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Register a new userUsing temporal distributions of transient events to characterize cosmological source populations
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The brightest events in a time series of cosmological transients obey an observation time dependence which is often overlooked. This dependence can be exploited to probe the global properties of electromagnetic and gravitational wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new relation based on a peak flux--observation time distribution and show that it is invariant to the luminosity distribution of the sources (Howell et al. 2007b). Applying this relation, in combination with a new data analysis filter, to emph{Swift} gamma-ray burst data, we demonstrate that it can constrain their rate density.
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The Omicron software is a tool developed to perform a multi-resolution time-frequency analysis of data from gravitational-wave detectors: the LIGO, Virgo, and KAGRA detectors. Omicron generates spectrograms from whitened data streams, offering a visual representation of transient detector noises and gravitational-wave events. In addition, these events can be parameterized with an optimized resolution. They can be written to disk to conduct offline noise characterization and gravitational-wave event validation studies. Omicron is optimized to process, in parallel, thousands of data streams recorded by gravitational-wave detectors. The Omicron software plays an important role in vetting gravitational-wave detection candidates and characterization of transient noise.
We investigate the properties of galaxies as they shut off star formation over the 4 billion years surrounding peak cosmic star formation. To do this we categorize $sim7000$ galaxies from $1<z<4$ into $90$ groups based on the shape of their spectral energy distributions (SEDs) and build composite SEDs with $Rsim 50$ resolution. These composite SEDs show a variety of spectral shapes and also show trends in parameters such as color, mass, star formation rate, and emission line equivalent width. Using emission line equivalent widths and strength of the 4000AA break, $D(4000)$, we categorize the composite SEDs into five classes: extreme emission line, star-forming, transitioning, post-starburst, and quiescent galaxies. The transitioning population of galaxies show modest H$alpha$ emission ($EW_{rm REST}sim40$AA) compared to more typical star-forming composite SEDs at $log_{10}(M/M_odot)sim10.5$ ($EW_{rm REST}sim80$AA). Together with their smaller sizes (3 kpc vs. 4 kpc) and higher Sersic indices (2.7 vs. 1.5), this indicates that morphological changes initiate before the cessation of star formation. The transitional group shows a strong increase of over one dex in number density from $zsim3$ to $zsim1$, similar to the growth in the quiescent population, while post-starburst galaxies become rarer at $zlesssim1.5$. We calculate average quenching timescales of 1.6 Gyr at $zsim1.5$ and 0.9 Gyr at $zsim2.5$ and conclude that a fast quenching mechanism producing post-starbursts dominated the quenching of galaxies at early times, while a slower process has become more common since $zsim2$.
We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors and their candidate sky locations were observed by the Swift observatory. Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a blind injection challenge. With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.
The detection of gravitational waves from neutron star merger events has opened up a new field of multi-messenger astronomy linking gravitational waves events to short-gamma ray bursts and kilonova afterglows. A further - yet to be discovered - electromagnetic counterpart is precursor emission produced by the non-trivial interaction of the magnetospheres of the two neutron stars prior to merger. By performing special-relativistic force-free simulations of orbiting neutron stars we discuss the effect of different magnetic field orientations and show how the emission can be significantly enhanced by differential motion present in the binary, either due to stellar spins or misaligned stellar magnetospheres. We find that the built-up of twist in the magnetic flux tube connecting the two stars can lead to the repeated emission of powerful flares for a variety of orbital configurations. We also discuss potential coherent radio emission mechanisms in the flaring process.
Risaliti and Lusso have compiled X-ray and UV flux measurements of 1598 quasars (QSOs) in the redshift range $0.036 leq z leq 5.1003$, part of which, $z sim 2.4 - 5.1$, is largely cosmologically unprobed. In this paper we use these QSO measurements, alone and in conjunction with baryon acoustic oscillation (BAO) and Hubble parameter [$H(z)$] measurements, to constrain cosmological parameters in six different cosmological models, each with two different Hubble constant priors. In most of these models, given the larger uncertainties, the QSO cosmological parameter constraints are mostly consistent with those from the $H(z)$ + BAO data. A somewhat significant exception is the non-relativistic matter density parameter $Omega_{m0}$ where the QSO data favors $Omega_{m0} sim 0.5 - 0.6$ in most models. Consequently in joint analyses of QSO data with $H(z)$ + BAO data the one-dimensional $Omega_{m0}$ distributions shift slightly toward larger values. A joint analysis of the QSO + $H(z)$ + BAO data is consistent with the current standard model, spatially-flat $Lambda$CDM, but mildly favors closed spatial hypersurfaces and dynamical dark energy. Since the higher $Omega_{m0}$ values favored by the QSO data appear to be associated with the $z sim 2 - 5$ part of these data, and conflict somewhat with strong indications for $Omega_{m0} sim 0.3$ from most $z < 2.5$ data as well as from the cosmic microwave background anisotropy data at $z sim 1100$, in most models, the larger QSO data $Omega_{m0}$ is possibly more indicative of an issue with the $z sim 2 - 5$ QSO data than of an inadequacy of the standard flat $Lambda$CDM model.
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