Signatures of Nucleon Disappearance in Large Underground Detectors

For neutrons bound inside nuclei, baryon instability can manifest itself as a decay into undetectable particles (e.g., $\it n \to \nu \nu \bar{\nu}$), i.e., as a disappearance of a neutron from its nuclear state. If electric charge is conserved, a similar disappearance is impossible for a proton. The existing experimental lifetime limit for neutron disappearance is 4-7 orders of magnitude lower than the lifetime limits with detectable nucleon decay products in the final state [PDG2000]. In this paper we calculated the spectrum of nuclear de-excitations that would result from the disappearance of a neutron or two neutrons from $^{12}$C. We found that some de-excitation modes have signatures that are advantageous for detection in the modern high-mass, low-background, and low-threshold underground detectors, where neutron disappearance would result in a characteristic sequence of time- and space-correlated events. Thus, in the KamLAND detector [Kamland], a time-correlated triple coincidence of a prompt signal, a captured neutron, and a $\beta^{+}$ decay of the residual nucleus, all originating from the same point in the detector, will be a unique signal of neutron disappearance allowing searches for baryon instability with sensitivity 3-4 orders of magnitude beyond the present experimental limits.Comment: 13 pages including 6 figures, revised version, to be published in Phys.Rev.

Discovery of the Binary Pulsar PSR B1259-63 in Very-High-Energy Gamma Rays around Periastron with H.E.S.S

We report the discovery of very-high-energy (VHE) gamma-ray emission of the binary system PSR B1259-63/SS 2883 of a radio pulsar orbiting a massive, luminous Be star in a highly eccentric orbit. The observations around the 2004 periastron passage of the pulsar were performed with the four 13 m Cherenkov telescopes of the H.E.S.S. experiment, recently installed in Namibia and in full operation since December 2003. Between February and June 2004, a gamma-ray signal from the binary system was detected with a total significance above 13 sigma. The flux was found to vary significantly on timescales of days which makes PSR B1259-63 the first variable galactic source of VHE gamma-rays observed so far. Strong emission signals were observed in pre- and post-periastron phases with a flux minimum around periastron, followed by a gradual flux decrease in the months after. The measured time-averaged energy spectrum above a mean threshold energy of 380 GeV can be fitted by a simple power law F_0(E/1 TeV)^-Gamma with a photon index Gamma = 2.7+-0.2_stat+-0.2_sys and flux normalisation F_0 = (1.3+-0.1_stat+-0.3_sys) 10^-12 TeV^-1 cm^-2 s^-1. This detection of VHE gamma-rays provides unambiguous evidence for particle acceleration to multi-TeV energies in the binary system. In combination with coeval observations of the X-ray synchrotron emission by the RXTE and INTEGRAL instruments, and assuming the VHE gamma-ray emission to be produced by the inverse Compton mechanism, the magnetic field strength can be directly estimated to be of the order of 1 G.Comment: 10 pages, 8 figures, accepted in Astronomy and Astrophysics on 2 June 2005, replace: document unchanged, replaced author field in astro-ph entry - authors are all members of the H.E.S.S. collaboration and three additional authors (99+3, see document

Dark Matter and Fundamental Physics with the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 deg. In the following study, we investigate the prospects for CTA to study several science questions that influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations, we employ a Monte Carlo based approach to evaluate the prospects for detection. First, we discuss CTA prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, in the region close to the Galactic Centre, and in clusters of galaxies. The possible search for spatial signatures, facilitated by the larger field of view of CTA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma rays from very distant blazars. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz Invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.Comment: (31 pages, Accepted for publication in Astroparticle Physics

A low level of extragalactic background light as revealed by big gamma-rays from blazars

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light1. An alternative approach2, 3, 4, 5 is to study the absorption features imprinted on the -ray spectra of distant extragalactic objects by interactions of those photons with the background light photons6. Here we report the discovery of -ray emission from the blazars7 H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies8. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources—in particular from the first stars formed9. This result also indicates that intergalactic space is more transparent to -rays than previously thought

Constraints on axionlike particles with H.E.S.S. from the irregularity of the PKS 2155-304 energy spectrum

Axionlike particles (ALPs) are hypothetical light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of ALPs can modify the energy spectrum of the gamma rays for a sufficiently large coupling between ALPs and photons. This modification would take the form of an irregular behavior of the energy spectrum in a limited energy range. Data from the H.E.S.S. observations of the distant BL Lac object PKS 2155-304 (z=0.116) are used to derive upper limits at the 95% C.L. on the strength of the ALP coupling to photons, ggammaa<2.1×10-11GeV-1 for an ALP mass between 15 and 60 neV. The results depend on assumptions on the magnetic field around the source, which are chosen conservatively. The derived constraints apply to both light pseudoscalar and scalar bosons that couple to the electromagnetic fieldFil: Medina, Maria Clementina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto Argentino de Radioastronomia (i); ArgentinaFil: H.E.S. S. collaboration

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behavior, and is one of only a few FSRQs detected at very high energy (VHE, E >100 GeV) -rays. VHE -ray observations with H.E.S.S. and MAGIC during late May and early June 2016 resulted in the detection of an unprecedented flare, which reveals for the first time VHE -ray intranight variability in this source. While a common variability timescale of 1.5 hr is found, there is a significant deviation near the end of the flare with a timescale of ∼ 20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, curvature is detected in the VHE -ray spectrum of PKS 1510-089, which is fully explained through absorption by the extragalactic background light. Optical R-band observations with ATOM reveal a counterpart of the -ray flare, even though the detailed flux evolution differs from the VHE lightcurve. Interestingly, a steep flux decrease is observed at the same time as the cessation of the VHE flare. In the high energy (HE, E >100 MeV) -ray band only a moderate flux increase is observed with Fermi-LAT, while the HE -ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the -ray spectrum indicates that the emission region is located outside of the BLR. Radio VLBI observations reveal a fast moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located ∼ 50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this correlation is indeed true, VHE rays have been produced far down the jet where turbulent plasma crosses a standing shock.Accepted manuscrip

Prospects for a Dark Matter Annihilation Signal toward the Sagittarius Dwarf Galaxy with Ground-based Cherenkov telescopes

Dwarf galaxies are widely believed to be among the best targets for indirect dark matter searches using high-energy gamma rays; and indeed gamma-ray emission from these objects has long been a subject of detailed study for ground- based atmospheric Cherenkov telescopes. Here, we update current exclusion limits obtained on the closest dwarf, the Sagittarius dwarf galaxy, in light of re- cent realistic dark matter halo models. The constraints on the velocity-weighted annihilation cross section of the dark matter particle are of a few 10−23 cm^3 s^{−1} in the TeV energy range for a 50 h exposure. The limits are extrapolated to the sensitivities of future Cherenkov Telescope Arrays. For 200 h of observation time, the sensitivity at 95% C.L. reaches 10−25 cm^3 s^{−1} . Possible astrophysical back- grounds from gamma-ray sources dissembled in Sagittarius dwarf are studied. It is shown that with long-enough observation times, gamma-ray background from millisecond pulsars in a globular cluster contained within Sagittarius dwarf may" "limit the sensitivity to dark matter annihilations.Fil: Viana, A.. Institute of Research into the Fundamental Laws of the Universe; FranciaFil: Medina, Maria Clementina. Institute of Research into the Fundamental Laws of the Universe; Francia. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; ArgentinaFil: Peñarrubia, J.. University of Cambridge; Reino UnidoFil: Brun, P.. Institute of Research into the Fundamental Laws of the Universe; FranciaFil: Glicenstein, J.F.. Institute of Research into the Fundamental Laws of the Universe; FranciaFil: Kosack, K.. Institute of Research into the Fundamental Laws of the Universe; FranciaFil: Moulin, E.. Institute of Research into the Fundamental Laws of the Universe; FranciaFil: Naumann Godo, M.. Institute of Research into the Fundamental Laws of the Universe; FranciaFil: Peyaud, B.. Institute of Research into the Fundamental Laws of the Universe; Franci

Dark matter searches with H.E.S.S.: nearby dwarf galaxies and IMBH mini-spikes

International audienceWIMP pair annihilations produce high energy gamma-rays in the final state, which can be detected by Imaging Atmospheric Cherenkov Telescopes such as the H.E.S.S. array. We focus in this contribution on searches towards dwarf galaxies and mini-spikes around intermediate mass black holes (IMBHs) in the Galactic halo. H.E.S.S. observations towards the nearby dwarf galaxies Sagittarius and Canis Major are presented. Using realistic modellings for the dark matter (DM) density profiles, constraints on the velocity-weighted annihilation cross section sigmav of DM particles are derived in the framework of Supersymmetric and Kaluza-Klein models. A search for DM mini-spikes around IMBHs is described as well as constraints on the particle physics parameters

The Nectar GHz digitizer ASIC for the Cherenkov telescope array

The proceedings of the TWEPP-11 will be published in the proceedings section of the Journal of Instrumentation (JINST). This offers us a fast, peer-reviewed, open-access publication of the proceedings with easy referencing possibilit