arXiv subjects

C. Pinto

Publications and source records attributed to C. Pinto.

At least 127 records · Page 7Linked to original sources

arXiv2017

Performance of the diamond active target prototype for the PADME experiment at the DA$Φ$NE BTF

The PADME experiment at the DA$Φ$NE Beam-Test Facility (BTF) is designed to search for the gauge boson of a new $\rm U(1)$ interaction in the process e$^+$e$^-\rightarrowγ$+$\rm A'$, using the intense positron beam hitting a light target. The $\rm A'$, usually referred as dark photon, is assumed to decay into invisible particles of a secluded sector and it can be observed by searching for an anomalous peak in the spectrum of the missing mass measured in events with a single photon in the final state. The measurement requires the determination of the 4-momentum of the recoil photon, performed by a homogeneous, highly segmented BGO crystals calorimeter. A significant improvement of the missing mass resolution is possible using an active target capable to determine the average position of the positron bunch with a resolution of less than 1 mm. This report presents the performance of a real size $\rm (2x2 cm^2)$ PADME active target made of a thin (50 $μ$m) diamond sensor, with graphitic strips produced via laser irradiation on both sides. The measurements are based on data collected in a beam test at the BTF in November 2015.

physics.ins-det↗

arXiv2017

CHEERS: The chemical evolution RGS sample

The chemical yields of supernovae and the metal enrichment of the hot intra-cluster medium (ICM) are not well understood. This paper introduces the CHEmical Enrichment RGS Sample (CHEERS), which is a sample of 44 bright local giant ellipticals, groups and clusters of galaxies observed with XMM-Newton. This paper focuses on the abundance measurements of O and Fe using the reflection grating spectrometer (RGS). The deep exposures and the size of the sample allow us to quantify the intrinsic scatter and the systematic uncertainties in the abundances using spectral modeling techniques. We report the oxygen and iron abundances as measured with RGS in the core regions of all objects in the sample. We do not find a significant trend of O/Fe as a function of cluster temperature, but we do find an intrinsic scatter in the O and Fe abundances from cluster to cluster. The level of systematic uncertainties in the O/Fe ratio is estimated to be around 20-30%, while the systematic uncertainties in the absolute O and Fe abundances can be as high as 50% in extreme cases. We were able to identify and correct a systematic bias in the oxygen abundance determination, which was due to an inaccuracy in the spectral model. The lack of dependence of O/Fe on temperature suggests that the enrichment of the ICM does not depend on cluster mass and that most of the enrichment likely took place before the ICM was formed. We find that the observed scatter in the O/Fe ratio is due to a combination of intrinsic scatter in the source and systematic uncertainties in the spectral fitting, which we are unable to disentangle. The astrophysical source of intrinsic scatter could be due to differences in AGN activity and ongoing star formation in the BCG. The systematic scatter is due to uncertainties in the spatial line broadening, absorption column, multi-temperature structure and the thermal plasma models. (Abbreviated).

astro-ph.GA↗

arXiv2017

Chasing obscuration in type-I AGN: discovery of an eclipsing clumpy wind at the outer broad-line region of NGC 3783

In 2016 we carried out a Swift monitoring program to track the X-ray hardness variability of eight type-I AGN over a year. The purpose of this monitoring was to find intense obscuration events in AGN, and thereby study them by triggering joint XMM-Newton, NuSTAR, and HST observations. We successfully accomplished this for NGC 3783 in December 2016. We found heavy X-ray absorption produced by an obscuring outflow in this AGN. As a result of this obscuration, interesting absorption features appear in the UV and X-ray spectra, which are not present in the previous epochs. Namely, the obscuration produces broad and blue-shifted UV absorption lines of Ly$α$, C IV, and N V, together with a new high-ionisation component producing Fe XXV and Fe XXVI absorption lines. In soft X-rays, only narrow emission lines stand out above the diminished continuum as they are not absorbed by the obscurer. Our analysis shows that the obscurer partially covers the central source with a column density of few $10^{23}$ cm$^{-2}$, outflowing with a velocity of few thousand km s$^{-1}$. The obscuration in NGC 3783 is variable and lasts for about a month. Unlike the commonly-seen warm-absorber winds at pc-scale distances from the black hole, the eclipsing wind in NGC 3783 is located at about 10 light days. Our results suggest the obscuration is produced by an inhomogeneous and clumpy medium, consistent with clouds in the base of a radiatively-driven disk wind at the outer broad-line region of the AGN.

astro-ph.HE↗

arXiv2017

From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link

In recent work with high-resolution grating spectrometers (RGS) aboard XMM-Newton Pinto et al. (2016) have discovered that two bright and archetypal ultraluminous X-ray sources (ULXs) have strong relativistic winds in agreement with theoretical predictions of high accretion rates. It has been proposed that such winds can become optically thick enough to block and reprocess the disk X-ray photons almost entirely, making the source appear as a soft thermal emitter or ultraluminous supersoft X-ray source (ULS). To test this hypothesis we have studied a ULX where the wind is strong enough to cause significant absorption of the hard X-ray continuum: NGC 55 ULX. The RGS spectrum of NGC 55 ULX shows a wealth of emission and absorption lines blueshifted by significant fractions of the light speed (0.01 - 0.20)c indicating the presence of a powerful wind. The wind has a complex dynamical structure with the ionization state increasing with the outflow velocity, which may indicate launching from different regions of the accretion disk. The comparison with other ULXs such as NGC 1313 X-1 and NGC 5408 X-1 suggests that NGC 55 ULX is being observed at higher inclination. The wind partly absorbs the source flux above 1 keV, generating a spectral drop similar to that observed in ULSs. The softening of the spectrum at lower (~ Eddington) luminosities and the detection of a soft lag agree with the scenario of wind clumps crossing the line of sight, partly absorbing and reprocessing the hard X-rays from the innermost region.

astro-ph.HE↗

arXiv2017

Improved measurements of turbulence in the hot gaseous atmospheres of nearby giant elliptical galaxies

We present significantly improved measurements of turbulent velocities in the hot gaseous halos of nearby giant elliptical galaxies. Using deep XMM-Newton Reflection Grating Spectrometer (RGS ) observations and a combination of resonance scattering and direct line broadening methods, we obtain well bounded constraints for 13 galaxies. Assuming that the turbulence is isotropic, we obtain a best fit mean 1D turbulent velocity of ~110 km/s. This implies a typical 3D Mach number ~0.45 and a typical non-thermal pressure contribution of ~6 per cent in the cores of nearby massive galaxies. The intrinsic scatter around these values is modest - consistent with zero, albeit with large statistical uncertainty - hinting at a common and quasi-continuous mechanism sourcing the velocity structure in these objects. Using conservative estimates of the spatial scales associated with the observed turbulent motions, we find that turbulent heating can be sufficient to offset radiative cooling in the inner regions of these galaxies (<10 kpc, typically 2-3 kpc). The full potential of our analysis methods will be enabled by future X-ray microcalorimeter observations.

astro-ph.HE↗

arXiv2016

An in-depth study of a neutron star accreting at low Eddington rate: On the possibility of a truncated disk and an outflow

Due to observational challenges our knowledge of low-level accretion flows around neutron stars is limited. We present Nustar, Swift and Chandra observations of the low-mass X-ray binary IGR J17062-6143, which has been persistently accreting at ~0.1 per cent of the Eddington limit since 2006. Our simultaneous Nustar/Swift observations show that the 0.5-79 keV spectrum can be described by a combination of a power law with a photon index of Gamma~2, a black body with a temperature of kT_bb~0.5 keV (presumably arising from the neutron star surface), and disk reflection. Modeling the reflection spectrum suggests that the inner accretion disk was located at R_in>100 GM/c2 (>225 km) from the neutron star. The apparent truncation may be due to evaporation of the inner disk into a radiatively-inefficient accretion flow, or due to the pressure of the neutron star magnetic field. Our Chandra gratings data reveal possible narrow emission lines near 1 keV that can be modeled as reflection or collisionally-ionized gas, and possible low-energy absorption features that could point to the presence of an outflow. We consider a scenario in which this neutron star has been able to sustain its low accretion rate through magnetic inhibition of the accretion flow, which gives some constraints on its magnetic field strength and spin period. In this configuration, IGR J17062-6143 could exhibit a strong radio jet as well as a (propeller-driven) wind-like outflow.

astro-ph.HE↗

arXiv2016

Do sound waves transport the AGN energy in the Perseus Cluster?

The level of random motions in the intracluster gas lying between 20 and 60 kpc radius in the core of the Perseus cluster has been measured by the Hitomi Soft X-ray Spectrometer at 164 +/- 10 km/s. The maximum energy density in turbulent motions on that scale is therefore low. If dissipated as heat the turbulent energy will be radiated away in less than 80 Myr and cannot spread across the core. A higher velocity is needed to prevent a cooling collapse. Gravity waves are shown to travel too slowly in a radial direction. Here we investigate propagation of energy by sound waves. The energy travels at about 1000 km/s and can cross the core in a cooling time. We show that the displacement velocity amplitude of the gas required to carry the power is consistent with the Hitomi result and that the inferred density and temperature variations are consistent with Chandra observations.

astro-ph.GA↗

arXiv2016

An Iron K Component to the Ultrafast Outflow in NGC 1313 X-1

We present the detection of an absorpton feature at $E=8.77^{+0.05}_{-0.06}$ keV in the combined X-ray spectrum of the ultraluminous X-ray source NGC 1313 X-1 observed with XMM-Newton and NuSTAR, significant at the 3$σ$ level. If associated with blueshifted ionized iron, the implied outflow velocity is ~0.2$c$ for Fe XXVI, or ~0.25$c$ for Fe XXV. These velocities are similar to the ultrafast outflow seen in absorption recently discovered in this source at lower energies by XMM-Newton, and we therefore conclude that this is an iron component to the same outflow. Photoionization modeling marginally prefers the Fe XXV solution, but in either case the outflow properties appear to be extreme, potentially supporting a super-Eddington hypothesis for NGC 1313 X-1.

astro-ph.HE↗

arXiv2016

HST imaging of the dusty filaments and nucleus swirl in NGC4696 at the centre of the Centaurus Cluster

Narrow-band HST imaging has resolved the detailed internal structure of the 10 kpc diameter H alpha+[NII] emission line nebulosity in NGC4696, the central galaxy in the nearby Centaurus cluster, showing that the dusty, molecular, filaments have a width of about 60pc. Optical morphology and velocity measurements indicate that the filaments are dragged out by the bubbling action of the radio source as part of the AGN feedback cycle. Using the drag force we find that the magnetic field in the filaments is in approximate pressure equipartition with the hot gas. The filamentary nature of the cold gas continues inward, swirling around and within the Bondi accretion radius of the central black hole, revealing the magnetic nature of the gas flows in massive elliptical galaxies. HST imaging resolves the magnetic, dusty, molecular filaments at the centre of the Centaurus cluster to a swirl around and within the Bondi radius.

astro-ph.GA↗

arXiv2015

Anatomy of the AGN in NGC 5548: V. A clear view of the X-ray narrow emission lines

Context. Our consortium performed an extensive multi-wavelength campaign of the nearby Seyfert 1 galaxy NGC 5548 in 2013-14. The source appeared unusually heavily absorbed in the soft X-rays, and signatures of outflowing absorption were also present in the UV. He-like triplets of neon, oxygen and nitrogen, and radiative recombination continuum (RRC) features were found to dominate the soft X-ray spectrum due to the low continuum flux. Aims. Here we focus on characterising these narrow emission features using data obtained from the XMM-Newton RGS (770 ks stacked spectrum). Methods. We use SPEX for our initial analysis of these features. Self-consistent photoionisation models from Cloudy are then compared with the data to characterise the physical conditions of the emitting region. Results. Outflow velocity discrepancies within the O VII triplet lines can be explained if the X-ray narrow-line region (NLR) in NGC 5548 is absorbed by at least one of the six warm absorber components found by previous analyses. The RRCs allow us to directly calculate a temperature of the emitting gas of a few eV ($\sim10^{4}$ K), favouring photoionised conditions. We fit the data with a Cloudy model of log $ξ= 1.45 \pm 0.05$ erg cm s$^{-1}$, log $N_H = 22.9 \pm 0.4$ cm$^{-2}$ and log v$_{turb} = 2.25 \pm 0.5$ km s$^{-1}$ for the emitting gas; this is the first time the X-ray NLR gas in this source has been modelled so comprehensively. This allows us to estimate the distance from the central source to the illuminated face of the emitting clouds as $13.9 \pm 0.6$ pc, consistent with previous work.

astro-ph.HE↗

arXiv2015

Effects of the variability of the nucleus of NGC1275 on X-ray observations of the surrounding intracluster medium

The active galaxy NGC1275 lies at the centre of the Perseus cluster of galaxies, which is the X-ray brightest cluster in the Sky. The nucleus shows large variability over the past few decades. We compile a lightcurve of its X-ray emission covering about 40 years and show that the bright phase around 1980 explains why the inner X-ray bubbles were not seen in the images taken with the Einstein Observatory. The flux had dropped considerably by 1992 when images with the ROSAT HRI led to their discovery. The nucleus is showing a slow X-ray rise since the first Chandra images in 2000. If it brightens back to the pre-1990 level, then X-ray absorption spectroscopy by ASTRO-H can reveal the velocity structure of the shocked gas surrounding the inner bubbles.

astro-ph.HE↗

arXiv2015

Anatomy of the AGN in NGC 5548 IV. The short-term variability of the outflows

During an extensive multiwavelength campaign that we performed in 2013-14 the prototypical Seyfert 1 galaxy NGC 5548 has been found in an unusual condition of heavy and persistent obscuration. The newly discovered "obscurer" absorbs most of the soft X-ray continuum along our line of sight and lowers the ionizing luminosity received by the classical warm absorber. Here we present the analysis of the high resolution X-ray spectra collected with XMM-Newton and Chandra throughout the campaign, which are suitable to investigate the variability of both the obscurer and the classical warm absorber. The time separation between these X-ray observations range from 2 days to 8 months. On these timescales the obscurer is variable both in column density and in covering fraction. This is consistent with the picture of a patchy wind. The most significant variation occurred in September 2013 when the source brightened for two weeks. A higher and steeper intrinsic continuum and a lower obscurer covering fraction are both required to explain the spectral shape during the flare. We suggest that a geometrical change of the soft X-ray source behind the obscurer cause the observed drop in the covering fraction. Due to the higher soft X-ray continuum level the September 2013 Chandra spectrum is the only X ray spectrum of the campaign where individual features of the warm absorber could be detected. The spectrum shows absorption from Fe-UTA, \ion{O}{iv}, and \ion{O}{v}, consistent to belong to the lower-ionization counterpart of the historical NGC 5548 warm absorber. Hence, we confirm that the warm absorber has responded to the drop in the ionizing luminosity caused by the obscurer.

astro-ph.HE↗

arXiv2015

Discovery of a ~2 hr high frequency X-ray QPO and iron K alpha reverberation in the active galaxy MS 2254.9-3712

We report the discovery of a $\sim 1.5 \times 10^{-4}$ Hz ($\sim 2$ hr) X-ray quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a $\sim 70$ ks XMM-Newton observation. The QPO is significantly detected ($\sim 3.3 σ$) in the $1.2 - 5.0$ keV band only, connecting its origin with the primary X-ray power-law continuum. We detect a highly coherent soft lag between the $0.3 - 0.7$ keV and $1.2 - 5.0$ keV energy bands at the QPO frequency and at a frequency band in a 3:2 ratio, strongly suggesting the presence of a QPO harmonic. An iron K$α$ reverberation lag is found at the harmonic frequency, indicating the reflecting material subtends some angle to the primary continuum, which is modulated by the QPO mechanism. Frequency resolved spectroscopy reveals the QPO and harmonic to have a hard energy dependence. These properties of the QPO variability, together with the current black hole mass estimate, $M_{\rm bh} \sim 4 \times 10^{6} M_{\rm sun}$, are consistent with the QPO originating from the same process as the high frequency QPO phenomenon observed in black hole X-ray binaries. Principle component analysis reveals the spectral variability in MS 2254.9-3712 is similar to that of the active galaxy RE J1034+396, a source which also displays an X-ray QPO. This suggests a distinct spectral variability pattern for accreting black holes when in a state where QPOs are present.

astro-ph.HE↗

arXiv2015

The Spatial Variation of the Cooling Lines in the Reflection Nebula NGC7023

Context: The north-west photo-dissociation region (PDR) in the reflection nebula NGC 7023 displays a complex structure. Filament-like condensations at the edge of the cloud can be traced via the emission of the main cooling lines, offering a great opportunity to study the link between the morphology and energetics of these regions. Aims: We study the spatial variation of the far-infrared fine-structure lines of [C II] (158 um) and [O I] (63 and 145 um). These lines trace the local gas conditions across the PDR. Methods: We used observations from the Herschel/PACS instrument to map the spatial distribution of these fine-structure lines. The observed region covers a square area of about 110" x 110" with an angular resolution that varies from 4" to 11". We compared this emission with ground-based and Spitzer observations of H2 lines, Herschel/SPIRE observations of CO lines, and Spitzer/IRAC 3.6 um images that trace the emission of polycyclic aromatic hydrocarbons. Results: The [C II] (158 um) and [O I] (63 and 145 um) lines arise from the warm cloud surface where the PDR is located and the gas is warm, cooling the region. We find that although the relative contribution to the cooling budget over the observed region is dominated by [O I]63 um (>30%), H2 contributes significantly in the PDR (35%), as does [C II]158 um outside the PDR (30%). Other species contribute little to the cooling ([O I]145 um 9%, and CO 4%). The [O I] maps resolve these condensations into two structures and show that the peak of [O I] is slightly displaced from the molecular H2 emission. The size of these structures is about 8" (0.015 pc) and in surface cover about 9% of the PDR emission. Finally, we did not detect emission from [N II]122 um, suggesting that the cavity is mostly filled with non-ionised gas.

astro-ph.GA↗

arXiv2014

Anatomy of the AGN in NGC 5548: II. The Spatial, Temporal and Physical Nature of the Outflow from HST/COS Observations

(Abridged) Our deep multiwavelength campaign on NGC 5548 revealed an unusually strong X-ray obscuration. The resulting dramatic decrease in incident ionizing flux allowed us to construct a comprehensive physical, spatial and temporal picture for the long-studied AGN wind in this object. Here we analyze the UV spectra of the outflow acquired during the campaign as well as from four previous epochs. We find that a simple model based on a fixed total column-density absorber, reacting to changes in ionizing illumination, matches the very different ionization states seen in five spectroscopic epochs spanning 16 years. Absorption troughs from C III* appeared for the first time during our campaign. From these troughs, we infer that the main outflow component is situated at 3.5+-1 pc from the central source. Three other components are situated between 5-70 pc and two are further than 100 pc. The wealth of observational constraints and the disparate relationship of the observed X-ray and UV flux between different epochs make our physical model a leading contender for interpreting trough variability data of quasar outflows.

astro-ph.GA↗

arXiv2014

Multiwavelength campaign on Mrk 509 XIV. Chandra HETGS spectra

We present in this paper the results of a 270 ks Chandra HETGS observation in the context of a large multiwavelength campaign on the Seyfert galaxy Mrk 509. The HETGS spectrum allows us to study the high ionisation warm absorber and the Fe-K complex in Mrk 509. We search for variability in the spectral properties of the source with respect to previous observations in this campaign, as well as for evidence of ultra-fast outflow signatures. The Chandra HETGS X-ray spectrum of Mrk 509 was analysed using the SPEX fitting package. We confirm the basic structure of the warm absorber found in the 600 ks XMM-Newton RGS observation observed three years earlier, consisting of five distinct ionisation components in a multikinematic regime. We find little or no variability in the physical properties of the different warm absorber phases with respect to previous observations in this campaign, except for component D2 which has a higher column density at the expense of component C2 at the same outflow velocity (-240 km/s). Contrary to prior reports we find no -700 km/s outflow component. The O VIII absorption line profiles show an average covering factor of 0.81 +/- 0.08 for outflow velocities faster than -100 km/s, similar to those measured in the UV. This supports the idea of a patchy wind. The relative metal abundances in the outflow are close to proto-solar. The narrow component of the Fe Kalpha emission line shows no changes with respect to previous observations which confirms its origin in distant matter. The narrow line has a red wing that can be interpreted to be a weak relativistic emission line. We find no significant evidence of ultra-fast outflows in our new spectrum down to the sensitivity limit of our data.

astro-ph.HE↗

arXiv2014

A fast and long-lived outflow from the supermassive black hole in NGC 5548

Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution X-ray and UV observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas never seen before. It blocks 90% of the soft X-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

astro-ph.HE↗

arXiv2014

Age, size, and position of H ii regions in the Galaxy. Expansion of ionized gas in turbulent molecular clouds

This work aims at improving the current understanding of the interaction between H ii regions and turbulent molecular clouds. We propose a new method to determine the age of a large sample of OB associations by investigating the development of their associated H ii regions in the surrounding turbulent medium. Using analytical solutions, one-dimensional (1D), and three-dimensional (3D) simulations, we constrained the expansion of the ionized bubble depending on the turbulent level of the parent molecular cloud. A grid of 1D simulations was then computed in order to build isochrone curves for H ii regions in a pressure-size diagram. This grid of models allowed to date large sample of OB associations and was used on the H ii Region Discovery Survey (HRDS). Analytical solutions and numerical simulations showed that the expansion of H ii regions is slowed down by the turbulence up to the point where the pressure of the ionized gas is in a quasi-equilibrium with the turbulent ram pressure. Based on this result, we built a grid of 1D models of the expansion of H ii regions in a profile based on Larson laws. The 3D turbulence is taken into account by an effective 1D temperature profile. The ages estimated by the isochrones of this grid agree well with literature values of well-known regions such as Rosette, RCW 36, RCW 79, and M16. We thus propose that this method can be used to give ages of young OB associations through the Galaxy such as the HRDS survey and also in nearby extra-galactic sources.

astro-ph.SR↗