Searcharxiv⌕ Search

arXiv subjects

L. Sidoli

Publications and source records attributed to L. Sidoli.

138 records · Page 8Linked to original sources
arXiv2000

BeppoSAX study of the broad-band properties of luminous globular cluster X-ray sources

We have performed a detailed study of the broadband spectra of the luminous globular cluster X-ray sources using BeppoSAX. With the exception of X2127+119, located in NGC7078, all the other spectra are well represented by a two component model consisting of a disk-blackbody and Comptonized emission. The measured low-energy absorptions are in good agreement with those predicted from optical measurements of the host globular clusters. This implies that there is little intrinsic X-ray absorption within the binaries themselves, and that the above spectral model provides a good representation of the low-energy continua. The sources can be divided into two groups. In the first group, composed of 3 ultra-compact (orbital period <1hr) sources, the disk-blackbody temperatures and inner-radii appear physically realistic and the Comptonization seed photons temperatures and radii of the emission areas are consistent with the disk temperatures and inner radii. For all the other sources, the disk-blackbody parameters appear not to be physically realistic and the Comptonization parameters are unrelated to those of the disk-blackbody emission. If this is a spectral signature of ultra-compact binaries, this implies that no other ultra-compact binaries are present among those studied here. It is unclear why this difference between the two types of binaries should exist.

astro-ph↗
arXiv2000

X-ray emission from the galactic center region Supernova Remnant G0.9+0.1

We report the results of a BeppoSAX observation of the composite supernova remnant G0.9+0.1, located in the Galactic Center region. This new observation, in which the core of G0.9+0.1 is observed on-axis, confirms our previous results obtained from a pointing in which the supernova remnant was serendipitously observed at a large off-axis angle. The better quality of the new data allows us to confirm the non-thermal nature of the X-ray source coincident with the central plerion, to significantly improve the estimate of its spectral parameters, to put more stringent upper limits on the presence of coherent pulsations (in the range of periods from 4ms to ~ 4\times10^4 s), to obtain marginal evidence of the possible extended nature of the X-ray plerion and to put a better upper limit on the 2--10 keV X-ray emission from the 8' diameter radio shell (L$_{\rm S}<3.4\times 10^{34} {\rm d}_{10}^{2}$ erg s^{-1}). The X-ray spectrum is best fit with a power-law model with a photon index Γ~ 2, N_{\rm H} ~ 10^{23} \hcm and a 2-10 keV luminosity of 7.5\times 10^{34} {\rm d}_{10}^{2} erg s^{-1}. The broad band (radio-X-ray) properties of the composite supernova remnant G0.9+0.1 are indicative of the likely presence of a young (~ 2,700 yr) neutron star in its central radio core.

astro-ph↗
arXiv2000

The BeppoSAX view of the Galactic Center region

The Galactic Center Region has been surveyed in 1997-1998 with the Narrow Field Instruments on-board the BeppoSAX satellite (2-10keV energy range). The X-ray emission from SgrA*, the putative supermassive black hole at the center of our Galaxy, has been measured and its spectrum studied, together with the X-ray emission from several bright X-ray sources, LMXBs containing neutron stars and black holes located within the region ($|l|<2°)\times(|b|<1°$). New point-like X-ray sources have also been discovered. The results on the diffuse emission coming from the SgrA Complex are summarized here: it displays a two-temperature thermal spectrum (kT1~0.6keV and kT2~8keV) and an energy-dependent morphology, with the hard emission (5-10 keV) elongated along the galactic plane and the soft one (2-5 keV) spatially correlated with the radio halo of SgrAEast. The results of the study of the diffuse X-ray emission from other three fields in the Galactic Center Region containing the giant molecular clouds SgrB2, SgrC and SgrD are reported for the first time. The diffuse emission from the direction of these three molecular clouds shows a double temperature nature as well, with a prominent iron line at \~6.7keV, the intensity and equivalent width of which depends on the galactic longitude. Moreover, the SgrB2 spectrum shows an intense 6.4keV line of fluorescent origin. While the hard component of the Galactic Center diffuse emission displays a similar temperature with respect to the Galactic Ridge, the low temperature plasma is significantly softer. This may be due to a net contribution produced from the accretion of material onto old isolated neutron stars located inside the giant molecular clouds.

astro-ph↗
arXiv2000

BeppoSAX Observations of the Galactic Center Region: Soft x-rays from the radio halo of SgrAEast

The BeppoSAX satellite performed a survey of the Galactic Center Region in the 1-10 keV energy band with its Narrow Field Instruments. Several bright X-ray sources containing neutron stars and black holes have been observed and studied, including the possible counterpart of SgrA*. Here we report the results on the diffuse emission coming from the SgrA Complex. The emission from within 8 arcmin from SgrA* has a double-temperature thermal spectrum (kT1~0.6 keV and kT2~8 keV) and an energy-dependent morphology: the hard emission (5-10 keV) is elongated along the galactic plane, while the soft one (2-5 keV) shows a triangular shape, very similar to the radio halo of SgrAEast. This spatial correlation and the physical parameters of the lower temperature component support the interpretation of the radio halo of the Sgr~A~East shell as a SNR.

astro-ph↗
arXiv2000

BeppoSAX spectroscopy of the NGC7078 (M15) globular cluster X-ray source X2127+119

Results of a 1999 November 16--17 BeppoSAX observation of the low-mass X-ray binary X2127+119 located in the globular cluster NGC7078 are presented. The system is believed to be one where the central neutron star is normally obscured by the accretion disk, and only X-rays scattered into our line of sight by an extended accretion disk corona (ADC) are observed. The 0.1--10 keV lightcurve is energy dependent and shows two partial eclipses separated by the 17.1 hr orbital period. The 0.1--100 keV spectrum is unusually complex, but can be successfully modeled using a partially covered power-law and disk-blackbody model. Together with a column consistent with the interstellar value to NGC7078, about 60% of the source is covered by an additional column of 1E22 atom/cm2. The absorbed component may be X-rays that pass through the outer layers of the accretion disk. The energy dependent intensity variations by a factor of ~2 may be modeled as due to a changing normalization of the disk-blackbody. None of the other spectral parameters appear to clearly depend on luminosity. The same spectral model is also able to fit an archival ASCA spectrum.

astro-ph↗
arXiv1999

The X-ray diffuse emission from the Galactic Center

A long BeppoSAX observation of the Galactic Center region shows that the spectrum of the diffuse X-ray emission from the SgrA Complex can be described with the sum of two thermal plasma models with temperatures of ~0.6 keV and \~8-9 keV. The spatial distribution of the diffuse emission is energy dependent. While the hard X-ray emission has a nearly symmetric distribution elongated along the Galactic Plane, the soft X-rays (E < 5 keV) are remarkably well correlated with the triangular radio halo of SgrA East. The parameters derived for the soft component support the interpretation of the SgrA East shell in terms of an evolved supernova remnant.

astro-ph↗
arXiv1999

The Zoo of X-ray sources in the Galactic Center Region: Observations with BeppoSAX

We report the results of a survey of the Galactic Center region (|l| < 2deg, |b| < 0.5deg) performed with the BeppoSAX satellite. The flux from the center of our Galaxy corresponds to a luminosity of ~3 10^{35} erg/s in the 2-10 keV range. Due to the limited angular resolution ($\gsim 1'$) only part of it is supposed to come from Sagittarius A*, the non-thermal radio source which is believed to mark the dynamical center of the Galaxy. In addition to the diffuse emission, several bright (L$_X\gsim10^{36} ergs/s) point sources have been observed, both persistent (A 1742-294, SLX 1744-299, SLX 1744-300, 1E 1743.1-2843, 1E 1740.7-2942) and transient (XTE J1748-288, SAX J1747.0-2853 and KS 1741-293). The Low Mass X-ray Binary AX J1745.6-2901, discovered with ASCA at only $1.3'$ from SgrA* was detected in a low luminosity state in August 1997. Two fainter sources are very likely associated with young neutron stars: the (possibly diffuse) X-ray source at the center of the composite supernova remnant G0.9+0.1, and the "head" of the axially symmetric radio source G359.23-0.92. The latter has been detected above 6 keV, supporting a non-thermal emission mechanism.

astro-ph↗
arXiv1998

Observations of the Galactic Center Region with Beppo-Sax

We are performing a survey of the Galactic Center region with the BeppoSAX satellite. Several known point sources are visible (including one at the position of SgrA*), as well as newly discovered sources and diffuse emission. Here we report the preliminary results of the on-going analysis of both the point sources and the diffuse X-ray emission.

astro-ph↗
arXiv1997

Discovery of X-rays from the supernova remnant G0.9+0.1

During the $BeppoSAX$ survey of the Galactic Center region, we have discovered X-ray emission from the central region of the supernova remnant G0.9+0.1. The high interstellar absorption (N_H about 3 times 10^{23} cm^-2) is consistent with a distance of order of 10 kpc and, correspondingly, an X-ray luminosity of about 10^{35} erg s^{-1}. Although we cannot completely rule out a thermal origin of the X-ray emission, its small angular extent (radius of about 2'), the good fit with a power law, the presence of a flat spectrum radio core, and the estimated SNR age of a few thousand years, favour the interpretation in terms of synchrotron emission powered by a young, energetic pulsar.

astro-ph↗
arXiv1997

Discovery of X-rays from the composite supernova remnant G0.9+0.1 with the BeppoSAX satellite

Using the BeppoSAX satellite we have obtained the first secure X-ray detection of the supernova remnant G0.9+0.1. The 1-10 keV spectrum can be described with an absorbed power law with photon index 3 and N_H = 3 times 10^{23} cm^2. The high column density supports a distance similar to that of the Galactic Center. The X-ray emission, with a luminosity L_x = 10^{35} d_{10kpc}^{2} erg/s, coincides with the central radio core, confirming the composite nature of this remnant. Though a search for periodic pulsations gave a negative result, the observed X-rays are probably related to the presence of a young radio pulsar at the center of G0.9+0.1.

astro-ph↗
arXiv1996

Is RXJ1856.5-3754 an old neutron star?

An unusual X-ray source, RXJ1856.5-3754, has recently been discovered with ROSAT: its spectrum resembles that of supersoft sources, but the very high X-ray to optical flux ratio excludes the presence of a companion star, pointing to an isolated compact object. It has been proposed that RXJ1856.5-3754 is an old, isolated neutron star accreting from the interstellar medium. Here we present a reanalysis of the ROSAT data. The HRI observation reveals an attitude reconstruction problem, resulting in a larger error box than previously reported. Deeper optical observations allow us to reveal a few optical counterparts inside the new error box, but the X-ray to optical flux ratio is still very high (greater than 20) and none of the candidates has peculiar colors.

astro-ph↗