A Search for Ultra-High Energy Counterparts to Gamma-Ray Bursts

A small air shower array operating over many years has been used to search for ultra-high energy (UHE) gamma radiation ($\geq 50$ TeV) associated with gamma-ray bursts (GRBs) detected by the BATSE instrument on the Compton Gamma-Ray Observatory (CGRO). Upper limits for a one minute interval after each burst are presented for seven GRBs located with zenith angles $\theta < 20^{\circ}$. A $4.3\sigma$ excess over background was observed between 10 and 20 minutes following the onset of a GRB on 11 May 1991. The confidence level that this is due to a real effect and not a background fluctuation is 99.8\%. If this effect is real then cosmological models are excluded for this burst because of absorption of UHE gamma rays by the intergalactic radiation fields.Comment: 4 pages LaTeX with one postscript figure. This version does not use kluwer.sty and will allow automatic postscript generatio

COALESCING NEUTRON STARS AS GAMMA RAY BURSTERS ?

We investigate the dynamics and evolution of coalescing neutron stars. The three-dimensional Newtonian equations of hydrodynamics are integrated by the `Piecewise Parabolic Method' However, we do include the effects of the emission of gravitational waves on the hydrodynamics. The properties of neutron star matter are described by the equation of state of Lattimer & Swesty. In addition to the fundamental hydrodynamic quantities, density, momentum, and energy, we follow the time evolution of the electron density in the stellar gas. Energy losses and changes of the electron abundance due to the emission of neutrinos are taken into account by an elaborate ``neutrino leakage scheme'', which employs a careful calculation of the lepton number and energy source terms of all neutrino types. The grid is Cartesian and equidistant with a resolution of 64**3 or 128**3, which allows us to calculate the self-gravity via fast Fourier transforms.Comment: extended abstract contribution to the proceedings of the 17th Texas Symposium, 2 pages, uuencoded compressed postscript

Cosmological Models of Gamma-Ray Bursts

We review models of cosmological gamma-ray bursts (GRBs). The statistical and $\gamma$-ray transparency issues are summarized. Neutron-star and black-hole merger scenarios are described and estimates of merger rates are summarized. We review the simple fireball models for GRBs and the recent work on non-simple fireballs. Alternative cosmological models, including models where GRBs are analogs of active galactic nuclei and where they are produced by high-field, short period pulsars, are also mentioned. The value of neutrino astronomy to solve the GRB puzzle is briefly reviewed.Comment: 12 pages, no figures, uuencoded compressed postscript file. Invited review to appear in the proceedings of the 29th ESLAB Symposium "Towards the Source of Gamma-Ray Bursts," Noordwijk, Netherlands, 25-27 April, 199

High-redshift star formation rate up to z~8.3 derived from gamma-ray bursts and influence of background cosmology

The high-redshift star formation rate (SFR) is difficult to measure directly even by modern approaches. Long-duration gamma-ray bursts (GRBs) can be detected to the edge of the visible universe because of their high luminorsities. The collapsar model of long gamma-ray bursts indicates that they may trace the star formation history. So long gamma-ray bursts may be a useful tool of measuring the high-redshift SFR. Observations show that long gamma-ray bursts prefer to form in a low-metallicity environment. We study the high-redshift SFR up to z~8.3 considering the Swift GRBs tracing the star formation history and the cosmic metallicity evolution in different background cosmological models including $\Lambda$CDM, quintessence, quintessence with a time-varying equation of state, and brane-world model. We use latest Swift GRBs including two highest-$z$ GRBs, GRB 080913 at $z=6.7$ and GRB 090423 at $z=8.3$. We find that the SFR at $z>4$ shows a steep decay with a slope of $\sim -5.0$ in $\Lambda$CDM. In the other three models, the high-redshift SFR is slightly different from $\Lambda$CDM model, and also shows a steep decay.Comment: 5 pages, 5 figures, 2 tables, two references adde

Gamma-Ray Burst Energy Spectra: Theoretical Models, Old and New

The modelling of gamma-ray burst (GRB) spectra has considerable potential for increasing the understanding of these enigmatic sources. A diversity of ideas and analyses has been generated over the last two decades to explain line features and continuum shapes, encompassing both older galactic neutron star and ``new age'' cosmological source models. This paper reviews some of the highlights of these studies, discussing the merits and limitations of various ideas, and in particular their compatibility with the observational data. The first focus will be on continuum models for GRBs, which include optically thin synchrotron emission and resonant Compton upscattering near galactic neutron stars, while the synchrotron and non-magnetic inverse Compton scattering mechanisms are prominent in the less well-developed cosmological scenarios. Line formation scenarios will then be discussed, in particular the scattering model for producing cyclotron features, which remains the only viable explanation for the Ginga observations of double lines. Absorption-like line production in cosmological burst models is generally difficult, though interesting notions such as femtolensing interference patterns have been proffered.Comment: 8 pages with no figures, as a compressed, uuencoded, Postscript file. Invited review, to appear in Astrophysics and Space Science as part of the proceedings of the 29th ESLAB Symposium ``Towards the Source of Gamma-Ray Bursts'' held in Noordwijk, 199

Multi-wavelength observations of the energetic GRB 080810: detailed mapping of the broadband spectral evolution

GRB 080810 was one of the first bursts to trigger both Swift and the Fermi Gamma-ray Space Telescope. It was subsequently monitored over the X-ray and UV/optical bands by Swift, in the optical by ROTSE and a host of other telescopes and was detected in the radio by the VLA. The redshift of z= 3.355 +/- 0.005 was determined by Keck/HIRES and confirmed by RTT150 and NOT. The prompt gamma/X-ray emission, detected over 0.3-10^3 keV, systematically softens over time, with E_peak moving from ~600 keV at the start to ~40 keV around 100 s after the trigger; alternatively, this spectral evolution could be identified with the blackbody temperature of a quasithermal model shifting from ~60 keV to ~3 keV over the same time interval. The first optical detection was made at 38 s, but the smooth, featureless profile of the full optical coverage implies that this originated from the afterglow component, not the pulsed/flaring prompt emission. Broadband optical and X-ray coverage of the afterglow at the start of the final X-ray decay (~8 ks) reveals a spectral break between the optical and X-ray bands in the range 10^15 - 2x10^16 Hz. The decay profiles of the X-ray and optical bands show that this break initially migrates blueward to this frequency and then subsequently drifts redward to below the optical band by ~3x10^5 s. GRB 080810 was very energetic, with an isotropic energy output for the prompt component of 3x10^53 erg and 1.6x10^52 erg for the afterglow; there is no evidence for a jet break in the afterglow up to six days following the burst.Comment: 15 pages, 9 figures, 4 in colour. Accepted for publication in MNRA

Signatures of a Maxwellian Component in Shock-Accelerated Electrons in GRBs

Recent particle-in-cell simulations suggest that a large fraction of the energy dissipated in a relativistic shock is deposited into a Maxwellian distribution of electrons that is connected to the high-energy power-law tail. Here, we explore the observational implications of such a mixed thermal-nonthermal particle distribution for the afterglow and prompt emission of gamma-ray bursts. When the Maxwellian component dominates the energy budget, the afterglow lightcurves show a very steep decline phase followed by a more shallow decay when the characteristic synchrotron frequency crosses the observed band. The steep decay appears in the X-rays at ~100 sec after the burst and is accompanied by a characteristic hard-soft-hard spectral evolution that has been observed in a large number of early afterglows. If internal shocks produce a similar mixed electron distribution, a bump is expected at the synchrotron peak of the nu*f_nu spectrum.Comment: 7 pages, 9 figures, with added fig. to compare with observations, MNRAS, 400, 330 (2009

Immunodetection of retinoblastoma-related protein and its phosphorylated form in interphase and mitotic alfalfa cells

Plant retinoblastoma-related (RBR) proteins are primarily considered as key regulators of G1/S phase transition, with functional roles in a variety of cellular events during plant growth and organ development. Polyclonal antibody against the C-terminal region of the Arabidopsis RBR1 protein also specifically recognizes the alfalfa 115 kDa MsRBR protein, as shown by the antigen competition assay. The MsRBR protein was detected in all cell cycle phases, with a moderate increase in samples representing G2/M cells. Antibody against the human phospho-pRb peptide (Ser807/811) cross-reacted with the same 115 kDa MsRBR protein and with the in vitro phosphorylated MsRBR protein C-terminal fragment. Phospho-MsRBR protein was low in G1 cells. Its amount increased upon entry into the S phase and remained high during the G2/M phases. Roscovitine treatment abolished the activity of alfalfa MsCDKA1;1 and MsCDKB2;1, and the phospho-MsRBR protein level was significantly decreased in the treated cells. Colchicine block increased the detected levels of both forms of MsRBR protein. Reduced levels of the MsRBR protein in cells at stationary phase or grown in hormone-free medium can be a sign of the division-dependent presence of plant RBR proteins. Immunolocalization of the phospho-MsRBR protein indicated spots of variable number and size in the labelled interphase nuclei and high signal intensity of nuclear granules in prophase. Structures similar to phospho-MsRBR proteins cannot be recognized in later mitotic phases. Based on the presented western blot and immunolocalization data, the possible involvement of RBR proteins in G2/M phase regulation in plant cells is discussed

Dental Health and Mortality in People With End-Stage Kidney Disease Treated With Hemodialysis: A Multinational Cohort Study

Background Dental disease is more extensive in adults with chronic kidney disease, but whether dental health and behaviors are associated with survival in the setting of hemodialysis is unknown. Study Design Prospective multinational cohort. Setting & Participants 4,205 adults treated with long-term hemodialysis, 2010 to 2012 (Oral Diseases in Hemodialysis [ORAL-D] Study). Predictors Dental health as assessed by a standardized dental examination using World Health Organization guidelines and personal oral care, including edentulousness; decayed, missing, and filled teeth index; teeth brushing and flossing; and dental health consultation. Outcomes All-cause and cardiovascular mortality at 12 months after dental assessment. Measurements Multivariable-adjusted Cox proportional hazards regression models fitted with shared frailty to account for clustering of mortality risk within countries. Results During a mean follow-up of 22.1 months, 942 deaths occurred, including 477 cardiovascular deaths. Edentulousness (adjusted HR, 1.29; 95% CI, 1.10-1.51) and decayed, missing, or filled teeth score ≥ 14 (adjusted HR, 1.70; 95% CI, 1.33-2.17) were associated with early all-cause mortality, while dental flossing, using mouthwash, brushing teeth daily, spending at least 2 minutes on oral hygiene daily, changing a toothbrush at least every 3 months, and visiting a dentist within the past 6 months (adjusted HRs of 0.52 [95% CI, 0.32-0.85], 0.79 [95% CI, 0.64-0.97], 0.76 [95% CI, 0.58-0.99], 0.84 [95% CI, 0.71-0.99], 0.79 [95% CI, 0.65-0.95], and 0.79 [95% CI, 0.65-0.96], respectively) were associated with better survival. Results for cardiovascular mortality were similar. Limitations Convenience sample of clinics. Conclusions In adults treated with hemodialysis, poorer dental health was associated with early death, whereas preventive dental health practices were associated with longer survival