On the Outbursts of Soft X-ray Transients

We suggest a new scenario to explain the outburst light curves of black hole soft X-ray transients together with the secondary maximum and the bump seen on their decay phases. Our explanations are based on the disk instability models considering the effect of X-ray irradiation. The scenario is consistent with the observed X-ray delays by a few days with respect to the optical rise for both the main outburst and the later maxima. We test our scenario by numerically solving the disk diffusion equation. The obtained model curve fits well to the observed X-ray outburst photon flux curve of the black hole soft X-ray transient GS/GRS 1124-68, a typical representative of the four BH SXTs with very similar light curves.Comment: 11 pages, 8 figures, accepted for publication in A&

Fallback disks, magnetars and other neutron stars

The presence of matter with angular momentum, in the form of a fallback disk around a young isolated neutron star will determine its evolution. This leads to an understanding of many properties of different classes of young neutron stars, in particular a natural explanation for the period clustering of AXPs, SGRs and XDINs. The spindown or spinup properties of a neutron star are determined by the dipole component of the magnetic field. The natural possibility that magnetars and other neutron stars may have different strengths of the dipole and higher multipole components of the magnetic field is now actually required by observations on the spindown rates of some magnetars. This talk gives a broad overview and some applications of the fallback disk model to particular neutron stars. Salient points are: (i) A fallback disk has already been observed around the AXP 4U 0142+61 some years ago. (ii) The low observed spindown rate of the SGR 0418+5729 provides direct evidence that the dipole component of the field is in the 1012G range. All properties of the SGR 0418+5729 at its present age can be explained by spindown under torques from a fallback disk. (iii) The anomalous braking index of PSR J1734-3333 can also be explained by the fallback disk model which gives the luminosity, period, period derivative and the period second derivative at the present age. (iv) These and all applications to a variety of other sources employ the same disk physics and evolution, differing only in the initial conditions of the disk

The anomalous x-ray pulsar 4U 0142+61: a neutron star with a gaseous fallback disk

The recent detection of the anomalous X-ray pulsar (AXP) 4U 0142+61 in the mid infrared with the Spitzer Observatory (Wang, Chakrabarty & Kaplan 2006) constitutes the first instance for a disk around an AXP. We show, by analyzing earlier optical and near IR data together with the recent data, that the overall broad band data can be reproduced by a single irradiated and viscously heated disk model

On the evolution of the radio pulsar PSR J1734−3333

Recent measurements showed that the period derivative of the ‘hig h-B’ radio pulsar PSR J1734−3333 is increasing with time. For neutron stars evolving with fallback disks, this rotational behavior is expected in certain phases of the long-term evolution. Using the same model as employed earlier to explain the evolution of anomalous X-ray pulsars and soft gamma-ray repeaters, we show that the period,the first and second period derivatives and the X-ray luminosity of this source can simultaneously acquire the observed values for a neutron star evolving with a fallback disk. We find that the required strength of the dipole field that can produce the source properties is in the range of 10^12 − 10^13 G on the pole of the neutron star. When the model source reaches the current state properties of PSR J1734−3333, accretion onto the star has not started yet, allowing the source to operate as a regular radio pulsar. Our results imply that PSR J1734−3333 is at an age of ∼3×10^4 −2×10^5years. Such sources will have properties like the X-ray dim isolated neutron stars or transient AXPs at a later epoch of weak accretion from the diminished fallback disk

X-ray and infrared enhancement of anomalous x-ray pulsar 1E 2259+586

The long-term ( 1.5 yr) X-ray enhancement and the accompanying infrared enhancement light curves of the anomalous X-ray pulsar 1E 2259+586 following the major bursting epoch can be accounted for by the relaxation of a fallback disk that has been pushed back by a gamma-ray flare. The required burst energy estimated from the results of our model fits is low enough for such a burst to have remained below the detection limits. We find that an irradiated disk model with a low irradiation efficiency is in good agreement with both X-ray and infrared data. Nonirradiated disk models also give a good fit to the X-ray light curve, but are not consistent with the infrared data for the first week of the enhancement

On the Enhanced X-ray Emission from SGR 1900+14 after the August 27 Giant Flare

We show that the giant flares of soft-gamma ray repeaters (E~10^44 ergs) can push the inner regions of a fall-back disk out to larger radii by radiation pressure, while matter remains bound to the system for plausible parameters. The subsequent relaxation of this pushed-back matter can account for the observed enhanced X-ray emission after the August 27 giant flare of SGR 1900+14. Based on the results of our models, we estimate that the ratio of the fluences of the enhanced X-ray emissions to that of the preceding bursts remains constant for a particular SGR with similar preburst inner disk conditions, which is consistent with the four different burst observations of SGR 1900+14.Comment: 13 pages, 3 figures, accepted for publication in ApJ

A natural limit on the observable periods of anomalous x-ray pulsars and soft gamma-ray repeaters

We investigate the dependence of the evolution of neutron stars with fallback disks on the strength of the magnetic dipole field of the star. Using the same model as employed by Ertan et al. (2009), we obtain model curves for different dipole fields showing that the neutron stars with magnetic dipole fields greater than ∼ 1013 G on the surface of the star are not likely to become anomalous X‐ray pulsars (AXPs) and soft gamma‐ray repeaters (SGRs). Other sources with conventional dipole fields evolve into the AXP phase if their disk can penetrate the light cylinder. The upper limits to the observed periods of AXP and SGRs could be understood if the disk becomes inactive below a low temperature around 100 K. We summarize our present and earlier results indicated by the evolutionary model curves of these sources with an emphasis on the importance of the minimum disk temperature and the X‐ray irradiation in the long‐term evolution of AXPs and SGRs with fallback disks

Stereochemical Studies on a New Ciramadol Analogue by NMR-Spectroscopy

The absol. configuration of a Ciramadol analogue obtained from (-)-menthone is established by 'H-NMR-. simulated NMR-, COSY-90-, and NOEmeasurements. The final compound 2-(a-1 -pyrrolidino)benzy 1-4-isopropyl- 1 -methyl-cyclohexan-3-one (4b), e.g.. has 1R.2S,4S.l IS-configuration due to stereoselective Michael-type addition of pyrrolidine to the pertinent benzylidene intermediate 3. Die absol. Konfiguration einer Ciramadol-analogen Verbindung aus (-)- Menthon wurde durch 'H-NMR-. simulierte NMR-. COSY-90- und NOEUntersuchungen geklärt. Danach hat die als Beispiel untersuchte Verbindung 2-(a-1 -Pyrrolidino)benzyl-4-isopropyl-1 -methyl-cyclohexan-3-on (4b) 1R,2S.4S.l IS-Konfiguration, die durch eine stereoselektive Michael-analoge Addition des Pyrrolidins an die entspr. Benzyliden-Verbindung 3 entsteht