Hasil untuk "astro-ph"

Y. Ishisaki, R. Kelley, H. Awaki et al.

The resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM) consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput x-ray mirror assembly (XMA) with a focal length of 5.6 m. XRISM is a recovery mission of ASTRO-H/Hitomi, and the Resolve instrument is a rebuild of the ASTRO-H soft x-ray spectrometer (SXS) and the Soft X-ray Telescope (SXT) that achieved energy resolution of ∼5 eV FWHM on orbit, with several important changes based on lessons learned from ASTRO-H. The flight models of the Dewar and the electronics boxes were fabricated and the instrument test and calibration were conducted in 2021. By tuning the cryocooler frequencies, energy resolution better than 4.9 eV FWHM at 6 keV was demonstrated for all 36 pixels and high resolution grade events, as well as energy-scale accuracy better than 2 eV up to 30 keV. The immunity of the detectors to microvibration, electrical conduction, and radiation was evaluated. The instrument was delivered to the spacecraft system in 2022-04 and is under the spacecraft system testing as of writing. The XMA was tested and calibrated separately. Its angular resolution is 1.27′ and the effective area of the mirror itself is 570 cm2 at 1 keV and 424 cm2 at 6 keV. We report the design and the major changes from the ASTRO-H SXS, the integration, and the results of the instrument test.

J. Hodge

A comparison is made between Greaves, E. D., Bracho, C., Gift, S., and Rodrigues, A. N., 2021. A Solution to the Pioneer Anomalous Annual and Diurnal Residuals, Progress in Physics, vol. 17, 2, p. 168. and Hodge, J. C. 2006. Scalar potential model of the Pioneer Anomaly.arXiv: astro-ph/0612567v1. Both papers suggest the Pioneer Anomaly obser- vation is due to the signal being modified by a characteristic of space that is influenced by the Sun and Earth. The papers differ by what that characteristic is and how it influences the signal. The former paper uses “energy density” (a scalar) which is proportional to distance (r-4) from bodies. All the characteristics of the former paper were accounted in the original calculation of the Pioneer Anomaly. The latter paper used a vector proportional to r-2, a gravitational force exerted on photons that was not accounted. The different treatment of r by the latter provides a more accurate treatment of the periodicities and all 10 anomalous characteristics of the Pioneer Anomaly. The conclusions of the former that the velocity of light is Galilean additive and the use of the “gravitational density” are not supported.

Ayan Chatterjee, Biswajit Jana, A. Bandyopadhyay

It has been shown by Scherrer (Phys Rev Lett 93:011301, 2004. https://doi.org/10.1103/PhysRevLett.93.011301. arXiv:astro-ph/0402316 [astro-ph]) and de Putter and Linder (Astropart Phys 28:263–272, 2007. https://doi.org/10.1016/j.astropartphys.2007.05.011. arXiv:0705.0400 [astro-ph]) that, when dynamics of dark energy is driven by a homogeneous k-essence scalar field ϕ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document}, with a Lagrangian of the form L=V0F(X)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L = V_0F(X)$$\end{document} with a constant potential V0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V_0$$\end{document} and X=12∇μϕ∇μϕ=12ϕ˙2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$X = \frac{{1}}{{2}}\nabla ^\mu \phi \nabla _\mu \phi = \frac{{1}}{{2}}{\dot{\phi }}^2$$\end{document}, one obtains a scaling relation X(dF/dX)2=Ca-6\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$X(\mathrm{d}F/\mathrm{d}X)^2 = Ca^{-6}$$\end{document} , where C is a constant and a is the FRW scale factor of the universe. The separate energy conservation in the dark energy sector and the constancy of k-essence potential are instrumental in obtaining such a scaling. In this paper, we have shown that, even when considering time-dependent interactions between dark energy and dark matter, the constancy of k-essence potential may lead to a modified form of scaling. We have obtained such a scaling relation for a particular class of parametrisation of the source term occurring in the continuity equation of dark energy and dark matter in the interacting scenario. We used inputs from the JLA analysis of luminosity distance and redshift data from Supernova Ia observations, to obtain the modified form of the scaling.

G. Fastner, C. Gaisberger, J. Kaiser et al.

The aim of this review is to provide a comprehensive overview of the role of intraoperative radiation therapy with electrons (IOERT) in breast conserving therapy (BCT), both as partial breast irradiation (PBI) as well as anticipated boost ("IOERT-Boost"). For both applications, the criteria for patient selection, technical details/requirements, physical aspects and outcome data are presented. IOERT as PBI The largest evidence comes from Italian studies, especially the ELIOT randomized trial. Investigators showed that the rate of in-breast relapses (IBR) in the IOERT group was significantly greater than with whole breast irradiation (WBI), even when within the pre-specified equivalence margin. Tumour sizes > 2 cm, involved axillary nodes, Grade 3 and triple negative molecular subtypes emerged as statistically significant predictors of IBR. For patients at low risk for in-breast recurrence (ASTRO/ESTRO recommendations), full dose IOERT was isoeffective with standard WBI. Hence, several national guidelines now include this treatment strategy as one of the standard techniques for PBI in carefully selected patients. IOERT Boost The largest evidence for boost IOERT preceding WBI comes from pooled analyses performed by the European Group of the International Society of Intraoperative Radiation Therapy (ISIORT Europe), where single boost doses (mostly around 10 Gy) preceded whole-breast irradiation (WBI) with 50 Gy (conventional fractionation). At median follow-up periods up to ten years, local recurrence rates around 1% were observed for low risk tumours. Higher local relapse rates were described for grade 3 tumours, triple negative breast cancer as well as for patients treated after primary systemic therapy for locally advanced tumours. Even in this settings, long-term (> 5y) local tumour control rates beyond 95% were achieved. These encouraging results are interpreted as being attributable to utmost precision in dose delivery (by avoiding a "geographic and/or temporal miss"), and the possible radiobiological superiority of a single high dose fraction, compared to the conventionally fractionated boost. IOERT also showed favourable results in terms of cosmetic outcome, assumedly thanks to the small treated volumes combined with complete skin sparing.

Chih-Hao Li, A. Benedick, P. Fendel et al.

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s-1 (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of ∼5 cm s-1 is necessary. The combination of a laser frequency comb with a Fabry–Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (∼1-Å) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or ‘astro-comb’, is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s-1 in astronomical radial velocity measurements.

K. Asad, J. Girard, M. D. Villers et al.

After a decade of design and construction, South Africa's SKA-MID precursor MeerKAT has begun its science operations. To make full use of the widefield capability of the array, it is imperative that we have an accurate model of the primary beam of its antennas. We have used an available L-band full-polarization astro-holographic observation and electromagnetic simulation to create sparse representations of the beam using principal components and Zernike polynomials. The spectral behaviour of the spatial coefficients has been modelled using discrete cosine transform. We have provided the Zernike-based model over a diameter of 10 degrees in an associated software tool that can be useful for direction dependent calibration and imaging. The model is more accurate for the diagonal elements of the beam Jones matrix and at lower frequencies. As we get more accurate beam measurements and simulations in the future, especially for the cross-polarization patterns, our pipeline can be used to create more accurate sparse representations of MeerKAT beam.

R. Zia, D. C. Maurya, A. Pradhan

In this paper, spatially homogeneous and anisotropic Bianchi type-[Formula: see text] dark energy (DE) cosmological transit models with string fluid source in [Formula: see text] gravity [T. Harko et al., Phys. Rev. D 84 (2011) 024020], where [Formula: see text] is the Ricci scalar and [Formula: see text] the trace of the stress energy–momentum tensor, have been studied in the context of early time decelerating and late-time accelerating expansion of the Universe as suggested by the recent observations. The exact solutions of the field equations are obtained first by using generalized hybrid expansion law (HEL) [Formula: see text] which yields a time-dependent deceleration parameter [Formula: see text] and second by considering the metric coefficient [Formula: see text]. By using recent constraints from supernovae type-Ia union data [Cunha, arXiv:0811.2379[astro-ph]], we obtain [Formula: see text] and [Formula: see text] for transit model [Formula: see text]. The Universe has an initial singularity and is anisotropic closed and it tends to be flat at the late time, i.e. our Universe is in accelerating expansion. Our model shows a phase transition property from decelerating to accelerating. It is remarkable to mention here that our Universe is homogeneous and anisotropic in the early phase whereas it becomes homogeneous and isotropic for [Formula: see text]. We have also discussed the stability of the background solution with respect to perturbations of the metric along with the properties of future singularities in the Universe dominated by DE including the phantom-type fluid. Various physical and dynamical parameters are also calculated and investigated in terms of time and redshift both.

C. Hahn, B. Kavanagh, A. Bhatnagar et al.

S. Freedland, R. Rumble, A. Finelli et al.

S. Nojiri, S. Odintsov

Abstract It is suggested [ astro-ph/0306438 ] that current cosmic acceleration arises due to modification of general relativity by the terms with negative powers of curvature. We argue that time-dependent (hyperbolic) compactifications of (4+ n )-dimensional gravity (string/M-theory) lead to the effective 4d gravity which naturally contains such terms. The same may be achieved in the braneworld by the proper choice of the boundary action. Hence, such a model which seems to eliminate the need for dark energy may have the origin in M-theory.

M. Laine, M. Shaposhnikov

It has been pointed out by one of the authors (Shaposhnikov 2008 Preprint 0804.4542) that in the νMSM (Standard Model extended with three right-handed neutrinos with masses smaller than the electroweak scale), there is a corner in the parameter space where CP-violating resonant oscillations among the two heaviest right-handed neutrinos continue to operate below the freeze-out temperature of sphaleron transitions, leading to a lepton asymmetry which is considerably larger than the baryon asymmetry. Consequently, the lightest right-handed (‘sterile’) neutrinos, which may serve as dark matter, are generated through an efficient resonant mechanism proposed by Shi and Fuller (1999 Phys. Rev. Lett. 82 2832 [astro-ph/9810076]). We re-compute the dark matter relic density and non-eq uilibrium momentum distribution function in this situation with quantum field theoretic methods and, confronting the results with existing astrophysical data, derive bounds on the properties of the lightest right-handed neutrinos. Our spectra can be used as an input for structure formation simulations in warm dark matter cosmologies, for a Lyman-α analysis of the dark matter distribution on small scales, and for studying the properties of haloes of dwarf spheroidal galaxies.

D. Phillips, A. Glenday, Chih-Hao Li et al.

We deployed two wavelength calibrators based on laser frequency combs ("astro-combs") at an astronomical telescope. One astro-comb operated over a 100 nm band in the deep red (∼ 800 nm) and a second operated over a 20 nm band in the blue (∼ 400 nm). We used these red and blue astro-combs to calibrate a high-resolution astrophysical spectrograph integrated with a 1.5 m telescope, and demonstrated calibration precision and stability sufficient to enable detection of changes in stellar radial velocity < 1 m/s.

S. Carroll

M. Horbatsch, C. Burgess

An old result (astro-ph/9905303) by Jacobson implies that a black hole with Schwarzschild radius rs acquires scalar hair, Qrs2μ, when the (canonically normalized) scalar field in question is slowly time-dependent far from the black hole, ∂t μMp with μrs << 1 time-independent. Such a time dependence could arise in scalar-tensor theories either from cosmological evolution, or due to the slow motion of the black hole within an asymptotic spatial gradient in the scalar field. Most remarkably, the amount of scalar hair so induced is independent of the strength with which the scalar couples to matter. We argue that Jacobson's Miracle Hair-Growth Formula© implies, in particular, that an orbiting pair of black holes can radiate dipole radiation, provided only that the two black holes have different masses. Quasar OJ287, situated at redshift z 0.306, has been argued to be a double black-hole binary system of this type, whose orbital decay recently has been indirectly measured and found to agree with the predictions of General Relativity to within 6%. We argue that the absence of observable scalar dipole radiation in this system yields the remarkable bound |μ| < (16 days)−1 on the instantaneous time derivative at this redshift (as opposed to constraining an average field difference, Δ, over cosmological times), provided only that the scalar is light enough to be radiated — i.e. m10−23 eV — independent of how the scalar couples to matter. This can also be interpreted as constraining (in a more model-dependent way) the binary's motion relative to any spatial variation of the scalar field within its immediate vicinity within its host galaxy.

P. Slane, L. Kaluzienski

A. Dolgov, S. Hansen, D. V. Semikoz

Abstract We repeat our previous calculation of the spectrum distortion of massless neutrinos in the early universe with a considerably better accuracy and corrected for a missing numerical factor in one of the two ways of calculations presented in our paper [Nucl. Phys. B 503 (1997) 426]. Now both ways of calculations are in perfect agreement and we essentially reproduce our old results presented in the abstract of the paper and used in the calculations of light element abundances. We disagree with the criticism of our calculations presented in astro-ph/9712199 by N.Y. Gnedin and O.Y. Gnedin.

Tirthabir Biswas, A. Notari

We study an exact Swiss-cheese model of the universe, where inhomogeneous LTB patches are embedded in a flat FLRW background, in order to see how observations of distant sources are affected. We focus mainly on the redshift, both perturbatively and non-perturbatively: the net effect given by one patch is suppressed by (L/RH)3 (where L is the size of one patch and RH is the Hubble radius). We disentangle this effect from the Doppler term (which is much larger and has been used recently (Biswas et al 2007 J. Cosmol. Astropart. Phys. JCAP12(2007)017 [astro-ph/0606703]) to try to fit the SN curve without dark energy) by making contact with cosmological perturbation theory. Then, the correction to the angular distance is discussed analytically and estimated to be larger, , perturbatively and non-perturbatively (although it should go to zero after angular averaging).

S. Ng, N. Nunes, F. Rosati

Dipartimento di Fisica ‘Galileo Galilei’, Universit`a di Padova, via Marzolo 8, 35131 Padova, Italyand INFN - Sezione di Padova, via Marzolo 8, 35131 Padova, Italy(February 1, 2008)We develop a framework to study the phase space of a system consisting of a scalar field rollingdown an arbitrary potential with varying slope and a background fluid, in a cosmological setting. Wegive analytical approximate solutions of the field evolution and discuss applications of its featuresto the issues of quintessence, moduli stabilisation and quintessential inflation.PACS numbers: 98.80.Cq astro-ph/xxx SUSX-TH/01-030 DFPD-01/TH/20I. INTRODUCTION

Andrei Linde, V. Mukhanov

We discuss nontrivial features of the large scale structure of the universe in the simplest curvaton model proposed in our paper astro-ph/9610219. The amplitude of metric perturbations in this model takes different values in different parts of the universe. The spatial distribution of the amplitude looks like a web consisting of exponentially large cells. Depending on the relation between the cell size λ0 and the scale of the horizon lH, one may either live in a part of the universe dominated by Gaussian perturbations (inside a cell with ), or in the universe dominated by non-Gaussian perturbations (for ). We show that the curvaton contribution to the total amplitude of adiabatic density perturbations can be strongly suppressed if the energy density of the universe prior to the curvaton decay was dominated not by the classical curvaton field but by the curvaton particles produced during reheating. We describe the curvaton–inflaton transmutation effect: the same field in different parts of the universe may play either the role of the curvaton or the role of the inflaton. Finally, we discuss an interplay between the curvaton web and anthropic considerations in the string theory landscape.

G. D'Agostini

The aim of this paper, triggered by some discussions in the astrophysics community raised by astro-ph/0508529, is to introduce the issue of `fits' from a probabilistic perspective (also known as Bayesian), with special attention to the construction of model that describes the `network of dependences' (a Bayesian network) that connects experimental observations to model parameters and upon which the probabilistic inference relies. The particular case of linear fit with errors on both axes and extra variance of the data points around the straight line (i.e. not accounted by the experimental errors) is shown in detail. Some questions related to the use of linear fit formulas to log-linearized exponential and power laws are also sketched, as well as the issue of systematic errors.