arXiv subjects

Alex Drlica-Wagner

Publications and source records attributed to Alex Drlica-Wagner.

135 records · Page 8Linked to original sources

arXiv2015

Using Likelihood for Combined Data Set Analysis

The joint likelihood is a simple extension of the standard likelihood formalism that enables the estimation of common parameters across disjoint datasets. Joining the likelihood, rather than the data itself, means nuisance parameters can be dealt with independently. Application of this technique, particularly to Fermi-LAT dwarf spheroidal analyses, has already been met with great success. We present a description of the method's general implementation along with a toy Monte-Carlo study of its properties and limitations.

astro-ph.HE↗

arXiv2014

Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially-extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section ($\sim 3\times10^{-26}{\rm cm}^{3}{\rm s}^{-1}$) for dark matter masses $\lesssim 30$ GeV annihilating via the $b \bar b$ or $τ^{+}τ^{-}$ channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

astro-ph.HE↗

arXiv2014

Complementarity of Dark Matter Searches in the pMSSM

As is well known, the search for and eventual identification of dark matter in supersymmetry requires a simultaneous, multi-pronged approach with important roles played by the LHC as well as both direct and indirect dark matter detection experiments. We examine the capabilities of these approaches in the 19-parameter p(henomenological)MSSM which provides a general framework for complementarity studies of neutralino dark matter. We summarize the sensitivity of dark matter searches at the 7, 8 (and eventually 14) TeV LHC, combined with those by \Fermi, CTA, IceCube/DeepCore, COUPP, LZ and XENON. The strengths and weaknesses of each of these techniques are examined and contrasted and their interdependent roles in covering the model parameter space are discussed in detail. We find that these approaches explore orthogonal territory and that advances in each are necessary to cover the Supersymmetric WIMP parameter space. We also find that different experiments have widely varying sensitivities to the various dark matter annihilation mechanisms, some of which would be completely excluded by null results from these experiments.

hep-ph↗

arXiv2013

Dark Matter in the Coming Decade: Complementary Paths to Discovery and Beyond

In this Report we discuss the four complementary searches for the identity of dark matter: direct detection experiments that look for dark matter interacting in the lab, indirect detection experiments that connect lab signals to dark matter in our own and other galaxies, collider experiments that elucidate the particle properties of dark matter, and astrophysical probes sensitive to non-gravitational interactions of dark matter. The complementarity among the different dark matter searches is discussed qualitatively and illustrated quantitatively in several theoretical scenarios. Our primary conclusion is that the diversity of possible dark matter candidates requires a balanced program based on all four of those approaches.

hep-ph↗

arXiv2012

Constraints on Dark Matter and Supersymmetry from LAT Observations of Dwarf Galaxies

Due to a large mass-to-light ratio and low astrophysical backgrounds, dwarf spheroidal galaxies (dSphs) are considered to be one of the most promising targets for dark matter searches via gamma rays. The Fermi LAT Collaboration has recently reported robust constraints on the dark matter annihilation cross section from a combined analysis of 10 dSphs. These constraints have been applied to experimentally valid, super-symmetric particle models derived from a phenomenological scan of the Minimal Supersymmetric Standard Model (the pMSSM). Additionally, the LAT Collaboration has searched for spatially extended, hard-spectrum gamma-ray sources lacking counterparts in other wavelengths, since they may be associated with dark matter substructures predicted from simulations.

astro-ph.HE↗

arXiv2012

Search for Spatially Extended Fermi-LAT Sources Using Two Years of Data

Spatial extension is an important characteristic for correctly associating gamma-ray-emitting sources with their counterparts at other wavelengths and for obtaining an unbiased model of their spectra. We present a new method for quantifying the spatial extension of sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi). We perform a series of Monte Carlo simulations to validate this tool and calculate the LAT threshold for detecting the spatial extension of sources. We then test all sources in the second Fermi-LAT catalog (2FGL) for extension. We report the detection of seven new spatially extended sources.

astro-ph.HE↗

arXiv2011

Search for Unknown Dark Matter Satellites of the Milky Way

We present a search for Galactic dark matter (DM) satellites using the Large Area Telescope (LAT). N-body simulations based on the Lambda-CDM model of cosmology predict a large number of as yet unobserved Galactic DM satellites. These satellites could potentially produce gamma rays through the self-annihilation of DM particles. Some DM satellites are expected to have hard gamma-ray spectra, finite angular extents, and a lack of counterparts at other wavelengths. We searched for LAT sources with these characteristics. We found no candidate DM satellites matching these criteria in one year of LAT data and interpreted this result in the context of N-body simulations.

astro-ph.HE↗

arXiv2011

Using TMine for the Fermi-LAT Event Analysis

The Large Area Telescope (LAT) event analysis is the final stage in the event reconstruction responsible for the creation of high-level variables (e.g., event energy, incident direction, particle type, etc.). We discuss the development of TMine, a powerful new tool for designing and implementing event classification analyses (e.g., distinguishing photons from charged particles). TMine is structured on ROOT, a data analysis framework that is the de-facto standard for current high energy physics experiments; thus, TMine fits naturally into the ROOT-based data processing pipeline of the LAT. TMine provides a visual development environment for the LAT event analysis and utilizes advanced multivariate classification algorithms implemented in ROOT. We discuss the application of TMine to the next iteration of the event analysis (Pass 8), the LAT charged particle analyses, and the classification of unassociated LAT gamma-ray sources.

astro-ph.IM↗

arXiv2010

The Observed Growth of Massive Galaxy Clusters II: X-ray Scaling Relations

(Abridged) This is the second in a series of papers in which we derive simultaneous constraints on cosmology and X-ray scaling relations using observations of massive, X-ray flux-selected galaxy clusters. The data set consists of 238 clusters drawn from the ROSAT All-Sky Survey with 0.1-2.4 keV luminosities >2.5e44 erg/second, and incorporates extensive follow-up observations using the Chandra X-ray Observatory. Our analysis accounts self-consistently for all selection effects, covariances and systematic uncertainties. Here we describe the reduction of the follow-up X-ray observations, present results on the cluster scaling relations, and discuss their implications. Our constraints on the luminosity-mass and temperature-mass relations, measured within r_500, lead to three important results. First, the data support the conclusion that excess heating of the intracluster medium has altered its thermodynamic state from that expected in a simple, gravitationally dominated system; however, this excess heating is primarily limited to the central regions of clusters (r<0.15r_500). Second, the intrinsic scatter in the center-excised luminosity-mass relation is remarkably small, being undetected at the <10% level in current data; for the hot, massive clusters under investigation, this scatter is smaller than in either the temperature-mass or Y_X-mass relations (10-15%). Third, the evolution with redshift of the scaling relations is consistent with the predictions of simple, self-similar models of gravitational collapse, indicating that the mechanism responsible for heating the central regions of clusters was in operation before redshift 0.5 (the limit of our data) and that its effects on global cluster properties have not evolved strongly since then.

astro-ph.CO↗