Had I special: The Astronomical Contributions of the Herschel Family

НазваниеHad I special: The Astronomical Contributions of the Herschel Family
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Multi-Wavelength Variability of Fermi Selected Blazars

Meghan Frate1, K. Marshall1, M. Aller2, H. Aller2, H. Miller3, J. Eggen3, D. Gudkova3, H. Marine3, J. Maune3
1Bucknell University, 2U. of Michigan, 3GSU.

Exhibit Hall

It is known that blazars are among the most variable and luminous objects in the sky due to their orientation relative to our line of sight. Our work has been to map the variability in four energy bands to search for correlations, in hopes of finding better relationships between the energy bands and supplementing existing multi-wavelength studies. We’ve done this with seven blazars monitored by the Fermi Gamma-ray Space Telescope and collected radio, optical, and X-ray data. We found strong correlation between optical and gamma-ray emissions in most of our objects, with X-rays generally uncorrelated with all other wavelengths, and were able to match these results up to existing emission models.


Vri/gri Photometry And Polarimetry Of Blazars At The Table Mountain Observatory, 2005-2010

Alma C. Zook1, M. M. Amezcua1, M. W. Hasling1, W. A. Morrison1
1Pomona College.

Exhibit Hall

We present VRI/gri photometry and polarimetry of several objects studied by the blazar monitoring program at Pomona College’s Table Mountain Observatory, which has now been operating for six summers. Initially only VRI photometric observations were possible; a polarimeter was added and tested during the summer of 2007 and a set of gri filters added in 2008. A total of sixteen blazars have been monitored during this time, most notably 3C279, 1510-089, 1611+343, 1652+398 (= Mrk 501), 1727+502, 3C 371, 1959+650, and 3C 454.3. The blazar 3C454.3 is particularly interesting, since it has undergone two outbursts during the monitoring period, in May 2005 and July 2007.


Investigating The AGN Population In Cluster Environments Across Different Wavelengths

Eleanor Byler1, D. Norman2
1Wellesley College, 2NOAO.

Exhibit Hall

Currently, there is no complete picture of AGN formation and evolution in galaxy clusters. A general understanding of the AGN population has been impeded by cluster and selection biases and recent studies have shown that there is a large population of obscured or optically unremarkable AGN in galaxy clusters. We used SDSS data to look at the AGN distribution in 12 clusters over a range of redshifts (z = 0.16 - 0.35) and compared the optical and X-ray AGN content with that of six ‘blank’ fields. We found that on average the cluster fields had a small optical AGN excess as compared to blank fields. The AGN population and distribution was also compared by cluster morphology, and non-virialized clusters were found to have a higher X-ray and optical AGN content than virialized clusters. We also compare our optical AGN to Gilmour et al.’s (2009) X-ray survey to compare assumptions made about cluster membership.
Byler was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program, which is funded by the National Science Foundation Research Experiences for Undergraduates Program and the Department of Defense ASSURE program through Scientific Program Order No. 13 (AST-0754223) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF.


Unusual Swift-BAT Detected AGN

James Hogg1, L. Winter1
1University of Colorado.

Exhibit Hall

The goals of our study were to analyze two odd AGN sources, NVSS 193013+341047 and IRAS 05218-1212, and determine if they were Compton-thick and low-redshift ERO analogs. The sources are strange because initial Swift XRT data lead us to believe the sources could be Compton-thick, typical of Seyfert 2 galaxies but they have broadlines in their optical spectra, typical of Seyfert 1 galaxies. These are two contradictory categorizations which made these sources very unique. In addition to the puzzling spectra, their SEDs are similar to the SED of a high redshift ERO and unlike things we typically see at their lower redshift. In order to study these sources further, we acquired and reduced higher quality XMM-Newton X-ray data. We then modeled the two spectra using XSPEC and learned that both sources had many complex components. From the higher quality data, we determined that they were heavily obscured, but not to the point of being considered Compton-thick. Both of the spectral fit models were heavily dependent on partial covering and reflection models. We found very high covering fractions and high column densities in both of our models, which was consistent with the galaxies being heavily obscured as we initially assumed. Further, we believe that future study of the sources as low-redshift ERO analogs can assist in better understanding of the early universe EROs we often see. If further study confirms the analogous relationship, these sources provide a great opportunity to add to our scientific knowledge about ERO evolution.


XMM Follow-Up Observations of Three Swift BAT-Selected Active Galactic Nuclei

Margaret Trippe1, C. Reynolds1, M. Koss1, R. Mushotzky1, L. Winter2
1University of Maryland, 2University of Colorado.

Exhibit Hall

We present follow-up XMM observations of three AGN that were selected from the Swift BAT hard X-ray survey as candidate Compton-thick AGN: ESO 417-G006, IRAS 05218-1212, and MCG -01-05-047. The XMM spectra, however, rule out reflection-dominated models based on the weakness of the observed Fe K-alpha lines. Instead, the spectra are well-fit by a model of a powerlaw continuum obscured by a Compton-thin absorber, plus a soft excess. This result is consistent with previous follow-up observations of two other flat-spectrum BAT detected AGN. Thus, out of the six AGN in the 22-month BAT catalog with flat Swift XRT spectra, all five that have had follow-up observations are not likely Compton-thick.


Variability in Quasar Broad Absorption Line Outflows

Daniel M. Capellupo1, F. Hamann1, J. C. Shields2, T. A. Barlow3, J. P. Halpern4, P. Rodriguez Hidalgo5
1University of Florida, 2Ohio University, 3California Institute of Technology, 4Columbia University, 5Pennsylvania State University.

Exhibit Hall

Broad absorption lines (BALs) in quasar spectra identify high velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. Studying the variability in these BALs can help us understand the structure, evolution, and basic physical properties of these outflows. We are conducting an ongoing BAL monitoring program that has produced over 160 spectra of 24 luminous quasars at z of 1.2-2.9, covering time-scales from 7 days to 7.7 years in the quasar rest-frame. We first investigate changes in the CIV 1550A BALs, and we see a variety of phenomena, including some absorption that either appeared or disappeared completely and other BALs that did not change at all over the whole observation period. The incidence of variability declines from 65% to 39% between the time domains of several years and a few months, and typically, only portions of the BAL troughs vary. We also compare the variability in the CIV 1550A BAL to the SiIV 1400A BAL to help distinguish between moving clouds and ionization changes as the cause of the variability. Using the multiple epochs of data from our program, we can characterize the variability over time in individual objects. Our most recent data covers the poorly sampled time domain of <1 month in the quasar rest-frame, which we can use to put constraints on the location of the outflowing gas.


Multi-frequency Optical-depth Maps And The Case For Free-free Absorption In Two Compact Symmetric Objects: 1321+410 And 0026+346

Thomas M. Perry1, J. M. Marr1, J. W. Read1, G. B. Taylor2
1Union College, 2University of New Mexico.

Exhibit Hall

We obtained VLBI observations at six frequencies of two Compact Symmetric Objects, 1321+410 and 0026+346. By comparing the lower frequency maps with spectral extrapolations of the higher frequency maps, we produced maps of the optical depth as a function of frequency.
The optical-depth maps of 1321+410 are strikingly uniform, consistent with a foreground screen of absorbing gas; the optical depths as a function of frequency are consistent with free-free absorption; and no net polarization was detected. We conclude that the case for free-free absorption in 1321+410 is strong.
The optical-depth maps of 0026+346 exhibit structure but the morphology does not correlate with that in the intensity maps, in conflict with that expected in the case of synchrotron self-absorption. No net polarization was detected. The frequency dependence of the optical depths does not fit well to a simple free-free absorption model, but this does not take into account possible structure in the absorbing gas on smaller scales. We conclude that free-free absorption by a thin amount of gas with structure on the scale of our maps and smaller is possible in 0026+346, although no definitive conclusion can be made.
A compact feature between the lobes in 0026+346 has an inverted spectrum even at the highest frequencies, suggesting that this component is synchrotron self-absorbed. We infer this to be the location of the core. We estimate an upper limit to the magnetic field in the core of 50 Gauss at a radius of 1 pc.
This research was supported by an award from the Research Corporation, a NASA NY Space Grant, and a Booth-Ferris Research Fellowship. The VLBA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.


Polarized Radio Source Counts and the Evolution of Galactic Magnetism

Christopher A. Hales1, B. M. Gaensler2, R. P. Norris3, E. Middelberg4
1The University of Sydney / Australia Telescope National Facility, Australia, 2The University of Sydney, Australia, 3Australia Telescope National Facility, Australia, 4University of Bochum, Germany.

Exhibit Hall

Polarized radio source counts can address important unsolved problems in astrophysics such as the fundamental origin and subsequent evolution of large-scale coherent magnetic fields observed in galaxies, which remain poorly constrained by observational data.
Here we present differential source counts of polarized radio galaxies using the Australia Telescope Compact Array, where we have imaged two 3.5 square degree fields at 1.4 GHz to a depth of ~20 microjanskys per beam in polarization. We discuss the nature of our faint polarized radio sources (which extend beyond z~2) using multiwavelength cross-identifications, and investigate the distribution of fractional polarization for our sources. Our polarized source counts can be used to place immediate constraints on evolutionary models of radio sources as well as the evolution of their magnetic fields with cosmic time.


A Stochastic Model for the Luminosity Fluctuations of Accreting Black Holes

Brandon C. Kelly1, M. Sobolewska1, A. Siemiginowska1
1Harvard-Smithsonian Center for Astrophysics.

Exhibit Hall

I will present a new statistical model for the X-ray fluctuations of accreting black holes. The model is formulated in the time domain via a set of stochastic differential equations, and fitting the model is done in the time domain via a likelihood-based approach. Out technique is not biased by red noise leak, aliasing, irregular sampling, and measurement error, and is computationally efficient. We apply our model to the RXTE+XMM X-ray lightcurves of 10 local AGN and show that our model is both a good fit to the data, and is able to recover previous results with increased accuracy. We find a tight anti-correlation between the black hole mass and the amplitude of the driving noise field in our model, which is proportional to the amplitude of the high frequency X-ray PSD, and we estimate that this parameter gives black hole mass estimates to within ~ 0.2 dex precision.


Modeling the Distribution of Linear and Circular Polarization from AGN Jet Cores

Christopher B. Wotta1, D. C. Homan1, M. L. Lister2
1Denison University, 2Purdue University.

Exhibit Hall

We present the results of full radiative transfer simulations of AGN jet cores to study the common physical properties of jets, such as their magnetic field structure and particle properties, that may be responsible for the observed distributions of polarization. To constrain these values we compare the results of our simulations to the first epoch MOJAVE observations of a complete, flux-density limited sample of AGN jets at 15 GHz. A key feature of the observational data is a lack of correlation between observed linear and circular polarization, and we found that this lack of correlation could be reproduced in our simulations if the circular polarization is produced stochastically, likely by Faraday conversion, in a magnetic field dominated by tangled components on a length scale of ~ 1/15 to 1/20 of a jet diameter. The tangled field components must also be shocked to explain the levels of observed linear polarization. We note that other possible explanations exist for the lack of observed correlation between linear and circular polarization, including un-resolved sub-structure and Faraday depolarization in external screens.
This work has been supported by National Science Foundation grants AST-0707693 and AST-0807860.


Hydrodynamic Simulations of Double-Bent Radio Sources

Jacob Miller1, B. Morsony1
1University of Wisconsin.

Exhibit Hall

Using three-dimensional hydrodynamic modeling, we simulate the development and evolution of Active Galactic Nuclei in galaxy groups in order to better understand the relationship between jet curvature and various properties of the Intergalactic Medium and of the AGN itself, with an emphasis on the use of radius of curvature as a density probe of the IGM.


Hubble/COS Observations of AGN Ionizing Continua

Matthew L. Stevans1, J. M. Shull1, C. W. Danforth1
1University of Colorado - Boulder.

Exhibit Hall

The high-throughput Cosmic Origins Spectrograph (COS) installed on the Hubble Space Telescope (HST) allows us to obtain high-quality UV spectra of active galactic nuclei (AGN), many of which served as background targets for studies of the low-redshift intergalactic medium (IGM). We present power-law continuum fits for a sample of 13 AGN with redshifts 0.0296 < z < 0.852, sufficient to explore their far ultraviolet (FUV) and extreme ultraviolet (EUV) continua. New spectra from HST/COS provide spectral coverage in the rest-frame Lyman continuum of AGN at z > 0.24, with high sensitivity and moderate resolution (20 km/s) in the G130M grating. This allows broad emission lines (Ne VIII, O IV) to be resolved. In cases when Far Ultraviolet Spectroscopic Explorer (FUSE) and International Ultraviolet Explorer (IUE) data are available, we create and fit composite spectra covering between 900 - 3300 Å; in the observed frame. We compare COS-based power-law spectra to these data. Describing the EUV continuum fluxes by a power-law spectrum, Fν = A να with index α, gives insight into the formation of emission lines, defines the "big blue bump" in the spectral energy distribution of AGNs, and constrains the ionization state of the IGM. We examine our results for correlations of spectral slope with redshift and compare our results to previous spectral fits from HST/FOS (Telfer et al. 2002, ApJ, 565, 773) and FUSE (Scott et al. 2004, ApJ, 615, 135). This work is supported by the COS-support grant from the STScI (NNX08-AC14G).  

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