arXiv subjects

Guido Chincarini

Publications and source records attributed to Guido Chincarini.

At least 19 recordsLinked to original sources

arXiv2013

Large Scale Structure. The seventies & Forty years later: From Clusters to Clusters

I describe the beginning, ~ 1970, of the spectroscopic redshift surveys and the discovery of the superclusters filamentary structures and voids. This changed the view of the distribution of luminous light from the way we knew it at the end of the sixties, a uniform distribution of galaxies with clusters superimposed, and the way we understood it during the seventies, clusters imbedded in filamentary structures. We planned in brief to understand the distribution of galaxies and the effect of their environment since to learn about the formation and evolution of the Universe, we need to know first how it is now. The very large surveys, first among these the CfA, started in the eighties thanks also to dedicated telescopes; during that period, the distribution of mass on large scales was also measured. A next step, in addition to the many and deep galaxies survey that are going on, could be a deep cluster survey to detect distant clusters, improve the accuracy of the clusters physical parameters as a function of redshift and have a more robust probe for Cosmology.

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arXiv2013

Gamma-ray burst optical light-curve zoo: comparison with X-ray observations

We present a comprehensive analysis of the optical and X-ray light curves (LCs) and spectral energy distributions (SEDs) of a large sample of gamma-ray burst (GRB) afterglows to investigate the relationship between the optical and X-ray emission after the prompt phase. We collected the optical data from the literature and determined the shapes of the optical LCs. Then, using previously presented X-ray data we modeled the optical/X-ray SEDs. We studied the SED parameter distributions and compared the optical and X-ray LC slopes and shapes. The optical and X-ray spectra become softer as a function of time while the gas-to-dust ratios of GRBs are higher than the values calculated for the Milky Way and the Large and Magellanic Clouds. For 20% of the GRBs the difference between the optical and X-ray slopes is consistent with 0 or 1=4 within the uncertainties (we did it not consider the steep decay phase), while in the remaining 80% the optical and X-ray afterglows show significantly different temporal behaviors. Interestingly, we find an indication that the onset of the forward shock in the optical LCs (initial peaks or shallow phases) could be linked to the presence of the X-ray flares. Indeed, when X-ray flares are present during the steep decay, the optical LC initial peak or end plateau occurs during the steep decay; if instead the X-ray flares are absent or occur during the plateau, the optical initial peak or end plateau takes place during the X-ray plateau. The forward-shock model cannot explain all features of the optical (e.g. bumps, late re-brightenings) and X-ray (e.g. flares, plateaus) LCs. However, the synchrotron model is a viable mechanism for GRBs at late times. In particular, we found a relationship between the presence of the X-ray flares and the shape of the optical LC that indicates a link between the prompt emission and the optical afterglow.

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arXiv2012

The Highly Energetic Expansion of SN2010bh Associated with GRB 100316D

We present the spectroscopic and photometric evolution of the nearby (z = 0.059) spectroscopically confirmed type Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Owing to the detailed temporal coverage and the extended wavelength range (3000--24800 A), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 +/- 1.0 rest-frame days) and a fainter absolute peak luminosity (L_bol~3e42 erg/s) than previously observed SN events associated with GRBs. Our estimate of the ejected (56)Ni mass is 0.12 +/- 0.02 Msun. From the broad spectral features we measure expansion velocities up to 47,000 km/s, higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines He I lambda5876 and He I 1.083 microm, blueshifted by ~20,000--30,000 km/s and ~28,000--38,000 km/s, respectively, may be present in the optical spectra. However, the lack of coverage of the He I 2.058 microm line prevents us from confirming such identifications. The nebular spectrum, taken at ~186 days after the explosion, shows a broad but faint [O I] emission at 6340 A. The light-curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic explosion with a small ejected mass (E_k ~ 1e52 erg and M_ej ~ 3 Msun). The observed properties of SN 2010bh further extend the heterogeneity of the class of GRB supernovae.

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arXiv2011

GRB 081029: A Gamma-Ray Burst with a Multi-Component Afterglow

We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift UltraViolet/Optical Telescope with ground-based optical and infrared data obtained using the REM, ROTSE, and CTIO 1.3-m telescopes to construct a detailed data set extending from 86 s to approximately 100,000 s after the BAT trigger. Our data cover a wide energy range, from 10 keV to 0.77 eV (1.24 to 16,000 Angstrom). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18,000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 3000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray burst jets are complex and will require detailed modelling to fully understand them.

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arXiv2011

The Swift/XRT Catalogue of GRBs

We present the preliminary analysis of the GRB light curves obtained by Swift/XRT between November 2004 and December 2010.

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arXiv2009

High energy emission from massive stars: the precocious X-Ray recovery of Eta Carinae after January 2009 minimum

We observed the massive binary stellar system of Eta Carinae in the 0.3-10 keV energy range with the X-ray Telescope onboard the Swift satellite during the period 15 December 2008 - 11 March 2009, i.e. 1 month before to 2 months after the X-ray drop from maximum to minimum, thought to be associated with the periastron encounter of the primary star by the hot companion. Beginning a few months before eclipse, the interaction between the winds of the two stars intensifies and the X-ray flux reaches maximum. The flux drops dramatically thereafter, subsiding in about 20 days to a level that is at least a factor 10 lower than the 'high state', i.e. the X-ray emission state of the system during the largest fraction of its 5.52 yr orbit (~e-11 erg/s/cm2). Unlike in previous cycles, when the low state lasted about 2.5 months, observations with RXTE showed that the X-ray flux started its recovery to normal level about 1.5 months after the minimum. We suggest that this early recovery may be due to the fact that the companion wind reaches terminal velocity before encountering the shock.

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arXiv2008

The metamorphosis of Supernova SN2008D/XRF080109: a link between Supernovae and GRBs/Hypernovae

The only supernovae (SNe) to have shown early gamma-ray or X-ray emission thus far are overenergetic, broad-lined Type Ic SNe (Hypernovae - HNe). Recently, SN 2008D shows several novel features: (i) weak XRF, (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SNIc HNe, (iv) development of He lines as in SNeIb. Detailed analysis shows that SN 2008D was not a normal SN: its explosion energy (KE ~ 6*10^{51} erg) and ejected mass (~7 Msun) are intermediate between normal SNeIbc and HNe. We derive that SN 2008D was originally a ~30Msun star. When it collapsed a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

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arXiv2007

Swift and XMM-Newton Observations of the Extraordinary GRB 060729: An afterglow with a more than 100 days X-ray light curve

We report the results of the Swift and XMM observations of the Swift-discovered long Gamma-Ray Burst GRB 060729 ($T_{90}$=115s). The afterglow of this burst was exceptionally bright in X-rays as well as at UV/Optical wavelengths showing an unusually long slow decay phase ($α$=0.14\plm0.02) suggesting a larger energy injection phase at early times than in other bursts. The X-ray light curve displays a break at about 60 ks after the burst. The X-ray decay slope after the break is $α$=1.29\plm0.03. Up to 125 days after the burst we do not detect a jet break, suggesting that the jet opening angle is larger than 28 degrees. In the first 2 minutes after the burst (rest frame) the X-ray spectrum of the burst changed dramatically from a hard X-ray spectrum to a very soft one. We find that the X-ray spectra at this early phase can all be fitted by an absorbed single power law model or alternatively by a blackbody plus power law model. The power law fits show that the X-ray spectrum becomes steeper while the absorption column density decreases. In Swift's UV/Optical telescope the afterglow was clearly detected up to 9 days after the burst in all 6 filters and even longer in some of the UV filters with the latest detection in the UVW1 31 days after the burst. A break at about 50 ks is clearly detected in all 6 UVOT filters from a shallow decay slope of about 0.3 and a steeper decay slope of 1.3. In addition to the \swift observations we also present and discuss the results from a 61 ks ToO observation by XMM. (Abriviated)

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arXiv2006

Gamma Ray Bursts Flares detected and observed by the Swift Satellite

The detection of flares with the Swift satellite triggered a lot of bservational and theoretical interest in these phenomena. As a consequence a large analysis effort started within the community to characterize the phenomenon and at the same time a variety of theoretical speculations have been proposed to explain it. In this presentation we discuss part of the results we obtained analyzing a first statistical sample of GRBs observed with Swift. The first goal of this research is very simple: derive those observational properties that could distinguish between internal and external shock and between an ever active central engine and delayed shocks (refreshing) related to a very small initial Lorentz bulk factor. We discuss first the method of analysis and the morphology evidencing the similarities such flares have with the prompt emission pulses. We conclude that GRB flares are due to internal shocks and leave still open the question of whether or not the central engine is active for a time of the order of 105 seconds after the prompt emission.

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arXiv2006

GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short

We systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by {\em Swift} before September 2005, and estimate the GRB radiative efficiency. BAT's narrow band inhibits a precise determination of the GRB spectral parameters, and we have developed a method to estimate these parameters with the hardness ratio information. The shallow decay component commonly existing in early X-ray afterglows, if interpreted as continuous energy injection in the external shock, suggests that the GRB efficiency previously derived from the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic energy E_K derived at the putative deceleration time t_{dec}) and at the break time (t_b) when the energy injection phase ends, respectively. At t_b XRFs appear to be less efficient than normal GRBs. However, when we analyze the data at t_{dec} XRFs are found to be as efficient as GRBs. Short GRBs have similar radiative efficiencies to long GRBs despite of their different progenitors. Twenty-two bursts in the sample are identified to have the afterglow cooling frequency below the X-ray band. Assuming ε_e = 0.1, we find η_γ(t_b) usually <10% and η_γ(t_{dec}) varying from a few percents to > 90%. Nine GRBs in the sample have the afterglow cooling frequency above the X-ray band for a very long time. This suggests a very small ε_B and/or a very low ambient density n.

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arXiv2006

POLARIX: a small mission of x-ray polarimetry

X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber in the focus of a telescope. It requires large area optics for most important scientific targets. But since the technique is additive a dedicated mission with a cluster of small telescopes can perform many important measurements and bridge the 40 year gap between OSO-8 data and future big telescopes such as XEUS. POLARIX has been conceived as such a pathfinder. It is a Small Satellite based on the optics of JET-X. Two telescopes are available in flight configuration and three more can be easily produced starting from the available superpolished mandrels. We show the capabilities of such a cluster of telescopes each equipped with a focal plane photoelectric polarimeter and discuss a few alternative solutions.

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arXiv2006

Swift XRT Observations of the Afterglow of XRF 050416A

Swift discovered XRF 050416A with the BAT and began observing it with its narrow field instruments only 64.5 s after the burst onset. Its very soft spectrum classifies this event as an X-ray flash. The afterglow X-ray emission was monitored up to 74 days after the burst. The X-ray light curve initially decays very fast, subsequently flattens and eventually steepens again, similar to many X-ray afterglows. The first and second phases end about 172 and 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index Gamma ~ 3.0 during the initial steep decay, to a harder emission with Gamma ~ 2.0 during the following evolutionary phases. The spectra show intrinsic absorption in the host galaxy. The consistency of the initial photon index with the high energy BAT photon index suggests that the initial phase of the X-ray light curve may be the low-energy tail of the prompt emission. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with empirical relations between the source rest-frame peak energy and the collimation-corrected energy of the burst. The standard uniform jet model can give a possible description of the XRF 050416A X-ray afterglow for an opening angle larger than a few tens of degrees, although numerical simulations show that the late time decay is slightly flatter than expected from on-axis viewing of a uniform jet. A structured Gaussian-type jet model with uniform Lorentz factor distribution and viewing angle outside the Gaussian core is another possibility, although a full agreement with data is not achieved with the numerical models explored.

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arXiv2006

Jet Breaks in Short Gamma-Ray Bursts. II: The Collimated Afterglow of GRB 051221A

We report the best evidence to date of a jet break in a short Gamma-Ray Burst (GRB) afterglow, using Chandra and Swift XRT observations of the X-ray afterglow of GRB 051221A. The combined X-ray light curve, which has three breaks, is similar to those commonly observed in Swift observations of long GRBs. A flat segment of the light curve at ~0.1 days after the burst represents the first clear case of strong energy injection in the external shock of a short GRB afterglow. The last break occurs at ~4 days post-burst and breaks to a power-law decay index of ~2. We interpret this as a jet break, with important implications for models of short GRBs, since it requires collimation of the afterglow into a jet with an initial opening angle ~4-8 degrees and implies a total jet kinetic energy of E_jet ~(1-5) x 10^{49} erg. Combined with the lack of a jet break in GRB 050724, this suggests a wide range in jet collimation in short GRBs, with at least some having collimation similar to that found in long GRBs, though with significantly lower jet energies.

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arXiv2006

The Swift X-ray flaring afterglow of GRB 050607

The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected Gamma-Ray Burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray afterglows, such as the steep early lightcurve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the Fast Rise, Exponential Decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of approximately 25,peaking for 30 seconds at a count rate of approximately 30 counts s-1, and it presented hints of addition short time scale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short time scale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.

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arXiv2006

Models for the Type Ic Hypernova SN 2003lw associated with GRB 031203

The Gamma-Ray Burst 031203 at a redshift z=0.1055 revealed a highly reddened Type Ic Supernova, SN 2003lw, in its afterglow light. This is the third well established case of a link between a long-duration GRB and a type Ic SN. The SN light curve is obtained subtracting the galaxy contribution and is modelled together with two spectra at near-maximum epochs. A red VLT grism 150I spectrum of the SN near peak is used to extend the spectral coverage, and in particular to constrain the uncertain reddening, the most likely value for which is E_{G+H}(B-V) about 1.07 +/- 0.05. Accounting for reddening, SN 2003lw is about 0.3 mag brighter than the prototypical GRB-SN 1998bw. Light curve models yield a 56Ni mass of about 0.55 solar mass. The optimal explosion model is somewhat more massive (ejecta mass about 13 solar mass) and energetic (kinetic energy about 6 times 10^52 erg) than the model for SN 1998bw, implying a massive progenitor (40 - 50 solar mass). The mass at high velocity is not very large (1.4 solar mass above 30000 km/s, but only 0.1 solar mass above 60000 km/s), but is sufficient to cause the observed broad lines. The similarity of SNe 2003lw and 1998bw and the weakness of their related GRBs, GRB031203 and GRB980425, suggest that both GRBs may be normal events viewed slightly off-axis or a weaker but possibly more frequent type of GRB.

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arXiv2005

Swift XRT and VLT Observations of the Afterglow of GRB 041223

The Swift Gamma-Ray Burst Explorer, launched on 2004 November 20, is a multiwavelength, autonomous, rapid-slewing observatory for gamma-ray burst (GRB) astronomy. On 2004 December 23, during the activation phase of the mission, the Swift X-Ray Telescope (XRT) was pointed at a burst discovered earlier that day by the Swift Burst Alert Telescope. A fading, uncataloged X-ray source was discovered by the XRT and was observed over a period of about 3 hours, beginning 4.6 hours after the burst. The X-ray detection triggered a VLT observation of the optical/NIR counterpart, located about 1.1 arcseconds from the XRT position. The X-ray counterpart faded rapidly, with a power law index of -1.72 +/- 0.20. The average unabsorbed X-ray flux 4.6-7.9 hours after the burst was 6.5 x 10^{-12} erg cm^{-2} s^{-1} in the 0.5-10 keV band, for a power-law spectrum of photon index 2.02 +/- 0.13 with Galactic absorption. The NIR counterpart was observed at three epochs between 16 and 87 hours after the burst, and faded with a power-law index of -1.14 +/- 0.08 with a reddening-corrected SED power-law slope of -0.40 +/- 0.03. We find that the X-ray and NIR data are consistent with a two-component jet in a wind medium, with an early jet break in the narrow component and an underlying electron index of 1.8-2.0.

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arXiv2002

The Halo Density Profiles with Non-Standard N-body Simulations

We propose a new numerical procedure to simulate a single dark halo of any size and mass in a hierarchical framework coupling the extended Press-Schechter formalism (EPSF) to N-body simulations. The procedure consists of assigning cosmological initial conditions to the particles of a single halo with a EPSF technique and following only the dynamical evolution using a serial N-body code. The computational box is fixed with a side of $0.5 h^{-1}$ Mpc. This allows to simulate galaxy cluster halos using appropriate scaling relations, to ensure savings in computing time and code speed. The code can describe the properties of halos composed of collisionless or collisional dark matter. For collisionless Cold Dark Matter (CDM) particles the NFW profile is reproduced for galactic halos as well as galaxy cluster halos. Using this numerical technique we study some characteristics of halos assumed to be isolated or placed in a cosmological context in presence of weak self-interacting dark matter: the soft core formation and the core collapse. The self-interacting dark matter cross section per unit mass is assumed to be inversely proportional to the particle collision velocity: $σ/m_{x} \propto 1/v$.

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arXiv2001

REM - Rapid Eye Mount. A fast slewing robotized infrared telescope

The main goal of the REM project is the observation of prompt afterglow of Gamma-Ray Burst (GRB) events. Such observations at Near InfraRed (NIR) wavelengths are even very promising, since they allow to monitor high-z Ly-$α$ absorbed bursts as well as events occurring in dusty star-forming regions. In addition to GRB science, a large amount of time ($\sim 40%$) will be available for different scientific targets: among these the study of variability of stellar objects open exciting new perspectives.

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