Multi-GeV Neutrino Emission from Magnetized Gamma Ray Bursts

We investigate the expected neutrino emissivity from nuclear collisions in magnetically dominated collisional models of gamma-ray bursts, motivated by recent observational and theoretical developments. The results indicate that significant multi-GeV neutrino fluxes are expected for model parameter values which are typical of electromagnetically detected bursts. We show that for detecting at least one muon event in Icecube and its Deep Core sub-array, a single burst must be near the high end of the luminosity function and at a redshift $z\lesssim 0.2$. We also calculate the luminosity and distance ranges that can generate $0.01-1$ muon events per GRB in the same detectors, which may be of interest if simultaneously detected electromagnetically, or if measured with future extensions of Icecube or other neutrino detectors with larger effective volume and better sensitivity.Comment: 12 pages, 7 figures, accepted version for Phys.Rev.

Photon acceleration in variable ultra-relativistic outflows and high-energy spectra of Gamma-Ray Bursts

MeV seed photons produced in shocks in a variable ultra-relativistic outflow gain energy by the Fermi mechanism, because the photons Compton scatter off relativistically colliding shells. The Fermi-modified high-energy photon spectrum has a non-universal slope and a universal cutoff. A significant increase in the total radiative efficiency is possible. In some gamma ray bursts, most of the power might be emitted at the high-energy cutoff for this mechanism, which would be close to 100 MeV for outflows with a mean bulk Lorentz factor of 100.Comment: 8 pages, submitted to ApJ

Physical parameters and emission mechanism in Gamma-Ray Bursts

Detailed information on the physical parameters in the sources of cosmological Gamma-Ray Bursts (GRBs) is obtained from few plausible assumptions consistent with observations. Model-independent requirements posed by these assumptions on the emission mechanism in GRBs are formulated. It is found that the observed radiation in sub-MeV energy range is generated by the synchrotron emission mechanism, though about ten per cent of the total GRB energy should be converted via the inverse Compton process into ultra-hard spectral domain (above 100 GeV). We estimate the magnetic field strength in the emitting region, the Lorentz factor of accelerated electrons, and the typical energy of IC photons. We show that there is a "line-of-death" relation for GRBs and derive from this relation the lower limits on both GRB duration and GRB variability timescale. The upper limit on the Lorentz factor of GRB fireballs is also found. We demonstrate that steady-state electron distribution consistent with the Compton losses may produce different spectral indices, e.g., 3/4 as opposed to the figure 1/2 widely discussed in the literature. It is suggested that the changes in the decline rate observed in the lightcurves of several GRB afterglows may be due to the time evolution of spectral break, which appears in the synchrotron emission generated by steady-state self-consistent electron distribution.Comment: Journal reference added, introduction extended, minor changes in notation

Hidden source of high-energy neutrinos in collapsing galactic nucleus

We propose the model of a short-lived very powerful source of high energy neutrinos. It is formed as a result of the dynamical evolution of a galactic nucleus prior to its collapse into a massive black hole and formation of high-luminosity AGN. This stage can be referred to as ``pre-AGN''. A dense central stellar cluster in the galactic nucleus on the late stage of evolution consists of compact stars (neutron stars and stellar mass black holes). This cluster is sunk deep into massive gas envelope produced by destructive collisions of a primary stellar population. Frequent collisions of neutron stars in a central stellar cluster are accompanied by the generation of ultrarelativistic fireballs and shock waves. These repeating fireballs result in a formation of the expanding rarefied cavity inside the envelope. The charged particles are effectively accelerated in the cavity and, due to pp-collisions in the gas envelope, they produce high energy neutrinos. All high energy particles, except neutrinos, are absorbed in the thick envelope. Duration of this pre-AGN phase is about 10 yr, the number of the sources can be \~ 10 per cosmological horizon. High energy neutrino signal can be detected by underground neutrino telescope with effective area ~1 km^2.Comment: small changes, to be published in Astroparticle Physic

Theory of photospheric emission from relativistic outflows

In this paper we reexamine the optical depth of ultrarelativistic spherically symmetric outflows and reevaluate the photospheric radius for each model during both the acceleration and coasting phases. It is shown that for both the wind and the shell models there are two asymptotic solutions for the optical depth during the coasting phase of the outflow. In particular we show that quite counterintuitively a geometrically thin shell may appear as a thick wind for photons propagating inside it. For this reason we introduce notions of photon thick and photon thin outflows, which appear more general and better physically motivated with respect to winds and shells. Photosphere of relativistic outflow is a dynamic surface. We study its geometry and find that the photosphere of photon thin outflow has always a convex shape, while in the photon thick one it is initially convex (there is always a photon thin layer in any outflow) and then it becomes concave asymptotically approaching the photosphere of an infinitely long wind. We find that both instantaneous and time integrated observed spectra are very close to the thermal one for photon thick outflows, in line with existing studies. It is our main finding that the photospheric emission from the photon thin outflow produces non thermal time integrated spectra, which may be described by the Band function well known in the GRB literature. We find that energetic GRBs should produce photon thin outflows with photospheric emission lasting less than one second for the total energy $E_0\leq10^{54}$ erg and baryonic loading parameter $B\leq10^{-2}$. It means that only time integrated spectra may be observed from such GRBs.Comment: Revision of the previous version, new effect is discussed. Conclusions remain unchange

Radiative cooling in relativistic collisionless shocks. Can simulations and experiments probe relevant GRB physics?

We address the question of whether numerical particle-in-cell (PIC) simulations and laboratory laser-plasma experiments can (or will be able to, in the near future) model realistic gamma-ray burst (GRB) shocks. For this, we compare the radiative cooling time, t_cool, of relativistic electrons in the shock magnetic fields to the microscopic dynamical time of collisionless relativistic shocks -- the inverse plasma frequency of protons, omega_pp^{-1}. We obtain that for t_cool*omega_pp^{-1}\lesssim ~few hundred, the electrons cool efficiently at or near the shock jump and are capable of emitiing away a large fraction of the shock energy. Such shocks are well-resolved in existing PIC simulations; therefore, the microscopic structure can be studied in detail. Since most of the emission in such shocks would be coming from the vicinity of the shock, the spectral power of the emitted radiation can be directly obtained from finite-length simulations and compared with observational data. Such radiative shocks correspond to the internal baryon-dominated GRB shocks for the conventional range of ejecta parameters. Fermi acceleration of electrons in such shocks is limited by electron cooling, hence the emitted spectrum should be lacking a non-thermal tail, whereas its peak likely falls in the multi-MeV range. Incidentally, the conditions in internal shocks are almost identical to those in laser-produced plasmas; thus, such GRB-like plasmas can be created and studied in laboratory experiments using the presently available Petawatt-scale laser facilities. An analysis of the external shocks shows that only the highly relativistic shocks, corresponding to the extremely early afterglow phase, can have efficient electron cooling in the shock transition. We emphasize the importance of radiative PIC simulations for further studies.Comment: 15 pages, submitted to Ap

Recovering a spinning inspiralling compact binary waveform immersed in LIGO-like noise with spinning templates

We investigate the recovery chances of highly spinning waveforms immersed in LIGO S5-like noise by performing a matched filtering with 10^6 randomly chosen spinning waveforms generated with the LAL package. While the masses of the compact binary are reasonably well recovered (slightly overestimated), the same does not hold true for the spins. We show the best fit matches both in the time-domain and the frequency-domain. These encompass some of the spinning characteristics of the signal, but far less than what would be required to identify the astrophysical parameters of the system. An improvement of the matching method is necessary, though may be difficult due to the noisy signal.Comment: 5 pages, 1 figure + 4 figure panels; Proceedings of the Eight Edoardo Amaldi Conference on Gravitational Waves (Amaldi8), New York, 2009; to be published in J. Phys.: Conf. Series (JPCS

TeV Neutrinos from Successful and Choked Gamma-Ray Bursts

Core collapse of massive stars resulting in a relativistic fireball jet which breaks through the stellar envelope is a widely discussed scenario for gamma-ray burst production. For very extended or slow rotating stars, the fireball may be unable to break through the envelope. Both penetrating and choked jets will produce, by photo-meson interactions of accelerated protons, a burst of neutrinos with energies in excess of 5 TeV while propagating in the envelope. The predicted flux, from both penetrating and chocked fireballs, should be easily detectable by planned cubic kilometer neutrino telescopes.Comment: Phys.Rev.Letters, in press, final version accepted 8/31/01 (orig. 3/17/01

MAP kináz jelátvitel funkcionális vizsgálat mitokondriumban = Functional studies on mitochondrial MAP kinase signalling

Munkánk során a növényekre specifikus, kevésbé vizsgált, D típusú MAPKok családjának egyik tagját az AtMPK9-t tanulmányoztuk. Élesztő kettős-hibrid rendszerrel a kalmodulint, mint lehetséges AtMPK9 fehérje partnert azonosítottuk, majd a kölcsönhatást in vitro transzlációval előállított fehérjékkel többféle megközelítéssel igazoltuk. Az AtMPK9 poszttranszlációs módosításokon keresztül történő szabályozása korábban ismeretlen volt. A pályázat keretében tömegspektrometriás vizsgálatokkal és in vitro mutagenezissel előállított AtMPK9 variánsokkal bizonyítottuk, hogy az aktiválásért felelős T hurok régióban elhelyezkedő TDY aminosav triplet treoninjának és tirozinjának foszforilálása nélkül a kináz nem rendelkezik aktivitással. A tömegspektrometriás adatok alapján az is nyilvánvaló vált, hogy az AtMPK9 kináz doménjét követő C-terminális doménben további négy aminosav foszforilálódik. Vizsgálataink szerint az összes általunk azonosított foszforiláció autofoszforiláció eredménye. Feltételezésünk szerint a kináz autofoszforilációs aktivitásának szabályozásában a kölcsönható partnerként azonosított kalmodulin kaphat szerepet. Az AtMPK9 in planta funkcióját protoplaszt tranziens expresszióval és null-mutáns növényekkel tanulmányoztuk. Vizsgálataink alapján a fehérje kináz abiotikus stresszel aktiválható, azonban ennek ellenére a null-mutáns növények fenotípusa még stressz körülmények között sem tér el a vadtípusétól, így az AtMPK9 valószínűsíthetően funkcionálisan redudáns kináz. | The project aimed at studying AtMPK9, a member of plant specific, D type mitogen activated protein kinase (MAPK). We identified calmodulin as its putative protein interacting partner by yeast two-hybrid assay. In order to evaluate this result, AtMPK9 and calmodulin were produced by in vitro translation and the interaction was confirmed by pull-down assays and surface plasmone resonance analysis. The kinase activity regulation of AtMPK9 was unknown previously. We demonstrated by mass spectrometry and in vitro mutagenesis studies that phosphorylation of threonine and tyrosine of TDY amino acid triad of T loop is inevitable for kinase activity. Further mass spectrometry analysis revealed another four phosphorylated amino acids in the C-terminal domain of AtMPK9. According to our in vitro translation based data, all the identified phosphorylations are caused by autophosphorylation. We hypothesize that the interacting partner calmodulin regulates the autophosphorylation activity of kinase. The in planta function of the protein kinase was studied by protoplast transient overexpression and application of AtMPK9 knock-out plants. Although the kinase activity of AtMPK9 was inducible by abiotic stress, the knock-out plants did not show any difference in phenotype, not even in stress conditions. These data imply that AtMPK9 is a functionally redundant protein kinase