J. Singal

University of Richmond, Ричмонд, Virginia, United States

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Publications (40)86.06 Total impact

  • Source
    J. Singal · A. Kogut · E. Jones · H. Dunlap
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    ABSTRACT: We use surface brightness contour maps of nearby edge-on spiral galaxies to determine whether extended bright radio halos are common. In particular, we test a recent model of the spatial structure of the diffuse radio continuum by Subrahmanyan and Cowsik which posits that a substantial fraction of the observed high-latitude surface brightness originates from an extended Galactic halo of uniform emissivity. Measurements of the axial ratio of emission contours within a sample of normal spiral galaxies at 1500 MHz and below show no evidence for such a bright, extended radio halo. Either the Galaxy is atypical compared to nearby quiescent spirals or the bulk of the observed high-latitude emission does not originate from this type of extended halo.
    01/2015; 799(1). DOI:10.1088/2041-8205/799/1/L10
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    Vahe Petrosian · Jack Singal
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    ABSTRACT: Active galactic nuclei jets are detected via their radio and/or gamma-ray emissions while the accretion disks are detected by their optical and UV radiation. Observations of the radio and optical luminosities show a strong correlation between the two luminosities. However, part of this correlation is due to the redshift or distances of the sources that enter in calculating the luminosities from the observed fluxes and part of it could be due to the differences in the cosmological evolution of luminosities. Thus, the determination of the intrinsic correlations between the luminosities is not straightforward. It is affected by the observational selection effects and other factors that truncate the data, sometimes in a complex manner (e.g. Antonucci (2011) and Pavildou et al. (2010)). In this paper we describe methods that allow us to determine the evolution of the radio and optical luminosities, and determine the true intrinsic correlation between the two luminosities. We find a much weaker correlation than observed and sub-linear relations between the luminosities. This has a significant implication for jet and accretion disk physics.
    Proceedings of the International Astronomical Union 12/2014; 10(S313). DOI:10.1017/S1743921315002458
  • Vahe Petrosian · Jack Singal · Lukasz Stawarz
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    ABSTRACT: The dichotomy of jet dominated versus accretion disk dominated AGNs or “radio-loud” vs “radio-quiet” quasars can be investigated by a simultaneous determination of the relative shape and evolution of the radio and optical luminosity functions, and the distribution of the radio loudness R defined as the ratio of radio to optical luminosities. This can be done from a multivariate data set containing observed fluxes, redshift, spectra, etc. We emphasize that when dealing with a multivariate data set it is imperative to first determine the true correlations, not those introduced by the observational selection effects, among the variables (e.g. Luminosity-luminosity, redshift-luminosity) before obtaining the individual distributions of the variables (e.g. Luminosity functions and density evolution). We use data from several sources including the SDSS (Data Release 7) and FIRST radio catalogs, with well defined optical and radio flux limits, and employ the non-parametric methods developed by Efron and Petrosian, designed to obtain unbiased correlations, distributions and evolution with redshift from data truncated due to observational biases. We determine the density and the luminosity evolutions in both wavebands, which shows significantly higher radio than optical luminosity evolution. From these we obtain true distribution of the radio loudness parameter which shows no sign of bi-modality and indicates that quasars were more radio loud at earlier epochs.
    Proceedings of the International Astronomical Union 10/2014; 9(S304):172. DOI:10.1017/S174392131400369X
  • Jack Singal · Allan Ko · Vahe Petrosian
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    ABSTRACT: We discuss an analysis of the redshift evolutions and distributions of the gamma-ray luminosity and photon spectral index of flat spectrum radio quasar (FSRQ) type blazars. We utilize data from the Fermi Gamma-ray Space Telescope, with redshfits as determined from optical spectroscopy by Shaw et al. We find that FSRQs have evolved significantly in luminosity but negligibly in photon index, and contribute in toto roughly 20% of the total gamma-ray output of the Universe.
    Proceedings of the International Astronomical Union 10/2014; 9(S304):149-152. DOI:10.1017/S1743921314003597
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    J. Singal · Allan Ko · V. Petrosian
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    ABSTRACT: We present the redshift evolutions and distributions of the gamma-ray luminosity and photon spectral index of flat spectrum radio quasar (FSRQ) type blazars, using non-parametric methods to obtain the evolutions and distributions directly from the data. The sample we use for analysis consists of almost all FSRQs observed with a greater than approximately 7 sigma detection threshold in the first year catalog of the Fermi Gamma-ray Space Telescope's Large Area Telescope, with redshfits as determined from optical spectroscopy by Shaw et al. We find that FSQRs undergo rapid gamma-ray luminosity evolution, but negligible photon index evolution, with redshift. With these evolutions accounted for we determine the density evolution and luminosity function of FSRQs, and calculate their total contribution to the extragalactic gamma-ray background radiation, resolved and unresolved, which is found to be 16(+10/-4)%, in agreement with previous studies.
    The Astrophysical Journal 03/2014; 786(2). DOI:10.1088/0004-637X/786/2/109 · 6.28 Impact Factor
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    ABSTRACT: Gamma-ray bursts (GRBs), which have been observed up to redshifts $z \approx 9.5$ can be good probes of the early universe and have the potential of testing cosmological models. The analysis by Dainotti of GRB Swift afterglow lightcurves with known redshifts and definite X-ray plateau shows an anti-correlation between the \underline{rest frame} time when the plateau ends (the plateau end time) and the calculated luminosity at that time (or approximately an anti-correlation between plateau duration and luminosity). We present here an update of this correlation with a larger data sample of 101 GRBs with good lightcurves. Since some of this correlation could result from the redshift dependences of these intrinsic parameters, namely their cosmological evolution we use the Efron-Petrosian method to estimate the luminosity and time evolution and to correct for this effects to determine the intrinsic nature of this correlation.
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    ABSTRACT: Gamma-ray bursts (GRBs), which have been observed up to redshifts z approx 9.5 can be good probes of the early universe and have the potential of testing cosmological models. The analysis by Dainotti of GRB Swift afterglow lightcurves with known redshifts and definite X-ray plateau shows an anti-correlation between the rest frame time when the plateau ends (the plateau end time) and the calculated luminosity at that time (or approximately an anti-correlation between plateau duration and luminosity). We present here an update of this correlation with a larger data sample of 101 GRBs with good lightcurves. Since some of this correlation could result from the redshift dependences of these intrinsic parameters, namely their cosmological evolution we use the Efron-Petrosian method to reveal the intrinsic nature of this correlation. We find that a substantial part of the correlation is intrinsic and describe how we recover it and how this can be used to constrain physical models of the plateau emission, whose origin is still unknown. The present result could help clarifing the debated issue about the nature of the plateau emission.
    The Astrophysical Journal 07/2013; 774(2). DOI:10.1088/0004-637X/774/2/157 · 6.28 Impact Factor
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    Jack Singal · J. Brian Langton · Rafe Schindler
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    ABSTRACT: We discuss a novel use of the Geant4 simulation toolkit to model molecular transport in a vacuum environment, in the molecular flow regime. The Geant4 toolkit was originally developed by the high energy physics community to simulate the interactions of elementary particles within complex detector systems. Here its capabilities are utilized to model molecular vacuum transport in geometries where other techniques are impractical. The techniques are verified with an application representing a simple vacuum geometry that has been studied previously both analytically and by basic Monte Carlo simulation. We discuss the use of an application with a very complicated geometry, that of the Large Synoptic Survey Telescope camera cryostat, to determine probabilities of transport of contaminant molecules to optical surfaces where control of contamination is crucial.
    02/2013; DOI:10.1142/S1793962313500256
  • J. Singal · L. Stawarz · A. Lawrence · V. Petrosian
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    ABSTRACT: We investigate possible origins of the extragalactic radio background reported by the ARCADE 2 collaboration. The surface brightness of the background is several times higher than that which would result from currently observed radio sources. We consider contributions to the background from diffuse synchrotron emission from clusters and the intergalactic medium, previously unrecognized flux from low surface brightness regions of radio sources, and faint point sources below the flux limit of existing surveys. By examining radio source counts available in the literature, we conclude that most of the radio background is produced by radio point sources that dominate at sub µJy fluxes. We show that a truly diffuse background produced by electrons far from galaxes is ruled out because such energetic electrons would overproduce the obserevd X-ray/γ-ray background through inverse Compton scattering of the other photon fields. Unrecognized flux from low surface brightness regions of extended radio sources, or moderate flux sources missed entirely by radio source count surveys, cannot explain the bulk of the observed background, but may contribute as much as 10%. We consider both radio supernovae and radio quiet quasars as candidate sources for the background, and show that both fail to produce it at the observed level because of insufficient number of objects and total flux, although radio quiet quasars contribute at the level of at least a few percent. We conclude that the most important population for production of the background is likely ordinary starforming galaxies above redshift 1 characterized by an evolving radio far-infrared correlation, which increases toward the radio loud with redshift.
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    ABSTRACT: We use absolutely calibrated data from the ARCADE 2 flight in July 2006 to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free-free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index βsynch = −2.5 ± 0.1, with free-free emission contributing 0.10 ± 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc(|b|) dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of Cii emission. Both methods are consistent with a single power-law over the frequency range 22 MHz to 10 GHz, with total Galactic emission towards the north polar cap TGal = 0.498 ±0.028 K and spectral index β = −2.55 ± 0.03 at reference frequency 1 GHz. The well calibrated ARCADE 2 maps provide a new test for spinning dust emission, based on the integrated intensity of emission from the Galactic plane instead of cross-correlations with the thermal dust spatial morphology. The Galactic plane intensity measured by ARCADE 2 is fainter than predicted by models without spinning dust, and is consistent with spinning dust contributing 0.4 ± 0.1 of the Galactic plane emission at 22 GHz.
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    ABSTRACT: The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure the radiometric temperature of the cosmic microwave background and Galactic and extra-Galactic emission at six frequencies from 3 to 90 GHz. ARCADE 2 utilizes a double-nulled design where emission from the sky is compared to that from an external cryogenic full-aperture blackbody calibrator by cryogenic switching radiometers containing internal blackbody reference loads. In order to further minimize sources of systematic error, ARCADE 2 features a cold fully open aperture with all radiometrically active components maintained at near 2.7 K without windows or other warm objects, achieved through a novel thermal design. We discuss the design and performance of the ARCADE 2 instrument in its 2005 and 2006 flights. Subject headings: instrumentation: detectors – cosmic microwave background – radio continuum: galaxies 1.
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    ABSTRACT: The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an in situ reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the CMB temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an extragalactic rise of 50 ± 7 mK at 3.3 GHz in addition to a CMB temperature of 2.730 ±.004 K. Combining the ARCADE 2 data with data from the literature shows a background power law spectrum of T = 1.26± 0.09 [K] (ν/ν0) −2.60±0.04 from 22 MHz to 10 GHz (ν0 = 1 GHz) in addition to a CMB temperature of 2.725 ±.001 K.
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    ABSTRACT: We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon flight of the AR-CADE 2 instrument, along with previous measurements at other frequencies, to constrain models of extragalactic emission. Such emission is a combination of the Cosmic Microwave Background (CMB) monopole, Galactic foreground emission, the integrated contribution of radio emission from external galaxies, any spectral distortions present in the CMB, and any other extragalactic source. After removal of estimates of foreground emission from our own Galaxy, and the estimated contribution of external galaxies, we present fits to a combination of the flat-spectrum CMB and potential spectral distortions in the CMB. We find 2 σ upper limits to CMB spectral distortions of µ < 5.8 × 10 −5 and |Yff | < 6.2 × 10 −5. We also find a significant detection of a residual signal beyond that which can be explained by the CMB plus the integrated radio emission from galaxies estimated from existing surveys. After subtraction of an estimate of the contribution of discrete radio sources, this unexplained signal is consistent with extragalactic emission in the form of a power law with amplitude 1.06±0.11 K at 1 GHz and a spectral index of −2.56 ± 0.04.
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    ABSTRACT: This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST dark energy data analysis. The technical working groups make the connection between dark energy science and the LSST system. The working groups have close linkages, especially through the use of the photon simulations to study the impact of instrument design and survey strategy on analysis methodology and cosmological parameter estimation. The white paper describes several high priority tasks identified by each of the 16 working groups. Over the next three years these tasks will help prepare for LSST analysis, make synergistic connections with ongoing cosmological surveys and provide the dark energy community with state of the art analysis tools. Members of the community are invited to join the LSST DESC, according to the membership policies described in the white paper. Applications to sign up for associate membership may be made by submitting the Web form at http://www.slac.stanford.edu/exp/lsst/desc/signup.html with a short statement of the work they wish to pursue that is relevant to the LSST DESC.
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    ABSTRACT: The design of the Large Synoptic Survey Telescope (LSST) requires a camera system of unprecedented size and complexity. Achieving the science goals of the LSST project, through design, fabrication, integration, and operation, requires a thorough understanding of the camera performance. Essential to this effort is the camera modeling which defines the effects of a large number of potential mechanical, optical, electronic or sensor variations which can only be captured with sophisticated instrument modeling that incorporates all of the crucial parameters. This paper presents the ongoing development of LSST camera instrument modeling and details the parametric issues and attendant analysis involved with this modeling.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; DOI:10.1117/12.926611 · 0.20 Impact Factor
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    J. Singal · V. Petrosian · L. Stawarz · A. Lawrence
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    ABSTRACT: We determine the radio and optical luminosity evolutions and the true distribution of the radio loudness parameter R, defined as the ratio of the radio to optical luminosity, for a set of more than 5000 quasars combining SDSS optical and FIRST radio data. We apply the method of Efron and Petrosian to access the intrinsic distribution parameters, taking into account the truncations and correlations inherent in the data. We find that the population exhibits strong positive evolution with redshift in both wavebands, with somewhat greater radio evolution than optical. With the luminosity evolutions accounted for, we determine the density evolutions and local radio and optical luminosity functions. The intrinsic distribution of the radio loudness parameter R is found to be quite different than the observed one, and is smooth with no evidence of a bi-modality in radio loudness. The results we find are in general agreement with the previous analysis of Singal et al. 2011 which used POSS-I optical and FIRST radio data.
    The Astrophysical Journal 07/2012; 764(1). DOI:10.1088/0004-637X/764/1/43 · 6.28 Impact Factor
  • Jack Singal · V. Petrosian
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    ABSTRACT: We present a new determination of the radio and optical luminosity evolution with redshift of quasars from data that is flux-limited in both bands. The methods employed are non-parametric and can deal with the detection selection biases to determine the intrinsic distributions directly from the observational data. Using data from several sources including the SDSS Data Release 7 quasar catalog, we show that as a population quasars were more radio loud at earlier epochs, with implications for the evolving physics of AGN and the contribution of quasars as a source class to the cosmic radio background radiation. Quantifying the differential evolutions allows a reconstruction of the intrinsic distribution of radio loudness as a function of redshift, and the reconstructed intrinsic distribution differs markedly from the observed one, in particular favoring the conclusion that quasars form a continuum rather than distinct radio loud and radio quiet sub-populations.
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    ABSTRACT: Gamma -ray bursts (GRBs) observed up to redshifts z>9.3 are fascinating objects to study due to their still unexplained relativistic outburst mechanisms and a possible probes of the early universe. Our analysis of a new and larger (100) sample of GRB afterglows with known redshifts and definite plateau confirms the correlation found earlier (Dainotti 2010) between the break time at the end of plateau T_a and the plateau luminosity L*_X(T_a) (called hereafter L^*_a) with a higher value of the Spearman correlation coefficient. Here we present a new test of the sample using the non-parametric method of Efron & Petrosian (1992) to determine the intrinsic correlation corrected for possible correlation induced due to large redshift range of the sample. In addition with this method we determine the redshift evolution in both the luminosity and time T_a. This test shows that the observed correlation is not redshift induced but it is intrinsic. The novelty of this approach is that the Efron & Petrosian method has been applied for the first time to a two parameters correlation that involves not only luminosities, but also time. Even though this correlation is not sufficiently tight to allow us to determine the distance for given $T_a$ Flux, and spectral index, nevertheless it can be useful to constrain physical models for the plateau emission.
    Proceedings of the International Astronomical Union 05/2012; DOI:10.1017/S1743921312013002
  • Vahe Petrosian · J. Singal · M. Ajello
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    ABSTRACT: We present a determination of the distributions of gamma-ray flux and photon index for the 352 blazars detected above ±20º Galactic latitude by the Fermi-LAT in its first year catalog. Because of the observational selection effects the data is truncated severely. We use the methods developed by Efron and Petrosian to reconstruct the intrinsic distribution of fluxes (the so-called LogN-LogS relation) and the true distribution of spectral index. Our method accounts robustly for the selection biases in the data and determines the correlations among the variables. Given the flux distribution, we estimate the contribution of blazars to the extragalactic gamma-ray background.
  • Vahe Petrosian · J. Singal
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    ABSTRACT: We use non-parametric methods developed by Efron and Petrosian for simultaneous determination of the radio and optical luminosity functions, the correlations and cosmological evolutions of quasars,using a flux limited data set containing 636 quasars with radio and optical fluxes. From these we determine the distribution and evolution of of the radio loudness parameter R (the ratio of radio to optical luminosity). These methods are designed to obtain unbiased correlations, distributions, and evolution with redshift from a data set truncated due to observational biases. We find that there is a strong luminosity evolution with redshift in both wavebands, with significantly higher radio than optical evolution. We also find a strong density evolution. We compare the distribution of the radio loudness obtained from careful treatment of the selection effects and luminosity evolutions with that obtained from the raw data without such considerations, and find a significant difference between the two distributions and find no clear sign of bi-modality in the true distribution.

Publication Stats

297 Citations
86.06 Total Impact Points

Institutions

  • 2013–2015
    • University of Richmond
      • Department of Physics
      Ричмонд, Virginia, United States
  • 2010–2012
    • Stanford University
      Palo Alto, California, United States
  • 2005–2007
    • University of California, Santa Barbara
      • Department of Physics
      Santa Barbara, California, United States