Massimo Persic

The discovery of rapid X-ray oscillations in the tail of the SGR 1806-20 hyperflare

We have discovered rapid quasi-periodic oscillations (QPOs) in RXTE/PCA measurements of the pulsating tail of the 2004 December 27 giant flare of SGR 1806-20. QPOs at ~92.5 Hz are detected in a 50 s interval starting 170 s after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ~18 and ~30 Hz are also detected ~200-300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected in the flux of a soft gamma-ray repeater or any other magnetar candidate. We interpret the highest QPOs in terms of the coupling of toroidal seismic modes with Alfven waves propagating along magnetospheric field lines. The lowest frequency QPO might instead provide indirect evidence on the strength of the internal magnetic field of the magnetar.

Rotation curves of 967 spiral galaxies

We present the rotation curves (RCs) of 967 spiral galaxies, obtained by folding and deprojecting the raw optical data by Mathewson et al. (1992). Out of these, we have identified 80 excellent RCs and 820 fair RCs. The 80 excellent RCs are smooth, symmetric, have negligible rms internal error, extend to at least the optical radius, and have high and homogeneus radial data coverage; they rival with the best optical one-slit RCs available in the literature and are ideally suited for detailed mass structure modelling. The 820 fair RCs do not meet at least one of the above criteria and hence are not suitable for direct mass modelling; however, they constitute a large database for methods aiming to recover statistical properties of DM. For these 900 RCs we also present, in figures and tables, the rotation curves smoothed on scales corresponding to 5%-20% of the optical size. By size, homogeneity, intrinsic quality, and spanned range of luminosities and asymptotic velocities, this sample constitutes by far the best sample of RCs available to date. As such, it will offer a unique opportunity for investigating in considerable depth the properties of DM in galaxies. The the deprojected folded curves, the smoothed curves, and various related quantities are available via anonymous ftp at galileo.sissa.it in the directory /users/ftp/pub/psrot.

The universal galaxy rotation curve

From the analysis of an extended set of selected galaxy rotation curves, it is found that for a given luminosity the rotation curves of spiral galaxies within the optical radius are a universal function. This result implies strong systematic variations of both the amplitude and the profil of the circular velocity with luminosity faint (bright) galaxies having low (high) velocities and steep (shallow) velocity gradients. Because luminous disk are self-similar, the observed progression of the shape of rotation curves with luminosity suggests that the dark-to-visible interplay varies with luminosity.

Counterrotating Stellar Disks in Early-Type Spirals: NGC 3593*

We report the discovery of two counterrotating stellar disks in the early-type spiral galaxy NGC 3593. The major axis kinematics shows the presence of two dynamically cold counterrotating components. The surface brightness profile is well reproduced by the sum of the contributions of two exponential disks of different scale lengths (r1 = 40; r2 = 10) and different central surface brightnesses (μr,1 = 19.9; μr,2 = 18.5 mag arcsec-2). The v and σ radial profiles are easily reproduced by the means of a kinematical model adopting the above photometric parameters. An ionized gas disk is present. It corotates with the smaller scale length and less massive (M2 = 2.7 × 109 M☉) disk, and counterrotates with the larger and more massive (M1 = 1.2 × 1010 M☉) one. We conclude that the smaller stellar disk is the result of a slow adiabatic acquisition of a conspicuous amount of counterrotating gas (Minfall ~ 4.3 × 109 M☉) by the preexisting galaxy, originally constituted mainly by a gas-free stellar disk (disk 1). The counterrotating gas settled into the equatorial plane and then formed the inner stellar disk (disk 2).

The baryonic mass function of spiral galaxies: clues to galaxy formation

We compute the baryonic mass function (BMF) of disc galaxies using the best LFs and baryonic M/L ratios reliable for this goal. For baryonic masses (M_b) ranging between 10^8 and 10^{11} solar masses, the BMF is featureless, i.e. it scales as M_b^{-1/2}. Outside this mass range, the BMF is a strong inverse function of M_b. The contributions to the baryon density Omega_b from objects of different mass highlight a characteristic mass scale of spirals at about 2x10^{11} solar masses, around which>50% of the total baryonic mass is concentrated. The integral value, Omega_b= 1.4x10^{-3}, confirms, to a higher accuracy, previous evidence (Persic&Salucci 1992) that the fraction of BBN baryons locked in disc galaxies is negligible and matches that of high-z Damped Lyman Alpha systems (DLAs). We investigate the scenario where DLAs are the progenitors of present-day spirals, and find a simple relationship between their masses and HI column densities by which the DLA mass function closely matches the spiral BMF.

Dark Matter Halos in Elliptical Galaxies

Values of the M/L B ratio in the inner regions of elliptical (E) galaxies are determined using ionized gas disks as tracers of the triaxial potential. These data, when combined with those provided by the H I disks extending to the outer regions, show that the variation of M/L B with galactocentric radius in Es is similar to that of spirals. In particular, it is found that in spirals and Es of the same visible mass the radius where the density of the dark matter equals that of the visible matter occurs at the same distance in units of r e , namely at 1.2r e . This suggests a similar picture of baryonic collapse into a preexisting DM halo for both Es and spirals

THE ENVIRONMENT AND DISTRIBUTION OF EMITTING ELECTRONS AS A FUNCTION OF SOURCE ACTIVITY IN MARKARIAN 421

For the high-frequency-peaked BL Lac object Mrk 421, we study the variation of the spectral energy distribution (SED) as a function of source activity, from quiescent to active. We use a fully automatized χ2-minimization procedure, instead of the eyeball procedure more commonly used in the literature, to model nine SED data sets with a one-zone synchrotron self-Compton (SSC) model and examine how the model parameters vary with source activity. The latter issue can finally be addressed now, because simultaneous broadband SEDs (spanning from optical to very high energy photon) have finally become available. Our results suggest that in Mrk 421 the magnetic field (B) decreases with source activity, whereas the electron spectrums break energy (γbr) and the Doppler factor (δ) increase—the other SSC parameters turn out to be uncorrelated with source activity. In the SSC framework, these results are interpreted in a picture where the synchrotron power and peak frequency remain constant with varying source activity, through a combination of decreasing magnetic field and increasing number density of γ ≤ γbr electrons: since this leads to an increased electron-photon scattering efficiency, the resulting Compton power increases, and so does the total (= synchrotron plus Compton) emission.

High-energy emission from the starburst galaxy NGC 253

Measurement sensitivity in the energetic -ray region has improved considerably, and is about to increase further in the near future, motivating a de tailed calculation of high-energy (HE: > 100 MeV) and very-high-energy (VHE:> 100 GeV) -ray emission from the nearby starburst galaxy NGC 253. Adopting the convection-diffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, we determine the steady-state energy distributions of thes e particles by a detailed numerical treatment. The electron distribution is directly norma lized by the measured synchrotron radio emission from the central starburst region; a commonl y expected theoretical relation is then used to normalize the proton spectrum in this region. Doing so fully specifies the electron spectrum throughout the galactic disk, and with an assumed spatial profile of the magnetic field, the predicted radio emission from the full di sk matches well the observed spectrum, confirming the validity of our treatment. The resu lting radiative yields of both particles are calculated; the integrated HE and VHE fluxes from t he entire disk are predicted to

Very-high-energy gamma astrophysics

Summary. — High-energy photons are a powerful probe for astrophysics and for fundamental physics under extreme conditions. During the recent years, our knowledge of the most violent phenomena in the Universe has impressively progressed thanks to the advent of new detectors for high-energy γ-rays. Observation of γrays gives an exciting view of the high-energy universe thanks to the satellite-based telescopes (AGILE, GLAST) and to the ground-based detectors like the Cherenkov telescopes (H.E.S.S. and MAGIC in particular), which recently discovered more than 60 new very-high-energy sources. The progress achieved with the last generation of Cherenkov telescopes is comparable to the one drawn by EGRET with respect to the previous γ-ray satellite detectors. This paper reviews the present status of high-energy gamma astrophysics, with emphasis on the recent results and on the experimental developments.

EMITTING ELECTRONS AND SOURCE ACTIVITY IN MARKARIAN 501

We study the variation of the broadband spectral energy distribution (SED) of the BL Lac object Mrk 501 as a function of source activity, from quiescent to flaring. Through {chi}{sup 2}-minimization we model eight simultaneous SED data sets with a one-zone synchrotron self-Compton (SSC) model, and examine how model parameters vary with source activity. The emerging variability pattern of Mrk 501 is complex, with the Compton component arising from {gamma}-e scatterings that sometimes are (mostly) Thomson and sometimes (mostly) extreme Klein-Nishina. This can be seen from the variation of the Compton to synchrotron peak distance according to source state. The underlying electron spectra are faint/soft in quiescent states and bright/hard in flaring states. A comparison with Mrk 421 suggests that the typical values of the SSC parameters are different in the two sources: however, in both jets the energy density is particle-dominated in all states.