J. Singal

University of Richmond, Richmond, Virginia, United States

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Publications (31)79.09 Total impact

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    J. Singal, A. 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.
    03/2014; 786(2).
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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.
    07/2013;
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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). · 6.73 Impact Factor
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    J. Singal, J. Langton, R. 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;
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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.
    11/2012;
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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.
    Proc SPIE 09/2012;
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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; · 6.73 Impact Factor
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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;
  • 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.
    05/2012;
  • 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.
    09/2011;
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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.
    09/2011;
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    J. Singal, V. Petrosian, M. Ajello
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    ABSTRACT: We present a determination of the distributions of photon spectral index and gamma-ray flux - the so called LogN-LogS relation - for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above +/- 20 degrees Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law with high and low indexes of -2.37 +/- 0.13 and -1.70 +/- 0.26, respectively, and the intrinsic photon index distribution can be represented by a Gaussian with mean of 2.41 +/- 0.13 and width of 0.25 +/- 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of Fermi blazars to the diffuse extragalactic gamma-ray background radiation. Under the assumption that the flux distribution of blazars continues to arbitrarily low fluxes, we calculate the best fit contribution of all blazars to the total extragalactic gamma-ray output to be 60%, with a large uncertainty.
    The Astrophysical Journal 06/2011; · 6.73 Impact Factor
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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 cosmic microwave background (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 excess radio rise of 54 ± 6 mK at 3.3 GHz in addition to a CMB temperature of 2.731 ± 0.004 K. Combining the ARCADE 2 data with data from the literature shows an excess power-law spectrum of T = 24.1 ± 2.1 (K) (ν/ν0)–2.599 ± 0.036 from 22 MHz to 10 GHz (ν0 = 310 MHz) in addition to a CMB temperature of 2.725 ± 0.001 K.
    The Astrophysical Journal 05/2011; 734(1):5. · 6.73 Impact Factor
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    ABSTRACT: We use absolutely calibrated data from the ARCADE 2 flight in 2006 July 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 C II emission. Both methods are consistent with a single power law over the frequency range 22 MHz to 10 GHz, with total Galactic emission toward the north polar cap T Gal = 10.12 ± 0.90 K and spectral index β = –2.55 ± 0.03 at reference frequency 0.31 GHz. Emission associated with the plane-parallel structure accounts for only 30% of the observed high-latitude sky temperature, with the residual in either a Galactic halo or an isotropic extragalactic background. 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 23 GHz.
    The Astrophysical Journal 05/2011; 734(1):4. · 6.73 Impact Factor
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    ABSTRACT: We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon flight of the ARCADE 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 an 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 2σ upper limits to CMB spectral distortions of μ < 6 × 10–4 and |Y ff| < 1 × 10–4. 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. This residual signal may be due to an underestimated galactic foreground contribution, an unaccounted for contribution of a background of radio sources, or some combination of both. The residual signal is consistent with emission in the form of a power law with amplitude 18.4 ± 2.1 K at 0.31 GHz and a spectral index of –2.57 ± 0.05.
    The Astrophysical Journal 05/2011; 734(1):6. · 6.73 Impact Factor
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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 extragalactic 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.
    The Astrophysical Journal 03/2011; 730(2):138. · 6.73 Impact Factor
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    ABSTRACT: We calculate simultaneously the radio and optical luminosity evolutions of quasars, and the distribution in radio loudness R defined as the ratio of radio and optical luminosities, using a flux limited data set containing 636 quasars with radio and optical fluxes from White et al. We first note that when dealing with multivariate data it is imperative to first determine the true correlations among the variables, not those introduced by the observational selection effects, before obtaining the individual distributions of the variables. We use the methods developed by Efron and Petrosian which are designed to obtain unbiased correlations, distributions, and evolution with redshift from a data set truncated due to observational biases. It is found that the population of quasars exhibits strong positive correlation between the radio and optical luminosities. With this correlation, whether intrinsic or observationally induced accounted for, we find that there is a strong luminosity evolution with redshift in both wavebands, with significantly higher radio than optical evolution. We also construct the local radio and optical luminosity functions and the density evolution. Finally, we consider the distribution of the radio loudness parameter R obtained from careful treatment of the selection effects and luminosity evolutions with that obtained from the raw data without such considerations. We find a significant difference between the two distributions and no clear sign of bi-modality in the true distribution for the range of R values considered. Our results indicate therefore, somewhat surprisingly, that there is no critical switch in the efficiency of the production of disk outflows/jets between very radio quiet and very radio loud quasars, but rather a smooth transition. Also, this efficiency seems higher for the high-redshift and more luminous sources in the considered sample.
    The Astrophysical Journal 01/2011; · 6.73 Impact Factor
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    ABSTRACT: We present a determination of the effects of including galaxy morphological parameters in photometric redshift estimation with an artificial neural network method. Neural networks, which recognize patterns in the information content of data in an unbiased way, can be a useful estimator of the additional information contained in extra parameters, such as those describing morphology, if the input data are treated on an equal footing. We use imaging and five band photometric magnitudes from the All-wavelength Extended Groth Strip International Survey (AEGIS). It is shown that certain principal components of the morphology information are correlated with galaxy type. However, we find that for the data used the inclusion of morphological information does not have a statistically significant benefit for photometric redshift estimation with the techniques employed here. The inclusion of these parameters may result in a tradeoff between extra information and additional noise, with the additional noise becoming more dominant as more parameters are added.
    Publications of the Astronomical Society of the Pacific 01/2011; 123(903):615-621. · 3.69 Impact Factor
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    ABSTRACT: We report on the camera materials test chamber, a multivessel apparatus that analyzes the outgassing consequences of candidate materials for use in the vacuum cryostat of a new telescope camera. The system measures the outgassing products and rates of samples of materials at different temperatures and collects films of outgassing products to measure the effects on light transmission in six optical bands. The design of the apparatus minimizes potential measurement errors introduced by background contamination.
    The Review of scientific instruments 02/2010; 81(2):025101. · 1.52 Impact Factor
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    ABSTRACT: The recently characterized Cosmic Radio Background provides a unique perspective in which to study the nonthermal universe, including properties and cosmological evolution of active galaxies and their outflows. As much as 1/3 of the total intensity of the radio background can be due to emission resulting from classical jet processes in radio galaxies and radio quiet quasars. Furthermore, weak jet activity in Seyferts and ordinary star-forming galaxies may also be important.
    International Journal of Modern Physics D 01/2010; 19(06):965-969. · 1.03 Impact Factor

Publication Stats

215 Citations
79.09 Total Impact Points

Institutions

  • 2013–2014
    • University of Richmond
      • Department of Physics
      Richmond, Virginia, United States
  • 2010–2013
    • Stanford University
      • • Department of Physics
      • • Kavli Institute for Particle Physics and Cosmology (KIPAC)
      Palo Alto, California, United States
  • 2005–2006
    • University of California, Santa Barbara
      • Department of Physics
      Santa Barbara, CA, United States