Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream

The X-ray binary system GX301-2 consists of a neutron star in an eccentric orbit accreting from the massive early-type star WRAY 977. It has previously been shown that the X-ray orbital light curve is consistent with existence of a gas stream flowing out from Wray 977 in addition to its strong stellar wind. Here, X-ray monitoring observations by the Rossi X-ray Timing Explorer (RXTE)/ All-Sky-Monitor (ASM) and pointed observations by the RXTE/ Proportional Counter Array (PCA) over the past decade are analyzed. We analyze both the flux and column density dependence on orbital phase. The wind and stream dynamics are calculated for various system inclinations, companion rotation rates and wind velocities, as well as parametrized by the stream width and density. These calculations are used as inputs to determine both the expected accretion luminosity and the column density along the line-of-sight to the neutron star. The model luminosity and column density are compared to observed flux and column density vs. orbital phase, to constrain the properties of the stellar wind and the gas stream. We find that the change between bright and medium intensity levels is primarily due to decreased mass loss in the stellar wind, but the change between medium and dim intensity levels is primarily due to decreased stream density. The mass-loss rate in the stream exceeds that in the stellar wind by a factor of 2.5. The quality of the model fits is significantly better for lower inclinations, favoring a mass for WRAY 977 of 53 to 62 Msun.Comment: 19 pages, 6 figure

A Monte Carlo Study of the 6.4 keV Emission at the Galactic Center

Strong fluorescent Fe line emission at 6.4 keV has been observed from the Sgr B2 giant molecular cloud located in the Galactic Center region. The large equivalent width of this line and the lack of an apparent illuminating nearby object indicate that a time-dependent source, currently in a low-activity state, is causing the fluorescent emission. It has been suggested that this illuminator is the massive black hole candidate, Sgr A*, whose X-ray luminosity has declined by an unprecedented six orders of magnitude over the past 300 years. We here report the results of our Monte Carlo simulations for producing this line under a variety of source configurations and characteristics. These indicate that the source may in fact be embedded within Sgr B2, although external sources give a slightly better fit to the data. The weakened distinction between the internal and external illuminators is due in part to the instrument response function, which accounts for an enhanced equivalent width of the line by folding some of the continuum radiation in with the intrinsic line intensity. We also point out that although the spectrum may be largely produced by K$\alpha$ emission in cold gas, there is some evidence in the data to suggest the presence of warm (~10^5 K) emitting material near the cold cloud.Comment: 11 pages, 4 figure

Multi-epoch Analysis of Pulse Shapes from the Neutron Star SAX J1808.4-3658

The pulse shapes detected during multiple outbursts of SAX J1808 are analyzed in order to constrain the neutron star's mass and radius. We use a hot-spot model with a small scattered-light component to jointly fit data from two different epochs, under the restriction that the star's mass and radius and the binary's inclination do not change from epoch to epoch. All other parameters describing the spot location, emissivity, and relative fractions of blackbody to Comptonized radiation are allowed to vary with time. The joint fit of data from the 1998 "slow decay" and the 2002 "end of outburst maximum" epochs using the constraint i<90 degrees leads to the 3 sigma confidence constraint on the neutron star mass 0.8 M_sun < M < 1.7 M_sun and equatorial radius 5 km < R < 13 km. Inclinations as low as 41 degrees are allowed. The best-fit models with M > 1.0 M_sun from joint fits of the 1998 data with data from other epochs of the 2002 and 2005 outbursts also fall within the same 3 sigma confidence region. This 3 sigma confidence region allows a wide variety of hadronic equations of state, in contrast with an earlier analysis (Leahy et al 2008) of only the 1998 outburst data that only allowed for extremely small stars.Comment: 12 pages, 9 figures, accepted by ApJ. This revised version includes an expanded Section

Letter from M. A. Leahy to John Muir, 1913 Apr 24.

[1]Marshfield Wis.April 24th 1913John Muir Esq.Martinez Calif.My dear SirA few days ago I saw in the Record Herald of Chicago a brief Sketch of John Muir. As I once knew a John Muir I examined the reference and came to the conclusion that the gentleman referred to was the same John Muir with whom I was acquainted more than fifty years ago at the Wis. University. A vivid recollection of the old days at the University came to me and I felt that I would be delighted to grasp your hand once more and give it a hearty shake.Fifteen years ago I met Prof Butler at his home in Madison. In the course of our conversation he asked me if I remembered John Muir. I responded that the last things that I would forget would be John Muir and his famous clock and bedHe called my attention to the great work05430 [2]you had accomplished on the Pacific slope; and the distinguished honors you had won in the realms of natural Science.I am an old man, friend Muir; The children call me Santa Claus. The sun of my brief day long since passed its meridian is now low down the western sky and will soon set in night. I may never enjoy the pleasure of meeting you again in this world but I hope that when life\u27s journey is ended, we may be permitted to renew our acquaintance in the land of the leal.I trust this letter will find you enjoying the choicest blessings of lifeM. A. Leahy0543

Letter from M. A. Leahy to John Muir, 1913 Jul 27.

[1]Marshfield WisJuly 27th 1913Friend MuirYour kind letter of May 12th was received in due time. I was delighted to hear from my old friend and schoolmate how the time flies More than half a century has come and gone since last we metAs you will remember I went into the Army in 1862. I returned to my home in May 1866 We spent a part of 66 & 67 on the Rio Grande trying to persuade Napoleon III to withdraw his troops from Mexico When we had succeeded we left that region and went home I will try to give you a brief outline of my history since 1866.I concluded to try my fortune in the legal profession. I went to the Michigan University and completed the legal course in that institution in March of 1868. I concluded to follow the advice of Horace Greely Go west young man and after some wandering I located at Hampton Franklin Co. Iowa, and entered upon the practice of the law. In 1871 the people of that county sent me to the Legislature In 1873 my friends concluded that I was entitled to another term and honored me with a re-election05500 [2]During my stay in the Legislature I made the acquaintance of many of the leading politicians of Iowa Among my friends of those days is James Wilson who has been the head of the Agricultural Dept. at Washington during the past sixteen years. He was born in Scotland, came to this country when a little boy, grew up on a farm in Tama Co Iowa and by tireless industry and perseverance he has won a national reputation.In 1882 I disposed of my interests in Iowa moved to Wausau Wis. and went into the lumber business with my brother J. E. Leahy In 1889 my friends secured for me the office of Indian Agent at Ashland Wis. Among my influential friends in this matter was John C. Spooner who was a student at the Wis. University in 1861 I held this office during Harrison\u27s Administration.In my family have grown up six boys and two girls. Death has deprived me of my good wife and a noble boy. The others are widely scattered. Two of the boys are officers in the Navy, one of them is a lawyer in Montana and two of them are farmers in that State. Such, friend Muir, is the brief story of my little life I have had my share of life\u27s joys and sorrows What remains for me in the impenetrable future, God alone knows We hope for the bestI hope friend Muir this letter will find you enjoying life\u27s choicest blessingsOne of your old old friendsM. A. Leahy0550

The 144 second periodic flux variations during x ray turn-on of Hercules X-1

Hercules X-1 is a well known bright binary X ray pulsator. It has a 1.70 day orbital period, a pulsation period of 1.24 second, and a 35 day semiperiodic variability. The discovery is reported of a new 144 second periodicity in the X ray emission from Her X-1. The periodicity is seen in X ray observations of Her X-1 by the LAC instrument onboard the Ginga satellite during Aug. to Sep. 1988. The periodic flux variations occur during the time of X ray turnon at the beginning of a high state of Her X-1, in the same time that a pre-eclipse dip also occurs. An analysis of the LAC spectra of Her X-1 during this period is also presented. Large changes in spectral shape occur associated with the dip

The Oblate Schwarzschild Approximation for Light Curves of Rapidly Rotating Neutron Stars

We present a simple method for including the oblateness of a rapidly rotating neutron star when fitting X-ray light curves. In previous work we showed that the oblateness induced by rotation at frequencies above 300 Hz produces a geometric effect which needs to be accounted for when modelling light curves to extract constraints on the neutron star's mass and radius. In our model X-rays are emitted from the surface of an oblate neutron star and propagate to the observer along geodesics of the Schwarzschild metric for a spherical neutron star. Doppler effects due to rotation are added in the same manner as in the case of a spherical neutron star. We show that this model captures the most important effects due to the neutron star's rotation. We also explain how the geometric oblateness effect can rival the Doppler effect for some emission geometries.Comment: 8 pages, 4 figures. v2: minor changes. Accepted by the Astrophysical Journa