INTEGRAL observation of hard X-ray variability of the TeV binary LS5039 / RX J1826.2-1450

LS 5039/RX J1826.2-1450 is one of the few High Mass X-ray binary systems from which radio and high energy TeV emission has been observed. Moreover, variability of the TeV emission with orbital period was detected. We investigate the hard X-ray (25 - 200keV) spectral and timing properties of the source with the monitoring IBIS/ISGRI instrument on-board the INTEGRAL satellite. We present the analysis of INTEGRAL observations for a total of about 3 Msec exposure time, including both public data and data from the Key Programme. We search for flux and spectral variability related to the orbital phase. The source is observed to emit from 25 up to 200 keV and the emission is concentrated around inferior conjunction. Orbital variability in the hard X-ray band is detected and established to be in phase with the orbitally modulated TeV emission observed with H.E.S.S. For this energy range we determine an average flux for the inferior conjunction phase interval of $(3.54 \pm 2.30) \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$, and a flux upper limit for the superior conjunction phase interval of $1.45 \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ (90% conf. level respectively). The spectrum for the inferior conjunction phase interval follows a power law with an index $\Gamma = 2.0^{+0.2}_{-0.2}$ (90% conf. level).Comment: 4 pages, 4 figures, accepted by A&

Long Term X-ray Monitoring Of The TeV Binary LS I +61 303 with RXTE

We report on the results of a long term X-ray monitoring campaign of the galactic binary LS I +61 303 performed by the Rossi X-ray Timing Explorer. This dataset consists of 1 ks pointings taken every other day between 2007 August 28 until 2008 February 2. The observations covered six full cycles of the 26.496 day binary period and constitute the largest continuous X-ray monitoring dataset on LS I +61 303 to date with this sensitivity. There is no statistically strong detection of modulation of flux or photon index with orbital phase; however, we do find a strong correlation between flux and photon index, with the spectrum becoming harder at higher fluxes. The dataset contains three large flaring episodes, the largest of these reaching a flux level of 7.2 (+0.1,-0.2)*10^-11 erg cm^-2 s^-1 in the 3-10 keV band, which is a factor of three times larger than flux levels typically seen in the system. Analysis of these flares shows the X-ray emission from LS I +61 303 changing by up to a factor of six over timescales of several hundred seconds as well as doubling times as fast as 2 seconds. This is the fastest variability ever observed from LS I +61 303 at this wavelength and places constraints on the size of the X-ray emitting region.Comment: 24 pages, 7 figures, 2 tables. Accepted for publication in Ap

Statistics of Core Lifetimes in Numerical Simulations of Turbulent, Magnetically Supercritical Molecular Clouds

We present measurements of the mean dense core lifetimes in numerical simulations of magnetically supercritical, turbulent, isothermal molecular clouds, in order to compare with observational determinations. "Prestellar" lifetimes (given as a function of the mean density within the cores, which in turn is determined by the density threshold n_thr used to define them) are consistent with observationally reported values, ranging from a few to several free-fall times. We also present estimates of the fraction of cores in the "prestellar", "stellar'', and "failed" (those cores that redisperse back into the environment) stages as a function of n_thr. The number ratios are measured indirectly in the simulations due to their resolution limitations. Our approach contains one free parameter, the lifetime of a protostellar object t_yso (Class 0 + Class I stages), which is outside the realm of the simulations. Assuming a value t_yso = 0.46 Myr, we obtain number ratios of starless to stellar cores ranging from 4-5 at n_thr = 1.5 x 10^4 cm^-3 to 1 at n_thr = 1.2 x 10^5 cm^-3, again in good agreement with observational determinations. We also find that the mass in the failed cores is comparable to that in stellar cores at n_thr = 1.5 x 10^4 cm^-3, but becomes negligible at n_thr = 1.2 x 10^5 cm^-3, in agreement with recent observational suggestions that at the latter densities the cores are in general gravitationally dominated. We conclude by noting that the timescale for core contraction and collapse is virtually the same in the subcritical, ambipolar diffusion-mediated model of star formation, in the model of star formation in turbulent supercritical clouds, and in a model intermediate between the previous two, for currently accepted values of the clouds' magnetic criticality.Comment: 25 pages, 8 figures, ApJ accepted. Fig.1 animation is at http://www.astrosmo.unam.mx/~e.vazquez/turbulence/movies/Galvan_etal07/Galvan_etal07.htm

H-alpha Emission Variability in the gamma-ray Binary LS I +61 303

LS I +61 303 is an exceptionally rare example of a high mass X-ray binary (HMXB) that also exhibits MeV-TeV emission, making it one of only a handful of "gamma-ray binaries". Here we present H-alpha spectra that show strong variability during the 26.5 day orbital period and over decadal time scales. We detect evidence of a spiral density wave in the Be circumstellar disk over part of the orbit. The H-alpha line profile also exhibits a dramatic emission burst shortly before apastron, observed as a redshifted shoulder in the line profile, as the compact source moves almost directly away from the observer. We investigate several possible origins for this red shoulder, including an accretion disk, mass transfer stream, and a compact pulsar wind nebula that forms via a shock between the Be star's wind and the relativistic pulsar wind.Comment: Accepted to Ap

Pairing, crystallization and string correlations of mass-imbalanced atomic mixtures in one-dimensional optical lattices

We numerically determine the very rich phase diagram of mass-imbalanced binary mixtures of hardcore bosons (or equivalently -- fermions, or hardcore-Bose/Fermi mixtures) loaded in one-dimensional optical lattices. Focusing on commensurate fillings away from half filling, we find a strong asymmetry between attractive and repulsive interactions. Attraction is found to always lead to pairing, associated with a spin gap, and to pair crystallization for very strong mass imbalance. In the repulsive case the two atomic components remain instead fully gapless over a large parameter range; only a very strong mass imbalance leads to the opening of a spin gap. The spin-gap phase is the precursor of a crystalline phase occurring for an even stronger mass imbalance. The fundamental asymmetry of the phase diagram is at odds with recent theoretical predictions, and can be tested directly via time-of-flight experiments on trapped cold atoms.Comment: 4 pages, 4 figures + Supplementary Materia

Gravitational microlensing of gamma-ray blazars

We present a detailed study of the effects of gravitational microlensing on compact and distant $\gamma$-ray blazars. These objects have $\gamma$-ray emitting regions which are small enough as to be affected by microlensing effects produced by stars lying in intermediate galaxies. We analyze the temporal evolution of the gamma-ray magnification for sources moving in a caustic pattern field, where the combined effects of thousands of stars are taken into account using a numerical technique. We propose that some of the unidentified $\gamma$-ray sources (particularly some of those lying at high galactic latitude whose gamma-ray statistical properties are very similar to detected $\gamma$-ray blazars) are indeed the result of gravitational lensing magnification of background undetected Active Galactic Nuclei (AGNs).Comment: 30 pages, 27 figures. Four figures are being submitted only as .gif files, and should be printed separately. The abstract below has been shortened from the actual version appearing in the pape

Scanning the critical fluctuations -- application to the phenomenology of the two-dimensional XY-model --

We show how applying field conjugated to the order parameter, may act as a very precise probe to explore the probability distribution function of the order parameter. Using this `magnetic-field scanning' on large-scale numerical simulations of the critical 2D XY-model, we are able to discard the conjectured double-exponential form of the large-magnetization asymptote.Comment: 4 pages, 4 figure

Gamma Rays from Compton Scattering in the Jets of Microquasars: Application to LS 5039

Recent HESS observations show that microquasars in high-mass systems are sources of VHE gamma-rays. A leptonic jet model for microquasar gamma-ray emission is developed. Using the head-on approximation for the Compton cross section and taking into account angular effects from the star's orbital motion, we derive expressions to calculate the spectrum of gamma rays when nonthermal jet electrons Compton-scatter photons of the stellar radiation field. Calculations are presented for power-law distributions of nonthermal electrons that are assumed to be isotropically distributed in the comoving jet frame, and applied to $\gamma$-ray observations of LS 5039. We conclude that (1) the TeV emission measured with HESS cannot result only from Compton-scattered stellar radiation (CSSR), but could be synchrotron self-Compton (SSC) emission or a combination of CSSR and SSC; (2) fitting both the HESS data and the EGRET data associated with LS 5039 requires a very improbable leptonic model with a very hard electron spectrum. Because the gamma rays would be variable in a leptonic jet model, the data sets are unlikely to be representative of a simultaneously measured gamma-ray spectrum. We therefore attribute EGRET gamma rays primarily to CSSR emission, and HESS gamma rays to SSC emission. Detection of periodic modulation of the TeV emission from LS 5039 would favor a leptonic SSC or cascade hadron origin of the emission in the inner jet, whereas stochastic variability alone would support a more extended leptonic model. The puzzle of the EGRET gamma rays from LS 5039 will be quickly solved with GLAST. (Abridged)Comment: 17 pages, 11 figures, ApJ, in press, June 1, 2006, corrected eq.