development in response to the 2017 call for proposals. It is a free-flying, soft X-ray grating spectrometer with the highest-ever spectral resolution in the 8-51Å (0.24-1.55 keV) energy range. The Arcus bandpass includes the most sensitive tracers of diffuse million-degree gas: spectral lines from O VII and O VIII, H- and He-like lines of C, N, Ne and Mg, and unique density- and temperature-sensitive lines from Si and Fe ions. These capabilities enable an advance in our understanding of the formation and evolution of baryons in the Universe that is unachievable with any other present or planned observatory. The mission will address multiple key questions posed in the Decadal Survey and NASA's 2013 Roadmap: How do baryons cycle in and out of galaxies? How do black holes and stars grow and influence their surroundings and the cosmic web via feedback? How do stars, circumstellar disks and exoplanet atmospheres form and evolve? Arcus data will answer these questions by leveraging recent developments in off-plane gratings and silicon pore optics to measure X-ray spectra at high resolution from a wide range of sources within and beyond the Milky Way. CCDs with strong Suzaku heritage combined with electronics based on the Swift mission will detect the dispersed X-rays. Arcus will support a broad astrophysical research program, and its superior resolution and sensitivity in soft X-rays will complement the forthcoming Athena calorimeter, which will have comparably high resolution from 2-10 keV.
I will present the key result from the Chandra COSMOS Legacy Survey, a 4.6 Ms Chandra survey of the extragalactic sky. For each results I will highlight how Chandra in the next years can significantly improve our knowledge on AGN and galaxy evolution, in particular in the high redshift Universe.
Colliding ring galaxies are not only spectacular objects in the visible light, but also a unique laboratory in which to study peculiar phases of galaxy evolution. They contain large numbers of Ultra Luminous X-ray sources (ULXs) which are possible hosts for the elusive Intermediate Mass Black Holes (IMBHs) - compact objects with masses in the range 100-105 M☉, intermediate between stellar mass Black Holes and Supermassive Black Holes in the center of galaxies. We will present data for all the bright ring galaxies already observed by Chandra: four from the literature and three previously unpublished. We have derived the X-ray Luminosity Function (XLF) from the bright point sources along all the rings and compared it with models (e.g. the X-ray Binaries XLF) and other surveys of ULXs. We will discuss the possible presence of IMBHs.
Galaxy clusters offer a unique laboratory for studying galaxy evolution from early in the universe to the present day. However, few high-z, spectroscopically confirmed galaxy clusters are known. Recent techniques including infrared overdensity searches and AGN targeting show promising results in revealing new distant clusters. Here, we present results from the Clusters Occupied by Bent Radio AGN (COBRA) survey of high-z galaxy clusters, which combines optical, IR, radio, and X-ray observations. The COBRA survey consists of 646 bent, double-lobed radio sources selected from the VLA FIRST Survey and extends up to z~3.0. The bent radio morphology results from interactions between the AGN host galaxy and the surrounding intracluster medium – the relative motion results in ram pressure on the lobes, bending them. Since low-z bent, double-lobed radio sources are found to frequently reside in clusters and the radio emission is easily detected at high-z, these sources are ideal tracers for high-z clusters. We measure galaxy overdensities with our Spitzer observations, and find that approximately 40% of our sources are cluster candidates. We have followed many of these sources up with optical observations at the Discovery Channel Telescope. Additionally, some of our targets have been detected in X-ray archives. Here, we present initial results from the COBRA survey, which include some of the highest-z cluster candidates known. Future Chandra observations of these targets will lend insight into the evolution of X-ray properties in clusters, including the effects of AGN feedback.
High-angular resolution spectral imaging with Chandra, combined with other powerful new observatories and instruments in other wavebands have revealed a wealth of detailed information on the inhabitants of the Galactic Center: Sgr A*, SNRs, XRBs, CVs, magnetars, etc. Here we discuss some of the interesting scientific questions that have arisen over the past 17 years and some of the efforts to address them in the coming decade.
Red Dwarfs (M dwarfs or dM stars) make up ~75% of the local stellar inventory, and a recent statistical analysis data from the Kepler Mission indicates that ~15% of red dwarfs host Earth-size planets orbiting within their liquid water Habitable Zones (HZ). This is among the reasons they have been targeted by an increasing number of planet-hunting programs. As such, developing a method to accurately estimate the age of a field M dwarf is of critical importance to a number of fields. However, due to their long lifetimes and very slow nuclear evolution, the best method for determining ages is likely through "magnetic tracers" such as X-UV activity levels and stellar rotation rates. The Living with a Red Dwarf program's database of M dwarfs with photometrically determined rotation periods (via starspot modulations) is becoming substantial, and a full range of "calibrators" is being realized. We report on our current results and continuing efforts to build reliable Activity-Rotation-Age relationships for M dwarfs, utilizing X-UV measures obtained with HST, IUE Chandra and XMM (both proposed by us, and archival). Such relationships permit the assessment of the habitability of planets hosted by red dwarfs, by delineating the X-UV radiation environments these planets are exposed to, and have been exposed to in the past. After proper calibration, the relationships can also permit the age of a field red dwarf (and any hosted planets) to be determined through measures of either the stellar rotation period or X-UV activity level.
We gratefully acknowledge the support from NSF/RUI Grant AST 1009903, Chandra Grant GO-13200633, HST Grants GO-12124X and GO-13020X.
Over the past several years, we have carried out UV and X-ray observations of Cepheids with HST, Chandra and XMM. The Cepheids observed to date have dynamic outer atmospheres that vary in phase with their radial pulsations. UV observations show a relatively narrow phase-space of enhanced activity, coinciding with the Cepheid's piston phase where the photosphere begins to expand. This is consistent with a pulsation-driven shock exciting the outer atmosphere. Progress in the X-ray region has been slower, due in large part to the much longer exposures normally required for sufficient signal-to-noise. Initial Cepheid X-ray detections were argued to in fact be the result of unseen (cool, main sequence) companions. Two Cepheids, δ Cep and β Dor, were the first to achieve X-ray activity curves of sufficient phase coverage that pulsation-related X-ray variability started to present itself, but with very different phasing compared to the UV. This points to a possible second (perhaps magnetic) heating mechanism. Recently, we re-visited δ Cep with Chandra at the phase where enhanced X-ray activity was observed almost a decade prior with XMM. Chandra observed the same enhanced X-ray activity as XMM had shown almost a decade prior at the exact same phase. This makes δ Cep the first of a new class of X-ray variables, and we are now looking to confirm similar X-ray variations in β Dor. These results will be presented, along with interesting differences in the Cepheid atmospheres when compared to each other and to non-variable supergiants.
The authors wish to thank the gracious support of numerous NASA grants: HST-GO11726X, HST-GO12302X, HST-GO13019X, XMM-GO050314X, XMM-GO055241X, XMM-GO060374X, XMM-GO06547X, XMM-GO072354X and Chandra-GO5-16020X.
We realized a systematic study of the physical, dynamical and geometrical state of the ionized absorbers/emitters ubiquitously found in the nuclear environment of Active Galactic Nuclei (AGNs), and evaluated their contribution to the problem of the interplay between AGNs and their host galaxy and its surrounding Circum-Galactic Medium (CGM), known as Cosmological AGNs Feedback.We started with mining the XMM-Newton archive to select a Signal-to-Noise per resolution element (SNRE) limited sample of RGS (Reflection Grating Spectrometer) spectra of type-1 AGNs. We then modeled these data, by first determining a source-by-source best-fitting continuum, and then adding, when required, additional spectral component either in absorption or in emission. We make use of our in-house Photoionized Absorber Spectral Engine (PHASE) to model the physical and dynamical state of the ionized outflow components, when present and determine the mass outflow load of these highly ionized winds and their energetics.Here we present preliminary results of our analysis.
Earth's position on the outskirts of the Milky Way galaxy means that the Galactic Center is obscured by a particularly large column of dust and gas. With NH~×1023 cm-2, this sight line is optically thick to the scattering of soft X-rays (τ~5). The dust scattering halos around compact objects in the dense GC environment cause significant blurring, casting a fog over the heart of our Galaxy. By studying the foreground ISM, we can measure and correct for the effects of dust scattering. We report the preliminary discovery of a dust scattering halo around a recently discovered X-ray transient, SWIFT J174540.7-290015, which underwent one of the brightest flares ever observed from a GC compact object. We show corrections for pileup, PSF construction, and background. Residual surface brightness around the object gives evidence of foreground dust scattering.
In the current picture of hierarchical structure formation, galaxy groups play a vital role as the seeds from which large assemblies of matter form. Compact groups are also important environments in which to watch the fueling of star formation and AGN activity, as the conditions are ideal for galaxy-galaxy interactions. We have identified a galaxy system that may represent an intermediate or transition stage in group evolution. Shakhbazyan 1 (or SHK 1) is a remarkably compact collection of about ten massive, red-sequence galaxies within a region 100 kpc across. Several of these galaxies show signs of AGN activity, and new, deep optical observations with the Discovery Channel Telescope reveal an extended envelope of stars surrounding the galaxies. This envelope is much more extended than what would be expected from a superposition of normal galaxy stellar distributions, and it indicates a large amount of intra-group starlight, evidence that the galaxies in SHK 1 are dynamically interacting.
We here present new Chandra spectral imaging observations of this unusual system that confirm the presence of an X-ray-emitting diffuse intra-group medium (IGM), with a temperature of 1.5 keV and X-ray luminosity of 1×1043 erg/s. Assuming hydrostatic equilibrium, the system is about 1/3 as massive as expected from the optical richness. In addition, three of the ten central galaxies exhibit signatures of X-ray AGN. The under-luminous IGM, high density of bright galaxies, and evidence for galaxy-galaxy interaction indicate that this system may be in a transition stage of galaxy merging, similar to that expected in the formation of a fossil group. Alternatively, SHK 1 may consist of multiple poor groups in the final stages of merging along our line of sight. We explore these scenarios and outline paths of future study for this enigmatic system.
In the near future, eROSITA is expected to detect ~100000 galaxy clusters, which will be important for both, galaxy cluster astrophysics and cosmological studies. The synthesis of eROSITA and Chandra could on the one hand help to better characterize instrumental systematics like the effective area cross calibration, but is also essential to follow-up eROSITA detected clusters of selected subsamples. These follow-up observations can for example define the point source contamination, the cool core characteristics and selection function of eROSITA or studies of merging and morphologically interesting systems. This requires high spatial resolution, that only Chandra can provide.
The next decade of Chandra promises to add a wealth of observations of galaxy clusters and galaxy cluster mergers to those already observed, and its high spatial resolution will make it the instrument of choice for multiwavelength studies of clusters. Mergers are observed in a variety of stages and along unknown lines of sight, so making definitive comparisons of observations to simulated merging clusters requires detailed studies of simulations in these aspects. This is challenging, due to the large quantities of data involved. I present a new initiative, the Galaxy Cluster Merger Catalog, an browseable archive of simulated cluster merger observations along many lines of sight, at many epochs, and in several simulated wavebands, including Chandra. The catalog provides downloadable FITS files as well as an in-browser interface to JS9. The goal is to invite the community to include simulated observations from their simulations.
The Chandra telescope has played a key role in understanding the intracluster medium (ICM) properties of the central regions in galaxy clusters. Thanks to its unmatched spatial resolution, Chandra has enabled us to understand the connection between cooling flows and self-regulated radio-mode AGN feedback, and the influence of these processes on X-ray scaling relations. In this work, we focus on a different mode of AGN feedback, namely the quasar mode, which is radiatively efficient, and is characterised by high accretion rates in the supermassive black hole present in the centrally located brightest cluster galaxy (BCG). The quasar mode includes a highly obscured stage, and to date only five BCGs have been shown to be obscured quasars (I.e. type-II AGN). Given the small number of such objects, the influence of quasar mode feedback on the ICM, and a potential evolution into the self-regulated radio mode, is poorly understood.
We obtained Chandra data for the intermediate redshift galaxy cluster ACT J0320.4+0032 which hosts a type-II AGN in the BCG. We constrained the temperature distribution, and identified potential X-ray cavities (i.e. surface brightness depressions) to detect signatures of AGN feedback. The cooling time profile was generated to identify a cool-core, and to determine the X-ray luminosity within the cooling radius, which was compared to the cavity power. The influence of feedback on global cluster properties such as gas mass, temperature, and gas fraction were tested by comparing it to other clusters in literature. Our results indicate that the cluster while showing signatures of quasar mode feedback, also shows signs of having a nascent cool-core, which could eventually fuel the central AGN in a self-regulated manner, and transition the AGN from the quasar mode to the radio mode.
The recent discovery of the "Phoenix cluster" which, at z = 0.6, is the most X-ray luminous clusters known and harbors a massive starburst at its center, begs the question: Why was is not discovered until recently? In fact, the object has been previously detected by several all-sky surveys at a variety of wavelengths, but it is consistently classified as a quasar (QSO) because of the extremely bright central galaxy and a (relative) lack of extended X-ray emission due to its distance. This lead us to question of how many of these Phoenix-like clusters are currently mislabelled in existing all-sky surveys.
A unique property of the Phoenix cluster which helps us identify other Phoenix-like objects is that it is bright at multiple wavelength, including X-ray (intracluster medium and central AGN), near-IR (giant central elliptical galaxy), mid-IR (warm dust from starburst and AGN) and radio (radio-loud central AGN). Therefore, we can identify potential Phoenix-like clusters by cross-correlating all-sky surveys from ROSAT (X-ray), 2MASS (near-IR), WISE (mid-IR) and both SUMSS and NVSS (radio). By requiring sources to be bright in all four surveys, we can quickly find (among other sources) a sample of Phoenix-like clusters that can be followed up either by using archival images from SDSS for Northern-hemisphere objects or taking new images from the Magellan telescope for Southern-hemisphere objects. For candidates exhibiting an optical cluster counterpart, we use Chandra to confirm the presence of extended X-ray emission from the intracluster medium. Here, we will present the preliminary result from the project.
We present the results from the Michigan Swift X-ray observations of the Sloan Giant Arcs Survey (SGAS). These clusters were selected because of the presence of a giant arc visible in the SDSS survey. Observations from Swift can be used to confirm the presence of X-ray gas which can then be followed up with Chandra. We characterize the morphology of the sample, and discuss the offset between the X-ray centroid, the mass centroid as determined by strong lensing analysis, and the BCG position.
Considerable work supports the notion that long-duration gamma-ray bursts and some energetic supernovae are driven by the formation of black holes and the strong magnetic fields of mangetars. However, is this framework certain? We argue that the present body of evidence remains circumstantial, and that a true test of this paradigm is to confidently identify a post-explosion compact remnant that could have acted as the central engine. The unexpected recent discovery by Chandra of a black hole candidate in SN1979C demonstrates how patience and persistence is the winning strategy to achieve this goal. Through the careful analysis of persistent X-ray light curves spanning more than ten years after explosion, one can successfully detect emission associated with a central accreting black hole by patiently waiting until absorption by the expanding ejecta becomes negligible. SN1998bw and SN2002ap are particularly exciting and obvious targets, but Chandra is capable of providing a global understanding of massive star explosions by monitoring dozens of candidate events over the next decade in search of "baby black holes" that will become visible to the X-ray eye. Our proposed strategy benefits from coordinated radio and optical observations that can disentangle possible emission from strong interaction with circumstellar material, and represents one of the only means by which to achieve a landmark confirmation of the hypernova---black hole connection.
We present the first results from our X-ray study of young radio sources classified as compact symmetric objects (CSOs). Using the Chandra X-ray Observatory we observed six CSOs for the first time in X-rays, and re-observed four CSOs already observed with XMM-Newton or BeppoSAX. We also included six other CSOs with archival data to built a pilot study of a sample of the 16 CSO sources observed in X-rays to date. All the sources are nearby, z<1, and the age of their radio structures (<3000 yr) has been derived from the expansion velocity of their hot spots. Our results show the heterogeneous nature of the CSOs' X-ray emission, indicating a complex environment associated with young radio sources. The sample covers a range in X-ray luminosity and intrinsic absorbing column density. In particular, in different sources we detected the following properties: an extended X-ray emission, a hard photon index consistent with either a Compton-thick absorber or non-thermal emission from compact radio lobes, an ionized iron emission line at Erest=6.62±0.04 keV and EW~0.15-1.4 keV, a decrease by an order of magnitude in the 2-10 keV flux since the 2008 XMM-Newton observation. Moreover, we report on the gamma-ray emission detected with Fermi/LAT from a position consistent with that of the youngest and nearest CSO in our sample. We conclude that our pilot study of CSOs provides a variety of high-energy exceptional diagnostics and highlights the importance of deep X-ray observations of large samples of young radio sources. This is necessary in order to constrain theoretical models for the earliest stage of radio source evolution and to study the interactions of young radio sources with the interstellar environment of their host galaxies.