Mon.Not.Roy.Astron.Soc. 315 (2000) L29 Within the framework of the cold dark matter (CDM) cosmogony, a central cusp
in the density profiles of virialized dark haloes is predicted. This prediction
...disagrees with the soft inner halo mass distribution inferred from observations
of dwarf and low surface brightness galaxies, and some clusters of galaxies. By
analysing data for some of these objects, we find that the halo central density
is nearly independent of the mass from galactic to galaxy cluster scales with
an average value of around 0.02 M_sun/pc^3. We show that soft cores can be
produced in the CDM haloes by introducing a lower cut-off in the power spectra
of fluctuations and assuming high orbital thermal energies during halo
formation. However, the scale invariance of the halo central density is not
reproduced in these cases. The introduction of self-interaction in the CDM
particles offers the most attractive alternative to the core problem. We
propose gravothermal expansion as a possible mechanism to produce soft cores in
the CDM haloes with self-interacting particles. A global thermodynamical
equilibrium can explain the central density scale invariance. We find a minimum
cross section capable of establishing isothermal cores in agreement with the
observed shallow cores. If \sigma and m_x are the cross section and mass of the
dark matter particle, and v is the halo velocity dispersion, then (\sigma/m_x)
\~ 4 10^{-25} (100 km s^{-1}/v) cm^2/GeV.
We present prompt gamma-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the ...prompt gamma-ray pulse as well as for the early and late multi-band afterglow of GRB 070311. We fitted with empirical functions the gamma-ray and optical light curves and scaled the result to the late time X-rays. The H-band light curve taken by REM shows two pulses peaking 80 and 140 s after the peak of the gamma-ray burst and possibly accompanied by a faint gamma-ray tail. Remarkably, the late optical and X-ray afterglow underwent a major rebrightening between 3x10^4 and 2x10^5 s after the burst with an X-ray fluence comparable with that of the prompt emission extrapolated in the same band. Notably, the time profile of the late rebrightening can be described as the combination of a time-rescaled version of the prompt gamma-ray pulse and an underlying power law. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightening of GRB 070311 within the external shock scenario. The main fireball would be responsible for the prompt emission, while a second shell would produce the rebrightening when impacting the leading blastwave in a refreshed shock (abridged).
We initiated a large project aimed to estimate the Luminosity Function of galaxies in clusters and to evaluate its relation to cluster morphology. With this paper we deem necessary to outline the ...general procedures of the data reduction and details of the data analysis. The cluster sample includes the brightest southern ROSAT all-sky survey clusters with z < 0.1. These have been observed in three colours g, r, i, and mapped up to a few core radii using a mosaic of CCD frames. E/S0 galaxies in the cluster core are singled out both by morphology (for the brightest galaxies), and by colour. The details of the data reduction procedure are illustrated via the analysis of the cluster Abell 496, which has been used as a pilot cluster for the whole program. The related photometric catalogue consists of 2355 objects. The limiting magnitudes (the reference Surface Brightness is given in parenthesis) in the various colours are respectively g(25.5) = 24.14, r(25.5) = 24.46, i(25.0) = 23.75$. These correspond to the limiting absolute magnitudes -12.28, -11.96 and -12.67 (H_0=50 km/sec/Mpc).
Astron.Astrophys.456:509-515,2006 Context. GRB050721 was detected by Swift and promptly followed-up, in the
X-ray by Swift itself and, in the optical band, by the VLT operated, for the
first time, in ...rapid response mode. A multiwavelength monitoring campaign was
performed in order to study its afterglow behavior. Aims. We present the
analysis of the early and late afterglow emission in both the X-ray and optical
bands, as observed by Swift, a robotic telescope, and the VLT. We compare early
observations with late afterglow observations obtained with Swift and the VLT
in different bands in order to constrain the density of the medium in which the
fireball is expanding. Methods. We have analyzed both the X-ray and the optical
light curves and compared the spectral energy distribution of the afterglow at
two different epochs. Results. We observed an intense rebrightening in the
optical band at about one day after the burst which was not seen in the X-ray
band. This is the first observation of a GRB afterglow in which a rebrightening
is observed in the optical but not in the X-ray band. The lack of detection in
X-ray of such a strong rebrightening at lower energies can be described with a
variable external density profile. In such a scenario, the combined X-ray and
optical observations allow us to derive the matter density at 10^15 cm from the
burst. This is about a factor of 10 higher than in the inner region.
We report the discovery of ROXA J081009.9+384757.0 = SDSS J081009.9+384757.0, a z=3.95 blazar with a highly unusual Spectral Energy Distribution (SED). This object was first noticed as a probable ...high \(f_x/f_r\), high-luminosity blazar within the error region of a \(\approx 10^{-12}\) erg/s cm\(^2\) ROSAT source which, however, also included a much brighter late-type star. We describe the results of a recent Swift observation that establishes beyond doubt that the correct counterpart of the X-ray source is the flat spectrum radio quasar. With a luminosity well in excess of \(10^{47}\) erg/s, ROXA J081009.9+384757.0 is therefore one of the most luminous blazars known. We consider various possibilities for the nature of the electromagnetic emission from this source. In particular, we show that the SED is consistent with that of a blazar with synchrotron power peaking in the hard X-ray band. If this is indeed the case, the combination of high-luminosity and synchrotron peak in the hard-X-ray band contradicts the claimed anti-correlation between luminosity and position of the synchrotron peak usually referred to as the "blazar sequence". An alternative possibility is that the X-rays are not due to synchrotron emission, in this case the very peculiar SED of ROXA J081009.9+384757.0 would make it the first example of a new class of radio loud AGN.
The flat-spectrum radio quasar 3C 454.3 is well known to be a highly active
and variable source with outbursts occurring across the whole electromagnetic
spectrum over the last decades. In spring ...2005, 3C 454.3 has been reported to
exhibit a strong optical outburst which subsequently triggered multi-frequency
observations of the source covering the radio up to gamma-ray bands. Here, we
present first results of our near-IR/optical (V, R, I, H band) photometry
performed between May 11 and August 5, 2005 with the Rapid Eye Mount (REM) at
La Silla in Chile and the Automatic Imaging Telescope (AIT) of the Perugia
University Observatory. 3C 454.3 was observed during an exceptional and
historical high state with a subsequent decrease in brightness over our 86 days
observing period. The continuum spectral behaviour during the flaring and
declining phase suggests a synchrotron peak below the near-IR band as well as a
geometrical origin of the variations e.g. due to changes in the direction of
forward beaming.
Short duration (<2 s) Gamma-ray bursts (GRBs) have been a mystery since their
discovery. Until May 2005 very little was known about short GRBs, but this
situation has changed rapidly in the last few ...months since the Swift and HETE-2
satellites have made it possible to discover X-ray and optical counterparts to
these sources. Positional associations indicate that short GRBs arise in
close-by galaxies (z<0.7). Here we report on a detailed study of the short GRB
050724 X-ray afterglow. This burst shows strong flaring variability in the
X-ray band. It clearly confirms early suggestions of X-ray activity in the
50-100 s time interval following the GRB onset seen with BATSE. Late flare
activity is also observed. These observations support the idea that flares are
related to the inner engine for short GRBs, as well as long GRBs.
The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured before launch. We describe the CCD calibration ...program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Comparison of observed spectra with models folded through the instrument response produces negative residuals around and below the Oxygen edge. We discuss several possible causes for such residuals. Traps created by proton damage on the CCD increase the charge transfer inefficiency (CTI) over time. We describe the evolution of the CTI since the launch and its effect on the CCD spectral resolution and the gain.
Abridged We present the rest-frame Js-band and Ks-band luminosity function of a sample of about 300 galaxies selected in the HDF-S at Ks<23 (Vega). We use calibrated photometric redshift together ...with spectroscopic redshift for 25% of the sample. The sample has allowed to probe the evolution of the LF in the three redshift bins 0;0.8), 0.8;1.9) and 1.9;4) centered at the median redshift z_m ~ 0.6,1.2,3. The values of alpha we estimate are consistent with the local value and do not show any trend with redshift. We do not see evidence of evolution from z=0 to z_m ~ 0.6 suggesting that the population of local bright galaxies was already formed at z<0.8. On the contrary, we clearly detect an evolution of the LF to z_m ~ 1.2 characterized by a brightening of M* and by a decline of phi*. To z_m ~ 1.2 M* brightens by about 0.4-0.6 mag and phi* decreases by a factor 2-3. This trend persists, even if at a less extent, down to z_m ~ 3 both in the Js-band and in the Ks-band LF. The decline of the number density of bright galaxies seen at z>0.8 suggests that a significant fraction of them increases their stellar mass at 1<z<2-3 and that they underwent a strong evolution in this redshift range. On the other hand, this implies also that a significant fraction of local bright/massive galaxies was already in place at z>3. Thus, our results suggest that the assembly of high-mass galaxies is spread over a large redshift range and that the increase of their stellar mass has been very efficient also at very high redshift at least for a fraction of them.
