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E. Montanari

Publications and source records attributed to E. Montanari.

At least 19 recordsLinked to original sources
arXiv2022

Halting hyaluronidase activity with hyaluronan-based nanohydrogels: development of versatile injectable formulations

Hyaluronan (HA) is among the most used biopolymers for viscosupplementation and cosmetic applications. However, the current injectable HA-based formulations present relevant limitations: I) unmodified HA is quickly degraded by endogenous hyaluronidases (HAase), resulting in short lasting properties; II) cross-linked HA, although shows enhanced stability against HAase, often contains toxic chemical cross-linkers. As such, herein, we present biocompatible self-assembled hyaluronan-cholesterol nanohydrogels (HA-CH NHs) able to bind to HAase and inhibit the enzyme activity in vitro, more efficiently than currently marketed HA-based cross-linked formulations (e.g. JonexaTM). HA-CH NHs inhibit HAase through a mixed mechanism, by which NHs bind to HAase with an affinity constant 7-fold higher than that of HA. Similar NHs, based on gellan-cholesterol, evidenced no binding to HAase, neither inhibition of the enzyme activity, suggesting this effect might be due to the specific binding of HA-CH to the active site of the enzyme. Therefore, HA-CH NHs were engineered into injectable hybrid HA mixtures or physical hydrogels, able to halt the enzymatic degradation of HA.

cond-mat.soft↗
arXiv2013

IPN localizations of Konus short gamma-ray bursts

Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration gamma-ray bursts (including 23 bursts which can be classified as short bursts with extended emission). During this period, the IPN consisted of up to eleven spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, $\sim$18 per year, exceeds that of many individual experiments.

astro-ph.HE↗
arXiv2010

Spectral catalogue of bright gamma-ray bursts detected with the BeppoSAX/GRBM

The emission process responsible for the so-called "prompt" emission of gamma-ray bursts is still unknown. A number of empirical models fitting the typical spectrum still lack a satisfactory interpretation. A few GRB spectral catalogues derived from past and present experiments are known in the literature and allow to tackle the issue of spectral properties of gamma-ray bursts on a statistical ground. We extracted and studied the time-integrated photon spectra of the 200 brightest GRBs observed with the Gamma-Ray Burst Monitor which flew aboard the BeppoSAX mission (1996-2002) to provide an independent statistical characterisation of GRB spectra. The spectra were fit with three models: a simple power-law, a cut-off power law or a Band function. The typical photon spectrum of a bright GRB consists of a low-energy index around 1.0 and a peak energy of the nuFnu spectrum E_p~240 keV in agreement with previous results on a sample of bright CGRO/BATSE bursts. Spectra of ~35% of GRBs can be fit with a power-law with a photon index around 2, indicative of peak energies either close to or outside the GRBM energy boundaries. We confirm the correlation between E_p and fluence, with a logarithmic dispersion of 0.13 around the power-law with index 0.21+-0.06. The low-energy and peak energy distributions are not yet explained in the current literature. The capability of measuring time-resolved spectra over a broadband energy range, ensuring precise measurements of parameters such as E_p, will be crucial for future experiments (abridged).

astro-ph.HE↗
arXiv2010

The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs

Between 1996 July and 2002 April, one or more spacecraft of the interplanetary network detected 787 cosmic gamma-ray bursts that were also detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera experiments aboard the BeppoSAX spacecraft. During this period, the network consisted of up to six spacecraft, and using triangulation, the localizations of 475 bursts were obtained. We present the localization data for these events.

astro-ph.HE↗
arXiv2008

The Gamma--Ray Burst catalog obtained with the Gamma Ray Burst Monitor aboard BeppoSAX

We report on the catalog of Gamma--Ray Bursts (GRBs) detected with the Gamma Ray Burst Monitor aboard the BeppoSAX satellite. It includes 1082 GRBs with 40--700 keV fluences in the range from $1.3\times 10^{-7}$ to $4.5\times 10^{-4}$ erg cm$^{-2}$, and with 40--700 keV peak fluxes from $3.7\times 10^{-8}$ to $7.0\times 10^{-5}$ erg cm$^{-2}$s$^{-1}$. We report in the catalog some relevant parameters of each GRB and discuss the derived statistical properties.

astro-ph↗
arXiv2008

Measuring the cosmological parameters with the Ep,i-Eiso correlation of Gamma-Ray Bursts

We have used the Ep,i-Eiso correlation of GRBs to measure the cosmological parameter Omega_M. By adopting a maximum likelihood approach which allows us to correctly quantify the extrinsic (i.e. non--Poissonian) scatter of the correlation, we constrain (for a flat universe) Omega_M to 0.04-0.40 (68% confidence level), with a best fit value of Omega_M ~ 0.15, and exclude Omega_M = 1 at 99.9% confidence level. If we release the assumption of a flat universe, we still find evidence for a low value of Omega_M (0.04-0.50 at 68% confidence level) and a weak dependence of the dispersion of the Ep,i-Eiso correlation on Omega_Lambda (with an upper limit of Omega_Lambda ~ 1.15 at 90% confidence level). Our approach makes no assumptions on the Ep,i-Eiso correlation and it does not use other calibrators to set the "zero' point of the relation, therefore our treatment of the data is not affected by circularity and the results are independent of those derived via type Ia SNe (or other cosmological probes). Unlike other multi-parameters correlations, our analysis grounds on only two parameters, then including a larger number (a factor ~3) of GRBs and being less affected by systematics. Simulations based on realistic extrapolations of ongoing (and future) GRB experiments (e.g., Swift, Konus-Wind, GLAST) show that: i) the uncertainties on cosmological parameters can be significantly decreased; ii) future data will allow us to get clues on the "dark energy" evolution.

astro-ph↗
arXiv2008

Testing the E_p,i - L_p,iso - T_0.45 correlation on a BeppoSAX and Swift sample of gamma-ray bursts

Using a sample of 14 BeppoSAX and 74 Swift GRBs with measured redshift we tested the correlation between the intrinsic peak energy of the time-integrated spectrum, E_p,i, the isotropic-equivalent peak luminosity, L_p,iso, and the duration of the most intense parts of the GRB computed as T_0.45 ("Firmani correlation"). For 41 out of 88 GRBs we could estimate all of the three required properties. Apart from 980425, which appears to be a definite outlier and notoriously peculiar in many respects, we used 40 GRBs to fit the correlation with the maximum likelihood method discussed by D'Agostini, suitable to account for the extrinsic scatter in addition to the intrinsic uncertainties affecting every single GRB. We confirm the correlation. However, unlike the results by Firmani et al., we found that the correlation does have a logarithmic scatter comparable with that of the E_p,i-E_iso ("Amati") correlation. We also find that the slope of the product L_p,iso T_0.45 is equal to ~0.5, which is consistent with the hypothesis that the E_p,i-L_p,iso-T_0.45 correlation is equivalent to the E_p,i-E_iso correlation (slope ~0.5). We conclude that, based on presently available data, there is no clear evidence that the E_p,i-L_p,iso-T_0.45 correlation is different (both in terms of slope and dispersion) from the E_p,i-E_iso correlation.

astro-ph↗
arXiv2007

Structural anomalies at the magnetic transition in centrosymmetric BiMnO$_3$

The structural properties of BiMn$O_3$ were determined from neutron powder diffraction data as a function of temperature and magnetic field. The structure at all temperatures was found to be centrosymmetric with space group $C2/c$, which is incompatible with ferroelectricity. At T$_C\simeq 100 K$, we observed the onset of a large magnetoelastic strain, proportional to the square of the magnetization. We interpret this structural rearrangement, together with the previously observed magnetodielectric anomalies, as due to the need to optimize the partially frustrated magnetic interactions.

cond-mat.str-el↗
arXiv2007

On the temporal variability classes found in long gamma-ray bursts with known redshift

Based on the analysis of a small sample of BATSE and Konus gamma-ray bursts (GRBs) with know redshift it has been reported that the width of the autocorrelation function (ACF) shows a remarkable bimodal distribution in the rest-frame of the source. However, the origin of these two well-separated ACF classes remains unexplained.We complement previous ACF analysis studying the corresponding power density spectra (PDS). With the addition of Beppo-SAX data and taken advantage of its broad-band capability, we not only increase the burst sample but we extend the analysis to X-ray energies. The rest-frame PDS analysis at gamma-ray energies shows that the two ACF classes are not simply characterised by a different low frequency cut-off, but they have a distinct variability as a whole in the studied frequency range. Both classes exhibit average PDS with power-law behaviour at high frequencies (f' > 0.1 Hz) but significantly different slopes, with index values close to those of Brownian (-2) and Kolmogorov (-5/3) spectra for the narrow and broad classes respectively. The latter spectrum presents an additional PDS component, a low-frequency noise excess with a sharp cut-off. At X-ray energies we find the power-law index unchanged for the broad class, but a significantly steeper slope in the narrow case (~ -3). We interpret this as an indication that the broad class bursts have weaker spectral evolution than the narrow ones, as suggested also by our analysis of the ACF energy dependence. The low and high frequency PDS components may then arise from two radiating regions involving different emission mechanisms.

astro-ph↗
arXiv2006

On the consistency of the peculiar GRBs 060218 and 060614 with the Ep,i - Eiso correlation

We analyze and discuss the position of GRB 060218 and GRB 060614 in the Ep,i - Eiso plane. GRB 060218 is important because of its similarity with GRB 980425, the proto-type event of the GRB-SN connection. While GRB 980425 is an outlier of the Ep,i - Eiso correlation, we find that GRB 060218 is fully consistent with it. This evidence, combined with the `chromatic' behavior of the afterglow light curves, is at odds with the hypothesis that GRB 060218 was a `standard' GRB seen off-axis and supports the existence of a class of truly sub--energetic GRBs. GRB 060614 is a peculiar event not accompanied by a bright Supernova. Based on published spectral information, we find that also this event is consistent with the Ep,i - Eiso correlation. We discuss the implications of our results for the rate of sub--energetic GRBs, the GRB/SN connection and the properties of the newly discovered sub-class of long GRBs not associated with bright Supernovae. We have included in our analysis other recent GRBs with clear evidence (or clear no evidence) of associated SNe.

astro-ph↗
arXiv2006

The slope of the GRB Variability/Peak Luminosity Correlation

From a sample of 32 GRBs with known redshift (Guidorzi et al. 2005) and then a sample of 551 BATSE GRBs with derived pseudo-redshift (Guidorzi 2005), the time variability/peak luminosity correlation (V vs. L) found by Reichart et al. (2001) was tested. For both samples the correlation is still found but less relevant due to a much higher spread of the data. Assuming a straight line in the logL-logV plane (logL = m logV + b), as done by Reichart et al., the slope was found lower than that derived by Reichart et al.: m = 1.3_{-0.4}^{+0.8} (Guidorzi et al. 2005), m = 0.85 +- 0.02 (Guidorzi 2005), to be compared with m = 3.3^{+1.1}_{-0.9} (Reichart et al. 2001). Reichart & Nysewander (2005) attribute the different slope to the fact we do not take into account in the fit the variance of the sample, and demonstrate that, using the method by Reichart (2001), the data set of Guidorzi et al. (2005) in logL-logV plane is still well described with slope m = 3.4^{+0.9}_{-0.6}. Here we compare the results of two methods accounting for the variance of the sample, that implemented by Reichart (2001) and that by D'Agostini (2005). We demonstrate that the method by Reichart (2001) provides an inconsistent estimate of the slope when the sample variance is comparable with the interval of values covered by the variability. We also show that, using the D'Agostini method, the slope is consistent with that derived by us earlier and inconsistent with that derived by Reichart & Nysewander (2005). Finally we discuss the implications on the interpretations and show that our results are in agreement with the peak energy/variability correlation found by Lloyd-Ronning & Ramirez-Ruiz (2002) and the peak energy/peak luminosity correlation (Yonetoku et al. 2004; Ghirlanda et al. 2005) [abridged].

astro-ph↗
arXiv2006

The gamma-ray burst monitor for Lobster-ISS

Lobster-ISS is an X-ray all-sky monitor experiment selected by ESA two years ago for a Phase A study (now almost completed) for a future flight (2009) aboard the Columbus Exposed Payload Facility of the International Space Station. The main instrument, based on MCP optics with Lobster-eye geometry, has an energy passband from 0.1 to 3.5 keV, an unprecedented daily sensitivity of 2x10^{-12} erg cm^{-2}s$^{-1}, and it is capable to scan, during each orbit, the entire sky with an angular resolution of 4--6 arcmin. This X-ray telescope is flanked by a Gamma Ray Burst Monitor, with the minimum requirement of recognizing true GRBs from other transient events. In this paper we describe the GRBM. In addition to the minimum requirement, the instrument proposed is capable to roughly localize GRBs which occur in the Lobster FOV (162x22.5 degrees) and to significantly extend the scientific capabilities of the main instrument for the study of GRBs and X-ray transients. The combination of the two instruments will allow an unprecedented spectral coverage (from 0.1 up to 300/700 keV) for a sensitive study of the GRB prompt emission in the passband where GRBs and X-Ray Flashes emit most of their energy. The low-energy spectral band (0.1-10 keV) is of key importance for the study of the GRB environment and the search of transient absorption and emission features from GRBs, both goals being crucial for unveiling the GRB phenomenon. The entire energy band of Lobster-ISS is not covered by either the Swift satellite or other GRB missions foreseen in the next decade.

astro-ph↗
arXiv2005

The GRB Variability/Peak Luminosity Correlation: new results

We report test results of the correlation between time variability and peak luminosity of Gamma-Ray Bursts (GRBs), using a larger sample (32) of GRBs with known redshift than that available to Reichart et al. (2001), and using as variability measure that introduced by these authors. The results are puzzling. Assuming an isotropic-equivalent peak luminosity, as done by Reichart et al. (2001), a correlation is still found, but it is less relevant, and inconsistent with a power law as previously reported. Assuming as peak luminosity that corrected for GRB beaming for a subset of 16 GRBs with known beaming angle, the correlation becomes little less significant.

astro-ph↗
arXiv2005

The puzzling case of GRB 990123: prompt emission and broad-band afterglow modeling

We report on BeppoSAX simultaneous X- and gamma-ray observations of the bright GRB 990123. We present the broad-band spectrum of the prompt emission, including optical, X- and gamma-rays, confirming the suggestion that the emission mechanisms at low and high frequencies must have different physical origins. In the framework of the standard fireball model, we discuss the X-ray afterglow observed by the NFIs and its hard X-ray emission up to 60 keV several hours after the burst, detected for about 20 ks by the PDS. Considering the 2-10 keV and optical light curves, the 0.1-60 keV spectrum during the 20 ks in which the PDS signal was present and the 8.46 GHz upper limits, we find that the multi-wavelength observations cannot be readily accommodated by basic afterglow models. While the temporal and spectral behavior of the optical afterglow is possibly explained by a synchrotron cooling frequency between the optical and the X-ray energy band during the NFIs observations, in X-rays this assumption only accounts for the slope of the 2-10 keV light curve, but not for the flatness of the 0.1-60 keV spectrum. Including the contribution of Inverse Compton (IC) scattering, we solve the problem of the flat X-ray spectrum and justify the hard X-ray emission; we suggest that the lack of a significant detection of 15-60 keV emission in the following 75 ks and last 70 ks spectra, should be related to poorer statistics rather than to an important suppression of IC contribution. However, considering also the radio band data, we find the 8.46 GHz upper limits violated. On the other hand, leaving unchanged the emission mechanism requires modifying the hydrodynamics by invoking an ambient medium whose density rises rapidly with radius and by having the shock losing energy. Thus we are left with an open puzzle which requires further inspection.

astro-ph↗
arXiv2005

The GRB of 1999 January 23: prompt emission and broad-band afterglow modeling

We report on BeppoSAX simultaneous X- and gamma-ray observations of the bright gamma-ray burst (GRB) 990123. We present the broad-band spectrum of the prompt emission, including optical, X- and gamma-rays, confirming the suggestion that the emission mechanisms at low and high frequencies must have different physical origins. We discuss the X-ray afterglow observed by the Narrow Field Instruments (NFIs) on board BeppoSAX and its hard X-ray emission up to 60 keV several hours after the burst, in the framework of the standard fireball model. The effects of including an important contribution of Inverse Compton scattering or modifying the hydrodynamics are studied.

astro-ph↗
arXiv2005

SN/GRB connection: a statistical approach with BATSE and Asiago Catalogues

Recent observations suggest that some types of GRB are physically connected with SNe of type Ib/c. However, it has been pointed out by several authors that some GRBs could be associated also with other types of core-collapse SNe (type IIdw/IIn). On the basis of a comphrensive statistical study, which has made use of the BATSE and Asiago catalogues, we have found that: i) the temporal and spacial distribution of SNe-Ib/c is marginally correlated with that of the BATSE GRBs; ii) we do not confirm the existence of an association between GRBs and SNe-IIdw/IIn.

astro-ph↗
arXiv2005

The puzzling case of GRB 990123: multiwavelength afterglow study

We report on the BeppoSAX data analysis of the afterglow of Gamma-Ray Burst (GRB) 990123, one of the brightest GRBs detected by BeppoSAX. Mainly due to its exceptional brightness, this is the only source for which the Wide Field Cameras have allowed an early detection of the X-ray afterglow between about 20 and 60 min after the GRB trigger. Besides, again for the first time, high-energy emission from the afterglow was detected up to 60 keV. For the X-ray afterglow we found a power-law decay with index alpha = 1.46 +/- 0.04; the spectrum has a power-law shape with photon index Gamma about 1.9. The backward extrapolation of the afterglow decay smoothly reconnects with the late GRB emission, thus suggesting that both emissions are produced by the same phenomenon. An extensive set of multiwavelength observations for the GRB 990123 afterglow made during the BeppoSAX pointing was collected from the literature. The hard X-ray to radio range coverage allowed to construct a spectral flux distribution and to perform an analysis of the GRB afterglow in the context of the "fireball" model. We also report the results of temporal and spectral analysis of an X-ray source serendipitously observed about 22 arcmin north of the GRB afterglow, along with the optical spectroscopy of its possible counterpart to establish the nature of this source.

astro-ph↗