Large X-ray Flares from LMC X-4: Discovery of Milli-hertz Quasi-periodic Oscillations and QPO-modulated Pulsations

We report the discovery of milli-hertz (mHz) quasi-periodic oscillations (QPOs) and QPO-modulated pulsations during large X-ray flares from the high-mass X-ray binary pulsar LMC X-4 using data from the Rossi X-Ray Timing Explorer (RXTE). The lightcurves of flares show that, in addition to ~74 mHz coherent pulsations, there exist two more time-varying temporal structures at frequencies of ~0.65-1.35 and ~2-20 mHz. These relatively long-term structures appear in the power density spectra as mHz QPOs and as well-developed sidebands around the coherent pulse frequency as well, indicating that the amplitudes of the coherent pulsation is modulated by those of the mHz QPOs. One interesting feature is that, while the first flare shows symmetric sidebands around the coherent pulse frequency, the second flare shows significant excess emission in the lower-frequency sidebands due to the ~2-20 mHz QPOs. We discuss the origin of the QPOs using a combination of the beat-frequency model and a modified version of the Keplerian-frequency model. According to our discussion, it seems to be possible to attribute the origin of the ~0.65-1.35 and ~2-20 mHz QPOs to the beating between the rotational frequency of the neutron star and the Keplerian frequency of large accreting clumps near the corotation radius and to the orbital motion of clumps at Keplerian radii of 2-10 times 10^9 cm, respectively.Comment: 12 pages, including 4 figures; accepted by ApJ Letter

Long-Term X-ray Monitoring of 1E 1740.7-2942 and GRS 1758-258

We report on long-term observations of the Galactic-bulge black hole candidates 1E 1740.7-2942 and GRS 1758-258 with the Rossi X-Ray Timing Explorer. 1E 1740.7-2942 has been observed 77 times and GRS 1758-258 has been observed 82 times over the past 1000 days. The flux of each object has varied by no more than a factor of 2.5 during this period, and the indices of the energy spectra have varied by no more than 0.4. The power spectra are similar to other black-hole candidates: flat-topped noise, breaking to a power law. Each object has exhibited a brightening that lasted for several months, and we have a found a time lag between the photon power-law index and the count rate. In both sources, the spectrum is softest during the decline from the brightening. This behavior can be understood in the context of thin-disk and advection-dominated accretion flows coexisting over a wide range of radii, with the implication that both sources have low-mass companions and accrete via Roche-lobe overflow.Comment: Accepted for publication in The Astrophysical Journa

Discovery of a Third Harmonic Cyclotron Resonance Scattering Feature in the X-ray Spectrum of 4U 0115+63

We have discovered a third harmonic cyclotron resonance scattering feature (CRSF) in observations of the recent outburst of 4U 0115+63 with the Rossi X-ray Timing Explorer (RXTE). The spectrum in a narrow pulse phase range shows CRSFs at 12.40+0.65/-0.35, 21.45+0.25/-0.38, and 33.56+0.70/-0.90 keV. With centroid energy ratios to the fundamental of 1.73+/-0.08 and 2.71+/-0.13, the CRSFs are not harmonically spaced. Strong variability of the continuum and CRSFs with pulse phase indicate a complex emission geometry near the neutron star polar cap. In addition, one RXTE observation, which spanned periastron passage, revealed a strong 2 mHz quasi-periodic oscillation (QPO). This is slower by two orders of magnitude than the beat-frequency QPO expected in this system and slower by a factor of more than 5 compared with other QPOs seen in accreting X-ray pulsars.Comment: To appear in The Astrophysical Journal Letters. 4 pages, 5 figures. Uses "emulateapj.sty". Revised version includes new figures and additions to the analysi

Completing the puzzle of the 2004-2005 outburst in V0332+53: the brightening phase included

Analysis of the data obtained with the RXTE observatory during a powerful outburst of the X-ray pulsar V0332+53 in 2004-2005 is presented. Observational data covering the outburst brightening phase are analysed in detail for the first time. A comparison of source parameters and their evolution during the brightening and fading phases shows no evidence for any hysteresis behaviour. It is found that the dependences of the energy of the cyclotron absorption line on the luminosity during the brightening and fading phases are almost identical. The complete data sequence including the outburst brightening and fading phases makes it possible to impose the more stringent constraints on the magnetic field in the source. The pulse profile and pulsed fraction are studied as functions of the luminosity and photon energy.Comment: 9 pages, 10 figures, accepted for publication in MNRA

Discovery of a Cyclotron Resonance Scattering Feature in the X-ray Spectrum of XTE J1946+274

Observations of the transient accreting pulsar XTE J1946+274 made with the Rossi X-ray Timing Explorer during the course of the 1998 September-November outburst, reveal a cyclotron resonance scattering feature (or "cyclotron line") in the hard X-ray spectrum near 35 keV. We determine a centroid energy of 36.2 +0.5/-0.7 keV, which implies a magnetic field strength of 3.1(1+z)x10^12 G, where z is the gravitational redshift of the scattering region. The optical depth, Tau = 0.33 +0.07/-0.06, and width, sigma = 3.37 +0.92/-0.75 keV, are typical of known cyclotron lines in other pulsars. This discovery makes XTE J1946+274 one of thirteen pulsars with securely detected cyclotron lines resulting in direct magnetic field measurements.Comment: Five pages including four postscript figures and two tables. Uses emulateapj5. Published in ApJ Letters: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...563L..35

Multifrequency Observations of the Virgo Blazars 3C 273 and 3C 279 in CGRO Cycle 8

We report first observational results of multifrequency campaigns on the prominent Virgo blazars 3C 273 and 3C 279 which were carried out in January and February 1999. Both blazars are detected from radio to gamma-ray energies. We present the measured X- to gamma-ray spectra of both sources, and for 3C 279 we compare the 1999 broad-band (radio to gamma-ray) spectrum to measured previous ones.Comment: 5 pages including 3 figures, latex2e, to appear in: 'Proc. of the 5th Compton Symposium', AIP, in pres

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

INTEGRAL observation of the high-mass X-ray transient V 0332+53 during the 2005 outburst decline

The decline of the high mass X-ray transient V 0332+53 during the Dec. 2004 to Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is shown to decrease exponentially until 2005 Feb. 10, with a decay time scale of ∼30 days above 20 keV and ∼20 days at lower energies, and to decrease linearly thereafter. The energy spectrum is well modelled throughout the decay by a power law with a folding energy of ∼7.5 keV, and with two cyclotron absorption features. The folding energy does not vary significantly over the decay, but the spectrum becomes harder with time. Most importantly, we show that the parameters describing the fundamental cyclotron line around 27 keV do vary with time: its energy and depth increase (by about 17% for the energy in ∼6 weeks), while its width decreases. These changes of the cyclotron line parameters are interpreted as resulting from a change in the extent of the cyclotron scattering region. Two quasi-periodic oscillations are also observed at various times during the observations, one at 0.05 Hz and another one near the pulsation frequency around 0.23 Hz