119109461
Comparing the light curves of simulated Type Ia Supernovae with observations using data-driven models
We propose a robust, quantitative method to compare the synthetic light curves of a Type Ia supernova (SN Ia) explosion model with a large set of observed SNe Ia, and derive a figure of merit for the explosion model's agreement with observations. The synthetic light curves are fit with the data-driven model SALT2 which returns values for stretch, color, and magnitude at peak brightness, as well as a goodness-of-fit parameter. Each fit is performed multiple times with different choices of filter bands and epoch range in order to quantify the systematic uncertainty on the fitted parameters. We use a parametric population model for the distribution of observed SN Ia parameters from large surveys, and extend it to represent red, dim, and bright outliers found in a low-redshift SN Ia data set. We discuss the potential uncertainties of this population model and find it to be reliable given the current uncertainties on cosmological parameters. Using our population model, we assign each set of fitted parameters a likelihood of being observed in nature, and a figure of merit based on this likelihood. We define a second figure of merit based on the quality of the light curve fit, and combine the two measures into an overall figure of merit for each explosion model. We compute figures of merit for a variety of one-, two-, and three-dimensional explosion models and show that our evaluation method allows meaningful inferences across a wide range of light curve quality and fitted parameters.
14117521
Evidence for reionization at z ∼ 6: Detection of a gunn-peterson trough in a z = 6.28 quasar
We present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Ly? absorption in the spectra of these quasars evolves strongly with redshift. To z ~ 5.7, the Ly? absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest-redshift object, SDSSp J103027.10+052455.0 (z = 6.28), the average transmitted flux is 0.0038 ? 0.0026 times that of the continuum level over 8450 ? 20, on the optical depth to Ly? absorption at z = 6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Ly? forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z ~ 5 to 6, and the universe is approaching the reionization epoch at z ~ 6.
16569483
The Extinction toward the GRB 970228 Field
We determine the local Galactic extinction toward the field of gamma-ray burst GRB 970228 using a variety of methods. We develop a maximum-likelihood method for measuring the extinction that compares galaxy counts in different bands in the field of interest to those in a field of known extinction, and we apply this method to the GRB 970228 field. We also measure the extinction by comparing the observed broadband colors of stars in the GRB 970228 field to the colors of library spectra of the same spectral type. Finally, we estimate the extinction using the neutral hydrogen column density and the amount of infrared dust emission toward this field. Combining the results of these methods, we find a best-fit Galactic extinction in the optical of AV = 1.09, which implies that the intrinsic afterglow of GRB 970228 is significantly brighter and bluer than it appears.
121347557
Evidence that gamma-ray bursts repeat and are Galactic in origin
Abstract We describe work which has provided evidence that there are two distinct classes of γ-ray bursts, that the bursts repeat, and that they are Galactic in origin.
14195621
Likelihood methods and classical burster repetition
We develop a likelihood methodology which can be used to search for evidence of burst repetition in the BATSE catalog, and to study the properties of the repetition signal. We use a simplified model of burst repetition in which a number Nr of sources which repeat a fixed number of times Nrep are superposed upon a number Nnr of non‐repeating sources. The instrument exposure is explicitly taken into account. By computing the likelihood for the data, we construct a probability distribution in parameter space that may be used to infer the probability that a repetition signal is present, and to estimate the values of the repetition parameters. The likelihood function contains contributions from all the bursts, irrespective of the size of their positional errors—the more uncertain a burst’s position is, the less constraining is its contribution. Thus this approach makes maximal use of the data, and avoids the ambiguities of sample selection associated with data cuts on error circle size. We present the results ...
14468375
High-energy observations of XRF 030723: Evidence for an off-axis gamma-ray burst?
We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-ray Monitor (WXM) and French Gamma Telescope observations of XRF 030723 along with observations of the XRF afterglow made using the 6.5 m Magellan Clay telescope and Chandra. The observed peak energy E of the νFν burst spectrum is found to lie within (or below) the WXM 2-25 keV passband at 98.5% confidence, and no counts are detected above 30 keV. Our best-fit value is E = 8.4 keV. The ratio of X-ray to γ-ray flux for the burst follows a correlation found for GRBs observed with HETE-2, and the duration of the burst is similar to that typical of long-duration GRBs. If we require that the burst isotropic equivalent energy Eiso and Epk satisfy the relation discovered by Amati et al. (2002), a redshift of z = 0.38 can be determined, in agreement with constraints determined from optical observations. We are able to fit the X-ray afterglow spectrum and to measure its temporal fade. Although the best-fit fade is shallower than the concurrent fade in the optical, the spectral similarity between the two bands indicates that the X-ray fade may actually trace the optical fade. If this is the case, the late-time rebrightening observed in the optical cannot be due to a supernova bump. We interpret the prompt and afterglow X-ray emission as arising from a jetted GRB observed off-axis and possibly viewed through a complex circumburst medium that is due to a progenitor wind.
6075521
Search for compositeness, leptoquarks and large extra dimensions in eq contact interactions at HERA
Abstract The reaction e + p → e + X is studied with the H1 detector at Hera . The data cover momentum transfers Q 2 between 200 GeV 2 and 30 000 GeV 2 and correspond to an integrated luminosity of 35.6 pb −1 . The differential cross section d σ /d Q 2 is compared to the Standard Model expectation for neutral current scattering and analysed to search for ( e e)( q q) contact interactions. No evidence for new phenomena is observed. The results are used to set limits on scales within models of electron–quark compositeness, quark form factors and the exchange of virtual heavy leptoquarks. A search for gravitational effects mediated through the exchange of virtual gravitons which propagate into large extra dimensions is presented.
123599707
Measurement of open beauty production at HERA
Abstract The first observation of open b production in ep collisions is reported. An event sample containing muons and jets has been selected which is enriched in semileptonic b quark decays. The visible cross section σ(ep → b b X → μ X′) for Q 2 GeV 2 , 0.1 0.176 ± 0.016 (stat.) +0.026 −0.017 (syst.) nb for the muons to be detected in the range 35° p ⊥ μ >2.0 GeV in the laboratory frame. The expected visible cross section based on a NLO QCD calculation is 0.104 ± 0.017 nb . The cross sections for electroproduction with Q 2 GeV 2 and photoproduction are derived from the data and found to be σ(ep→eb b X)=7.1±0.6 (stat.) +1.5 −1.3 (syst.) nb and σ(γp→b b X)=111 ± 10 (stat.) +23 −20 (syst.) nb at an average 〈W γp 〉∼180 GeV , respectively.
122848941
Deep inelastic inclusive e p scattering at low x and a determination of alpha(s)
A precise measurement of the inclusive deep-inelastic \(e^+ p\) scattering cross section is reported in the kinematic range \(1.5 \le Q^2 \le 150\) GeV\(^2\) and \( 3 \cdot 10^{-5} \le x \le 0.2\). The data were recorded with the H1 detector at HERA in 1996 and 1997, and correspond to an integrated luminosity of 20 pb\(^{-1}\). The double differential cross section, from which the proton structure function \(\) and the longitudinal structure function \(F_L(x,Q^2)\) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured derivative \((\partial F_2(x,Q^2) / \partial \ln Q^2)_x \) is observed to rise continuously towards small x for fixed \(Q^2\). The cross section data are combined with published H1 measurements at high \(Q^2\) for a next-to-leading order DGLAP QCD analysis. The H1 data determine the gluon momentum distribution in the range \(3 \cdot 10^{-4} \le x \le 0.1\) to within an experimental accuracy of about 3% for \(Q^2 =20\) GeV\(^2\). A fit of the H1 measurements and the \(\mu p \) data of the BCDMS collaboration allows the strong coupling constant \(\alpha_s\) and the gluon distribution to be simultaneously determined. A value of \(\alpha_s (M_Z^2) =0.1150 \pm 0.0017 (exp)^{+0.0009}_{-0.0005} (model)\) is obtained in NLO, with an additional theoretical uncertainty of about \(\pm 0.005\), mainly due to the uncertainty of the renormalisation scale.
9067395
Measurement of dijet electroproduction at small jet separation
Deep-inelastic scattering data in the range 150 < Q^2 < 35000 GeV^2 are used to investigate the minimum jet separation necessary to allow accurate description of the rate of dijet production using next-to-leading order perturbative QCD calculations. The required jet separation is found to be small, allowing about 1/3 of DIS data to be classified as dijet, as opposed to approximately 1/10 with more typical jet analyses. A number of precision measurements made using this dijet sample are well described by the calculations. The data are also described by the combination of leading order matrix elements and parton showers, as implemented in the QCD based Monte Carlo model RAPGAP.
13227053
Search for leptoquark bosons in ep collisions at HERA
A search for scalar and vector leptoquarks coupling to first generation fermions is performed using the e(+) p and e(-) p scattering data collected by the H1 experiment between 1994 and 2000. The data correspond to a total integrated luminosity of 117 pb(-1). No evidence for the direct or indirect production of such particles is found in data samples with a large transverse momentum final state electron or with large missing transverse momentum. Constraints on leptoquark models are established. For leptoquark couplings of electromagnetic strength, leptoquarks with masses up to 275-325 GeV are ruled out at 95% confidence level. These limits improve and supercede earlier H1 limits based on subsamples of the data used here.