XMM-Newton Observations of the Be/X-ray transient A0538-66 in quiescence

We present XMM-Newton observations of the recurrent Be/X-ray transient A0538-66, situated in the Large Magellanic Cloud, in the quiescent state. Despite a very low luminosity state of (5-8)E33 ergs/s in the range 0.3-10 keV, the source is clearly detected up to ~8 keV. and can be fitted using either a power law with photon index alpha=1.9+-0.3 or a bremsstrahlung spectrum with kT=3.9+3.9-1.7 keV. The spectral analysis confirms that the off-state spectrum is hard without requiring any soft component, contrary to the majority of neutron stars observed in quiescence up to now.Comment: Accepted for proceedings of 5th INTEGRAL Worksho

Keck Measurement of the XTE J2123-058 Radial Velocity Curve

We measured the radial velocity curve of the companion of the neutron star X-ray transient XTE J2123-058. Its semi-amplitude (K_2) of 298.5 +/- 6.9 km/s is the highest value that has been measured for any neutron star LMXB. The high value for K_2 is, in part, due to the high binary inclination of the system but may also indicate a high neutron star mass. The mass function (f_2) of 0.684 +/- 0.047 solar masses, along with our constraints on the companion's spectral type (K5V-K9V) and previous constraints on the inclination, gives a likely range of neutron star masses from 1.2 to 1.8 solar masses. We also derive a source distance of 8.5 +/- 2.5 kpc, indicating that XTE J2123-058 is unusually far, 5.0 +/- 1.5 kpc, from the Galactic plane. Our measurement of the systemic radial velocity is -94.5 +/- 5.5 km/s, which is significantly different from what would be observed if this object corotates with the disk of the Galaxy.Comment: 4 pages, accepted by ApJ Letters after minor revision

Disappearing Pulses in Vela X-1

We present results from a 20 h RXTE observation of Vela X-1, ncluding a peculiar low state of a few hours duration, during which the pulsation of the X-ray emission ceased, while significant non-pulsed emission remained. This ``quiescent state'' was preceded by a ``normal state'' without any unusual signs and followed by a ``high state'' of several hours of increased activity with strong, flaring pulsations. while there is clear spectral evolution from the normal state to the low state, the spectra of the following high state are surprisingly similar to those of the low state.Comment: 5 pages, 5 figures, Proceedings of the 5th Compton Symposium, AIP, in pres

Infrared scintillation yield in gaseous and liquid argon

The study of primary and secondary scintillations in noble gases and liquids is of paramount importance to rare-event experiments using noble gas media. In the present work, the scintillation yield in gaseous and liquid Ar has for the first time been measured in the near infrared (NIR) and visible region, both for primary and secondary (proportional) scintillations, using Geiger-mode avalanche photodiodes (G-APDs) and pulsed X-ray irradiation. The primary scintillation yield of the fast component was measured to be 17000 photon/MeV in gaseous Ar in the NIR, in the range of 690-1000 nm, and 510 photon/MeV in liquid Ar, in the range of 400-1000 nm. Proportional NIR scintillations (electroluminescence) in gaseous Ar have been also observed; their amplification parameter at 163 K was measured to be 13 photons per drifting electron per kV. Possible applications of NIR scintillations in high energy physics experiments are discussed.Comment: 6 pages, 5 figures. Submitted to Europhysics Letter. Revised Figs. 3 and

Produktivität, Narbendichte und Vegetation einer Kurzrasenweide

Productivity, sward structure and floristic diversity of a continuous grazed pasture on organic permanent grassland were determined in 2015. Daily pasture growth reached less than 50 kg dry matter per hectare in May and stayed low due to unfavorable weather conditions in 2015 (cold spring, dry and hot summer). Forage quality was quite high (> 6,5 MJ NEL/kg dm) most of the grazing season. Tiller density was moderate during summer but increased after sufficient rain in late summer. Perennial ryegrass, Kentucky bluegrass and white clover were the dominant plant species and yielded more the 85 % of dry matter

Confirmation of Two Cyclotron Lines in Vela X-1

We present pulse phase-resolved X-ray spectra of the high mass X-ray binary Vela X-1 using the Rossi X-ray Timing Explorer. We observed Vela X-1 in 1998 and 2000 with a total observation time of ~90 ksec. We find an absorption feature at 23.3 +1.3 -0.6 kev in the main pulse, that we interpret as the fundamental cyclotron resonant scattering feature (CRSF). The feature is deepest in the rise of the main pulse where it has a width of 7.6 +4.4 -2.2 kev and an optical depth of 0.33 +0.06 -0.13. This CRSF is also clearly detected in the secondary pulse, but it is far less significant or undetected during the pulse minima. We conclude that the well known CRSF at 50.9 +0.6 -0.7 kev, which is clearly visible even in phase-averaged spectra, is the first harmonic and not the fundamental. Thus we infer a magnetic field strength of B=2.6 x 10^12 G.Comment: 12 pages, LaTeX, 15 Figures, accepted by A&

INTEGRAL and RXTE monitoring of GRS 1758-258 in 2003 and 2004. A transition from the dim soft state to the hard state

The Galactic Center black hole candidate (BHC) GRS 1758-258 has been observed extensively within INTEGRAL's Galactic Center Deep Exposure (GCDE) program in 2003 and 2004, while also being monitored with RXTE. We present quasi-simultaneous PCA, ISGRI, and SPI spectra from four GCDE observation epochs, as well as the evolution of energy-resolved PCA and ISGRI light curves on time scales of days to months. We find that during the first epoch GRS 1758-258 displayed another of its peculiar dim soft states like the one observed in 2001, increasing the number of observed occurrences of this state to three. During the other epochs the source was in the hard state. The hard X-ray emission component in the epoch-summed spectra can be well described either by phenomenological models, namely a cutoff power law in the hard state and a pure power law in the dim soft state, or by thermal Comptonization models. A soft thermal component is clearly present in the dim soft state and might also contribute to the softer hard state spectra. We argue that in the recently emerging picture of the hardness-intensity evolution of black hole transient outbursts in which hard and soft states are observed to occur in a large overlapping range of luminosities (hysteresis), the dim soft state is not peculiar. As noted before for the 2001 dim soft state, these episodes seem to be triggered by a sudden decrease (within days) of the hard emission, with the soft spectral component decaying on a longer time scale (weeks). We discuss this behavior in terms of the existence of two independent accretion flows, the model previously suggested for the 2001 episode. (Abridged)Comment: Replaced to match accepted versio

Timing and Spectroscopy of Accreting X-ray Pulsars: the State of Cyclotron Line Studies

A great deal of emphasis on timing in the RXTE era has been on pushing toward higher and higher frequency phenomena, particularly kHz QPOs. However, the large areas of the RXTE pointed instruments provide another capability which is key for the understanding of accreting X-ray pulsars -- the ability to accumulate high quality spectra in a limited observing time. For the accreting X-ray pulsars, with their relatively modest spin frequencies, this translates into an ability to study broad band spectra as a function of pulse phase. This is a critical tool, as pulsar spectra are strong functions of the geometry of the "accretion mound" and the observers' viewing angle to the ~10^12 G magnetic field. In particular, the appearance of "cyclotron lines" is sensitively dependent on the viewing geometry, which must change with the rotation of the star. These spectral features, seen in only a handful of objects, are quite important, as they give us our only direct measure of neutron star magnetic fields. Furthermore, they carry a great deal of information as to the geometry and physical conditions in the accretion mound. In this paper, we review the status of cyclotron line studies with the RXTE. We present an overview of phase-averaged results and give examples of observations which illustrate the power of phase-resolved spectroscopy.Comment: 8 pages, 13 figures. to appear in the proceedings of "X-Ray Timing 2003: Rossi and Beyond", eds. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville, NY: AIP