119454410
Calculating exclusion limits for weakly interacting massive particle direct detection experiments without background subtraction
Competitive limits on the weakly interacting massive particle (WIMP) spin-independent scattering cross section are currently being produced by ${}^{76}\mathrm{Ge}$ detectors originally designed to search for neutrinoless double beta decay, such as the Heidelberg-Moscow and IGEX experiments. In the absence of background subtraction, limits on the WIMP interaction cross section are set by calculating the upper confidence limit on the theoretical event rate, given the observed event rate. The standard analysis technique involves calculating the $90%$ upper confidence limit on the number of events in each bin, and excluding any set of parameters (WIMP mass and cross section) which produces a theoretical event rate for any bin which exceeds the $90%$ upper confidence limit on the event rate for that bin. We show that, if there is more than one energy bin, this produces exclusion limits that are actually at a lower degree of confidence than $90%,$ and are hence erroneously tight. We formulate criteria which produce true $90%$ confidence exclusion limits in these circumstances, including calculating the individual bin confidence limit for which the overall probability that no bins exceed this confidence limit is $90%$ and calculating the $90%$ minimum confidence limit on the number of bins which exceed their individual bin $90%$ confidence limits. We then compare the limits on the WIMP cross section produced by these criteria with those found using the standard technique, using data from the Heidelberg-Moscow and IGEX experiments.
119021467
PRIMORDIAL BLACK HOLES AND EARLY COSMOLOGY
We describe the changes to the standard primordial black hole constraints on density perturbations if there are modifications to the standard cosmology between the time of formation and nucleosynthesis.
117989592
Extracting Information about WIMP Properties from Direct Detection Experiments: Astrophysical Uncertainties
WIMP direct detection experiments probe the ultra-local dark matter density and velocity distribution. We review how uncertainties in these quantities affect the accuracy with which the WIMP mass and cross-section can be constrained or determined.
8787684
Determining the WIMP mass from a single direct detection experiment
The energy spectrum of nuclear recoils in Weakly Interacting Massive Particle (WIMP) direct detection experiments depends on the underlying WIMP mass (strongly for light WIMPs, weakly for heavy WIMPs). We discuss how the accuracy with which the WIMP mass could be determined by a single direct detection experiment depends on the detector configuration and the WIMP properties. In particular we examine the effects of varying the underlying WIMP mass, the detector target nucleus, exposure, energy threshold and maximum energy, the local velocity distribution and the background event rate and spectrum.
16034831
Probing the width of the MACHO mass function
The simplest interpretation of the microlensing events observed towards the Large Magellanic Cloud is that approximately half of the mass of the Milky Way halo is in the form of MAssive Compact Halo Objects with $M \sim 0.5 M_{\odot}$. This poses severe problems for stellar MACHO candidates, and leads to the consideration of more exotic objects such as primordial black holes (PBHs). Constraining the MACHO mass function will shed light on their nature. Using the current data we find, for four halo models, the best fit delta-function, power law and PBH mass functions. The best fit PBH mass functions, despite having significant finite width, have likelihoods which are similar to, and for one particular halo model greater than, those of the best fit delta functions. We also find that if the correct halo model is known then $\sim$ 500 events will be sufficient to determine whether the MACHO mass function has significant width, and will also allow determination of the mass function parameters to $\sim 5%$.
55672557
WIMP physics with ensembles of direct-detection experiments
if dierent classes of experiments see consistent signals and infer the same WIMP properties. In this work, we review the ideas, methods, and status of direct-detection searches. We focus in particular on extracting WIMP physics (WIMP interactions and phase-space distribution) from direct-detection data in the early discovery days when multiple experiments see of order dozens to hundreds of events. To demonstrate the essential complementarity of dierent direct-detection experiments in this context, we create mock data intended to represent the data from the near-future Generation 2 experiments. We consider both conventional supersymmetry-inspired benchmark points (with spin-independent and -dependent elastic cross sections just below current limits), as well as benchmark points for other classes of models (inelastic and eective-operator paradigms). We also investigate the eect on parameter estimation of loosening or dropping the assumptions about the local WIMP phase-space distribution. We arrive at two main conclusions. Firstly, teasing out WIMP physics with experiments depends critically on having a wide set of detector target materials, spanning a large range of target nuclear masses and spin-dependent sensitivity. It is also highly desirable to obtain data from low-threshold experiments. Secondly, a general reconstruction of the local WIMP velocity distribution, which will only be achieved if there are multiple experiments using dierent target materials, is critical to obtaining a robust and unbiased estimate of the WIMP mass.
119374948
OH (1720 MHz) Maser Search toward the Large Magellanic Cloud
We have carried out a sensitive search for OH (1720 MHz) masers in the Large Magellanic Cloud (LMC) toward five regions using the Australia Telescope Compact Array. Our source list includes the 30 Doradus region and four supernova remnants (SNRs): N44, N49, N120, and N132D. These data have a typical resolution of ~8'' and rms noise levels of 5–10 mJy beam-1. We have detected OH (1720 MHz) masers in the northeast part of 30 Doradus and toward the SNR N49. The OH (1720 MHz) maser emission in 30 Doradus is coincident with a cluster of young stars known as "knot 1" and is almost certainly of the star formation variety. Our spectral resolution (0.68 km s-1) is insufficient to detect the Zeeman effect from the strongest (~320 mJy beam-1) of the 30 Doradus OH (1720 MHz) masers, leading to an upper limit to the field strength of 6 mG. The weak OH (1720 MHz) maser emission (35 mJy beam-1) detected toward the LMC SNR N49 is located just west of a previously identified CO cloud and is indicative of an interaction between the SNR and the molecular cloud. Although the statistics are low, the detection rate seems consistent with that seen for Galactic star-forming region and SNR type OH (1720 MHz) masers—both of which are low.
17916452
The Southern Galactic Plane Survey: Polarized Radio Continuum Observations and Analysis
The Southern Galactic Plane Survey (SGPS) is a radio survey in the 21 cm H I line and in 1.4 GHz full-polarization continuum, observed with the Australia Telescope Compact Array and the Parkes 64 m single-dish telescope. The survey spans a Galactic longitude of 253° < l < 358° and a latitude of |b| < 15 at a resolution of 100'' and a sensitivity below 1 mJy beam-1. This paper presents interferometer only polarized continuum survey data and describes the data taking, analysis processes, and data products. The primary data products are the four Stokes parameters I, Q, U, and V in 25 overlapping fields of 55 by 3°, from which polarized intensity, polarization angle, and rotation measure are calculated. We describe the effects of missing short spacings, and discuss the importance of the polarized continuum data in the SGPS for studies of fluctuations and turbulence in the ionized interstellar medium and for studying the strength and structure of the Galactic magnetic field.
118680225
Ultra- and hyper-compact H ii regions at 20 GHz
We present radio and infrared observations of 4 hyper-compact HII regions and 4 ultracompact HII regions in the southern Galactic plane. These objects were selected from a blind survey for UCHII regions using data from two new radio surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our knowledge, this is the first blind r adio survey for hyper- and ultra-compact HII regions. We have followed up these sources with the Australia Telescope Compact Array to obtain H70� recombination line measurements, higher resolution images at 20 GHz and flux density measurements at 30, 40 and 95 GHz. From this we have determined sizes and recombination line temperatures as well as modeling the spectral energy distributions to determine emission measures. We have classified the sources as hyper-compact or ultra-compact on the basis of their physical parameters, in comparison with benchmark parameters from the literature. Several of these bright, compact sources are potential cali brators for the Low Frequency Instrument (30 70 GHz) and the 100-GHz channel of the High Frequency Instrument of the Planck satellite mission. They may also be useful as calibrators for the Australia Telescope Compact Array, which lacks good non-variable primary flux ca librators at higher frequencies and in the Galactic plane region. Our spectral energy distri butions allow the flux densities within the Planck bands to be determined, although our high frequency observations show that several sources have excess emission at 95 GHz (3 mm) that can not be explained by current models.
84177776
A multiwavelength study of the radio source G296.7−0.9: confirmation as a Galactic supernova remnant
We present a multi-wavelength study of the radio source G296.7-0.9. This source has a bilateral radio morphology, a radio spectral index of 0.5 ± 0.1, sparse patches of linear polarisation, and thermal X-rays with a bright arc near the radio boundary. Considering these characteristics, we conclude that G296.7-0.9 is a supernova remnant (SNR). The age and morphology of the SNR in the context of its environment suggest that the source is co-located with an Hii region, and that portions of the shock front have broken out into a lower density medium. We see no evidence for a neutron star or pulsar wind nebula associated with SNR G296.7-0.9.
15631374
Investigation of the Large-scale Neutral Hydrogen near the Supernova Remnant W28
The distribution and kinematics of neutral hydrogen have been studied in a wide area around the supernova remnant (SNR) W28. A 25 ? 25 field centered at l = 65, b = 0? was surveyed using the Parkes 64 m radio telescope (half-power beamwidth of 147 at ?21 cm). Even though W28 is located in a complex zone of the Galactic plane, we have found different H I features, which are evidence of the interaction between W28 and its surrounding gas. An extended cold cloud with about 70 M? of neutral hydrogen was detected at the location of W28 as a self-absorption feature, near the local standard of rest velocity of +7 km s-1. This H I feature is the atomic counterpart of the molecular cloud shown by previous studies to be associated with W28. From this detection, we can independently confirm a kinematical distance of about 1.9 kpc for W28. In addition, the neutral hydrogen observed in emission around the SNR displays a ringlike morphology in several channel maps over the velocity interval [-25.0, +38.0] km s-1. We propose that these features are part of an interstellar H I shell that has been swept up by the supernova shock front. Emission from this shell is confused with unrelated gas. Hence, we derive an upper limit for the shell mass of 1200?1600 M?, a maximum radius of the order of 20 pc, an expansion velocity of ~30 km s-1, an initial energy of about 1.4?1.8 ? 1050 ergs, and an age of ~3.3 ? 104 yr. The preexisting ambient medium has a volume density on the order of 1.5?2 cm-3. W28 is probably in the radiative evolutionary phase, although it is not possible to identify the recombined thin neutral shell expected to form behind the shock front with the angular resolution of the present survey.