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.
53576835
Primordial black holes as a tool for constraining non-Gaussianity
Primordial Black Holes (PBH's) can form in the early Universe from thecollapse of large density fluctuations. Tight observational limits on theirabundance constrain the amplitude of the primordial fluctuations on very smallscales which can not otherwise be constrained, with PBH's only forming from theextremely rare large fluctuations. The number of PBH's formed is thereforesensitive to small changes in the shape of the tail of the fluctuationdistribution, which itself depends on the amount of non-Gaussianity present. Westudy, for the first time, how quadratic and cubic local non-Gaussianity ofarbitrary size (parameterised by f_nl and g_nl respectively) affects the PBHabundance and the resulting constraints on the amplitude of the fluctuations onvery small scales. Intriguingly we find that even non-linearity parameters oforder unity have a significant impact on the PBH abundance. The sign of thenon-Gaussianity is particularly important, with the constraint on the allowedfluctuation amplitude tightening by an order of magnitude as f_nl changes fromjust -0.5 to 0.5. We find that if PBH's are observed in the future, thenregardless of the amplitude of the fluctuations, non-negligible negative f_nlwould be ruled out. Finally we show that g_nl can have an even larger effect onthe number of PBH's formed than f_nl.
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.
11640854
Critical collapse and the primordial black hole initial mass function
It has normally been assumed that primordial black holes (PBHs) always form with a mass approximately equal to the mass contained within the horizon at that time. Recent work studying the application of critical phenomena in gravitational collapse to PBH formation has shown that in fact, at a fixed time, PBHs with a range of masses are formed. When calculating the PBH initial mass function it is usually assumed that all PBHs form at the same horizon mass. It is not clear, however, that it is consistent to consider the spread in the mass of PBHs formed at a single horizon mass, whilst neglecting the range of horizon masses at which PBHs can form. We use the excursion set formalism to compute the PBH initial mass function, allowing for PBH formation at a range of horizon masses, for two forms of the density perturbation spectrum. First we examine power-law spectra with $ng1,$ where PBHs form on small scales. We find that, in the limit where the number of PBHs formed is small enough to satisfy the observational constraints on their initial abundance, the mass function approaches that found by Niemeyer and Jedamzik under the assumption that all PBHs form at a single horizon mass. Second, we consider a flat perturbation spectrum with a spike at a scale corresponding to horizon mass $\ensuremath{\sim}{0.5M}_{\ensuremath{\bigodot}},$ and compare the resulting PBH mass function with that of the MACHOs (massive compact halo objects) detected by microlensing observations. The predicted mass spectrum appears significantly wider than the steeply falling spectrum found observationally.
14950553
The cosmic ray distribution in sagittarius B
The H.E.S.S. instrument has observed a diffuse flux of ~TeV γ-rays from a large solid angle around the Galactic center (GC). This emission is correlated with the distribution of gas in the region, suggesting that the γ-rays originate in collisions between cosmic-ray hadrons (CRHs) and ambient matter. Of particular interest, H.E.S.S. has detected γ-rays from the Sagittarius (Sgr) B molecular cloud complex. Prompted by the suggestion of a hadronic origin for the γ-rays, we have examined archival 330 and 74 MHz Very Large Array radio data and 843 MHz Sydney University Molonglo Sky Survey data covering Sgr B, looking for synchrotron emission from secondary electrons and positrons (expected to be created in the same interactions that supply the observed γ-rays). Intriguingly, we have uncovered nonthermal emission, but at a level exceeding expectation. Adding to the overall picture, recent observations by the Atacama Pathfinder Experiment telescope show that the cosmic-ray ionization rate is 10 times greater in the Sgr B2 region of Sgr B than the local value. Lastly, Sgr B2 is also a very bright X-ray source. We examine scenarios for the spectra of CRHs and/or primary electrons that would reconcile all these different data. We determine that (1) a hard (~E-2.2), high-energy (TeV) population of CRHs is unavoidably required by the H.E.S.S. γ-ray data, and (2) the remaining broadband, nonthermal phenomenology is explained either by a rather steep (~E-2.9) spectrum of primary electrons or a (~E-2.7) population of CRHs. Perhaps unsurprisingly, no single power-law population of either leptons or hadrons can explain the totality of broadband, nonthermal Sgr B phenomenology.
118443995
Opportunities for maser studies with the Square Kilometre Array
The Square Kilometre Array (SKA) is the radio telescope of the next generation, pro- viding an increase in sensitivity and angular resolution of two orders of magnitude over existing telescopes. Currently, the SKA is expected to span the frequency range 0.1 25 GHz with capa- bilities including a wide field-of-view and measurement of polarised emission. Such a telescope has enormous potential for testing fundamental physical laws and producing transformational discoveries. Important science goals include using H2O megamasers to make precise estimates of H0, which will anchor the extragalactic distance scale, and to probe the central structures of accretion disks around supermassive black holes in AGNs, to study OH megamasers associated with extreme starburst activity in distant galaxies and to study with unprecedented precision molecular gas and star formation in our Galaxy. 1. Overview The Square Kilometre Array (SKA) is a paradigm-shifting radio telescope for the next generation, providing an increase in sensitivity and angular resolution of two orders of magnitude over existing telescopes. It will be a truly global machine with an expected life- time of at least 50 years. Such a telescope has enormous potential for testing fundamental physical laws and producing transformational discoveries. The aim of the telescope is to answer some of the "big" questions in astronomy, such as what is the nature of dark energy, are we alone in the Universe, how did galaxies and black holes form, what is the origin and evolution of cosmic magnetism, can pulsars be used to detect gravity waves? The project is an international consortium of 50 institutions, spread over 17 coun- tries. Present governance is through the International SKA Steering Committee, with 21 members, which oversees the International SKA Project Officeand 6 targeted Working Groups. Engagement with inter-governmental agencies has begun to establish a gover- nance model and funding strategies. Currently, there are several pathfinder and demon- strator projects in progress for both science and technology developments.
17911645
Influence of the Neutron Star 1E 161348–5055 in RCW 103 on the Surrounding Medium
We have carried out a study of the neutral hydrogen in the direction of the X-ray source 1E 161348–5055, a compact central object (CCO) located in the interior of the supernova remnant (SNR) RCW 103. The H i 21 cm line observations were carried out using the Australia Telescope Compact Array, complemented with single dish data from the Parkes radio telescope to recover information at all spatial scales. We derive a distance to RCW 103 of 3.1 kpc, in agreement with previous distance measurements. We have also detected a small hole in the H i emission which is positionally and kinematically coincident with the location of the CCO which confirms the association between the SNR and the CCO. This is the third case of a depression in H i emission seemingly associated with CCOs in SNRs. The characteristic parameters of the holes such as their size, eccentricity and evacuated mass are similar in all three cases. We estimate the absorbing H I column density towards 1E 161348–5055 to be ∼6 × 10 21 cm –2 , a value compatible with a blackbody solution for the CCO X-ray emission. However, the implied temperature and luminosity are very high compared to most neutron stars. Moreover, the strong long-term variability in X-rays favours the hypothesis that 1E 161348–5055 is an accreting binary source rather than an isolated, cooling neutron star. An analysis of the continuum image obtained at 1.4 GHz from these observations shows no trace of a pulsar wind nebula around 1E 161348–5055, in spite of it being a young object.
16633350
The neutral gas in the environs of the Geminga gamma-ray pulsar
We present a high-resolution (24″) study of the HI interstellar gas distribution around the radio-quiet neutron star Geminga. Based on very large array and MPIfR Effelsberg telescope data, we analyzed a 40′ × 40′ field around Geminga. These observations have revealed the presence of a neutral gas shell, 0.4 pc in radius, with an associated HI mass of 0.8M⊙, which surrounds Geminga at a radial velocity compatible with the kinematical distance of the neutron star. In addition, morphological agreement is observed between the internal face of the HI shell and the brightest structure of Geminga’s tail observed in X-rays. We explore the possibility that this morphological agreement is the result of a physical association.
11866216
Spitzer IRAC observations of newly discovered planetary nebulae from the MACQUARIE-AAO-Strasbourg Hα planetary nebula project
We compare H?, radio continuum, and Spitzer Space Telescope images of 58 planetary nebulae (PNe) recently discovered by the Macquarie-AAO-Strasbourg H? PN Project (MASH) of the SuperCOSMOS H? Survey. Using Infrared Array Camera (IRAC) data, we examine the relationships between optical and MIR morphologies from 3.6 to 8.0 ?m and explore the ratio of mid-infrared (MIR) to radio nebular fluxes, which is a valuable discriminant between thermal and nonthermal emission. MASH emphasizes late evolutionary stages of PNe compared with previous catalogs, enabling study of the changes in MIR and radio flux that attend the aging process. Spatially integrated fluxes are constructed for all MASH PNe observed by the GLIMPSE Legacy Project, using the H? morphologies to define the areas of MIR and radio continuum emission observed by the Midcourse Space Experiment (MSX), IRAC, the Molonglo Observatory Synthesis Telescope, and the Very Large Array (VLA). The ratio of IRAC 8.0 ?m to MSX 8.3 ?m fluxes provides an assessment of the absolute diffuse calibration of IRAC at 8.0 ?m. We independently confirm the aperture correction factor to be applied to IRAC at 8.0 ?m to align it with the diffuse calibration of MSX. The result is in accord with the recommendations of the Spitzer Science Center and with our results from a parallel study of H II regions in the MIR and radio. However, these PNe probe the diffuse calibration of IRAC on a spatial scale of 9''-77'', as opposed to the many-arcminute scale from the H II regions' study.