Quantitative Estimates of Environmental Effects on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies

A simple model is constructed to evaluate the change of star formation rate of a disk galaxy due to environmental effects in clusters of galaxies. Three effects, (1) tidal force from the potential well of the cluster, (2) increase of external pressure when the galaxy plows into the intracluster medium, (3) high-speed encounters between galaxies, are investigated. General analysis indicates that the star formation rate increases significantly when the pressure of molecular clouds rises above $\sim 3\times 10^5 cm^{-3} K$ in $\sim 10^8$ yr. The tidal force from the potential well of the cluster increases pressures of molecular clouds in a disk galaxy infalling towards the cluster center. Before the galaxy reaches the cluster center, the star formation rate reaches a maximum. The peak is three to four times larger than the initial value. If this is the main mechanism of the Butcher-Oemler effect, blue galaxies are expected to be located within $\sim 300$ kpc from the center of the cluster. However this prediction is inconsistent with the recent observations. The increase of external pressure when the galaxy plows into the intracluster medium does not change star formation rate of a disk galaxy significantly. The velocity perturbation induced by a single high-speed encounter between galaxies is too small to affect star formation rate of a disk galaxy, while successive high-speed encounters (galaxy harassment) trigger star formation activity because of the accumulation of gas in the galaxy center. Therefore, the galaxy harassment remains as the candidate for a mechanism of the Butcher-Oemler effect.Comment: 12 pages, 13 figures. To be published in Ap

Temperature dependence of the ohmic conductivity and activation energy of Pb1+y(Zr0.3Ti0.7)O3 thin films

The ohmic conductivity of the sol-gel derived Pb1+y(Zr0.3Ti0.7)O3 thin films (with the excess lead y=0.0 to 0.4) are investigated using low frequency small signal alternate current (AC) and direct current (DC) methods. Its temperature dependence shows two activation energies of 0.26 and 0.12 eV depending on temperature range and excess Pb levels. The former is associated with Pb3+ acceptor centers, while the latter could be due to a different defect level yet to be identified.Comment: 13 pages, 3 figures, PostScript. Submitted to Applied Physics Letter

INTEGRAL High Energy Observations of 2S 0114+65

We report the first INTEGRAL timing and spectral analysis of the high mass X-ray binary source 2S 0114+65 at high energies (5-100 keV). The pulse period was found at 2.668 hr with a high pulsed fraction, ~80% in both the 20-40 keV and 40-80 keV energy bands. The spin-up trend over ~8 years was measured to be -8.9 * 10^{-7}. The hard X-ray spectrum obtained with JEM-X/ISGRI is well described by a high energy exponential cut-off power law model where the estimated luminosity is 1.8 * 10^{36} erg/s in the 5-100 keV energy band, for a source distance of 7.2 kpc. We tentatively identify a cyclotron resonance scattering feature at ~22 keV with one harmonic, implying a magnetic field of 2.5 * 10^{12} G.Comment: 4 pages, 5 figures, accepted to A&A Letter

V0332+53 in the outburst of 2004--2005: luminosity dependence of the cyclotron line and pulse profile

We present results of observations of the transient X-ray pulsar V0332+53 performed during a very powerful outburst in Dec, 2004 -- Feb, 2005 with the INTEGRAL and RXTE observatories in a wide (3-100 keV) energy band. A cyclotron resonance scattering line at an energy of ~26 keV has been detected in the source spectrum together with its two higher harmonics at ~50 and ~73 keV, respectively. We show that the energy of the line is not constant but linearly changes with the source luminosity. Strong pulse profile variations, especially near the cyclotron line, are revealed for different levels of the source intensity. We discuss the obtained results in terms of the theoretical models of X-ray pulsars.Comment: Accepted for publication in MNRAS. 10 pages, 9 figure

The broad band spectral properties of binary X-ray pulsars

The X-ray telescopes on board BeppoSAX are an optimal set of instruments to observe bright galactic binary pulsars. These sources emit very hard and quite complex X-ray spectra that can be accurately measured with BeppoSAX between 0.1 and 200 keV. A prototype of this complexity, the source Her X-1, shows at least seven different components in its spectrum. A broad band measure is therefore of paramount importance to have a thorough insight into the physics of the emitting region. Moreover the detection of cyclotron features, when present, allows a direct and highly significant measure of the magnetic field intensity in the emission region. In this paper we briefly report the results obtained with BeppoSAX on this class of sources, with emphasis on the detection and on the measured properties of the cyclotron lines.Comment: 10 Latex pages, 4 figures, uses psfig.sty. Accepted for publication in Advances in Space Research, in Proceedings of 32nd Scientific Assembly of COSPAR - Symposium E1.1: "Broad-Band X-ray Spectroscopy of Cosmic Sources

Discovery of a QPO in the X-ray pulsar 1A 1118-615: correlated spectral and aperiodic variability

Our goal is to investigate the X-ray timing and spectral variability of the high-mass X-ray binary 1A 1118-615 during a type-II outburst. We performed a detailed color, spectral and timing analysis of a giant outburst from 1A 1118-615, using RXTE data. Results. We report the discovery of a variable quasi-periodic oscillation (QPO) in the power spectral density of 1A 1118-615, with a centroid frequency of ~0.08 Hz. The centroid frequency of the QPO correlates with the X-ray flux, as expected according to the most accredited models for QPO production. For energies above ~4 keV, the QPO rms variability decreases as the energy increases. Pulse profiles display energy dependence, with a two-peak profile at lower energies, and a single peak at higher energies. From spectral analysis, we confirm the presence of a cyclotron absorption feature at ~60 keV, the highest value measured for an X-ray pulsar. We find that the spectral parameters (photon index, cutoff energy, iron fluorescence line strength) display a marked dependence with flux. We detect two different levels of neutral hydrogen column density, possibly due to the Be companion activity. We report for the first time a correlation between the timing and spectral parameters in an X-ray pulsar. All the correlations found between spectral/timing parameters and X-ray flux are present up to a flux of ~6x10^-9 erg cm^-2 s^-1, when a saturation level is reached. We propose that the saturation observed corresponds to the minimum extent of the neutron star magnetosphere. We estimate the magnetic field of the neutron star from two independent ways, using results from spectral (cyclotron line energy) and timing (QPO frequency) analysis, obtaining consistent values, of ~7-8x10^12 G. Results from the comprehensive spectral and timing analysis are discussed in comparison with other X-ray pulsars.Comment: 9 pages, 11 figures. Accepted for publication in Astronomy and Astrophysic

The first outburst of the black hole candidate MAXI J1836-194 observed by INTEGRAL, Swift, and RXTE

MAXI J1836-194 is a transient black-hole candidate discovered in outburst by MAXI on 30 August 2011. We report on the available INTEGRAL, Swift, and RXTE observations performed in the direction of the source during this event before 55 864 MJD. Combining the broad band (0.6-200 keV) spectral and timing information obtained from these data with the results of radio observations, we show that the event displayed by MAXI J1836-194 is another example of "failed" outburst. During the first ~20 days after the onset of the event, the source underwent a transition from the canonical low/hard to the hard intermediate state, while reaching the highest X-ray flux. In the ~40 days following the peak of the outburst, the source displayed a progressive spectral hardening and a decrease of the X-ray flux, thus it entered again the low/hard state and began its return to quiescence.Comment: Accepted for A&A Letters on 22 Dec. 201

Influence of a dynamical gluon mass in the pppp and pˉp\bar{p}p forward scattering

We compute the tree level cross section for gluon-gluon elastic scattering taking into account a dynamical gluon mass, and show that this mass scale is a natural regulator for this subprocess cross section. Using an eikonal approach in order to examine the relationship between this gluon-gluon scattering and the elastic $pp$ and $\bar{p}p$ channels, we found that the dynamical gluon mass is of the same order of magnitude as the {\it ad hoc} infrared mass scale $m_{0}$ underlying eikonalized QCD-inspired models. We argue that this correspondence is not an accidental result, and that this dynamical scale indeed represents the onset of non-perturbative contributions to the elastic hadron-hadron scattering. We apply the eikonal model with a dynamical infrared mass scale to obtain predictions for $\sigma_{tot}^{pp,\bar{p}p}$, $\rho^{pp,\bar{p}p}$, slope $B^{pp,\bar{p}p}$, and differential elastic scattering cross section $d\sigma^{\bar{p}p}/dt$ at Tevatron and CERN-LHC energies.Comment: 20 pages, 5 figures; misprints corrected and comments added. To appear in Phys. Rev.

Discovery of a flux-related change of the cyclotron line energy in Her X-1

We present the results of ten years of repeated measurements of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and report the discovery of a positive correlation of the centroid energy of this absorption feature in pulse phase averaged spectra with source luminosity.Our results are based on a uniform analysis of observations bythe RXTE satellite from 1996 to 2005, using sufficiently long observations of 12 individual 35-day Main-On states of the source. The mean centroid energy E_c of the CRSF in pulse phase averaged spectra of Her X-1 during this time is around 40 keV, with significant variations from one Main-On state to the next. We find that the centroid energy of the CRSF in Her X-1 changes by ~5% in energy for a factor of 2 in luminosity. The correlation is positive, contrary to what is observed in some high luminosity transient pulsars. Our finding is the first significant measurement of a positive correlation between E_c and luminosity in any X-ray pulsar. We suggest that this behaviour is expected in the case of sub-Eddington accretion and present a calculation of a quantitative estimate, which is very consistent with the effect observed in Her X-1.We urge that Her X-1 is regularly monitored further and that other X-ray pulsars are investigated for a similar behaviour.Comment: 4 pages, 2 figures, accepted by A&A Letter