Abstracts

NERQUAM-26     ABSTRACTS

Kazunori Akiyama (MIT/Haystack)    “The global radio structure of the archetypical quasar 3C 273”
Abstract: We present multi-frequency observations of the archetypal quasar 3C 273 performed with the VLBA at 1.4/15/22/43 GHz, the VLA at 5/8/22 GHz and the MERLIN at 1.6 GHz. The observations provide the detailed transverse structure resolved in a broad range of spatial scales from sub-parsec to kilo-parsec, allowing us to profile the jet width as a function of the core as already studied in some radio galaxies (e.g. M87, 3C 84 and Cyg A). We discovered a transition of the parabolic stream to the conical stream stably appeared at ~10^5-10^6 Rs from the 7-mm core, for the first time in the quasar jets. The similarity in these properties to the much lower-powered radio galaxy M87 would suggest the universality of the jet acceleration and collimation among the AGNs with different accretion rates of the central super-massive black hole. We also found that future ultra-high-resolution VLBI observations with the ALMA at 86 and 230 GHz can effectively constrain the active collimation region and the launching point of the visible jet at the end the collimation profile.

 Anna Barnacka (CfA)          “Resolving the High Energy Universe with Strong Gravitational Lensing”
Abstract: Extragalactic jets are the largest particle accelerators in the universe, producing radiation ranging from radio wavelengths up to very high-energy gamma rays. Spatial origin of gamma-ray radiation from these sources cannot be fathom due to the poor angular resolution of the detectors. We propose to investigate gravitationally lensed blazars. Cosmic lenses magnify the emission and produce time delays between mirage images. These time delays depend on the position of the emitting regions in the source plane. We combine the precisely measured time delays at gamma rays, well-resolved positions of radio images, a model of the lens and the Hubble constant to elucidate the origin of gamma-ray flares from bright blazar B2 0218+35. With this approach, we achieve 1 milliarcsecond spatial resolution of the source at gamma-ray energies. We find that the gamma-ray flares do not originate from the radio core as commonly assumed.

Wystan Benbow (CfA)                “Highlights from the VERITAS AGN Observation Program”
Abstract: The VERITAS array of four 12-m imaging atmospheric-Cherenkov telescopes began full-scale operations in 2007, and is one of the world’s most sensitive detectors of astrophysical VHE (E>100 GeV) gamma rays. Observations of active galactic nuclei (AGN) are a major focus of the VERITAS Collaboration, and more than 60 AGN, primarily blazars, are known to emit VHE photons. Approximately 4000 hours have been devoted to the VERITAS AGN observation program, resulting in 34 detections. Most of these detections are accompanied by contemporaneous, broadband observations, enabling a more detailed study of the underlying jet-powered processes. Recent highlights of the VERITAS AGN observation program will be presented.

McKinley Brumback  (Dartmouth)        “Exploring the warped accretion disk around the magnetized neutron  star LMC X-4”
Abstract: X-ray binaries offer an opportunity to study accretion disk physics on a small, local scale. Some X-ray pulsars display periodic or quasi-periodic changes in luminosity believed to be caused by the precession of a warped inner accretion disk. Analogous disks have been found in nearby AGN such as NGC 4258 and the Circinus galaxy. In order to examine the kinematics and geometry of warped accretion disks, we use joint observations with NuSTAR and XMM-Newton to perform pulse phase spectroscopy of the high mass X-ray binary LMC X-4. By measuring the relative phase between the hard pulsar beam and the softer photons reprocessed by the disk, we observe the complete precession of the warped accretion disk around the neutron star for the first time. Extracting the luminosities associated with the power law and blackbody components of the spectra will allow us to use tomography to explore the geometry of the inner magnetized accretion flow. This work is supported by NASA grant number NNX15AV32G.

Mike DiPompeo (Dartmouth)  “The halo masses of obscured quasars and evolutionary models”
Abstract: With the release of WISE all-sky mid-IR data, we can now assemble large, statistical obscured quasar samples. This allows us to probe their host dark matter halos and place them in the context of the growth of cosmic structure and galaxy evolution. Using both the angular autocorrelation function and cross-correlations with CMB lensing maps, we find that obscured quasars reside in halos with larger masses than their unobscured counterparts. Under the assumption that a subset of the obscured population is indeed obscured by a torus, and otherwise intrinsically identical to the unobscured population, our measurement places a lower limit on the halo masses of obscured quasars that may represent a particular evolutionary phase. Using analytical methods and cosmological simulations, we predict the halo masses of this distinct population. Finally, using a simple halo growth model and empirical relationships between halo, stellar, and black hole masses, we show that an evolutionary sequence from obscured to unobscured quasar phases in conjunction with a flux or luminosity limit can not only naturally reproduce our halo mass measurements, but explain some discrepant results in the literature.

Martin Elvis (CfA)                “What can Commercial Space do for Astronomy?”
Abstract: Access to the entire spectrum, from radio and far-IR through the mid-, near-IR, optical, UV, X-rays and gamma-rays, at comparable sensitivity has enabled many of the advances in quasar and AGN research for the past 35 years during which this is available. The Great Observatories – Chandra, Hubble and Spitzer – are the pillars on which this access rests. But they are old and replacing them at a level that matches the James Webb Space Telescope seems to involve daunting costs. Are the electromagnetic windows opened by the space age about to close?
I believe not. Within a few years the costs of launch to orbit will be lowered by factors of 2 – 3, thanks to SpaceX, and now its competitors ULA and Airbus. In addition, commercial transport to the International Space Station will become reality. By 2017 at least two companies, SpaceX and Orbital, will be offering private rides to orbit and by 2020 Bigelow Aerospace will have its first large orbiting habitat at ISS. Given the 20-year gestation periods for large space telescopes, the impact of commercial space development becomes immediately urgent as we plan the next generation of observatories. I will discuss how commercial space could change how we design missions and give specific examples of valuable developments.

Emmet Golden-Marx (BU)       “The High-Redshift COBRA Galaxy Cluster Survey”
Abstract: Galaxy clusters offer a unique laboratory for studying galaxy evolution from early in the universe to the present day. However, since traditional cluster detection methods — including optical overdensity and X-ray searches — are limited due to foreground contamination and surface brightness dimming, few high-z, spectroscopically confirmed galaxy clusters are known. Recent techniques including infrared overdensity searches and AGN targeting show promising results. Here, we present results from the Clusters Occupied by Bent Radio AGN (COBRA) survey of high-z galaxy clusters, which uses these techniques. The COBRA survey consists of 646 bent, double-lobed radio sources 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. Using our Spitzer observations we measure infrared galaxy overdensities, finding that ~50% of our sources are cluster candidates. We have followed these sources up with optical observations at the Discovery Channel Telescope. Here, we present initial estimates of optical overdensities and photometric redshifts, found by matching the host galaxy’s color to galaxy evolution models. Additionally, we use multi-band color cuts to examine red sequence populations and overdensities for a subset of the clusters in our sample.

Mark Gurwell (CfA)      “The Submillimeter Array Calibrator Flux Density History Database”
Abstract: The Submillimeter Array (SMA) is an eight element interferometer located near the summit of Mauna Kea, Hawaii, operating in the mm/submm atmospheric windows. Starting in 2002, and in continuous operation since 2003, the SMA routinely observes brighter radio-loud objects (such as blazars) as calibration sources since they typically appear as point sources (resolutions from 0.2″-10″). The primary data is derived from a combination of baseline determination tracks, irregularly scheduled flux measurement tracks, and selected science tracks; as such the data density is skewed toward brighter, well-known sources (such as 3C454.3) or sources near heavily subscribed regions on the sky (such as Taurus, Ophiuchus, the Galactic Center). As of June 1, the SMA Calibrator Flux Density database contains over 26,000 measurements on 414 different sources, covering the 1.3mm, 1.1mm, and 870 micron windows. The Submillimeter Calibrator list, hosted at the SMA Observer Center (http://sma1.sma.hawaii.edu/tools.html) is updated regularly, and is by far the most comprehensive publicly available source of data for these wavelength bands.
Rapid calibration of data provides up-to-date flux densities for brighter sources, useful for planning SMA observations. In addition, the database is a rich and unique resource documenting the mm/submm variability for more than 400 sources. Interest in the SMA as an observational resource has been particularly strong since the launch of the Fermi Gama-ray Space Telescope, with data from the SMA used in at least 60 peer-reviewed publications since 2008. While most use has been through mining the database, the SMA also solicits proposals and actively supports dedicated monitoring programs which can result in high cadence, long term monitoring of specific sources.
The SMA is currently in the midst of hardware upgrades which will result in a significant sensitivity increase (via an 4-fold increase in continuum bandwidth per polarization over the original SMA design) in addition to constant dual polarization measurement (another factor of 2 increase in total bandwidth, and allowing full polarization observations at will). These upgrades will allow the SMA to monitor fainter targets and further increase the utility of the database.

Ryan Hickox (Dartmouth)          “AGN synthesis of the cosmic X-ray background with NuSTAR”
Abstract: In the past decade, active galactic nucleus (AGN) synthesis models have proven remarkably successful in reproducing the overall spectrum of the cosmic X-ray background (CXB). However, our understanding of the accreting black holes that produce the CXB has been primarily based on observations at soft energies with Chandra and XMM, with only indirect constraints at energies > 10 keV. With the advent of NuSTAR, we can now probe the emission from AGN at the high energies that dominate the CXB. I will present a stacking analysis using NuSTAR extragalactic surveys and multiwavelength data to provide direct constraints on the contribution to the hard CXB from AGN at different luminosities, redshifts, and obscuring columns. This analysis with NuSTAR opens a new window in studying the full composition of the CXB, with implications for AGN physics and the cosmic evolution of black holes. This work is supported in part by NASA award NNX15AP24G.

Mackenzie Jones (Dartmouth) “The Intrinsic Eddington Ratio Distribution of Type 2 AGN in Star-forming galaxies from SDSS”
Abstract: Recent efforts have been made to probe the connection between active galactic nuclei (AGN) and their host galaxies. An important question in resolving this connection concerns the distribution of black hole accretion rates, i.e. the Eddington ratio distribution, of AGN. Determining the intrinsic Eddington ratio distribution can be strongly influenced by selection effects and dilution from the host galaxy star formation which may also vary across different wavebands. Using a sample of galaxies from SDSS DR7, we investigate whether an intrinsic AGN Eddington ratio distribution that takes the form of a broad Schechter function is in fact consistent with previous work that suggests instead that AGN in star forming galaxies from optical surveys have a more strongly peaked lognormal Eddington ratio distribution. Furthermore, we present an improved method for extracting the AGN contribution to the observed flux using BPT diagnostics that allows us to probe over one order of magnitude lower in Eddington ratio, counteracting the effects of dilution by star formation. We conclude that the intrinsic Eddington ratio distribution of optically selected AGN is consistent with a power law with an exponential cutoff, as is observed in the X-rays.

Manasvita Joshi (BU)  “Magnetic Field Geometry And Its Implications On the High-Energy Emission Of Blazars”
Abstract: The knowledge of the structure of the magnetic field inside a blazar jet, as deduced from polarization observations at radio to optical wavelengths, is closely related to the formation and propagation of relativistic jets that result from accretion onto super-massive black holes. However, a largely unexplored aspect of the theoretical understanding of radiation transfer physics in blazar jets has been the magnetic field geometry as revealed by the polarized emission and the connection between the variability in polarization and flux across the spectrum.
Here, we explore the effects of various magnetic geometries that can exist inside a blazar jet: parallel, transverse, oblique, toroidal, helical, and tangled. We investigate the effects of changing the orientation of the magnetic field, according to the above-mentioned geometries, on the resulting high-energy spectral energy distributions (SEDs) and spectral variability patterns (SVPs) of a typical blazar. We use the MUlti-ZOne Radiation Feedback (MUZORF) model of Joshi et al. (2014) to carry out this study and to relate the geometry of the field to the observed SEDs at X-ray and gamma-ray energies. One of the goals of the study is to understand the relationship between synchrotron and inverse Compton peaks in blazar SEDs and the reason for the appearance of gamma-ray “orphan flares” observed in some blazars. This can be associated with the orientation of the magnetic field, which creates a difference in the radiation field as seen by an observer versus that seen by the electrons in the emission region

Mason Keck (BU)  “Probing Blazar Jets Closer to the Black Hole via Faraday Rotation Measurements”
Abstract: We present Very Long Baseline Array total and polarized intensity images of ten blazars obtained simultaneously at 22, 43, and 86 GHz in 2014 April. We aim to study the Faraday rotation measure and degree of polarization at the location of the 86 GHz VLBI core, closer to the black hole than previous analyses done at lower frequencies. The goal of the project is to probe the nature of the Faraday rotation screen and structure of the magnetic field geometry in the inner parsec-scale jet. Alignment of the total intensity maps at different frequencies will allow us to analyze the shape of the jet closer to its base.

Joanna Kuraszkiewicz (SAO)   “Chandra observations of medium redshift 0.5<z<1 3CRR sources.”
Abstract: We report Chandra observations of a complete, flux limited sample of 36 medium (0.5<z<1) redshift, low frequency radio selected (and so unbiased by orientation) 3CRR radio sources. The sample includes: 13 quasars, 22 NLRGs and 1 LERG, with matched 178MHz radio luminosity (L(178MHz)~44-45). The quasars have high radio core fraction, high X-ray luminosity L(0.3-8keV)~45-46 and soft hardness ratios (HR<0), indicating low obscuration (log NH<10^22.5). The NLRGs, on the other hand, have lower radio core fraction, lower observed X-ray luminosities L(0.3-8keV)~43-45 and a wide range of hardness ratios (-0.7<HR<0.9) indicating a range of obscuration (20.5<log NH<24). These properties together with the observed trend of increasing obscuration with decreasing radio core fraction are roughly consistent with orientation-dependent obscuration as in unification models. However, we find 4 NLRGs with low NH (20.5<logNH<22), soft hardness ratios (HR<0), and relatively weak (compared to other sourcesin the sample) near-to-mid-IR emission and sSFR. Possible explanations include either an extremely thin and cool dusty torus or obscuration by a host galaxy lane (as seen in the red 2MASS AGN Kuraszkiewicz et al. 2009). The sample also includes 4 Compton-thick candidates
i.e. NLRGs with high (Compton-thick) [OIII] to L(2-8keV) ratios.

Dacheng Lin (UNH)       “A Wandering Massive Black Hole Caught Shredding a Star”
Abstract: Galaxies are believed to assemble through hierarchical merging. The cosmological simulations find that the merging process should leave many wandering massive black holes in galactic halos. Only a few candidates for such objects have been found. We report the discovery of an off-nuclear ultrasoft hyper-luminous X-ray source candidate 3XMM~J141711.1+522541 in an inactive S0 galaxy at a distance of d_L=2.3 Gpc) in the Extended Groth Strip. It is located at a projected offset of ~1 arcsec (5.2 kpc) from the nucleus of the galaxy and was serendipitously detected in five XMM-Newton observations in 2000 July. Two observations have enough counts and can be fitted with a standard thermal disk with an apparent inner disk temperature kT_disk ~ 0.13 keV and a 0.28-14.2 keV unabsorbed luminosity L_X ~4X10^43 erg/s in the source rest frame. The source was still detected in three Chandra observations in 2002 August, with similarly ultrasoft but slightly fainter spectra. It was not detected in several later observations, implying a long-term flux variation factor of >14. Therefore the source could be a transient with an outburst in 2000-2002. It has a faint optical counterpart candidate, with apparent magnitudes of m_F606W=26.3 AB mag and m_F814W=25.5 AB mag in 2004 December (implying an absolute V-band magnitude of -15.9 AB mag). We discuss various explanations for the source and find that it is best explained as a massive black hole (BH) embedded in the nucleus of a possibly stripped satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. The BH mass is ~10^5 solar mass, assuming the peak X-ray luminosity at around the Eddington limit. The work has been published in Lin et al. ApJ, 2016, 821, 25.

Michael Malmrose  (BU)           “Components of the Optical to UV Spectra of Gamma-Ray Bright Blazars: The Search for Variability in the Big Blue Bump”
Abstract: The fraction of Active Galactic Nuclei (AGN) in which a relativistic jet is aligned with the observer’s line of sight are classified as blazars (Urry & Padovani, 1995;). Radiation from the accretion disk and perhaps the jet is absorbed and reprocessed through various structures inside the AGN, and subsequently re-emitted across a broad range of frequencies (Antonucci, 1993). In some blazars, relatively unprocessed radiation from the accretion disk is visible in the optical-UV portion of the spectrum. In spectral energy distributions (SEDs) this produces the so-called big blue bump (BBB). Measuring the strength of the BBB emission is complicated by the fact that the synchrotron emission from the relativistic jet is also prominent in the optical-UV portion of the SED. In this work we seek to separate the unpolarized BBB emission of a sample of blazars from the polarized synchrotron emission present in the optical-UV emission through the use of spectropolarimetric observations obtained as part of the Steward Observatory spectropolarimetric monitoring project (Smith et al., 2009) spanning λ = 4000-7000 Å in the observer’s frame. With the assumption that the BBB emission is unpolarized, the spectral index of the synchrotron emission, α s , is determined from the polarized flux spectrum. Assuming that the BBB is caused by a standard thin accretion disk, the strength of the BBB is measured by fitting a two component model of the form F ν = A ν 1/3 + B ν αBBB , where α BBB is the spectral index of the BBB and is set to α BBB = 1/3 (Shang et al. 2005). This is repeated on a time series of spectra observed between 2008 and the present. We find evidence for a variable BBB in the quasar 1222+216 on by a factor of ~ 2. We also repeat the modeling while relaxing the requirement that α BBB = 1/3, both by adding a high temperature blackbody, and allowing α BBB to vary, both of which result in a better fit to 1222+216, providing evidence that the shape of the accretion disk spectrum is not that of a simple thin disk. We also perform the two-component fit on 3C66A, While a marginally variable BBB component can be detected, the small difference between the spectral indices of the full spectrum and the polarized spectrum indicates that wavelength dependent polarization, a situation that may arise due to turbulence in the jet (Marscher, 2014), may be present.

Alan Marscher (BU)     “The Blazar Conundrum”
Abstract: The blazar variability problem keeps becoming more severe, with flares of higher luminosities occurring on shorter time-scales. The latest is a gamma flare in 3C 279 in June 2015 with an apparent peak luminosity > 1E49 erg/s while the flux doubled over less than 5 minutes (Hayashida et al. 2016, preprint). The author will discuss possible explanations for such events and the extreme physical conditions that they require.

Herman Marshall (MIT/Kavli)  “The Chandra Survey of Quasar Jets”
Abstract: We have completed Chandra X-ray imaging of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like extended structure. X-rays are detected from 33 of the 59 jets in the sample for a detection rate of 59\%. Counterjets are not observed. The core spectra are fitted by power law spectra with an average photon index gamma_x of 1.61. We compute the distribution of the spectral index between the X-ray and radio bands, showing that it is broad, well fit as a Gaussian with mean 0.974 +/- 0.012 and dispersion of 0.077+/- 0.008. We test the model in which kpc-scale X-rays result from inverse Compton scattering of cosmic microwave background photons off of the jet’s relativistic electrons (the IC-CMB model), rejecting it at 99.5% confidence. Furthermore, if the IC-CMB model were valid for the bulk of the observed X-ray emission from kpc-scale jets, then the jets must either decelerate or bend away from the line of sight on average. Our results compound the problems that the IC-CMB model has in explaining the X-ray emission of kpc-scale jets. Instead, we favor synchrotron models with two populations such as spine-sheath models.

Mark McConnell (UNH)      “Gamma-ray Polarimetry as a Probe of the Central Engine of Gamma-Ray Bursts”  (unable to attend)
Abstract: Now known to originate at cosmological distances, GRBs are the most luminous objects in the universe.  It has been established that GRBs are emitted from outflows moving towards us at highly relativistic speeds. The outflow is thought to arise from either the collapse of a very massive star or the merger of two compact objects. Although the salient features of a GRB can be explained by the so-called fireball model of a rapidly expanding volume of hot material, several key aspects concerning the nature of the central engine (including the jet formation and jet structure) remain poorly understood. Some of these issues can best be addressed by studying the polarization of the prompt gamma-ray emission. We review the observations that have so far been reported for gamma-ray polarization of GRBs and discuss the prospects for future measurements, including our own work on the Gamma-Ray Polarimetry Experiment (GRAPE).

Joey Neilsen  (MIT) “X-ray Flares from Sgr A*, or How to Try to be an AGN Without Really Succeeding”
Abstract: A few hundred years ago, Sgr A* lit up the X-ray sky in a bright outburst, or so we are told by the echoes of this medieval light off molecular clouds in the Galactic Center. Today, however, observations of the black hole itself tell a different story, where the bolometric luminosity of the accretion flow is some ten orders of magnitude below the Eddington limit. The only inklings of Sgr A*’s active past can be found in the form of sporadic multiwavelength flares, which last roughly an hour but can involve increases in the X-ray luminosity by factors of several hundred to thousand. It has been suggested that these flares may represent a link between Sgr A* and other AGN via the fundamental plane of black hole activity, but even after nearly 20 years of monitoring Sgr A* with Chandra, the physics of flares is poorly understood. I will discuss our ongoing efforts to understand these flares and their significance, focusing on the statistics of the variability and our recent theoretical attempts to infer the associated radiation physics.

Mahito Sasada (BU)     “Polarization Connection between the Optical and Radio Emitting Regions in Blazar OJ 287”
Abstract: Blazars, which contain relativistic jets at small angles our line-of-sight, are the most variable class of active galactic nuclei. Synchrotron radiation by high-energy electrons dominates the emission of blazars from radio to optical, and sometimes X-ray, bands, owing to relativistic boosting. The location(s) of the region(s) of acceleration of the electrons, however, remains uncertain. We relate the polarization vectors at optical and radio bands simultaneously in one of the most famous blazars, OJ 287, to determine where electrons are energized. This object is highly polarized both in radio and optical bands. Radio polarization vectors in the core of the object agree fairly well with the optical polarization at every epoch of VLBA observations, but this is not the case for the brightest knot in the jet. This similarity indicates that the optical emission mainly comes from the radio core in OJ 287.

Dan Schwartz (SAO)     “Confronting 100 kpc X-ray Jets with an origin from maximally spinning black holes”
Abstract: We use the kinetic fluxes measured for 100 kpc X-ray jets to calculate the required mass loss for rapidly spinning supermassive black holes to supply the power. For the quasars in the survey by Marshall et al. (2005, 2011, 2016 in prep) this power can be accommodated, even with parameterized spins as low as a=0.2. If we assume the initial power is purely Poynting flux, then since the magnetic field carries both the energy and the angular momentum lost by the black hole, we can derive constraints on the magnetic field as a function of jet radius, r. This must break down at some distance prior to the initiation of radiation from the jet; e.g., where particles are accelerated.

Grant Tremblay (Yale)     “A Galaxy-Scale Fountain of Cold Molecular Gas Pumped by a Black Hole”
Abstract: A new ALMA observation of the cool core brightest cluster galaxy in Abell 2597 reveals that a supermassive black hole can act much like a mechanical pump in a water fountain, driving a convective flow of molecular gas that drains into the black hole accretion reservoir, only to be pushed outward again in a jet-driven outflow that then rains back toward the galaxy center from which it came. The ALMA data reveal “shadows” cast by giant molecular clouds falling on ballistic trajectories towards the black hole in the innermost hundred parsecs of the galaxy, manifesting as deep redshifted continuum absorption features. The black hole accretion reservoir, fueled by these infalling cold clouds, powers an AGN that drives a jet-driven molecular outflow in the form of a 10 kpc-scale, billion solar mass expanding molecular bubble. HST reveals that the molecular shell is permeated with young stars, perhaps triggered in situ by the jet. Buoyant X-ray cavities excavated by the propagating radio source may further uplift the molecular filaments, which are observed to fall inward toward the center of the galaxy from which they came, presumably keeping the fountain long-lived. I will discuss this specific result in the larger context of galaxies as a whole, as the results show that cold molecular gas can couple to black hole growth via both feedback and feeding, in alignment with “cold chaotic accretion” models for the regulation of star formation in galaxies.

Karen Williamson (BU)              “Comprehensive Monitoring of Gamma-Ray Bright Blazars. II. Correlation Analysis of Delays between Gamma-Ray and Optical Light Curves”
Abstract: The BU team + collaborators have been performing multi-wavelength monitoring of a sample of γ -ray blazars since the launch of the Fermi Gamma-ray Space Telescope in 2008. We present γ-ray and optical light curves for several quasars and BL Lac objects from the sample to illustrate different patterns of variability. We investigate correlations between γ-ray and R-band light curves and, if these are statistically significant, determine delays between variations at the two wavebands. Such time delays can reveal the relative locations of the emitting regions in AGN jets and the origin of the high-energy photons. We present preliminary results of this analysis. Of the 29 blazars with sufficient time coverage, 17 display a significant, singular, correlated time lag when tested over the entire 7-year period. Of these sources, the 6 that exhibit a consistent time lag across a majority of epochs of high activity have lags of 0±7 days; the 11 without consistency across epochs of high activity generally display longer mean lags, with optical leading γ–ray. Eleven sources displayed a significant singular correlation over neither the entire 7-year period nor across shorter intervals. No significant difference is apparent between BL Lac objects and FSRQs. Even after 8 years of monitoring, our correlation analysis remains plagued with uncertainties due to insufficient data.

Anna Wolter (INAF-OABrera)   “In search of the seeds of AGNs”
Abstract: Intermediate Masse Black holes (IMBH) are compact objects with masses in the range 100-10$^{5} M_\odot$ which are intermediate between stellar mass Black Holes and Supermassive Black Holes in the center of galaxies. They have fundamental cosmological implications as they are deemed e.g. to be seeds of Super-Massive BHs, For instance they could help solving the problem of having SMBHs already in place at z $\geq 7$, when the Universe was less than a billion years old. If IMBHs do exist, then we might expect that most of them are at high luminosities, in the range of Ultra Luminous X-ray sources (ULXs).
We have started a search for IMBH in Ring Galaxies (RG), a unique laboratory in which to study peculiar phases of galaxy evolution. We will present the RG already observed by Chandra (the Cartwheel, Arp 284, Arp 147, NGC 922, AM 0644-741 and Arp 148) and derive the Xray Luminosity Function (XLF) of their point sources and compare it with models (like the X-ray Binaries XLF) and other surveys’ results.

Wei Yan (Dartmouth)        “NuSTAR Observations of Heavily Obscured Quasars Selected by WISE”
Abstract: One of the main focus of NuSTAR program is to find heavily obscured quasars, luminous accreting supermassive black holes surrounded by gas and dust. Based on mid-IR photometry from WISE and SDSS, we have selected a large population of obscured quasars. Here we report NuSTAR observations of four WISE-selected heavily obscured quasars for which we have optical spectroscopy and redshifts from SALT. Three out of four objects are too faint to be detected, while the other one has only a marginal detection. From the upper limit and net counts of our X-ray observations in different bands, we confirm that our objects are luminous quasars with obscured X-ray luminosities at or below ~10^43 erg s-1. We find corresponding gas column densities N_H to be around 10^25 cm-2, confirming that WISE and optical selection can identify very heavily obscured quasars that may be missed in X-ray surveys.


Late Posters:

TITLE: The Time Domain Spectroscopic Survey

AUTHORS: P. Green, M. Eracleous, E. Morganson, J. Ruan, S. Anderson, J. Runnoe, C. MacLeod, and the TDSS team.

ABSTRACT: The Time-Domain Spectroscopic Survey (TDSS) is a subproject of the SDSS-IV eBOSS project, aimed at identifying variable objects and following up additional, interesting of objects. At the end of the 4–6 years of the eBOSS survey, the TDSS will have yielded 200,000 spectra of variables (90% initial spectra) at 17 < i < 21. Approximately half of these variables are expected to be quasars, observed spectroscopically for the first time.  The survey is also devoting 10% of its fibers to obtain additional spectra of interesting classes of objects that have previous spectra from SDSS I–III or other programs (these are the Few-Epoch Spectroscopy, or FES, programs). This allows the study of the variability of these classes through large samples (~1000 targets each) that could not be easily observed otherwise. We will describe the design of the survey and summarize the goals of the FES programs. will also describe the results from a pilot survey, carried out in spring 2014 as part of SDSS-III/SEQUELS and covering ~320 square degrees of the sky, that give us a preview of what TDSS will bring. For example, we find that, variability selection complements color selection by selecting redder quasars. Moreover variability selection yields larger fractions of blazars and BAL quasars than color selection alone.