Search
Nederlands
FNWI --- IMAPP Department of Astrophysics
Radboud University > Faculty of Science > Department of Astrophysics

Table of Contents

Student seminars

Regulations

Updated April 2016

  • The seminar is a mandatory part of the Particle/Astro physics master track. Keep in mind that your audience will consist not only of astronomers but also of physicists.
  • New master students should enroll in the Seminar course in Osiris at the beginning of their master.
  • The seminar will be graded as: pass or fail
  • It is your own responsibility to be ready on time; cancellation counts as a fail.

Some further instructions

Read the paper and try to understand its contents (you will be asked about it). This means you will also have to consult background literature, e.g. those papers which are referenced in the article, or those which cite this article. Your best resources to find additional literature are the NASA Astrophysics Data System and the ArXiv Preprint Server (astro-ph). It may also be useful to search for “review articles” (e.g., ARA&A or reviews on astro-ph). Wikipedia maybe helpful to get you started but is certainly not a sufficient information resource.

It is advisable that you inform the organisers of the Seminar course as soon as you have selected an article, to avoid duplication.

List


Heino Falcke:

G. Angloher, M. Bauer, I. Bavykina, A. Bento, C. Bucci, C. Ciemniak, G. Deuter, F. von Feilitzsch, D. Hauff, P. Huff, C. Isaila, J. Jochum, M. Kiefer, M. Kimmerle, J.-C. Lanfranchi, F. Petricca, S. Pfister, W. Potzel, F. Pr\“obst, F. Reindl, S. Roth, K. Rottler, C. Sailer, K. Sch\”affner, J. Schmaler, S. Scholl, W. Seidel, M. von Sivers, L. Stodolsky, C. Strandhagen, R. Strau\ss, A. Tanzke, I. Usherov, S. Wawoczny, M. Willers, A. Z\“oller

The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via elastic scattering off nuclei in CaWO$_4$ crystals, completed 730 kg days of data taking in 2011. We present the data collected with eight detector modules, each with a two-channel readout; one for a phonon signal and the other for coincidently produced scintillation light. The former provides a precise measure of the energy deposited by an interaction, and the ratio of scintillation light to deposited energy can be used to discriminate different types of interacting particles and thus to distinguish possible signal events from the dominant backgrounds. Sixty-seven events are found in the acceptance region where a WIMP signal in the form of low energy nuclear recoils would be expected. We estimate background contributions to this observation from four sources: 1) “leakage” from the e/\gamma-band 2) “leakage” from the \alpha-particle band 3) neutrons and 4) Pb-206 recoils from Po-210 decay. Using a maximum likelihood analysis, we find, at a high statistical significance, that these sources alone are not sufficient to explain the data. The addition of a signal due to scattering of relatively light WIMPs could account for this discrepancy, and we determine the associated WIMP parameters.

http://arxiv.org/abs/1109.0702

Slowly balding black holes

Maxim Lyutikov (Purdue University), Jonathan C. McKinney (Stanford University)

The “no hair” theorem, a key result in General Relativity, states that an isolated black hole is defined by only three parameters: mass, angular momentum, and electric charge; this asymptotic state is reached on a light-crossing time scale. We find that the “no hair” theorem is not formally applicable for black holes formed from collapse of a rotating neutron star. Rotating neutron stars can self-produce particles via vacuum breakdown forming a highly conducting plasma magnetosphere such that magnetic field lines are effectively “frozen-in” the star both before and during collapse. In the limit of no resistivity, this introduces a topological constraint which prohibits the magnetic field from sliding off the newly-formed event horizon. As a result, during collapse of a neutron star into a black hole, the latter conserves the number of magnetic flux tubes $N_B = e \Phi_\infty /(\pi c \hbar)$, where $\Phi_\infty \approx 2 \pi^2 B_{NS} R_{NS}^3 /(P_{\rm NS} c)$ is the initial magnetic flux through the hemispheres of the progenitor and out to infinity. We test this theoretical result via three-dimensional general relativistic plasma simulations of rotating black holes that start with a neutron star dipole magnetic field with no currents initially present outside the event horizon. The black hole's magnetosphere subsequently relaxes to the split monopole magnetic field geometry with self-generated currents outside the event horizon. The dissipation of the resulting equatorial current sheet leads to a slow loss of the anchored flux tubes, a process that balds the black hole on long resistive time scales rather than the short light-crossing time scales expected from the vacuum “no-hair” theorem.

http://arxiv.org/abs/1109.0584

Constraints on Black Hole Growth, Quasar Lifetimes, and Eddington Ratio Distributions from the SDSS Broad Line Quasar Black Hole Mass Function

Brandon C. Kelly (CfA), Marianne Vestergaard (DARK), Xiaohui Fan (U. Arizona), Philip Hopkins (Berkeley), Lars Hernquist (CfA), Aneta Siemiginowska (CfA)

We present an estimate of the black hole mass function (BHMF) of broad line quasars (BLQSOs) that self-consistently corrects for incompleteness and the statistical uncertainty in the mass estimates, based on a sample of 9886 quasars at 1 < z < 4.5 drawn from the Sloan Digital Sky Survey. We find evidence for `cosmic downsizing' of black holes in BLQSOs, where the peak in their number density shifts to higher redshift with increasing black hole mass. The cosmic mass density for black holes seen as BLQSOs peaks at z ~ 2. We estimate the completeness of the SDSS as a function of black hole mass and Eddington ratio, and find that at z > 1 it is highly incomplete at M_BH < 10^9 M_Sun and L / L_Edd < 0.5. We also estimate a lower limit on the lifetime of a single BLQSO phase and we place constraints on the maximum mass of a black hole in a BLQSO. Our estimated distribution of BLQSO Eddington ratios peaks at L / L_Edd ~ 0.05 and has a dispersion of ~ 0.4 dex, implying that most BLQSOs are not radiating at or near the Eddington limit; however the location of the peak is subject to considerable uncertainty. The steep increase in number density of BLQSOs toward lower Eddington ratios is expected if the BLQSO accretion rate monotonically decays with time. Furthermore, our estimated lifetime and Eddington ratio distributions imply that the majority of the most massive black holes spend a significant amount of time growing in an earlier obscured phase, a conclusion which is independent of the unknown obscured fraction. These results are consistent with models for self-regulated black hole growth, at least for massive systems at z > 1, where the BLQSO phase occurs at the end of a fueling event when black hole feedback unbinds the accreting gas, halting the accretion flow.

http://arxiv.org/abs/1006.3561

Evolution of supermassive stars as a pathway to black hole formation

Mitchell C. Begelman

Supermassive stars, with masses greater than a million solar masses, are possible progenitors of supermassive black holes in galactic nuclei. Because of their short nuclear burning timescales, such objects can be formed only when matter is able to accumulate at a rate exceeding ~ 1 solar mass/yr. Here we revisit the structure and evolution of rotationally-stabilized supermassive stars, taking into account their continuous accumulation of mass and their thermal relaxation. We show that the outer layers of supermassive stars are not thermally relaxed during much of the star's main sequence lifetime. As a result, they do not resemble n=3 polytropes, as assumed in previous literature, but rather consist of convective (polytropic) cores surrounded by convectively stable envelopes that contain most of the mass. We compute the structures of these envelopes, in which the specific entropy is proportional to the enclosed mass M(R) to the 2/3-power. By matching the envelope solutions to convective cores, we calculate the core mass as a function of time. We estimate the initial black hole masses formed as a result of core-collapse, and their subsequent growth via accretion from the bloated envelopes (“quasistars”) that result. The seed black holes formed in this way could have typical masses in the range ~ 10^4-10^5 solar masses, considerably larger than the remnants thought to be left by the demise of Population III stars. Supermassive black holes therefore could have been seeded during an epoch of rapid infall considerably later than the era of Pop III star formation.

(http://arxiv.org/abs/0910.4398)

A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder

Adam G. Riess (JHU, STScI), Lucas Macri (Texas A&M), Stefano Casertano (STScI), Megan Sosey (STScI), Hubert Lampeitl (UPort), Henry C. Ferguson (STScI), Alexei V. Filippenko (UCB), Saurabh W. Jha (Rutgers), Weidong Li (UCB), Ryan Chornock (UCB), and Devdeep Sarkar (UCI)

We report observations of 240 Cepheid variables obtained with the Near Infrared Camera (NICMOS) through the F160W filter on the Hubble Space Telescope (HST). The Cepheids are distributed across six recent hosts of Type Ia supernovae (SNe Ia) and the “maser galaxy” NGC 4258, allowing us to directly calibrate the peak luminosities of the SNe Ia from the precise, geometric distance measurements provided by the masers. New features of our measurement include the use of the same instrument for all Cepheid measurements across the distance ladder and homogeneity of the Cepheid periods and metallicities thus necessitating only a differential measurement of Cepheid fluxes and reducing the largest systematic uncertainties in the determination of the fiducial SN Ia luminosity. The NICMOS measurements reduce differential extinction in the host galaxies by a factor of 5 over past optical data. Combined with an expanded of 240 SNe Ia at z<0.1 which define their magnitude-redshift relation, we find H_0=74.2 +/-3.6, a 4.8% uncertainty including both statistical and systematic errors. We show that the factor of 2.2 improvement in the precision of H_0 is a significant aid to the determination of the equation-of-state of dark energy, w = P/(rho c^2). Combined with the WMAP 5-year measurement of Omega_M h^2, we find w= -1.12 +/- 0.12 independent of high-redshift SNe Ia or baryon acoustic oscillations (BAO). This result is also consistent with analyses based on the combination of high-z SNe Ia and BAO. The constraints on w(z) now with high-z SNe Ia and BAO are consistent with a cosmological constant and improved by a factor of 3 from the refinement in H_0 alone. We show future improvements in H_0 are likely and will further contribute to multi-technique studies of dark energy.

http://arxiv.org/abs/0905.0695

Relativistic plasma as the dominant source of the optical continuum emission in the broad-line radio galaxy 3C 120

J. Leon-Tavares, A. P. Lobanov, V. H. Chavushyan, T. G. Arshakian, V. T. Doroshenko, S. G. Sergeev, Y. S. Efimov, and S.V. Nazarov

We report a relation between radio emission in the inner jet of the Seyfert galaxy 3C 120 and optical continuum emission in this galaxy. Combining the optical variability data with multi-epoch high-resolution very long baseline interferometry observations reveals that the flaring optical emission is generated during passages of a dense relativistic plasma condensations through a stationary emitting region located in the inner jet, at a distance of ~1.3 parsecs from the jet origin. This indicates that a significant fraction of the optical continuum produced in 3C 120 is non-thermal and it can ionize material in a sub-relativistic wind or outflow. We discuss implications of this finding for the ionization and structure of the broad emission line region, as well as for the use of broad emission lines for determining black hole masses in radio-loud AGN.

http://arxiv.org/abs/0910.1320

The Trigonometric Parallax of Cygnus X-1

Authors: Mark J. Reid, Jeffrey E. McClintock, Ramesh Narayan, Lijun Gou, Ronald A. Remillard, and Jerome A. Orosz Categories: astro-ph.HE Comments: Paper I of three papers on Cygnus X-1; 13 pages, 3 figures, ApJ submitted
We report a direct and accurate measurement of the distance to the X-ray binary Cygnus X-1, which contains the first black hole to be discovered. The distance of 1.86(-0.11,+0.12) kpc was obtained from a trigonometric parallax measurement using the Very Long Baseline Array. The position measurements are also sensitive to the 5.6 d binary orbit and we determine the orbit to be clockwise on the sky. We also measured the proper motion of Cygnus X-1 which, when coupled to the distance and Doppler shift, gives the three-dimensional space motion of the system. When corrected for differential Galactic rotation, the non-circular (peculiar) motion of the binary is only about 21 km/s, indicating that the binary did not experience a large “kick” at formation.
( http://arxiv.org/abs/1106.3688 , 96kb)

The Mass of the Black Hole in Cygnus X-1

Authors: Jerome A. Orosz, Jeffrey E. McClintock, Jason P. Aufdenberg, Ronald A. Remillard, Mark J. Reid, Ramesh Narayan, and Lijun Gou Categories: astro-ph.HE Comments: Paper II of three papers on Cygnus X-1; 24 pages, 5 figures, ApJ submitted
Cygnus X-1 is a binary star system that is comprised of a black hole and a massive giant companion star in a tight orbit. Building on our accurate distance measurement reported in the preceding paper, we first determine the radius of the companion star, thereby constraining the scale of the binary system. Then, by modeling an extensive collection of optical data, we find a mass for the companion of M_{opt}=19.2\pm1.9 M_{\sun}. Of central importance, we further determine the mass of the black hole, M =14.8\pm1.0 M_{\sun}, and the angle of inclination of the orbital plane to our line of sight, i=27.1\pm0.8 deg. In the following paper, we use these precise values of M and i, and our secure value of the distance D, to determine the spin of the black hole.
( http://arxiv.org/abs/1106.3689 , 465kb)

The Extreme Spin of the Black Hole in Cygnus X-1

Authors: Lijun Gou, Jeffrey E. McClintock, Mark J. Reid, Jerome A. Orosz, James F. Steiner, Ramesh Narayan, Jingen Xiang, Ronald A. Remillard, Keith A. Arnaud, and Shane W. Davis
The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a/M>0.97 (3 \sigma). For a less probable (synchronous) dynamical model, we find a/M>0.91 (3 \sigma). Our results take into account all significant sources of observational and model-parameter uncertainties, which are dominated by the uncertainties in black hole mass, orbital inclination angle and distance. The uncertainties introduced by the thin-disk model we employ are particularly small in this case, given the disk's low luminosity (L/L_{Edd} \approx 0.02)

Discovery of Radio Emission from the Quasar SDSS J1536+0441, a Candidate Binary Black-Hole System

J.M. Wrobel, A. Laor

The radio-quiet quasar SDSS J1536+0441 shows two broad-line emission systems that Boroson & Lauer interpret as a candidate binary black-hole system with a separation of 0.1 pc (0.02 mas). From new VLA imaging at 8.5 GHz, two faint sources, separated by 0.97 arcsec (5.1 kpc), have been discovered within the quasar's optical localization region. Each radio source is unresolved, with a diameter of less than 0.37 arcsec (1.9 kpc). A double radio structure is seen in some other radio-quiet quasars, and the double may be energized here by the candidate 0.1-pc binary black-hole system. Alternatively, the radio emission may arise from a binary system of quasars with a projected separation of 5.1 kpc, and the two quasars may produce the two observed broad-line emission systems. Binary active galactic nuclei with a kpc scale separation are known from radio and X-ray observations, and a few such system are expected in the Boroson & Lauer sample based on the observed clustering of quasars down to the 10 kpc scale. Future observations designed to distinguish between the 0.1 pc and 5 kpc scales for the binary system are suggested.

http://arxiv.org/abs/0905.3566

The Electron Energy Distribution in the Hotspots of Cygnus A: Filling the Gap with the Spitzer Space Telescope

Authors: L. Stawarz, C.C. Cheung, D.E. Harris, M. Ostrowski

Here we present Spitzer Space Telescope imaging of Cyg A with the Infrared Array Camera, resulting in the detection of the high-energy tails or cut-offs in the synchrotron spectra for all four hotspots of this archetype radio galaxy. When combined with the other data collected from the literature, our observations allow for detailed modeling of the broad-band emission for the brightest spots A and D. We confirm that the X-ray flux detected previously from these features is consistent with the synchrotron self-Compton radiation for the magnetic field intensity 170 muG in spot A, and 270 muG in spot D. We also find that the energy density of the emitting electrons is most likely larger by a factor of a few than the energy density of the hotspots' magnetic field. We construct energy spectra of the radiating ultrarelativistic electrons. We find that for both hotspots A and D these spectra are consistent with a broken power-law extending from at least 100 MeV up to 100 GeV, and that the spectral break corresponds almost exactly to the proton rest energy of 1 GeV. We argue that the shape of the electron continuum reflects two different regimes of the electron acceleration process at mildly relativistic shocks, rather than resulting from radiative cooling and/or absorption effects. In this picture the protons' inertia defines the critical energy for the hotspot electrons above which Fermi-type acceleration processes may play a major role, but below which the operating acceleration mechanism has to be of a different type. At energies >100 GeV, the electron spectra cut-off/steepen again, most likely as a result of spectral aging due to radiative loss effects. We discuss several implications of the presented analysis for the physics of extragalactic jets.


( http://arXiv.org/abs/astro-ph/0701568 , 1498kb)

A candidate sub-parsec supermassive binary black hole system

Todd A. Boroson & Tod R. Lauer

Nature 458, 53-55 (5 March 2009)

The role of mergers in producing galaxies, together with the finding that most large galaxies harbour black holes in their nuclei1, implies that binary supermassive black hole systems should be common. Here we report that the quasar SDSS J153636.22+044127.0 is a plausible example of such a system. This quasar shows two broad-line emission systems, separated in velocity by 3,500 km s-1. A third system of unresolved absorption lines has an intermediate velocity. These characteristics are unique among known quasars. We interpret this object as a binary system of two black holes, having masses of 107.3 and 108.9 solar masses separated by 0.1 parsec with an orbital period of 100 years.

[[http://arxiv.org/abs/0901.3779]]
HI Observations of the Supermassive Binary Black Hole System in 0402+379

Authors: C. Rodriguez, G. B. Taylor, R. T. Zavala, Y. M. Pihlstrom, A. B. Peck

We have recently discovered a supermassive binary black hole system with a projected separation between the two black holes of 7.3 parsecs in the radio galaxy 0402+379. This is the most compact supermassive binary black hole pair yet imaged by more than two orders of magnitude. We present Global VLBI observations at 1.3464 GHz of this radio galaxy, taken to improve the quality of the HI data. Two absorption lines are found toward the southern jet of the source, one redshifted by 370 +/- 10 km/s and the other blueshifted by 700 +/- 10 km/s with respect to the systemic velocity of the source, which, along with the results obtained for the opacity distribution over the source, suggests the presence of two mass clumps rotating around the central region of the source. We propose a model consisting of a geometrically thick disk, of which we only see a couple of clumps, that reproduces the velocities measured from the HI absorption profiles. These clumps rotate in circular Keplerian orbits around an axis that crosses one of the supermassive black holes of the binary system in 0402+379. We find an upper limit for the inclination angle of the twin jets of the source to the line of sight of 66 degrees, which, according to the proposed model, implies a lower limit on the central mass of ~7 x 10^8 Msun and a lower limit for the scale height of the thick disk of ~12 pc . ( http://arxiv.org/abs/0902.4444 , 3932kb)

Host galaxies, clustering, Eddington ratios, and evolution of radio, X-ray, and infrared-selected AGNs

Authors: Ryan C. Hickox, Christine Jones, William R. Forman, Stephen S. Murray, Christopher S. Kochanek, Daniel Eisenstein, Buell T. Jannuzi, Arjun Dey, Michael J.I. Brown, Daniel Stern, Peter R. Eisenhardt, Varoujan Gorjian, Mark Brodwin, Ramesh Narayan, Richard J. Cool, Almus Kenter, Nelson Caldwell, Michael E. Anderson

We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, X-ray, and infrared. We study a sample of 585 AGNs at 0.25 < z < 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES) and data in the radio (WSRT 1.4 GHz), X-rays (Chandra XBootes), and mid-IR (IRAC Shallow Survey). The radio, X-ray, and IR AGN samples show modest overlap, indicating that to the flux limits of the survey, they represent largely distinct classes of AGNs. We derive host galaxy colors and luminosities, as well as Eddington ratios (lambda), for obscured or optically faint AGNs. We also measure the two-point cross-correlation between AGNs and galaxies on scales of 0.3-10 h^-1 Mpc, and derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly found in luminous red galaxies, are strongly clustered (with M_halo ~ 3×10^13 h^-1 M_sun), and have very low lambda <~ 10^-3; (2) X-ray-selected AGNs are preferentially found in galaxies in the “green valley” of color-magnitude space and are clustered similarly to typical AGES galaxies (M_halo ~ 10^13 h^-1 M_sun), with 10^-3 <~ lambda <~ 1; (3) IR AGNs reside in slightly bluer, less luminous galaxies than X-ray AGNs, are weakly clustered (M_halo <~ 10^12 h^-1 M_sun), and have lambda > 10^-2. We interpret these results in terms of a simple model of AGN and galaxy evolution, whereby a “quasar” phase and the growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a critical mass between ~10^12 and 10^13 M_sun. Subsequently, star formation ceases and AGN accretion shifts from radiatively efficient (optical- and IR- bright) to radiatively inefficient (optically-faint, radio-bright) modes.
( http://arxiv.org/abs/0901.4121 , 992kb)

Implications of primordial black holes on the first stars and the origin of the supermassive black holes

Authors: Cosimo Bambi, Douglas Spolyar, Alexander D. Dolgov, Katherine Freese, and Marta Volonteri

If the cosmological dark matter has a component made of small primordial black holes, they may have a significant impact on the physics of the first stars and on the subsequent formation of massive black holes. Primordial black holes would be adiabatically contracted into these stars and then would sink to the stellar center by dynamical friction, creating a larger black hole which may quickly swallow the whole star. The first stars would thus live only for a very short time and would not contribute much to reionization of the universe. They would instead become $10 - 10^3 M_\odot$ black holes which (depending on subsequent accretion) could serve as seeds for the super–massive black holes seen at high redshifts as well as those inside galaxies today.
( http://arxiv.org/abs/0812.0585 , 19kb)\

Overview of the Orion Complex

John Bally

The Orion star formation complex is the nearest region of on-going star formation that continues to produce both low and high mass stars. Orion is discussed in the larger context of star formation in the Solar vicinity over the last 100 Myr. The Orion complex is located on the far side of the Gould's Belt system of clouds and young stars throughwhich our Solar systemis drifting. A review is given of the overall structure and properties of the Orion star forming complex, the best studied OB association. Over the last 12 Myr, Orion has given birth to at least ten thousand stars contained in a half dozen sub-groups and short-lived clusters. The Orion OB association has been the source of several massive, high-velocity run-away stars, including mu-Columbae and AE Aurigae. Some of Orion's most massive members died in supernova explosions that created the 300 pc diameter Orion / Eridanus super-bubble whose near wall may be as close as 180 pc. The combined effects of UV radiation, stellar winds, and supernovae have impacted surviving molecular clouds in Orion. The large Orion A, IC 2118 molecular clouds and dozens of smaller clouds strewn throughout the interior of the superbubble have cometary shapes pointing back towards the center of the Orion OB association. Most are forming stars in the compressed layers facing the bubble interior.
( http://arxiv.org/abs/0812.0046 , 3541kb)

Testing Lorentz Invariance with Ultra High Energy Cosmic Ray Spectrum

Xiao-Jun Bi, Zhen Cao, Ye Li, Qiang Yuan

The GZK cutoff predicted at the Ultra High Energy Cosmic Ray (UHECR) spectrum as been observed by the HiRes and Auger experiments. The results put severe constraints on the effect of Lorentz Invariance Violation(LIV) which has been introduced to explain the absence of GZK cutoff indicated in the AGASA data. Assuming homogeneous source distribution with a single power law spectrum, we calculate the spectrum of UHECRs observed on Earth by taking the processes of photopion production, $e^+e^-$ pair production and adiabatic energy loss into account. The effect of LIV is also taken into account in the calculation. By fitting the HiRes monocular spectra and the Auger combined spectra, we show that the LIV parameter is constrained to $\xi=-0.8^{+3.2}_{-0.5}\times10^{-23}$ and $0.0^{+1.0}_{-0.4}\times10^{-23}$ respectively, which is well consistent with strict Lorentz Invariance up to the highest energy.
( http://arxiv.org/abs/0812.0121 , 391kb)

Synchrotron Radiation from the Galactic Center in Decaying Dark Matter Scenario

Authors: Koji Ishiwata, Shigeki Matsumoto, Takeo Moroi

We discuss the synchrotron radiation flux from the Galactic center in unstable dark matter scenario. Motivated by the anomalous excess of the positron fraction recently reported by the PAMELA collaboration, we consider the case that the dark matter particle is unstable (and long-lived), and that energetic electron and positron are produced by the decay of dark matter. Then, the emitted electron and positron becomes the source of the synchrotron radiation. We calculate the synchrotron radiation flux for models of decaying dark matter, which can explain the PAMELA positron excess. Taking the lifetime of the dark matter of O(10^26 sec), which is the suggested value to explain the PAMELA anomaly, the synchrotron radiation flux is found to be O(1 kJy/str) or smaller, depending on the particle-physics and cosmological parameters.
( http://arxiv.org/abs/0811.4492 , 42kb)


Gijs Nelemans:

The Star Formation History of the Solar Neighbourhood from the White Dwarf Luminosity Function
http://arxiv.org/abs/1306.4195

Rapidly accreting white dwarfs as supernova type Ia progenitors
http://arxiv.org/abs/1301.1368

http://arxiv.org/abs/1112.0315

http://arxiv.org/abs/1104.1174

http://arxiv.org/abs/1007.0987

http://xxx.lanl.gov/abs/0909.0004

http://xxx.lanl.gov/abs/0909.0486

http://xxx.lanl.gov/abs/0810.5123


Jörg Hörandel:
Søren Larsen:

Bastian et al. (2013): Early Disc Accretion as the Origin of Abundance Anomalies in Globular Clusters
http://adsabs.harvard.edu/abs/2013arXiv1309.3566B

Priestley, Ruffert & Salaris (2011): On the evolution of intracluster gas within Galactic globular clusters
http://adsabs.harvard.edu/abs/2011MNRAS.411.1935P

Elmegreen, Malhotra & Rhoads (2012): Formation of metal-poor globular clusters in Ly-alpha emitting galaxies in the early Universe
http://adsabs.harvard.edu/abs/2012ApJ...757....9E

Conroy & Spergel (2011): On the formation of multiple stellar populations in globular clusters
http://adsabs.harvard.edu/abs/2011ApJ...726...36C


Marijke Haverkorn:

Wiersma et al. (2013): LOFAR insights into the epoch of reionization from the cross-power spectrum of 21 cm emission and galaxies
http://adsabs.harvard.edu/abs/2013MNRAS.432.2615W

Schnitzeler (2012): Modelling the Galactic distribution of free electrons
http://adsabs.harvard.edu/abs/2012MNRAS.427..664S

Harvey-Smith et al. (2011): Magnetic Fields in Large-diameter H II Regions Revealed by the Faraday Rotation of Compact Extragalactic Radio Sources
http://adsabs.harvard.edu/abs/2011ApJ...736...83H

Crutcher et al. (2009): Testing Magnetic Star Formation Theory
http://adsabs.harvard.edu/abs/2009ApJ...692..844C

Taylor et al. (2009): A Rotation Measure Image of the Sky
http://adsabs.harvard.edu/abs/2009ApJ...702.1230T

Rainer Beck (2007): Magnetism in the spiral galaxy NGC 6946: magnetic arms, depolarization rings, dynamo modes, and helical fields
http://adsabs.harvard.edu/abs/2007A%26A...470..539B