40Ar/39Ar age of the Jurassic North Mountain Basalt, southwestern Nova Scotia

Two whole-rock samples of the Jurassic North Mountain Basalt have been dated using the 40Ar/39Ar method. A single sample of fresh, medium-grained, holocrystalline basalt from the lower flow unit of this thick (i.e., 400 m) sequence gave coincident plateau and isochron correlation ages of 201 ± 2.5 Ma, in agreement with a zircon U-Pb age of 202 ± 1 Ma for this same flow unit. This 40Ar/39Ar age contrasts with earlier conventional K-Ar whole-rock ages of ca. 192 Ma for the North Mountain Basalt, which are similar to other K-Ar and Ar/Ar ages for correlative basalts of eastern North America. The second dated sample is a zeolite-bearing basalt from the middle flow unit of the North Mountain Basalt. This sample gave a discordant age spectrum with excess argon, but the isochron correlation age of 206 Ma, albeit with a large error (i.e., 56 Ma), is similar to that for the fresh sample. The data indicate that reliable whole-rock 40Ar/39Ar ages for the basalts are attainable, but that fresh samples must be used. In light of this, it is suggested that the younger 192 Ma ages may reflect a widespread thermal event related to zeolite formation. RÉSUMÉ Deux échantillons de roche totale de basalte jurassique du mont North ont été datés au moyen de la méthode 40Ar/39Ar. Un échantillon unitaire de basalte holocristallin à grain moyen frais de l'unité d'écoulement inférieure de cette séquence épaisse (c.-à-d. 400 m) a fourni des âges concordants par corrélation tabulaire et isochrone de 201 ± 2,5 Ma, ce qui correspond à la datation au U-Pb à partir de zircon situant la même unité d'écoulement à 202 ± 1 Ma. Cette datation 40Ar/39Ar fait contraste avec les datations de la roche totale conventionnelles antérieures au K-Ar situant à environ 192 Ma le basalte du mont North, soit des âges semblables à d'autres datations au K-Ar et Ar/Ar de basaltes corrélatifs de l'Est de l'Amérique du Nord. Le deuxième échantillon daté est un basalte renfermant de la zéolite et provenant du milieu de l'unité d'écoulement du basalte du mont North. Cet échantillon a fourni un spectre d'âges discordant présentant un excès d'argon, mais la datation par corrélation isochrone le situant à 206 Ma, en dépit d'une erreur importante (c.-à-d. 56 Ma), fournit un âge semblable à celui de l'échantillon frais. Les données révèlent qu'il est possible d'obtenir des dates de roche totale fiables au moyen de la méthode 40Ar/39Ar, mais qu'il faut utiliser des échantillons frais. Compte tenu de ce fait, on suppose que les âges plus récents de 192 Ma pourraient correspondre à un phénomène thermique répandu apparenté à la formation de zéolite

A submillimetre survey of the star-formation history of radio galaxies

We present the results of the first major systematic submillimetre survey of radio galaxies spanning the redshift range 1 < z < 5. The primary aim of this work is to elucidate the star-formation history of this sub-class of elliptical galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the JCMT we have obtained 850-micron photometry of 47 radio galaxies to a consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The radio galaxy targets have been selected from a series of low-frequency radio surveys of increasing depth (3CRR, 6CE, etc), in order to allow us to separate the effects of increasing redshift and increasing radio power on submillimetre luminosity. Although the dynamic range of our study is inevitably small, we find clear evidence that the typical submillimetre luminosity (and hence dust mass) of a powerful radio galaxy is a strongly increasing function of redshift; the detection rate rises from 15 per cent at z 2.5, and the average submillimetre luminosity rises as (1+z)^3 out to z~4. Moreover our extensive sample allows us to argue that this behaviour is not driven by underlying correlations with other radio galaxy properties such as radio power, radio spectral index, or radio source size/age. Although radio selection may introduce other more subtle biases, the redshift distribution of our detected objects is in fact consistent with the most recent estimates of the redshift distribution of comparably bright submillimetre sources discovered in blank field surveys. The evolution of submillimetre luminosity found here for radio galaxies may thus be representative of massive ellipticals in general.Comment: 31 pages - 10 figures in main text, 3 pages of figures in appendix. This revised version has been re-structured, but the analysis and conclusions have not changed. Accepted for publication in MNRA

On the X-ray variability of magnetar 1RXS J170849.0-400910

We present a long-term X-ray flux and spectral analysis for 1RXS J170849.0-400910 using Swift/XRT spanning over 8 years from 2005-2013. We also analyze two observations from Chandra and XMM in the period from 2003-2004. In this 10-yr period, 1RXS J170849.0-400910 displayed several rotational glitches. Previous studies have claimed variations in the X-ray emission associated with some of the glitches. From our analysis we find no evidence for significant X-ray flux variations and evidence for only low-level spectral variations. We also present an updated timing solution for 1RXS J170849.0-400910, from RXTE and Swift observations, which includes a previously unreported glitch at MJD 56019. We discuss the frequency and implications of radiatively quiet glitches in magnetars.Comment: 9 pages, 2 figures, accepted for publication in Ap

X-ray Observations of XSS J12270-4859 in a New Low State: A Transformation to a Disk-Free Rotation-Powered Pulsar Binary

We present XMM-Newton and Chandra observations of the low-mass X-ray binary XSS J12270--4859, which experienced a dramatic decline in optical/X-ray brightness at the end of 2012, indicative of the disappearance of its accretion disk. In this new state, the system exhibits previously absent orbital-phase-dependent, large-amplitude X-ray modulations with a decline in flux at superior conjunction. The X-ray emission remains predominantly non-thermal but with an order of magnitude lower mean luminosity and significantly harder spectrum relative to the previous high flux state. This phenomenology is identical to the behavior of the radio millisecond pulsar binary PSR J1023+0038 in the absence of an accretion disk, where the X-ray emission is produced in an intra-binary shock driven by the pulsar wind. This further demonstrates that XSS J12270-4859 no longer has an accretion disk and has transformed to a full-fledged eclipsing "redback" system that hosts an active rotation-powered millisecond pulsar. There is no evidence for diffuse X-ray emission associated with the binary that may arise due to outflows or a wind nebula. An extended source situated 1.5' from XSS J12270--4859 is unlikely to be associated, and is probably a previously uncatalogued galaxy cluster.Comment: 8 pages, 6 figures; accepted for publication in the Astrophysical Journa

Equilibrium extraction characteristics of alkyl amines and nuclear fuel metals in nitrate systems: progress report for the period January 1 - September 31 [sic], 1963 : progress report XII

"December 2, 1963."Includes bibliographical references (pages 29-30)Progress report no. XII; January 1, 1963 - September 30, 1963Work performed under subcontract no. 1327 under contract no. W -7405 - Eng - 26 with Union Carbide Nuclear Corporation Oak Ridge, Tennesse

Equilibrium extraction characteristics of alkyl amines and nuclear fuel metals in nitrate systems: progress report for the period October 1 - May 30, 1964 : progress report XIII

"August 3, 1964."Includes bibliographical references (page 32)Progress report no. XIII; October 1, 1963 - May 30, 1964Work performed under subcontract no. 1327 under contract no. W -7405 - Eng - 26 with Union Carbide Nuclear Corporation Oak Ridge, Tennesse