M. S. Pshirkov

DERIVING THE GLOBAL STRUCTURE OF THE GALACTIC MAGNETIC FIELD FROM FARADAY ROTATION MEASURES OF EXTRAGALACTIC SOURCES

We made use of the two latest sets of rotational measures (RMs) of extra-galactic radio sources, namely the NRAO VLA Sky Survey rotation measures catalog, and a compilation by Kronberg and Newton-McGee, to infer the global structure of the Galactic magnetic field (GMF). We have checked that these two data sets are mutually consistent. Given the existence of clear patterns in all-sky RM distribution we considered GMF models consisting of two components: disk (spiral or ring) and halo. The parameters of these components were determined by fitting different model field geometries to the observed RMs. We found that the model consisting of a symmetric (with respect to the Galactic plane) spiral disk and anti-symmetric halo fits the data best and reproduces the observed distribution of RMs over the sky very well. We confirm that ring disk models are disfavored. Our results favor small pitch angles around ∼ −5 ◦ and an increased vertical scale of electron distribution, in agreement with some recent studies. Based on our fits, we select two benchmark models suitable for studies of cosmic ray propagation, including the ultra-high energies. Subject headings: Galaxy: structure –ISM: magnetic fields– methods: data analysis

Constraints on primordial black holes as dark matter candidates from capture by neutron stars

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred GeV/cm3 would imply that PBHs are excluded as comprising all of the dark matter in the mass range 3×1018 mBH 1024 g. At the DM density of 2×103 GeV/cm3 that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

Observing gravitational wave bursts in pulsar timing measurements

ABSTRACT We propose a novel method for observing the gravitational wave signature of super-massive black hole (SMBH) mergers. This method is based on detection of a specifictype of gravitational waves, namely gravitational wave burst with memory (BWM),using pulsar timing. We study the unique signature produced by BWM in anomalouspulsar timing residuals. We show that the present day pulsar timing precision allowsone to detect BWM due to SMBH mergersfrom distances up to 1 Gpc (forcase ofequalmass 10 8 M ⊙ SMBH). Improvements in precision of pulsar timing together with theincrease in number of observed pulsars should eventually lead to detection of a BWMsignal due to SMBH merger, thereby making the proposed technique complementaryto the capabilities of the planned LISA mission.Key words: gravitational waves – galaxies: evolution – (stars:) pulsars: general –cosmology: miscellaneous 1 INTRODUCTIONThe prospects of detecting gravitational waves (GWs) in the coming decade are looking ever more promising (Grishchuk et al.2001; Cutler & Thorne 2002; Sathyaprakash & Schutz 2009). There is currently a considerable experimental effort to detectgravitational waves in a wide range of frequencies. At high frequencies ν ∼ 10

Radio precursors to neutron star binary mergings

We discuss a possible generation of radio bursts preceding final stages of binary neutron star mergings which can be accompanied by short gamma-ray bursts. Detection of such bursts appear to be advantageous in the low-frequency radio band due to a time delay of ten to several hundred seconds required for radio signal to propagate in the ionized intergalactic medium. This delay makes it possible to use short gamma-ray burst alerts to promptly monitor specific regions on the sky by low-frequency radio facilities, especially by LOFAR. To estimate the strength of the radio signal, we assume a power-law dependence of the radio luminosity on the total energy release in a magnetically dominated outflow, as found in millisecond pulsars. Based on the planned LOFAR sensitivity at 120 MHz, we estimate that the LOFAR detection rate of such radio transients could be about several events per month from redshifts up to z∼1.3 in the most optimistic scenario. The LOFAR ability to detect such events would crucially depend on exact efficiency of low-frequency radio emission mechanism.

Constraints on primordial black holes as dark matter candidates from star formation

By considering adiabatic contraction of the dark matter (DM) during star formation, we estimate the amount of DM trapped in stars at their birth. If the DM consists partly of primordial black holes (PBHs), they will be trapped together with the rest of the DM and will be finally inherited by a star compact remnant --- a white dwarf (WD) or a neutron star (NS), which they will destroy in a short time. Observations of WDs and NSs thus impose constraints on the abundance of PBH. We show that the best constraints come from WDs and NSs in globular clusters which exclude the DM consisting entirely of PBH in the mass range

Mapping ultrahigh energy cosmic rays deflections through the turbulent galactic magnetic field with the latest rotation measure data

10^{16}{\rm g} - 3\times 10^{22}{\rm g}

Local constraints on cosmic string loops from photometry and pulsar timing

, with the strongest constraint on the fraction

Adiabatic contraction revisited: implications for primordial black holes

\Omega_{\rm PBH} /\Omega_{\rm DM}\lesssim 10^{-2}

Constraints on massive-graviton dark matter from pulsar timing and precision astrometry.

being in the range of PBH masses

Conversion of dark matter axions to photons in magnetospheres of neutron stars

10^{17}{\rm g} - 10^{18}