Very High Energy Gamma-Ray Emission from the Blazar Markarian 421

Very high energy gamma-ray emission from the BL Lac object Markarian 421 has been detected over three observing seasons on 59 nights between April 1992 and June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its initial detection in 1992, its flux above 500 GeV was 1.6$\times$10$^{-11}$photons cm$^{-2}$ s$^{-1}$. Observations in 1993 confirmed this level of emission. For observations made between December 1993 and April 1994, its intensity was a factor of 2.2$\pm$0.5 lower. Observations on 14 and 15 May, 1994 showed an increase over this quiescent level by a factor of $\sim$10 (Kerrick et al. 1995). This strong outburst suggests that 4 episodes of increased flux measurements on similar time scales in 1992 and 1994 may be attributed to somewhat weaker outbursts. The variability of the TeV gamma-ray emission from Markarian 421 stands in contrast to EGRET observations (Lin et al. 1994) which show no evidence for variability.Comment: gzip compressed tar file including LaTeX text and 4 postscript figures (14 pages total incl. 4 tables), accepted for publication in the Astrophysical Journal. Contact address is [email protected]

Self-Dual Conformal Supergravity and the Hamiltonian Formulation

In terms of Dirac matrices the self-dual and anti-self-dual decomposition of a conformal supergravity is given and a self-dual conformal supergravity theory is developed as a connection dynamic theory in which the basic dynamic variabes include the self-dual spin connection i.e. the Ashtekar connection rather than the triad. The Hamiltonian formulation and the constraints are obtained by using the Dirac-Bergmann algorithm. PACS numbers: 04.20.Cv, 04.20.Fy,04.65.+

Syntectonic mobility of supergene nickel ores of New Caledonia (Southwest Pacific). Evidence from faulted regolith and garnierite veins.

International audienceSupergene nickel deposits of New Caledonia that have been formed in the Neogene by weathering of obducted ultramafic rocks are tightly controlled by fracture development. The relationship of tropical weathering and tectonic structures, faults and tension gashes, have been investigated in order to determine whether fractures have play a passive role only, as previously thought; or alternatively, if brittle tectonics was acting together with alteration. From the observation of time-relationship, textures, and mineralogy of various fracture fills and fault gouges, it may be unambiguously established that active faulting has play a prominent role not only in facilitating drainage and providing room for synkinematic crystallisation of supergene nickel silicate, but also in mobilising already formed sparse nickel ore, giving birth to the very high grade ore nicknamed "green gold"

TEV gamma ray emission from the active galactic nucleus Markarian 421

TeV energy gamma ray emission from the blazar Markarian 421 was detected with the Whipple 10 meter imaging Cherenkov telescope initially during the observation period March‐June 1992 at an average photon flux of 1.5×10−11 cm2 s−1. The photon spectrum in the TeV range lies on the extrapolation of the data points observed by EGRET during viewing phase I and indicates that the emission follows an unchanged power law between 100 MeV and 10 TeV with no significant intergalactic absorption. More recent observations from the spring of 1993 confirm the 1992 measurements. Here we give an update on the status of the observations, the analysis for time variability, and the results from the analysis to determine the spectral index for Markarian 421 at TeV energies.The search for TeV emission from other extragalactic sources detected by the EGRET instrument on the Compton Gamma Ray Observatory at GeV energies have so far been negative.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87648/2/597_1.pd

High Energy Neutrinos from Quasars

We review and clarify the assumptions of our basic model for neutrino production in the cores of quasars, as well as those modifications to the model subsequently made by other workers. We also present a revised estimate of the neutrino background flux and spectrum obtained using more recent empirical studies of quasars and their evolution. We compare our results with other thoeretical calculations and experimental upper limits on the AGN neutrino background flux. We also estimate possible neutrino fluxes from the jets of blazars detected recently by the EGRET experiment on the Compton Gamma Ray Observatory. We discuss the theoretical implications of these estimates.Comment: 14 pg., ps file (includes figures), To be published in Space Science Review

Observations of the Crab nebula at TeV energies

The results of four years of observation of the Crab Nebula at TeV energies by the Whipple group are discussed and the status of the Crab Nebula as a standard candle for TeV astronomy is reviewed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87647/2/270_1.pd

Detection of TeV gamma rays from the AGN Markarian 421

We present here the detection of TeV gamma rays from the extragalactic source Markarian 421. Observations obtained with the Whipple 10 m imaging Cherenkov telescope in March–June 1992 give a gamma ray signal with statistical significance of 6.3σ above background. The excess corresponds to an average flux of 1.5×10−11 cm−2 s−1 above 0.5 TeV, equivalent to 0.3 of that from the Crab Nebula. The estimated location of the source agrees with the position of Mrk 421 to the angular uncertainty of the Whipple instrument (6 arc minutes).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87671/2/185_1.pd

Searches for bursts of TEV gamma rays on time‐scales of seconds

The Whipple Observatory gamma‐ray telescope has a high sensitivity to sources of gamma rays in the 0.4 to 4 TeV energy range. Although this sensitivity is used primarily to search for discrete sources of gamma‐rays the instrument also has sensitivity to gamma‐ray bursts on time‐scales from milliseconds to seconds. The field of view is limited but the source location capability is good. Such bursts could radiate with peak luminosity at TeV energies and could originate from(a) primordial black holes or (b) cosmic strings; they could also be the high energy counterparts of BATSE‐type bursts and hence of unknown origin. The search of the Whipple data‐base for statistically unlikely consecutive events on time‐scales of second will be described and compared with the theoretical predictions. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87630/2/470_1.pd

Tau Neutrinos Underground: Signals of νμ→ντ\nu_\mu \to \nu_\tau Oscillations with Extragalactic Neutrinos

The appearance of high energy tau neutrinos due to $\nu_\mu \to \nu_\tau$ oscillations of extragalactic neutrinos can be observed by measuring the neutrino induced upward hadronic and electromagnetic showers and upward muons. We evaluate quantitatively the tau neutrino regeneration in the Earth for a variety of extragalactic neutrino fluxes. Charged-current interactions of the upward tau neutrinos below and in the detector, and the subsequent tau decay create muons or hadronic and electromagnetic showers. The background for these events are muon neutrino and electron neutrino charged-current and neutral-current interactions, where in addition to extragalactic neutrinos, we consider atmospheric neutrinos. We find significant signal to background ratios for the hadronic/electromagnetic showers with energies above 10 TeV to 100 TeV initiated by the extragalactic neutrinos. We show that the tau neutrinos from point sources also have the potential for discovery above a 1 TeV threshold. A kilometer-size neutrino telescope has a very good chance of detecting the appearance of tau neutrinos when both muon and hadronic/electromagnetic showers are detected.Comment: section added and two new figs; accepted for publication in Physical Review

Enolase Inhibitors as Early Lead Therapeutics against Trypanosoma brucei

Glucose metabolism is critical for the African trypanosome, Trypanosoma brucei, serving as the lone source of ATP production for the bloodstream form (BSF) parasite in the glucose-rich environment of the host blood. Recently, phosphonate inhibitors of human enolase (ENO), the enzyme responsible for the interconversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP) in glycolysis or PEP to 2-PG in gluconeogenesis, have been developed for the treatment of glioblastoma multiforme (GBM). Here, we have tested these agents against T. brucei ENO (TbENO) and found the compounds to be potent enzyme inhibitors and trypanocides. For example, (1-hydroxy-2-oxopyrrolidin-3-yl) phosphonic acid (deoxy-SF2312) was a potent enzyme inhibitor (IC50 value of 0.60 ± 0.23 µM), while a six-membered ring-bearing phosphonate, (1-hydroxy-2-oxopiperidin-3-yl) phosphonic acid (HEX), was less potent (IC50 value of 2.1 ± 1.1 µM). An analog with a larger seven-membered ring, (1-hydroxy-2-oxoazepan-3-yl) phosphonic acid (HEPTA), was not active. Molecular docking simulations revealed that deoxy-SF2312 and HEX had binding affinities of -6.8 and -7.5 kcal/mol, respectively, while the larger HEPTA did not bind as well, with a binding of affinity of -4.8 kcal/mol. None of these compounds were toxic to BSF parasites; however, modification of enzyme-active phosphonates through the addition of pivaloyloxymethyl (POM) groups improved activity against T. brucei, with POM-modified (1,5-dihydroxy-2-oxopyrrolidin-3-yl) phosphonic acid (POMSF) and POMHEX having EC50 values of 0.45 ± 0.10 and 0.61 ± 0.08 µM, respectively. These findings suggest that HEX is a promising lead against T. brucei and that further development of prodrug HEX analogs is warranted