# Posts Tagged confidence level

## Today's Postings

### Estimating the uncorrelated dark energy evolution in the Planck era

The equation of state (EOS), $w(z)$, is the most important parameter of dark energy. We reconstruct the evolution of this EOS in a model-independent way using the latest cosmic microwave background (CMB) data from Planck and other observations, such as type Ia supernovae (SNe Ia), the baryonic acoustic oscillation measurements (SDSS, 6dF, BOSS, and WiggleZ), and the Hubble parameter value $H(z)$. The results show that the EOS is consistent with the cosmological constant at the $2\sigma$ confidence level, not preferring a dynamical dark energy. The uncorrelated EOS of dark energy constraints from Planck CMB data are much tighter than those from the WMAP 9-year CMB data.

### Search for a Stochastic Gravitational-wave Background using a pair of Torsion-bar Antennas

We have set a new upper limit on the stochastic gravitational wave background (SGWB) using two prototype Torsion-bar Antennas (TOBAs). TOBA is a low-frequency gravitational-wave detector with bar-shaped test masses rotated by the tidal force of gravitational waves. As a result of simultaneous 7-hour observations with TOBAs in Tokyo and Kyoto in Japan, our upper limit with a confidence level of 95% is $\Omega_{\rm gw}h_0^2 < 1.9 \times 10^{17}$ at 0.035 – 0.830 Hz, where $h_{0}$ is the Hubble constant in units of 100 km/s/Mpc and $\Omega_{\rm gw}$ is the gravitational wave energy density per logarithmic frequency interval in units of the closure density. We successfully updated the upper limit and extended the explored frequency band.

### Search for a Stochastic Gravitational-wave Background using a pair of Torsion-bar Antennas [Cross-Listing]

We have set a new upper limit on the stochastic gravitational wave background (SGWB) using two prototype Torsion-bar Antennas (TOBAs). TOBA is a low-frequency gravitational-wave detector with bar-shaped test masses rotated by the tidal force of gravitational waves. As a result of simultaneous 7-hour observations with TOBAs in Tokyo and Kyoto in Japan, our upper limit with a confidence level of 95% is $\Omega_{\rm gw}h_0^2 < 1.9 \times 10^{17}$ at 0.035 – 0.830 Hz, where $h_{0}$ is the Hubble constant in units of 100 km/s/Mpc and $\Omega_{\rm gw}$ is the gravitational wave energy density per logarithmic frequency interval in units of the closure density. We successfully updated the upper limit and extended the explored frequency band.

### Analysis of High Cadence In-Situ Solar Wind Ionic Composition Data Using Wavelet Power Spectra Confidence Levels

The variability inherent in solar wind composition has implications for the variability of the physical conditions in its coronal source regions, providing constraints on models of coronal heating and solar wind generation. We present a generalized prescription for constructing a wavelet power significance measure (confidence level) for the purpose of characterizing the effects of missing data in high cadence solar wind ionic composition measurements. We describe the data gaps present in the 12-minute ACE/SWICS observations of O7+/O6+ during 2008. The decomposition of the in-situ observations into a good measurement’ and a no measurement’ signal allows us to evaluate the performance of a filler signal, i.e., various prescriptions for filling the data gaps. We construct Monte Carlo simulations of synthetic O7+/O6+ composition data and impose the actual data gaps that exist in the observations in order to investigate two different filler signals: one, a linear interpolation between neighboring good data points, and two, the constant mean value of the measured data. Applied to these synthetic data plus filler signal combinations, we quantify the ability of the power spectra significance level procedure to reproduce the ensemble-averaged time-integrated wavelet power per scale of an ideal case, i.e. the synthetic data without imposed data gaps. Finally, we present the wavelet power spectra for the O7+/O6+ data using the confidence levels derived from both the Mean Value and Linear Interpolation data gap filling signals and discuss the results.

### Weighing "El Gordo" with a Pecision Scale: Hubble Space Telescope Weak-lensing Analysis of the Merging Galaxy Cluster ACT-CL J0102-4915 at z=0.87

(Abridged) We present a HST weak-lensing study of the merging galaxy cluster "El Gordo" (ACT-CL J0102-4915) at z=0.87 discovered by the Atacama Cosmology Telescope collaboration as the strongest SZ decrement in its ~1000 sq. deg survey. Our weak-lensing analysis confirms that ACT-CL J0102-4915 is indeed an extreme system consisting of two massive (~10^15 Msun each) subclusters with a projected separation of ~0.7 Mpc. This binary mass structure revealed by our lensing study is consistent with the cluster galaxy distribution and the dynamical study carried out with 89 spectroscopic members. We estimate the mass of ACT-CL J0102-4915 by simultaneously fitting two axisymmetric NFW profiles allowing their centers to vary. Our MCMC analysis shows that the masses of the northwestern (NW) and the southeastern (SE) components are M200c=(1.40+-0.31) x 10^15 Msun and (0.75+-0.17) x 10^15 Msun, respectively. The lensing-based velocity dispersions are consistent with their spectroscopic measurements. The centroids of both components are tightly constrained (~4") and close to the optical luminosity centers. The X-ray and mass peaks are spatially offset by ~13" (~100 kpc), which is significant at the ~3 sigma confidence level and confirms that the baryonic and dark matter in this cluster are disassociated. The dark matter peak, however, does not lead the gas peak in the direction expected if we are viewing the cluster soon after first core passage during a high speed merger. Under the assumption that the merger is happening in the plane of the sky, extrapolation of the two NFW halos to a radius r200a=2.4 Mpc yields a combined mass of M200a=(3.10+-0.70) x 10^15 Msun. This extrapolated total mass is consistent with our two-component-based dynamical analysis and previous X-ray measurements, projecting ACT-CL J0102-4915 to be the most massive cluster at z>0.6 known to date.

### Weighing "El Gordo" with a Precision Scale: Hubble Space Telescope Weak-lensing Analysis of the Merging Galaxy Cluster ACT-CL J0102-4915 at z=0.87 [Replacement]

(Abridged) We present a HST weak-lensing study of the merging galaxy cluster "El Gordo" (ACT-CL J0102-4915) at z=0.87 discovered by the Atacama Cosmology Telescope collaboration as the strongest SZ decrement in its ~1000 sq. deg survey. Our weak-lensing analysis confirms that ACT-CL J0102-4915 is indeed an extreme system consisting of two massive (~10^15 Msun each) subclusters with a projected separation of ~0.7 Mpc. This binary mass structure revealed by our lensing study is consistent with the cluster galaxy distribution and the dynamical study carried out with 89 spectroscopic members. We estimate the mass of ACT-CL J0102-4915 by simultaneously fitting two axisymmetric NFW profiles allowing their centers to vary. Our MCMC analysis shows that the masses of the northwestern (NW) and the southeastern (SE) components are M200c=(1.40+-0.31) x 10^15 Msun and (0.75+-0.17) x 10^15 Msun, respectively. The lensing-based velocity dispersions are consistent with their spectroscopic measurements. The centroids of both components are tightly constrained (~4") and close to the optical luminosity centers. The X-ray and mass peaks are spatially offset by ~13" (~100 kpc), which is significant at the ~3 sigma confidence level and confirms that the baryonic and dark matter in this cluster are disassociated. The dark matter peak, however, does not lead the gas peak in the direction expected if we are viewing the cluster soon after first core passage during a high speed merger. Under the assumption that the merger is happening in the plane of the sky, extrapolation of the two NFW halos to a radius r200a=2.4 Mpc yields a combined mass of M200a=(3.10+-0.70) x 10^15 Msun. This extrapolated total mass is consistent with our two-component-based dynamical analysis and previous X-ray measurements, projecting ACT-CL J0102-4915 to be the most massive cluster at z>0.6 known to date.

### Observational constraints on G-corrected holographic dark energy using a Markov chain Monte Carlo method

We constrain holographic dark energy (HDE) with time varying gravitational coupling constant in the framework of the modified Friedmann equations using cosmological data from type Ia supernovae, baryon acoustic oscillations, cosmic microwave background radiation and X-ray gas mass fraction. Applying a Markov Chain Monte Carlo (MCMC) simulation, we obtain the best fit values of the model and cosmological parameters within $1\sigma$ confidence level (CL) in a flat universe as: $\Omega_{\rm b}h^2=0.0222^{+0.0018}_{-0.0013}$, $\Omega_{\rm c}h^2 =0.1121^{+0.0110}_{-0.0079}$, $\alpha_{\rm G}\equiv \dot{G}/(HG) =0.1647^{+0.3547}_{-0.2971}$ and the HDE constant $c=0.9322^{+0.4569}_{-0.5447}$. Using the best fit values, the equation of state of the dark component at the present time $w_{\rm d0}$ at $1\sigma$ CL can cross the phantom boundary $w=-1$.

### Chromospherically Active Stars in the RAVE Survey. I. The Catalogue

RAVE, the unbiased magnitude limited survey of the southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the CaII IRT range which is a known indicator of chromospheric activity. Our previous work (Matijevi\v{c} et al. 2012) classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-LTE profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5\AA\ wide interval and their sum EW_IRT for ~44,000 candidate active dwarf stars with S/N>20 and with no respect to the source of their emission flux. From these ~14,000 show a detectable chromospheric flux with at least 2\sigma\ confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and in some cases radial velocities of active stars derived from automatic pipeline suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre main-sequence cases. The catalogue will be publicly available with the next RAVE public data releases.

### The Gemini NICI Planet-Finding Campaign: The Frequency of Planets around Young Moving Group Stars

We report results of a direct imaging survey for giant planets around 80 members of the Beta Pic, TW Hya, Tucana-Horologium, AB Dor, and Hercules-Lyra moving groups, observed as part of the Gemini NICI Planet-Finding Campaign. For this sample, we obtained median contrasts of \Delta H=13.9 mag at 1" in combined CH4 narrowband ADI+SDI mode and median contrasts of \Delta H=15.1 mag at 2" in H-band ADI mode. We found numerous (>70) candidate companions in our survey images. Some of these candidates were rejected as common-proper motion companions using archival data; we reobserved with NICI all other candidates that lay within 400 AU of the star and were not in dense stellar fields. The vast majority of candidate companions were confirmed as background objects from archival observations and/or dedicated NICI campaign followup. Four co-moving companions of brown dwarf or stellar mass were discovered in this moving group sample: PZ Tel B (36+-6 MJup, 16.4+-1.0 AU, Biller et al. 2010), CD -35 2722B (31+-8 MJup, 67+-4 AU, Wahhaj et al. 2011), HD 12894B (0.46+-0.08 MSun, 15.7+-1.0 AU), and BD+07 1919C (0.20+-0.03 MSun, 12.5+-1.4 AU). From a Bayesian analysis of the achieved H band ADI and ASDI contrasts, using power-law models of planet distributions and hot-start evolutionary models, we restrict the frequency of 1–20 MJup companions at semi-major axes from 10–150 AU to <18% at a 95.4% confidence level using DUSTY models and to <6% at a 95.4% using COND models.

Recently, the Planck collaboration has released the first cosmological papers providing the highest resolution, full sky, maps of the cosmic microwave background (CMB) temperature anisotropies. In this paper we study a phenomenological model which interpolates between the pure $\Lambda$CDM model and the Dvali-Gabadadze-Porrati (DGP) braneworld model with an additional parameter $\alpha$. Firstly, we calculate the "distance information" of Planck data which includes the "shift parameter" $R$, the "acoustic scale" $l_A$, and the photon decoupling epoch $z_\ast$ in different cosmological models and find that this information is almost independent on the input models we use. Then, we compare the constraints on the free parameter $\alpha$ of the DGP model from the "distance information" of Planck and WMAP data and find that the Planck data with high precision do not improve the constraint on $\alpha$, but give the higher median value and the better limit on the current matter density fraction $\Omega_m$. Then, combining the "distance information" of Planck measurement, baryon acoustic oscillations (BAO), type Ia supernovae (SNIa) and the prior on the current Hubble constant (HST), we obtain the tight constraint on the parameter $\alpha < 0.20$ at $95\%$ confidence level, which implies that the flat DGP model has been ruled out by the current cosmological data. Finally, we allow the additional parameter $\alpha < 0$ in our calculations and interestingly obtain $\alpha=-0.29\pm0.20$ ($68\%$ C.L.), which means the current data slightly favor the effective equation of state $w_{\rm eff}<-1$. More importantly, the tension between constraints on $H_0$ from different observational data has been eased.

### The primordial helium abundance from updated emissivities

Observations of metal-poor extragalactic H II regions allow the determination of the primordial helium abundance, Y_p. The He I emissivities are the foundation of the model of the H II region’s emission. Porter, Ferland, Storey, & Detisch (2012) have recently published updated He I emissivities based on improved photoionization cross-sections. We incorporate these new atomic data and update our recent Markov Chain Monte Carlo analysis of the dataset published by Izotov, Thuan, & Stasinska (2007). As before, cuts are made to promote quality and reliability, and only solutions which fit the data within 95% confidence level are used to determine the primordial He abundance. The previously qualifying dataset is almost entirely retained and with strong concordance between the physical parameters. Overall, an upward bias from the new emissivities leads to a decrease in Y_p. In addition, we find a general trend to larger uncertainties in individual objects (due to changes in the emissivities) and an increased variance (due to additional objects included). From a regression to zero metallicity, we determine Y_p = 0.2465 +/- 0.0097, in good agreement with the Planck result of Y_p = 0.2485 +/- 0.0002. In the future, a better understanding of why a large fraction of spectra are not well fit by the model will be crucial to achieving an increase in the precision of the primordial helium abundance determination.

### What do observations of the Lyman-alpha fraction tell us about reionization?

An appealing approach for studying the reionization history of the universe is to measure the redshift evolution of the Lyman-alpha fraction, the percentage of Lyman-break selected galaxies that emit appreciably in the Ly-alpha line. This fraction is expected to fall-off towards high redshift as the intergalactic medium becomes significantly neutral, and the galaxies’ Ly-alpha emission is progressively attenuated. Intriguingly, early measurements with this technique suggest a strong drop in the Ly-alpha fraction near z ~ 7. Previous work concluded that this requires a surprisingly neutral intergalactic medium — with neutral hydrogen filling more than 50 % of the volume of the universe — at this redshift. We model the evolving Ly-alpha fraction using cosmological simulations of the reionization process. Before reionization completes, the simulated Ly-alpha fraction has large spatial fluctuations owing to the inhomogeneity of reionization. Since existing measurements of the Ly-alpha fraction span relatively small regions on the sky, and sample these regions only sparsely, they may by chance probe mostly galaxies with above average Ly-alpha attenuation. We find that this sample variance is not exceedingly large for existing surveys, but that it does somewhat mitigate the required neutral fraction at z ~ 7. Quantitatively, in a fiducial model calibrated to match measurements after reionization, we find that current z = 7 observations require a volume-averaged neutral fraction of x_HI > 0.05 at 95 % confidence level. Hence, we find that the z ~ 7 Ly-alpha fraction measurements do likely probe the universe before reionization completes but that they do not require a very large neutral fraction.

### Probing the cosmic-ray content of galaxy clusters by stacking Fermi-LAT count maps

Observation in radio have shown that galaxy clusters are giant reservoirs of cosmic rays (CR). Although a gamma-ray signal from the cluster volume is expected to arise through interactions of CR protons with the ambient plasma, a confirming observation is still missing. We search for a cumulative gamma-ray emission in direction of galaxy clusters by analysing a collection of stacked Fermi-LAT count maps. Additionally, we investigate possible systematic differences in the emission between cool-core and non-cool core cluster populations. Making use of a sample of 53 clusters selected from the HIFLUGCS catalog, we do not detect a significant signal from the stacked sample. The flux upper limit derived for the total stacked sample is at the level of a few 1e-11 ph cm-2 s-1 at 95% confidence level in the 1-300 GeV band, assuming power-law spectra with photon indices 2.0, 2.4, 2.8 and 3.2. Separate stacking of the cool core and non-cool core clusters in the sample lead to similar values of around 5e-11 ph cm-2 s-1 and 2e-11 ph cm-2 s-1, respectively. Under the assumption that decaying \pi^0, produced in collisions between CRs and the ambient thermal gas, are responsible for the gamma-ray emission, we set upper limits on the average CR content in galaxy clusters. For the entire cluster population, our upper limit on the gamma-ray flux translates into an upper limit on the CR-to-thermal energy ratio of 4.6% for a photon index of 2.4. Our 95% upper limits are at the level expected from numerical simulations, which likely suggests that the injection of CR at cosmological shocks is less efficient than previously assumed.

### A lingering non-thermal component in the GRB prompt emission: predicting GeV emission from the MeV spectrum

The high energy GeV emission of gamma-ray bursts (GRBs), detected by \emph{Fermi}/LAT, has a significantly different morphology compared to the lower energy MeV emission, detected by \emph{Fermi}/GBM. Though the late time GeV emission is believed to be synchrotron radiation produced via an external shock, this emission as early as the prompt phase is puzzling. Meaningful connection between these two emissions can be drawn only by an accurate description of the prompt MeV spectrum. We perform a time-resolved spectroscopy of the GBM data of long GRBs having significant GeV emission, using a model consisting of 2 blackbodies and a power-law. We examine in detail the evolution of the spectral components and found that GRBs having high GeV emission (GRB 090902B and GRB 090926A) have a delayed onset of the power-law component, in the GBM spectrum, which lingers at the later part of the prompt emission. This behaviour mimics the flux evolution in LAT. In contrast, bright GBM GRBs with an order of magnitude lower GeV emission (GRB 100724B and GRB 091003) show a coupled variability of the total and the power-law flux. Further, by analyzing the data for a set of 17 GRBs, we find a strong correlation between the power-law fluence in the MeV and the LAT fluence (Pearson correlation: r=0.88 and Spearman correlation: $\rho=0.81$). We demonstrate that this correlation is not influenced by the correlation between the total and the power-law fluences at a confidence level of 2.3$\sigma$. We speculate the possible radiation mechanisms responsible for the correlation.

### Constraining dark matter late-time energy injection: decays and p-wave annihilations

We use the latest cosmic microwave background (CMB) observations to provide updated constraints on the dark matter lifetime as well as on p-wave suppressed annihilation cross sections in the 1 MeV to 1 TeV mass range. In contrast to scenarios with an s-wave dominated annihilation cross section, which mainly affect the CMB close to the last scattering surface, signatures associated with these scenarios essentially appear at low redshifts (z < 50) when structure began to form, and thus manifest at lower multipoles in the CMB power spectrum. We use data from Planck, WMAP9, SPT and ACT, as well as Lyman-alpha measurements of the matter temperature at z ~ 4 to set a 95% confidence level lower bound on the dark matter lifetime of ~ 4 x 10^25 s for m_chi = 100 MeV. This bound becomes lower by two orders of magnitude at m_chi = 1 TeV due to inefficient energy deposition into the intergalactic medium. We also show that structure formation can enhance the effect of p-wave suppressed annihilation cross sections by many orders of magnitude with respect to the background cosmological rate, although even with this enhancement, CMB constraints are not yet strong enough to reach the thermal relic value of the cross section.

### Primordial 4He abundance: a determination based on the largest sample of HII regions with a methodology tested on model HII regions

We verified the validity of the empirical method to derive the 4He abundance used in our previous papers by applying it to CLOUDY (v13.01) models. Using newly published HeI emissivities, for which we present convenient fits as well as the output CLOUDY case B hydrogen and HeI line intensities, we found that the empirical method is able to reproduce the input CLOUDY 4He abundance with an accuracy of better than 1%. The CLOUDY output data also allowed us to derive the non-recombination contribution to the intensities of the strongest Balmer hydrogen Halpha, Hbeta, Hgamma, and Hdelta emission lines and the ionisation correction factors for He. With these improvements we used our updated empirical method to derive the 4He abundances and to test corrections for several systematic effects in a sample of 1610 spectra of low-metallicity extragalactic HII regions, the largest sample used so far. From this sample we extracted a subsample of 111 HII regions with Hbeta equivalent width EW(Hbeta) > 150A, with excitation parameter x = O^{2+}/O > 0.8, and with helium mass fraction Y derived with an accuracy better than 3%. With this subsample we derived the primordial 4He mass fraction Yp = 0.254+/-0.003 from linear regression Y-O/H. The derived value of Yp is higher at the 68% confidence level (CL) than that predicted by the standard big bang nucleosynthesis (SBBN) model, possibly implying the existence of different types of neutrino species in addition to the three known types of active neutrinos. Using the most recently derived primordial abundances D/H = (2.60+/-0.12)x10^{-5} and Yp = 0.254+/-0.003 and the chi^2 technique, we found that the best agreement between abundances of these light elements is achieved in a cosmological model with baryon mass density Omegab h^2 = 0.0234+/-0.0019 (68% CL) and an effective number of the neutrino species Neff = 3.51+/-0.35 (68% CL).

### Discovery of a 7 mHz X-Ray Quasi-periodic Oscillation from the most Massive Stellar-mass Black Hole IC 10 X-1

We report the discovery with XMM-Newton of an approximately 7 mHz X-ray (0.3-10.0 keV) quasi-periodic oscillation (QPO) from the eclipsing, high-inclination black hole binary IC 10 X-1. The QPO is significant at > 4.33 sigma confidence level and has a fractional amplitude (% rms) and a quality factor, Q, of approximately 11 and 4, respectively. The overall X-ray (0.3-10.0 keV) power spectrum in the frequency range 0.0001 – 0.1 Hz can be described by a power-law with an index of -2, and a QPO at 7 mHz. At frequencies > 0.02 Hz there is no evidence for significant variability. The fractional amplitude (rms) of the QPO is roughly energy-independent in the energy range of 0.3-1.5 keV. Above 1.5 keV the low signal to noise ratio of the data does not allow us to detect the QPO. By directly comparing these properties with the wide range of QPOs currently known from accreting black hole and neutron stars, we suggest that the 7 mHz QPO of IC 10 X-1 may be linked to one of the following three categories of QPOs: (1) the "heartbeat" mHz QPOs of the black hole sources GRS 1915+105 and IGR J17091-3624, or (2) the 0.6-2.4 Hz "dipper QPOs" of high-inclination neutron star systems, or (3) the mHz QPOs of Cygnus X-3.

### Signatures of First Stars in Galaxy Surveys: Multi-Tracer Analysis of the Supersonic Relative Velocity Effect and the Constraints from the BOSS Power Spectrum Measurements

We study the effect of the supersonic relative velocity between dark matter and baryons on large-scale galaxy clustering and derive the constraint on the relative velocity bias parameter from the Baryonic Oscillation Spectroscopic Survey (BOSS) power spectrum measurements. Recent work has shown that the relative velocity effect may have a dramatic impact on the star formation at high redshifts, if first stars are formed in minihalos around z~20, or if the effect propagates through secondary effects to stars formed at later redshifts. The relative velocity effect has particularly strong signatures in the large scale clustering of these sources, including the BAO position. Assuming that a small fraction of stars in low-redshift massive galaxies retain the memory of the primordial relative velocity effect, galaxy clustering measurements can be used to constrain the signatures of the first stars. Luminous red galaxies contain some of the oldest stars in the Universe and are ideally suited to search for this effect. Using the BOSS power spectrum measurements from the Sloan Data Release 9, in combination with Planck, we derive the upper limit on the fraction of the stars sensitive to relative velocity effect f_star<3.3% at the 95% confidence level in the CMASS galaxy sample. If additional galaxy sample not sensitive to the effect is available in a given survey, a joint multi-tracer analysis can be applied to construct a sample-variance cancelling combination, providing a model-independent way to verify the presence of the relative velocity effect in the galaxy power spectrum on large scales. Such a multi-tracer analysis in future galaxy surveys can greatly improve the current constraint, achieving a 0.1% level in f_star.

### Fermi Large Area Telescope Detection of Two Very-High-Energy (E>100 GeV) Gamma-ray Photons from the z = 1.1 Blazar PKS 0426-380

We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E>100 GeV) gamma-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426-380. The null hypothesis probability that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 6.1 sigma confidence level. We therefore claim that at least one of the two VHE photons is securely associated with the blazar, making PKS 0426-380 the most distant VHE emitter known to date. The results are in agreement with the most recent Fermi-LAT constraints on the Extragalactic Background Light (EBL) intensity, which imply a $z \simeq 1$ horizon for $\simeq$ 100 GeV photons. The LAT detection of the two VHE gamma-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower gamma-ray energies. Modeling the gamma-ray continuum of PKS 0426-380 with daily bins revealed a significant spectral hardening around the time of detection of the first VHE event (LAT photon index \Gamma\ $\simeq$ 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in gamma rays during the flaring epochs. A possible flat component is present above ~10 GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ~8-month high state.

### Fermi Large Area Telescope Detection of Two Very-High-Energy (E>100 GeV) Gamma-ray Photons from the z = 1.1 Blazar PKS 0426-380 [Replacement]

We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E>100 GeV) gamma-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426-380. The null hypothesis that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 5.5 sigma confidence level. We therefore claim that at least one of the two VHE photons is securely associated with the blazar, making PKS 0426-380 the most distant VHE emitter known to date. The results are in agreement with the most recent Fermi-LAT constraints on the Extragalactic Background Light (EBL) intensity, which imply a $z \simeq 1$ horizon for $\simeq$ 100 GeV photons. The LAT detection of the two VHE gamma-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower gamma-ray energies. Modeling the gamma-ray continuum of PKS 0426-380 with daily bins revealed a significant spectral hardening around the time of detection of the first VHE event (LAT photon index \Gamma\ $\simeq$ 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in gamma rays during the flaring epochs. An additional flat component is possibly present above several tens of GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ~8-month high state.

### Dark Energy Constraints after Planck [Replacement]

The Planck collaboration has recently published maps of the Cosmic Microwave Background radiation with the highest precision. In the standard flat $\Lambda$CDM framework, Planck data show that the Hubble constant $H_0$ is in tension with that measured by the several direct probes on $H_0$. In this paper, we perform a global analysis from the current observational data in the general dark energy models and find that resolving this tension on $H_0$ requires the dark energy model with its equation of state (EoS) $w\neq-1$. Firstly, assuming the $w$ to be a constant, the Planck data favor $w < -1$ at about $2\,\sigma$ confidence level when combining with the supernovae "SNLS" compilation. And consequently the value derived on $H_0$, $H_0=71.3\pm2.0$ ${\rm km\,s^{-1}\,Mpc^{-1}}$ (68% C.L.), is consistent with that from direct $H_0$ probes. We then investigate the dark energy model with a time-evolving $w$, and obtain the 68% C.L. constraints $w_0=-0.81\pm0.19$ and $w_a=-1.9\pm1.1$ from the Planck data and the "SNLS" compilation. Current data still slightly favor the Quintom dark energy scenario with EoS across the cosmological constant boundary $w\equiv-1$.

### Dark Energy Constraints after Planck

The Planck collaboration has recently published maps of the Cosmic Microwave Background radiation with the highest precision. In the standard flat $\Lambda$CDM framework, Planck data show that the Hubble constant $H_0$ is in tension with that measured by the several direct probes on $H_0$. In this paper, we perform a global analysis from the current observational data in the general dark energy models and find that resolving this tension on $H_0$ requires the dark energy model with its equation of state (EoS) $w\neq-1$. Firstly, assuming the $w$ to be a constant, the Planck data favor $w < -1$ at about $2\,\sigma$ confidence level when combining with the supernovae "SNLS" compilation. And consequently the value derived on $H_0$, $H_0=71.3\pm2.0$ ${\rm km\,s^{-1}\,Mpc^{-1}}$ (68% C.L.), is consistent with that from direct $H_0$ probes. We then investigate the dark energy model with a time-evolving $w$, and obtain the 68% C.L. constraints $w_0=-0.81\pm0.19$ and $w_a=-1.9\pm1.1$ from the Planck data and the "SNLS" compilation. Current data still slightly favor the Quintom dark energy scenario with EoS across the cosmological constant boundary $w\equiv-1$.

### Optical spectral index - luminosity relation for the 17 mapped Palomar-Green quasars

In this paper, the optical spectra index – luminosity relationship is checked for the well-known 17 individual mapped QSOs, in order to give one more clearer conclusion on the so far conflicting dependence of the spectral index on the luminosity for AGN. Different from the global relationships based on the color difference (photometry parameters) for samples of AGN, the more reliable relationship is determined for the multi-epoch observed individual mapped QSOs with no contamination from the host galaxies, the line variabilities and the much different central properties. The final confirmed results are as follows. (1): No strong dependence of the optical spectral index on the continuum luminosity can be found for all the 17 QSOs, besides two objects (PG 0026 and PG 1613) having some weak trends (with $3\sigma$ confidence level) for the relationship. In other words, the common sense ‘AGNs get bluer when they get brighter’ is not so common. (2): There are much different damped intrinsic variability time scales for the variability modes of the optical spectral index and the continuum emission, through the well applied Damped Random Walk method for the AGN variability. In other words, there are some different intrinsic mechanisms controlling the variabilities of the optical spectral index and the power law AGN continuum emission. Therefore, the much weak dependence of the optical spectral index on the continuum luminosity can be further confirmed.

### Searching for new gamma-ray blazar candidates in the 3rd Palermo BAT Hard X-ray Catalog with WISE

We searched for gamma-ray blazar candidates among the 382 unidentified hard X-ray sources of the 3rd Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of SWIFT-BAT survey data and listing 1586 sources. We adopted a recently developed association method based on the peculiar infrared colors which characterize the gamma-ray blazars included in the second catalog of active galactic nuclei detected by the Fermi Large Area Telescope (2LAC). We used this method exploiting the data of the all-sky survey performed by the Wide-Field Infrared Survey Explorer (WISE) to establish correspondences between unidentified 3PBC sources and WISE gamma-ray blazar candidates located within the BAT positional uncertainty region at 99% confidence level. We obtained a preliminary list of candidates for which we analysed all the available data in the SWIFT archive to complement the information in the literature and in the radio, infrared and optical catalogs with the information on their optical-UV and soft X-ray emission. Requiring the presence of radio and soft X-ray counterparts consistent with the infrared positions of the selected WISE sources, as well as a blazar-like radio morphology, we finally obtained a list of 24 gamma-ray blazar candidates.

### Massive binaries in the vicinity of Sgr A*

A long-term spectroscopic and photometric survey of the most luminous and massive stars in the vicinity of the super-massive black hole Sgr A* revealed two new binaries; a long-period Ofpe/WN9 binary, GCIRS 16NE, with a modest eccentricity of 0.3 and a period of 224 days and an eclipsing Wolf-Rayet binary with a period of 2.3 days. Together with the already identified binary GCIRS 16SW, there are now three confirmed OB/WR binaries in the inner 0.2\,pc of the Galactic Center. Using radial velocity change upper limits, we were able to constrain the spectroscopic binary fraction in the Galactic Center to $F_{\rm SB}=0.27^{+0.29}_{-0.19}$ at a confidence level of 95%, a massive binary fraction similar to that observed in dense clusters. The fraction of eclipsing binaries with photometric amplitudes $\Delta m>0.4$ is $F^{\rm GC}_{\rm EB}=3\pm2%$, which is consistent with local OB star clusters ($F_{\rm EB}=1%$). Overall the Galactic Center binary fraction seems to be close to the binary fraction in comparable young clusters.

### Dust properties from GALEX observations of a UV halo around Spica

GALEX has detected ultraviolet halos extending as far as 5$^{\circ}$ around four bright stars (Murthy et al. (2011)). These halos are produced by scattering of starlight by dust grains in thin foreground clouds that are not physically associated with the star. Assuming a simple model consisting of a single layer of dust in front of the star, Murthy et al.(2011) have been able to model these halo intensities and constrain the value of the phase function asymmetry factor $g$ of the scattering grains in the FUV and NUV. However due to the uncertainty in the dust geometry they could not constrain the albedo. In this work we have tried to constrain the optical constants and dust geometry by modeling the UV halo of Spica. Since the halo emission is not symmetric, we have modeled the Northern and Southern parts of the halo separately. To the North of Spica, the best-fit albedo is 0.26$\pm$0.1 and $g$ is 0.58$\pm$0.11 in the FUV at the 90% confidence level. The corresponding limits on the distance and optical depth ($\tau$) of the dust sheet is 3.65$\pm$1.05 pc and 0.047$\pm$0.006 respectively. However, owing to a complicated dust distribution to the South of Spica, we were unable to uniquely constrain the dust parameters in that region. Nevertheless, by assuming the optical constants of the Northern region and assuming a denser medium, we were able to constrain the distance of the dust to 9.5$\pm$1.5 pc and the corresponding $\tau$ to 0.04$\pm$0.01.

### Restricting the LSND and MiniBooNE sterile neutrinos with the IceCube atmospheric neutrino data [Replacement]

We study oscillations of the high energy atmospheric neutrinos in the Earth into sterile neutrinos with the eV-scale mass. The MSW resonance and parametric enhancement of the $\bar{\nu}_\mu\to\bar{\nu}_s$ oscillations lead to distortion of the zenith angle distribution of the muon-track events which can be observed by IceCube. Due to matter effect, the IceCube signal depends not only on the mixing element $U_{\mu 4}$ relevant for LSND and MiniBooNE but also on $U_{\tau 4}$ and the CP-violating phase $\delta_{24}$. We show that the case with $U_{\tau 4} = \delta_{24} = 0$ leads to the weakest IceCube signal and therefore should be used to bound $U_{\mu 4}$. We compute the zenith angle distributions of the $\nu_\mu-$events for different energy intervals in the range (0.1 – 10) TeV and find that inclusion of the energy information (binning in energy) improves the sensitivity to $\nu_s$ drastically. We estimate that with already collected (during 3 – 4 years) IceCube statistics the mixing required by LSND and MiniBooNE can be excluded at $(4 – 6)\sigma$ confidence level.

### An improved upper limit to the CMB circular polarization at large angular scales

Circular polarization of the Cosmic Microwave Background (CMB) offers the possibility of detecting rotations of the universe and magnetic fields in the primeval universe or in distant clusters of galaxies. We used the Milano Polarimeter (MIPOL) installed at the Testa Grigia Observatory, on the italian Alps, to improve the existing upper limits to the CMB circular polarization at large angular scales. We obtain 95% confidence level upper limits to the degree of the CMB circular polarization ranging between 5.0×10^{-4} and 0.7×10^{-4} at angular scales between 8 and 24 deg, improving by one order of magnitude preexisting upper limits at large angular scales. Our results are still far from the nK region where today expectations place the amplitude of the V Stokes parameter used to characterize circular polarization of the CMB but improve the preexisting limit at similar angular scales. Our observations offered also the opportunity of characterizing the atmospheric emission at 33 GHz at the Testa Grigia Observatory.

### An improved upper limit to the CMB circular polarization at large angular scales [Replacement]

Circular polarization of the Cosmic Microwave Background (CMB) offers the possibility of detecting rotations of the universe and magnetic fields in the primeval universe or in distant clusters of galaxies. We used the Milano Polarimeter (MIPOL) installed at the Testa Grigia Observatory, on the italian Alps, to improve the existing upper limits to the CMB circular polarization at large angular scales. We obtain 95% confidence level upper limits to the degree of the CMB circular polarization ranging between 5.0×10^{-4} and 0.7×10^{-4} at angular scales between 8 and 24 deg, improving by one order of magnitude preexisting upper limits at large angular scales. Our results are still far from the nK region where today expectations place the amplitude of the V Stokes parameter used to characterize circular polarization of the CMB but improve the preexisting limit at similar angular scales. Our observations offered also the opportunity of characterizing the atmospheric emission at 33 GHz at the Testa Grigia Observatory.

### A Search for Fast Optical Transients in the Pan-STARRS1 Medium-Deep Survey: M Dwarf Flares, Asteroids, Limits on Extragalactic Rates, and Implications for LSST

[Abridged] We present a search for fast optical transients (~0.5 hr-1 day) using repeated observations of the Pan-STARRS1 Medium-Deep Survey (PS1/MDS) fields. Our search takes advantage of the consecutive g/r-band observations (16.5 min in each filter), by requiring detections in both bands, with non-detections on preceding and subsequent nights. We identify 19 transients brighter than 22.5 AB mag (S/N>10). Of these, 11 events exhibit quiescent counterparts in the deep PS1/MDS templates that we identify as M4-M9 dwarfs. The remaining 8 transients exhibit a range of properties indicative of main-belt asteroids near the stationary point of their orbits. With identifications for all 19 transients, we place an upper limit of R_FOT(0.5hr)<0.12 deg^-2 d^-1 (95% confidence level) on the sky-projected rate of extragalactic fast transients at <22.5 mag, a factor of 30-50 times lower than previous limits; the limit for a timescale of ~day is R_FOT<2.4e-3 deg^-2 d^-1. To convert these sky-projected rates to volumetric rates, we explore the expected peak luminosities of fast optical transients powered by various mechanisms, and find that non-relativistic events are limited to M~-10 mag (M~-14 mag) for a timescale of ~0.5 hr (~day), while relativistic sources (e.g., GRBs, magnetar-powered transients) can reach much larger luminosities. The resulting volumetric rates are <13 (M~-10 mag), <0.05 (M~-14 mag) and <1e-6 Mpc^-3 yr^-1 (M~-24 mag), significantly above the nova, supernova, and GRB rates, respectively, indicating that much larger surveys are required to provide meaningful constraints. Motivated by the results of our search we discuss strategies for identifying fast optical transients in the LSST main survey, and reach the optimistic conclusion that the veil of foreground contaminants can be lifted with the survey data, without the need for expensive follow-up observations.

### Weighting Neutrinos in $f(R)$ gravity

In this paper, we constrain the neutrino properties in $f(R)$ gravity using the latest observations from Cosmic Microwave Background(CMB) and Baryon Acoustic Oscillation(BAO) measurements. We first constrain separately the total mass of neutrinos $\sum m_\nu$ and the effective number of neutrino species $N_{\rm eff}$ respectively. Then we constrain $N_{\rm eff}$ and $\sum m_\nu$ simultaneously. We find $\sum m_\nu<0.462 {\rm eV}$ at 95% confidence level for the combination of Planck CMB data, WMAP CMB polarization data, BAO data and high-$l$ data from Atacama Cosmology Telescope(ACT) and South Pole Telescope(SPT). We also find $N_{\rm eff}=3.32^{+0.54}_{-0.51}$ at 95% confidence level for the same data set. When constraining $N_{\rm eff}$ and $\sum m_\nu$ simultaneously, we find $N_{\rm eff}=3.58^{+0.72}_{-0.69}$ and $\sum m_\nu<0.860{\rm eV}$ at 95% confidence level respectively.

### Weighing Neutrinos in $f(R)$ gravity [Replacement]

We constrain the neutrino properties in $f(R)$ gravity using the latest observations from Cosmic Microwave Background(CMB) and Baryon Acoustic Oscillation(BAO) measurements. We first constrain separately the total mass of neutrinos $\sum m_\nu$ and the effective number of neutrino species $N_{\rm eff}$ respectively. Then we constrain $N_{\rm eff}$ and $\sum m_\nu$ simultaneously. We find $\sum m_\nu<0.462 {\rm eV}$ at 95% confidence level for the combination of Planck CMB data, WMAP CMB polarization data, BAO data and high-$l$ data from Atacama Cosmology Telescope(ACT) and South Pole Telescope(SPT). We also find $N_{\rm eff}=3.32^{+0.54}_{-0.51}$ at 95% confidence level for the same data set. When constraining $N_{\rm eff}$ and $\sum m_\nu$ simultaneously, we find $N_{\rm eff}=3.58^{+0.72}_{-0.69}$ and $\sum m_\nu<0.860{\rm eV}$ at 95% confidence level respectively.

### Photohadronic Origin of the TeV-PeV Neutrinos Observed in IceCube

We perform an unbiased search of the origin of the recently observed 28 events above ~30 TeV in the IceCube neutrino observatory, assuming that these are (apart from the atmospheric background) of astrophysical origin produced by photohadronic interactions. Instead of relying on the normalization of the neutrino flux, we demonstrate that spectral shape and flavor composition can be used to constrain or identify the source class. We find that the lack of observed events with energies much larger than PeV points towards sources with strong magnetic fields, which do not exhibit a direct correlation between highest nucleon and neutrino energies. While AGNs are still allowed as possible source class at about the 3sigma confidence level from current data, we show that IceCube can rule out that the observed neutrinos stem from the sources of the ultra-high energy cosmic rays (including AGNs) with a factor of ten increased statistics at more than 5sigma if the current observations are confirmed. A possible caveat are sources with strong magnetic fields and high Lorentz factors, such as magnetic energy dominated GRBs.

### A new limit on local Lorentz invariance violation of gravity from solitary pulsars [Cross-Listing]

Gravitational preferred frame effects are generally predicted by alternative theories that exhibit an isotropic violation of local Lorentz invariance of gravity. They are described by three parameters in the parametrized post-Newtonian formalism. One of their strong-field generalizations, $\hat \alpha_2$, induces a precession of a pulsar’s spin around its movement direction with respect to the preferred frame. We constrain $\hat \alpha_2$ by using the non-detection of such a precession using the characteristics of the pulse profile. In our analysis we use a large number of observations from the 100-m Effelsberg radio telescope, which cover a time span of approximately 15 years. By combining data from two solitary millisecond pulsars, PSRs B1937+21 and J1744-1134, we get a limit of $|\hat \alpha_2| < 1.6 \times 10^{-9}$ at 95% confidence level, which is more than two orders of magnitude better than its best weak-field counterpart from the Solar system.

### An HST Optical to Near-IR Transmission Spectrum of the Hot Jupiter WASP-19b: Detection of Atmospheric Water and Likely Absence of TiO [Replacement]

We measure the transmission spectrum of WASP-19b from 3 transits using low-resolution optical spectroscopy from the HST Space Telescope Imaging Spectrograph (STIS). The STIS spectra cover a wavelength range of 0.29-1.03 microns with resolving power R=500. The optical data are combined with archival near-IR data from the HST Wide Field Camera 3 (WFC3) G141 grism, covering the wavelength range 1.087-1.687 micron, with resolving power R=130. We obtain the transmission spectrum from 0.53-1.687 microns with S/N levels between 3000 and 11,000 in 0.1 micron bins. WASP-19 is a very active star, with optical stellar flux varying by a few per cent over time. We correct the transit light curves for the effects of stellar activity using ground-based activity monitoring with the Cerro Tololo Inter-American Observatory (CTIO). While we were not able to construct a transmission spectrum using the blue optical data due to the presence of large occulted star spots, we were able to use the spot crossings to help constrain the mean stellar spot temperature. To search for predicted features in the hot-Jupiter atmosphere, we also define spectral indices for differential radius measurements to specifically search for the presence of TiO and alkali line features. Our measurements rule out TiO features predicted for a planet of WASP-19b’s equilibrium temperature (2050 K) in the transmission spectrum at the 2.7-2.9 sigma confidence level, depending on atmospheric model formalism. The WFC3 transmission spectrum shows strong absorption features due to the presence of H2O, which is detected at the 4 sigma confidence level between 1.1 and 1.4 microns. The results indicate that WASP-19b is a planet with no or low levels of TiO and without a high C/O ratio. The lack of observable TiO features are possibly due to rainout, breakdown from stellar activity or the presence of other absorbers in the optical.

### An HST Optical to Near-IR Transmission Spectrum of the Hot Jupiter WASP-19b: Detection of Atmospheric Water and Likely Absence of TiO

We measure the transmission spectrum of WASP-19b from 3 transits using low-resolution optical spectroscopy from the HST Space Telescope Imaging Spectrograph (STIS). The STIS spectra cover a wavelength range of 0.29-1.03 microns with resolving power R=500. The optical data are combined with archival near-IR data from the HST Wide Field Camera 3 (WFC3) G141 grism, covering the wavelength range 1.087-1.687 micron, with resolving power R=130. We obtain the transmission spectrum from 0.53-1.687 microns with S/N levels between 3000 and 11,000 in 0.1 micron bins. WASP-19 is a very active star, with optical stellar flux varying by a few per cent over time. We correct the transit light curves for the effects of stellar activity using ground-based activity monitoring with the Cerro Tololo Inter-American Observatory (CTIO). While we were not able to construct a transmission spectrum using the blue optical data due to the presence of large occulted star spots, we were able to use the spot crossings to help constrain the mean stellar spot temperature. To search for predicted features in the hot-Jupiter atmosphere, we also define spectral indices for differential radius measurements to specifically search for the presence of TiO and alkali line features. Our measurements rule out TiO features predicted for a planet of WASP-19b’s equilibrium temperature (2050 K) in the transmission spectrum at the 2.7-2.9 sigma confidence level, depending on atmospheric model formalism. The WFC3 transmission spectrum shows strong absorption features due to the presence of H2O, which is detected at the 4 sigma confidence level between 1.1 and 1.4 microns. The results indicate that WASP-19b is a planet with no or low levels of TiO and without a high C/O ratio. The lack of observable TiO features are possibly due to rainout, breakdown from stellar activity or the presence of other absorbers in the optical.

### TeV-PeV neutrinos over the atmospheric background: originating from two groups of sources?

In addition to the two ~1 PeV neutrinos, the IceCube Collaboration recently reported a detection of 26 neutrino candidates at energies from 30 TeV to 250 TeV, implying a confidence level of 4.3\sigma over the atmospheric background. We suggest that these TeV-PeV non-atmospheric neutrinos may originate from two groups of sources, motivated by the non-detection of neutrinos in the energy range 250 TeV- 1 PeV in current data. If intrinsic, the non-detection of 250 TeV-1 PeV neutrinos disfavors the single power-law spectrum model for the TeV-PeV non-atmospheric neutrinos at a confidence level of ~ 2\sigma. We then interpret the current neutrino data with a two-component spectrum model. One has a flat spectrum with a cutoff at the energy ~ 250 TeV and the other has a sharp peak at ~1 PeV. The former is likely via pp collision while the latter may be generated by the photomeson interaction.

### Search for muon neutrinos from gamma-ray bursts with the ANTARES neutrino telescope using 2008 to 2011 data

A search for muon neutrinos in coincidence with gamma-ray bursts with the ANTARES neutrino detector using data from the end of 2007 to 2011 is performed. Expected neutrino fluxes are calculated for each burst individually. The most recent numerical calculations of the spectra using the NeuCosmA code are employed, which include Monte Carlo simulations of the full underlying photohadronic interaction processes. The discovery probability for a selection of 296 gamma-ray bursts in the given period is optimised using an extended maximum-likelihood strategy. No significant excess over background is found in the data, and 90% confidence level upper limits are placed on the total expected flux according to the model.

### Forecasting constraints on the cosmic duality relation with galaxy clusters

One of the fundamental hypotheses in observational cosmology is the validity of the so-called cosmic distance-duality relation (CDDR). In this paper, we perform Monte Carlo simulations based on the method developed in Holanda, Goncalves & Alcaniz (2012) [JCAP 1206 (2012) 022] to answer the following question: what is the number of galaxy clusters observations N_{crit} needed to check the validity of this relation at a given confidence level? At 2\sigma, we find that N_{crit} should be increased at least by a factor of 5 relative to the current sample size if we assume the current observational uncertainty \sigma_{obs}. Reducing this latter quantity by a factor of 2, we show that the present number of data would be already enough to check the validity of the CDDR at 2\sigma.

### First results on low-mass WIMP from the CDEX-1 experiment at the China Jinping underground Laboratory [Cross-Listing]

The China Dark matter Experiment collaboration reports the first experimental limit on WIMP dark matter from 14.6 kg-day of data taken with a 994 g p-type point-contact germanium detector at the China Jinping underground Laboratory where the rock overburden is more than 2400 m. The energy threshold achieved was 400 eVee. According to the 14.6 kg-day live data, we placed the limit of N= 1.75 * 10^{-40} cm^{2} at 90% confidence level on the spin-independent cross-section at WIMP mass of 7 GeV before differentiating bulk signals from the surface backgrounds.

### First results on low-mass WIMP from the CDEX-1 experiment at the China Jinping underground Laboratory [Replacement]

The China Dark matter Experiment collaboration reports the first experimental limit on WIMP dark matter from 14.6 kg-day of data taken with a 994 g p-type point-contact germanium detector at the China Jinping underground Laboratory where the rock overburden is more than 2400 m. The energy threshold achieved was 400 eVee. According to the 14.6 kg-day live data, we placed the limit of N= 1.75 * 10^{-40} cm^{2} at 90% confidence level on the spin-independent cross-section at WIMP mass of 7 GeV before differentiating bulk signals from the surface backgrounds.

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