Prompt Optical Observations of Gamma-ray Bursts

The Robotic Optical Transient Search Experiment (ROTSE) seeks to measure simultaneous and early afterglow optical emission from gamma-ray bursts (GRBs). A search for optical counterparts to six GRBs with localization errors of 1 square degree or better produced no detections. The earliest limiting sensitivity is m(ROTSE) > 13.1 at 10.85 seconds (5 second exposure) after the gamma-ray rise, and the best limit is m(ROTSE) > 16.0 at 62 minutes (897 second exposure). These are the most stringent limits obtained for GRB optical counterpart brightness in the first hour after the burst. Consideration of the gamma-ray fluence and peak flux for these bursts and for GRB990123 indicates that there is not a strong positive correlation between optical flux and gamma-ray emission.Comment: 4 pages, 3 figures, submitted to ApJ Letter

The ROTSE detection of early optical light from GRB 990123

An overview is given of the Robotic Optical Transient Search Experiment, a ground-based observational astronomy project intended to detect visible radiation from gamma-ray bursts. The major result of the project was the detection of an early bright optical transient from a GRB. (AIP) © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87569/2/82_1.pd

Inflation and Dark Energy from spectroscopy at z > 2

The expansion of the Universe is understood to have accelerated during two epochs: in its very first moments during a period of Inflation and much more recently, at z < 1, when Dark Energy is hypothesized to drive cosmic acceleration. The undiscovered mechanisms behind these two epochs represent some of the most important open problems in fundamental physics. The large cosmological volume at 2 < z < 5, together with the ability to efficiently target high-$z$ galaxies with known techniques, enables large gains in the study of Inflation and Dark Energy. A future spectroscopic survey can test the Gaussianity of the initial conditions up to a factor of ~50 better than our current bounds, crossing the crucial theoretical threshold of $\sigma(f_{NL}^{\rm local})$ of order unity that separates single field and multi-field models. Simultaneously, it can measure the fraction of Dark Energy at the percent level up to $z = 5$, thus serving as an unprecedented test of the standard model and opening up a tremendous discovery space

GRB Afterglows and Other Transients in the SDSS

The Sloan Digital Sky Survey (SDSS) will image one quarter of the sky centered on the northern galactic cap and produce a 3‐D map of galaxies and quasars found in the sample. An additional 225 deg2 southern survey will be imaged repeatedly on varying timescales. Here we discuss both archival searches in the SDSS catalog (such as SDSS J24602.54+011318.8) and active searches with the SDSS instruments (such as for GRB 010222) for GRB afterglows and other transient objects. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87288/2/349_1.pd

Search for first generation leptoquark pair production in the electron + missing energy + jets final state

We present a search for the pair production of first generation scalar leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron Collider in ppbar collisions at $\sqrt{s}=1.96$ TeV. In the channel $LQ \bar{LQ} \rightarrow e\nu_e qq'$, where q, q' are u or d quarks, no significant excess of data over background is observed, and we set a 95% C.L. lower limit of 326 GeV on the leptoquark mass, assuming equal probabilities of leptoquark decays to eq and $\nu_e q'$.Comment: 7 pages, 6 figures, submitted to PRD-R

The DESI One-Percent survey: constructing galaxy-halo connections for ELGs and LRGs using auto and cross correlations

In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at $z \sim 1$. We measure the auto and cross correlation functions of ELGs and LRGs at $0.8<z\leq 1.0$ from the DESI One-Percent survey. Following Gao et al. (2022), we construct the galaxy-halo connections for ELGs and LRGs simultaneously. With the stellar-halo mass relation (SHMR) for the whole galaxy population (i.e. normal galaxies), LRGs can be selected directly by stellar mass, while ELGs can also be selected randomly based on the observed number density of each stellar mass, once the probability $P_{\mathrm{sat}}$ of a satellite galaxy becoming an ELG is determined. We demonstrate that the observed small scale clustering prefers a halo mass-dependent $P_{\mathrm{sat}}$ model rather than a constant. With this model, we can well reproduce the auto correlations of LRGs and the cross correlations between LRGs and ELGs at $r_{\mathrm{p}}>0.1$ $\mathrm{Mpc}\,h^{-1}$. We can also reproduce the auto correlations of ELGs at $r_{\mathrm{p}}>0.3$ $\mathrm{Mpc}\,h^{-1}$ ($s>1$ $\mathrm{Mpc}\,h^{-1}$) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of $0.8<z<1.6$, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions (HODs) for ELGs which can be used to produce ELG mocks in coarse simulations without resolving subhalos.Comment: 27 pages, 16 figures, accepted by Ap

Phonons in Slow Motion: Dispersion Relations in Ultra-Thin Si Membranes

We report the changes in dispersion relations of hypersonic acoustic phonons in free-standing silicon membranes as thin as \sim 8 nm. We observe a reduction of the phase and group velocities of the fundamental flexural mode by more than one order of magnitude compared to bulk values. The modification of the dispersion relation in nanostructures has important consequences for noise control in nano and micro-electromechanical systems (MEMS/NEMS) as well as opto-mechanical devices.Comment: 5 page

SDSS J124602.54+011318.8: A Highly Luminous Optical Transient at z=0.385

We report the discovery of a highly luminous optical transient (OT), SDSS J124602.54+011318.8, associated with a galaxy at a redshift of 0.385. In this paper we consider the possibility that the OT may be a GRB afterglow. Three sets of images and two sets of spectra were obtained as part of the normal operations of the Sloan Digital Sky Survey (SDSS). In the first two image sets, observed two nights apart, the object appears as a point source at $r^{*}\approx 17$. The third image set, observed about 410 days later, shows an extended source which is more than 2.5 magnitudes fainter. The spectra were observed about 400 and 670 days after the first two image sets, and both show an apparently normal galaxy at a redshift of 0.385. Associating the OT with the galaxy, the absolute magnitude was $M_{r^*}=-24.8$, which is over 4 magnitudes brighter than the most luminous supernova ever measured. The spectral energy distributions of the galaxy-subtracted OT derived from the first two image sets are well-fit by single power-laws with indices of $\beta_{\nu}=-0.92$ and -1.29 respectively, similar to most GRB afterglows. Based upon the luminosity of the OT, non-detections in contemporaneous ROTSE-I images, and the change in spectral slope, the OT, if an afterglow, was likely discovered early during a ``plateau'' or slowly-fading phase. The discovery of a GRB afterglow at this stage of the SDSS is consistent with expectations, but only if the optical emission is much less strongly beamed than the gamma-rays. We emphasize that other explanations for the OT cannot be ruled out; a recent follow-up study by [galyam02] provides strong evidence that this source is in fact an unusual AGN.Comment: Updated version to appear in Ap

The DESI One-Percent Survey: Exploring the Halo Occupation Distribution of Luminous Red Galaxies and Quasi-Stellar Objects with AbacusSummit

We present the first comprehensive Halo Occupation Distribution (HOD) analysis of the DESI One-Percent survey Luminous Red Galaxy (LRG) and Quasi-Stellar Object (QSO) samples. We constrain the HOD of each sample and test possible HOD extensions by fitting the redshift-space galaxy 2-point correlation functions in 0.15 < r < 32 Mpc/h in a set of fiducial redshift bins. We use AbacusSummit cubic boxes at Planck 2018 cosmology as model templates and forward model galaxy clustering with the AbacusHOD package. We achieve good fits with a standard HOD model with velocity bias, and we find no evidence for galaxy assembly bias or satellite profile modulation at the current level of statistical uncertainty. For LRGs in 0.4 < z < 0.6, we infer a satellite fraction of fsat = 11+-1%, a mean halo mass of log10 Mh = 13.40+0.02-0.02, and a linear bias of blin = 1.93+0.06-0.04. For LRGs in 0.6 < z < 0.8, we find fsat = 14+-1%, log10 Mh = 13.24+0.02-0.02, and blin = 2.08+0.03-0.03. For QSOs, we infer fsat = 3+8-2%, log10 Mh = 12.65+0.09-0.04, and blin = 2.63+0.37-0.26 in redshift range 0.8 < z < 2.1. Using these fits, we generate a large suite of high-fidelity galaxy mocks. We also study the redshift-evolution of the DESI LRG sample from z = 0.4 up to z = 1.1, revealing significant and interesting trends in mean halo mass, linear bias, and satellite fraction.Comment: Submitted to MNRAS, comments welcom