Lepton Models for TeV Emission from SNR RX J1713.7-3946

(Aims.) SNR RX J1713.7-3946 is perhaps one of the best observed shell-type supernova remnants with emissions dominated by energetic particles accelerated near the shock front. The nature of the TeV emission, however, is an issue still open to investigation. (Methods.) We carry out a systematic study of four lepton models for the TeV emission with the Markov chain Monte Carlo method. (Results.) It is shown that current data already give good constraints on the model parameters. Two commonly used parametric models do not appear to fit the observed radio, X-ray, and gamma-ray spectra. Models motivated by diffusive shock acceleration and by stochastic acceleration by compressive waves in the shock downstream give comparably good fits. The former has a sharper spectral cutoff in the hard X-ray band than the latter. Future observations with the HXMT and NuSTAR may distinguish these two models.Comment: 4 pages, 2 figures, accepted by A&A Lette

Magnetic fields in cosmic particle acceleration sources

We review here some magnetic phenomena in astrophysical particle accelerators associated with collisionless shocks in supernova remnants, radio galaxies and clusters of galaxies. A specific feature is that the accelerated particles can play an important role in magnetic field evolution in the objects. We discuss a number of CR-driven, magnetic field amplification processes that are likely to operate when diffusive shock acceleration (DSA) becomes efficient and nonlinear. The turbulent magnetic fields produced by these processes determine the maximum energies of accelerated particles and result in specific features in the observed photon radiation of the sources. Equally important, magnetic field amplification by the CR currents and pressure anisotropies may affect the shocked gas temperatures and compression, both in the shock precursor and in the downstream flow, if the shock is an efficient CR accelerator. Strong fluctuations of the magnetic field on scales above the radiation formation length in the shock vicinity result in intermittent structures observable in synchrotron emission images. Resonant and non-resonant CR streaming instabilities in the shock precursor can generate mesoscale magnetic fields with scale-sizes comparable to supernova remnants and even superbubbles. This opens the possibility that magnetic fields in the earliest galaxies were produced by the first generation Population III supernova remnants and by clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review

Problems of Kantian Nonconceptualism and the Transcendental Deduction

In this paper, I discuss the debate on Kant and nonconceptual content. Inspired by Kant’s account of the intimate relation between intuition and concepts, McDowell (1996) has forcefully argued that the relation between sensible content and concepts is such that sensible content does not severally contribute to cognition but always only in conjunction with concepts. This view is known as conceptualism. Recently, Kantians Robert Hanna and Lucy Allais, among others, have brought against this view the charge that it neglects the possibility of the existence of essentially nonconceptual content that is not conceptualised or subject to conceptualisation. Their critique of McDowell amounts to nonconceptualism. However, both views, conceptualist and nonconceptualist, share the assumption that intuition is synthesised content in Kant’s sense. My interest is not in the validity of the philosophical positions of conceptualism or nonconceptualism per se. I am particularly interested in the extent to which the views that McDowell and Hanna and Allais respectively advance are true to Kant, or can validly be seen as Kantian positions. I argue that although McDowell is right that intuition is only epistemically relevant in conjunction with concepts, Hanna and Allais are right with regard to the existence of essentially nonconceptual content (intuitions) independently of the functions of the understanding, but that they are wrong with regard to non-conceptualised intuition being synthesised content in Kant’s sense. Kantian conceptualists (Bowman 2011; Griffith 2012; Gomes 2014) have responded to the recent nonconceptualist offensive, with reference to A89ff./B122ff. (§13)—which, confusingly, the nonconceptualists also cite as evidence for their contrary reading—by arguing that the nonconceptualist view conflicts with the central goal of the Transcendental Deduction, namely, to argue that all intuitions are subject to the categories. I contend that the conceptualist reading of A89ff./B122ff. is unfounded, but also that the nonconceptualists are wrong to believe that intuitions as such refer strictly to objects independently of the functions of the understanding, and that they are mistaken about the relation between figurative synthesis and intellectual synthesis. I argue that Kant is a conceptualist, albeit not in the sense that standard conceptualists assume. Perceptual knowledge is always judgemental, though without this resulting in the standard conceptualist claim that, necessarily, all intuitions or all perceptions per se stand under the categories (strong conceptualism). I endorse the nonconceptualist view that, for Kant, perception per se, i.e. any mere or ‘blind’ intuition of objects (i.e. objects as indeterminate appearances) short of perceptual knowledge, does not necessarily stand under the categories. Perception is not yet perceptual knowledge. In this context, I point out the common failure in the literature on the Transcendental Deduction, both of the conceptualist and nonconceptualist stripe, to take account of the modal nature of Kant’s argument for the relation between intuition and concept insofar as cognition should arise from it

Six Years of Chandra Observations of Supernova Remnants

We present a review of the first six years of Chandra X-ray Observatory observations of supernova remnants. From the official "first-light" observation of Cassiopeia A that revealed for the first time the compact remnant of the explosion, to the recent million-second spectrally-resolved observation that revealed new details of the stellar composition and dynamics of the original explosion, Chandra observations have provided new insights into the supernova phenomenon. We present an admittedly biased overview of six years of these observations, highlighting new discoveries made possible by Chandra's unique capabilities.Comment: 82 pages, 28 figures, for the book Astrophysics Update

The value of privileged access

European Journal of Philosophy, EarlyView

Radically self-deceived? Not so fast

Contains fulltext : 219088pos.pdf (postprint version ) (Closed access)We don’t know our own mental states and we don’t have free will. These are Pelham et al.’s central claims in a nutshell. In principle, these two claims are independent: if one lacks free will because, say, all of one’s actions are controlled by an evil demon, it’s still possible for one to know that one believes it’s Friday or that one wants a cup of coffee. Conversely, it’s possible to have free will and to be radically self-deceived or ignorant about one’s mental states. The authors seem to take the two topics together because of their focus on “knowing why”. If we don’t know why we think what we think, we lack self-knowledge; if we don’t know why we do what we do, we lack free will. In this paper, we argue that Pelham et al. fail to acknowledge that “knowing why” one believes or does something is ambiguous between rationalizing and non-rationalizing explanations. The two dramatic claims do not follow in any straightforward sense once this ambiguity is properly recognized, or so we claim