STATISTICAL PROPERTIES OF GRB AFTERGLOW PARAMETERS AS EVIDENCE OF COSMOLOGICAL EVOLUTION OF THEIR HOST GALAXIES

The results of a study of 43 peaked R-band light curves of optical counterparts of gamma-ray bursts with known redshifts are presented. The parameters of optical transients were calculated in the comoving frame, and then a search for pair correlations between them was conducted. A statistical analysis showed a strong correlation between the peak luminosity and the redshift both for pure afterglows and for events with residual gamma activity, which cannot be explained as an effect of observational selection.This suggests a cosmological evolution of the parameters of the local interstellar medium around the sources of the gamma-ray burst. In the models of forward and reverse shock waves, a relation between the density of the interstellar medium and the redshift was built for gamma-ray burst afterglows, leading to a power-law dependence of the star-formation rate at regions around GRBs on redshift with a slope of about 6

Evidence of longterm cyclic evolution of radio pulsar periods

The measurements of pulsar frequency second derivatives have shown that they are 1e2...1e6 times larger than expected for standard pulsar spin-down law. Moreover, the second derivatives as well as braking indices are even negative for about half the pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters f0, f1 and f2 of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between f2 and f1 for both f2 > 0 (correlation coefficient r ~ 0.9) and f2 < 0 (r ~ 0.85), as well as between f0 and f1 (r ~ 0.6...0.7). We interpret these dependencies as evolutionary ones due to f1 being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values of f2 are well described by assuming the existence of long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of f0_{ev}(t), f1_{ev}(t) and f2_{ev}(t) according to the power law with n ~ 5, the irregularities, observed within the timespan as timing noise, and the non-monotonous variations on the timescale of several tens of years, which is larger than that of the timespan. It is possible that the nature of long-term variations is similar to that of short-term ones. The idea of non-constant secular pulsars' braking index n is also analysed.Comment: 8 pages, 8 figures. To appear in Advances in Space Research in the proceedings of the 36th COSPAR Scientific Assembly, Beijing, July 200

On the peculiarities in the rotational frequency evolution of isolated neutron stars

The measurements of pulsar frequency second derivatives have shown that they are $10^2-10^6$ times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters $\nu$, $\dot \nu$ and $\ddot \nu$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between $\ddot \nu$ and $\dot \nu$ for both $\ddot\nu > 0$ and $\ddot\nu < 0$, as well as between $\nu$ and $\dot\nu$. We interpret these dependencies as evolutionary ones due to $\dot\nu$ being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values of $\ddot\nu$ are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of $\nu_{ev}(t)$, $\dot\nu_{ev}(t)$ and $\ddot\nu_{ev}(t)$ according to the power law with $n \approx 5$, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that timespan -- several tens of years.Comment: 4 pages, 3 figures. Accepted for publication in ApSS, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. S. Zane, R. Turolla and D. Pag

Imprint of magnetic obliquity in apparent spin-down of radio pulsars

Numerical simulations predict that the spin-down rate of a single rotation-powered neutron star depends on the angle $\alpha$ between its spin and magnetic axes as $P\dot P \propto \mu^2 (k_0 + k_1\sin^2\alpha)$, where $P$ is the star spin period, $\mu$ is its magnetic moment, while $k_0 \sim k_1 \sim 1$. Here we describe a simple observational test for this prediction based on the comparison of spin-down rates of 50 nearly orthogonal (with $\alpha$ close to 90 deg) and 27 nearly aligned (with $\alpha$ close to 0 deg) pulsars. We found, that the apparent pulsar spin-down is consistent with the theory if assumed, that magnetic moments of orthogonal rotators are systematically larger than those of aligned ones for $\sim 0.15..0.2$ dex. Also, as a by-product of the analysis, we provide yet another constraint on the average braking index of radio pulsars as $1 \le n \le 4$ with formal significance not worse than 99\%.Comment: MNRAS accepte