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Peter L. Biermann

Publications and source records attributed to Peter L. Biermann.

At least 55 records · Page 3Linked to original sources
arXiv2009

Neutrinos from photo-hadronic interactions in Pks2155-304

The high-peaked BL Lac object Pks2155-304 shows high variability at multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around 1 hour at X-ray and TeV energies was observed in 2006. In this context, it is essential to understand the physical processes in terms of the primary spectrum and the radiation emitted, since high-energy emission can arise in both leptonic and hadronic processes. In this contribution, we investigate the possibility of neutrino production in photo-hadronic interactions. In particular, we predict a direct correlation between optical and TeV energies at sufficiently high optical radiation fields. We show that in the blazar Pks2155-304, the optical emission in the low-state is sufficient to lead to photo-hadronic interactions and therefore to the production of high-energy photons.

astro-ph.HE↗
arXiv2009

New Limits on Sterile Neutrinos from Suzaku Observations of the Ursa Minor Dwarf Spheroidal Galaxy

We present results of our search for X-ray line emission associated with the radiative decay of the sterile neutrino, a well-motivated dark matter candidate, in Suzaku Observatory spectra of the Ursa Minor dwarf spheroidal galaxy. These data represent the first deep observation of one of these extreme mass-to-light systems and the first dedicated dark matter search using an X-ray telescope. No such emission line is positively detected, and we place new constraints on the combination of the sterile neutrino mass and the active-sterile neutrino oscillation mixing angle. Line flux upper limits are derived using a maximum-likelihood-based approach that, along with the lack of intrinsic X-ray emission, enables us to minimize systematics and account for those that remain. The limits we derive match or approach the best previous results over the entire 1--20 keV mass range from a single Suzaku observation. These are used to place constraints on the existence of sterile neutrinos with given parameters in the general case and in the case where they are assumed to constitute all of the dark matter. The range allowed implies that sterile neutrinos remain a viable candidate to make up some -- or all -- of the dark matter and also explain pulsar kicks and various other astrophysical phenomena.

astro-ph↗
arXiv2009

On the detectability of primordial black holes in the Galaxy

In the mass range of 1e15 g up to 1e26 g, primordial black holes (PBHs) as a possible contribution to the dark matter are still unexplored. In this contribution, we investigate the possibility of an electromagnetic signal from PBH interactions with astrophysical objects in the Galaxy. We find that a signal from passages cannot be observed, since, depending on the mass, either the interaction probability or the energy loss is too small. Further, we discuss possible effects from high-mass PBHs at masses >1e26 g, where PBHs can still contribute to the dark matter at the order of ~10%. Here, we find that a significant fraction of PBHs can be captured in the Hubble time. These captures could therefore lead to detectable effects.

astro-ph.CO↗
arXiv2009

The spin-flip phenomenon in supermassive black hole binary mergers

Massive merging black holes will be the primary sources of powerful gravitational waves at low frequency, and will permit to test general relativity with candidate galaxies close to a binary black hole merger. In this paper we identify the typical mass ratio of the two black holes but then show that the distance when gravitational radiation becomes the dominant dissipative effect (over dynamical friction) does not depend on the mass ratio. However the dynamical evolution in the gravitational wave emission regime does. For the typical range of mass ratios the final stage of the merger is preceded by a rapid precession and a subsequent spin-flip of the main black hole. This already occurs in the inspiral phase, therefore can be described analytically by post-Newtonian techniques. We then identify the radio galaxies with a super-disk as those in which the rapidly precessing jet produces effectively a powerful wind, entraining the environmental gas to produce the appearance of a thick disk. These specific galaxies are thus candidates for a merger of two black holes to happen in the astronomically near future.

astro-ph↗
arXiv2009

Cosmic Rays VI - Starburst galaxies at multiwavelengths

We propose an explanation for the far-infrared/radio correlation of galaxies in terms of the energy balance of the interstellar medium and determine the flux from high-energy photons and neutrinos from starburst galaxies. We present a catalog of the 127 brightest starburst galaxies with redshifts of z<0.03. In order to investigate the correlation between radio- and far-infrared emission, we apply the leaky box approximation. Further, we derive photon- and neutrino spectra from proton-proton interactions in supernova remnants (SNRs). Here, we assume that a fraction of the SNR's energy is transferred to the acceleration of cosmic rays. We also investigate the possibility of detecting Gamma Ray Bursts from nearby starburst galaxies, using the catalog defined here. We show that the radio emission is only weakly dependent on the magnetic field. It turns out that the intensity of the radio signal is directly proportional to the number of supernova explosions, which scales with the far-infrared luminosity. In addition, we find that high-energy photons from proton-proton interactions in SNRs in starbursts can make up several percent of the diffuse gamma-ray background. The neutrino flux from the same sources has a maximum energy of ~1e5 GeV. Neutrinos can, on the other hand, can be observed if a Gamma Ray Burst happens in a nearby starburst. About 0.03 GRBs per year are expected to occur in the entire catalog. The true number is expected to be even higher, since we only include the brightest sources. The number of events per burst in IceCube varies between about one event and more than 1000 events. This provides good prospects for IceCube to detect a significant event, since the background for a GRB search is close to zero.

astro-ph.HE↗
arXiv2008

Neutrinos from active black holes, sources of ultra high energy cosmic rays

A correlation between the highest energy Cosmic Rays (above ~ EeV) and the distribution of active galactic nuclei (AGN) gives rise to a prediction of neutrino production in the same sources. In this paper, we present a detailed AGN model, predicting neutrino production near the foot of the jet, where the photon fields from the disk and synchrotron radiation from the jet itself create high optical depths for proton-photon interactions. The protons escape from later shocks where the emission region is optically thin for proton-photon interactions. Consequently, Cosmic Rays are predicted to come from FR-I galaxies, independent of the orientation of the source. Neutrinos, on the other hand, are only observable from sources directing their jet towards Earth, i.e. flat spectrum radio sources and in particular BL Lac type objects, due to the strongly boosted neutrino emission.

astro-ph↗
arXiv2008

Supermassive binary black hole mergers

When galaxies collide, dynamical friction drives their central supermassive black holes close enought to each other such that gravitational radiation becomes the leading dissipative effect. Gravitational radiation takes away energy, momentum and angular momentum from the compact binary, such that the black holes finally merge. In the process, the spin of the dominant black hole is reoriented. On observational level, the spins are directly related to the jets, which can be seen at radio frequencies. Images of the X-shaped radio galaxies together with evidence on the age of the jets illustrate that the jets are reoriented, a phenomenon known as spin-flip. Based on the galaxy luminosity statistics we argue here that the typical galaxy encounters involve mass ratios between 1:3 to 1:30 for the central black holes. Based on the spin-orbit precession and gravitational radiation we also argue that for this typical mass ratio in the inspiral phase of the merger the initially dominant orbital angular momentum will become smaller than the spin, which will be reoriented. We prove here that the spin-flip phenomenon typically occurs already in the inspiral phase, and as such is describable by post-Newtonian techniques.

astro-ph↗
arXiv2007

Sterile neutrinos and structure formation

Warm dark matter is consistent with the observations of the large-scale structure, and it can also explain the cored density profiles on smaller scales. However, it has been argued that warm dark matter could delay the star formation. This does not happen if warm dark matter is made up of keV sterile neutrinos, which can decay into X-ray photons and active neutrinos. The X-ray photons have a catalytic effect on the formation of molecular hydrogen, the essential cooling ingredient in the primordial gas. In all the cases we have examined, the overall effect of sterile dark matter is to facilitate the cooling of the gas and to reduce the minimal mass of the halo prone to collapse. We find that the X-rays from the decay of keV sterile neutrinos facilitate the collapse of the gas clouds and the subsequent star formation at high redshift.

astro-ph↗
arXiv2007

Astrophysical implications of high energy neutrino limits

Second generation high energy neutrino telescopes are being built to reach sensitivities of neutrino emission from galactic and extragalactic sources. Current neutrino detectors are already able to set limits which are in the range of some emission models. In particular, the Antarctic Muon And Neutrino Detection Array (AMANDA) has recently presented the so far most restrictive limit on diffuse neutrino emission (Achterberg et al. 2007). Stacking limits which apply to AGN point source classes rather than to single point sources (Achterberg et al. (IceCube Collab.) & P. L. Biermann 2006) are given as well. In this paper, the two different types of limits will be used to draw conclusions about different emission models. An interpretation of stacking limits as diffuse limits to the emission from considered point source class is presented. The limits can for instance be used to constrain the predicted correlation of EGRET-detected diffuse emission and neutrino emission. Also, the correlation between X-ray and neutrino emission is constrained. Further results for source classes like TeV blazars and FR-II galaxies are presented. Starting from the source catalogs so-far examined for the stacking method, we discuss further potential catalogs and examine the possibilities of the second generation telescopes IceCube and KM3NeT by comparing catalogs with respect to northern and southern hemisphere total flux.

astro-ph↗
arXiv2007

The Nature of Dark Matter

Dark matter has been recognized as an essential part of matter for over 70 years now, and many suggestions have been made, what it could be. Most of these ideas have centered on Cold Dark Matter, particles that are expected in extensions of standard particle physics, such as supersymmetry. Here we explore the concept that dark matter is sterile neutrinos, a concept that is commonly referred to as Warm Dark Matter. Such particles have keV masses, and decay over a very long time, much longer than the Hubble time. In their decay they produce X-ray photons which modify the ionization balance in the early universe, increasing the fraction of molecular Hydrogen, and thus help early star formation. Sterile neutrinos may also help to understand the baryon-asymmetry, the pulsar kicks, the early growth of black holes, the minimum mass of dwarf spheroidal galaxies, as well as the shape of dark matter halos. As soon as all these tests have been quantitative in its various parameters, we may focus on the creation mechanism of these particles, and could predict the strength of the sharp X-ray emission line, expected from any large dark matter assembly. A measurement of this X-ray emission line would be definitive proof for the existence of may be called weakly interacting neutrinos, or WINs.

astro-ph↗
arXiv2007

Origin and physics of the highest energy cosmic rays: What can we learn from Radio Astronomy?

Here in this lecture we will touch on two aspects, one the new radio methods to observe the effects of high energy particles, and second the role that radio galaxies play in helping us understand high energy cosmic rays. We will focus here on the second topic, and just review the latest developments in the first. Radio measurements of the geosynchrotron radiation produced by high energy cosmic ray particles entering the atmosphere of the Earth as well as radio Čerenkov radiation coming from interactions in the Moon are another path; radio observations of interactions in ice at the horizon in Antarctica is a related attempt. Radio galaxy hot spots are prime candidates to produce the highest energy cosmic rays, and the corresponding shock waves in relativistic jets emanating from nearly all black holes observed. We will review the arguments and the way to verify the ensuing predictions. This involves the definition of reliable samples of active sources, such as black holes, and galaxies active in star formation. The AUGER array will probably decide within the next few years, where the highest energy cosmic rays come from, and so frame the next quests, on very high energy neutrinos and perhaps other particles.

astro-ph↗
arXiv2007

Dark Matter and Sterile Neutrinos

Dark matter has been recognized as an essential part of matter for over 70 years now, and many suggestions have been made, what it could be. Most of these ideas have centered on Cold Dark Matter, particles that are predicted in extensions of standard particle physics, such as supersymmetry. Here we explore the concept that dark matter is sterile neutrinos, particles that are commonly referred to as Warm Dark Matter. Such particles have keV masses, and decay over a very long time, much longer than the Hubble time. In their decay they produce X-ray photons which modify the ionization balance in the very early universe, increasing the fraction of molecular Hydrogen, and thus help early star formation. Sterile neutrinos may also help to understand the baryon-asymmetry, the pulsar kicks, the early growth of black holes, the minimum mass of dwarf spheroidal galaxies, as well as the shape and smoothness of dark matter halos. As soon as all these tests have been made quantitative in their various parameters, we may focus on the creation mechanism of these particles, and could predict the strength of the sharp X-ray emission line, expected from any large dark matter assembly. A measurement of this X-ray emission line would be definitive proof for the existence of may be called weakly interacting neutrinos, or WINs.

astro-ph↗
arXiv2007

Thermal and chemical evolution of the primordial clouds in warm dark matter models with keV sterile neutrinos in one-zone approximation

We follow the evolution of the baryonic top-hat overdensity in a single-zone approximation. Our goal is to juxtapose the evolution of the gas temperature in the primordial clouds in the lambda cold dark matter model and the warm dark matter model with keV sterile neutrinos and to check the effects of their decays, into one X-ray photon and one active neutrino, on the structure formation. We find that, in all the cases we have examined, the overall effect of sterile dark matter is to facilitate the cooling of gas and to reduce the minimal mass of the halo able to collapse. Hence, we conclude that X-rays from the decays of dark matter in the form of sterile neutrinos can help the early collapse of gas clouds and the subsequent star formation.

astro-ph↗
arXiv2006

Degenerate sterile neutrino dark matter in the cores of galaxies

We study the distribution of fermionic dark matter at the center of galaxies using NFW, Moore and isothermal density profiles and show that dark matter becomes degenerate for particle masses of a few {\rm keV} and for distances less than a few parsec from the center of our galaxy. A compact degenerate core forms after galaxy merging and boosts the growth of supermassive black holes at the center of galaxies. To explain the galactic center black hole of mass of $\sim 3.5 \times 10^{6}M_{\odot}$ and a supermassive black hole of $\sim 3 \times 10^{9}M_{\odot}$ at a redshift of 6.41 in SDSS quasars, we require a degenerate core of mass between $3 \times 10^{3} M_{\odot}$ and $3.5 \times 10^{6}M_{\odot}$. This constrains the mass of the dark matter particle between $0.6 {\rm keV}$ and $82 {\rm keV}$. The lower limit on the dark matter mass is improved to {\rm 7 keV} if exact solutions of Poisson's equation are used in the isothermal power law case. We argue that the constrained particle could be the long sought dark matter of the Universe that is interpreted here as a sterile neutrino.

astro-ph↗
arXiv2006

Thermal evolution of the primordial clouds in warm dark matter models with keV sterile neutrinos

We analyze the processes relevant for star formation in a model with dark matter in the form of sterile neutrinos. Sterile neutrino decays produce an X-ray background radiation that has a two-fold effect on the collapsing clouds of hydrogen. First, the X-rays ionize the gas and cause an increase in the fraction of molecular hydrogen, which makes it easier for the gas to cool and to form stars. Second, the same X-rays deposit a certain amount of heat, which could, in principle, thwart the cooling of gas. We find that, in all the cases we have examined, the overall effect of sterile dark matter is to facilitate the cooling of gas. Hence, we conclude that dark matter in the form of sterile neutrinos can help the early collapse of gas clouds and the subsequent star formation.

astro-ph↗
arXiv2006

Relic keV sterile neutrinos and reionization

A sterile neutrino with mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that X-rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the universe at a high enough redshift to be consistent with the WMAP results.

astro-ph↗
arXiv2005

Ultra High Energy Cosmic Rays from Sequestered X Bursts

Assuming that there is no GZK (Greisen-Zatsepin-Kuzmin) cut-off and that super-GZK cosmic rays correlate with AGN (Active Galactic Nuclei) at cosmological distances, it is speculated that a relic superheavy particle (X) has its lifetime enhanced by sequestration in an extra dimension. This sequestration is assumed to be partially liberated by proximity of merging supermassive black holes in an AGN, temporarily but drastically reducing the lifetime, thus stimulating an X burst. Based on sequestration of the decay products of X, a speculative explanation of the observed $γ/N$ ratio is proposed.

astro-ph↗