arXiv subjects

Paolo Coppi

Publications and source records attributed to Paolo Coppi.

At least 37 records · Page 2Linked to original sources

arXiv2017

The e-ASTROGAM mission (exploring the extreme Universe with gamma rays in the MeV-GeV range)

e-ASTROGAM (`enhanced ASTROGAM') is a breakthrough Observatory mission dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. In the largely unexplored MeV-GeV domain, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on Galactic ecosystems. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and the promise of eLISA. Keywords: High-energy gamma-ray astronomy, High-energy astrophysics, Nuclear Astrophysics, Compton and Pair creation telescope, Gamma-ray bursts, Active Galactic Nuclei, Jets, Outflows, Multiwavelength observations of the Universe, Counterparts of gravitational waves, Fermi, Dark Matter, Nucleosynthesis, Early Universe, Supernovae, Cosmic Rays, Cosmic antimatter.

astro-ph.HE↗

arXiv2017

Hitomi constraints on the 3.5 keV line in the Perseus galaxy cluster

High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E=3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark-matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of Sxvi (E=3.44 keV rest-frame) -- a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

astro-ph.HE↗

arXiv2016

The Quiescent Intracluster Medium in the Core of the Perseus Cluster

Clusters of galaxies are the most massive gravitationally-bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and a host of astrophysical processes. Knowledge of the dynamics of the pervasive hot gas, which dominates in mass over stars in a cluster, is a crucial missing ingredient. It can enable new insights into mechanical energy injection by the central supermassive black hole and the use of hydrostatic equilibrium for the determination of cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50 million K diffuse hot plasma filling its gravitational potential well. The Active Galactic Nucleus of the central galaxy NGC1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These likely induce motions in the intracluster medium and heat the inner gas preventing runaway radiative cooling; a process known as Active Galactic Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus cluster core, which reveal a remarkably quiescent atmosphere where the gas has a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s is found across the 60 kpc image of the cluster core. Turbulent pressure support in the gas is 4% or less of the thermodynamic pressure, with large scale shear at most doubling that estimate. We infer that total cluster masses determined from hydrostatic equilibrium in the central regions need little correction for turbulent pressure.

astro-ph.GA↗

arXiv2015

Tidal Disruption Events by a Massive Black Hole Binary

Massive black hole binaries (MBHBs) are a natural byproduct of galaxy mergers. Previous studies have shown that flares from stellar tidal disruption events (TDEs) are modified by the presence of a secondary perturber, causing interruptions in the light curve. We study the dynamics of TDE debris in the presence of a milliparsec-separated MBHB by integrating ballistic particle orbits in the time-varying potential of the binary. We find that gaps in the light curve appear when material misses the accretion radius on its first return to pericentre. Subsequent recurrences can be decomposed into "continuous" and "delayed" components, which exhibit different behaviour. We find that this potential can substantially alter the locations of stream self-intersections. When debris is confined to the plane, we find that close encounters with the secondary BH leave noticeable signatures on the fallback rate and can result in significant accretion onto the secondary BH. Tight, equal-mass MBHBs accrete equally, periodically trading the infalling stream.

astro-ph.HE↗

arXiv2015

The QUEST-La Silla AGN Variability Survey

We present the characterization and initial results from the QUEST-La Silla AGN variability survey. This is an effort to obtain well sampled optical light curves in extragalactic fields with unique multi-wavelength observations. We present photometry obtained from 2010 to 2012 in the XMM-COSMOS field, which was observed over 150 nights using the QUEST camera on the ESO-Schmidt telescope. The survey uses a broadband filter, the $Q$-band, similar to the union of the $g$ and the $r$ filters, achieving an intrinsic photometric dispersion of $0.05$ mag, and a systematic error of $0.05$ mag in the zero-point. Since some detectors of the camera show significant non-linearity, we use a linear correlation to fit the zero-points as a function of the instrumental magnitudes, thus obtaining a good correction to the non-linear behavior of these detectors. We obtain good photometry to an equivalent limiting magnitude of $r\sim 20.5$. Studying the optical variability of X-ray detected sources in the XMM-COSMOS field, we find that the survey is $\sim75-80$% complete to magnitudes $r\sim20$, and $\sim67$% complete to a magnitude $r\sim21$. The determination and parameterization of the structure function (${SF}_{norm}(τ) = A τ^γ$) of the variable sources shows that most BL AGN are characterized by $A > 0.1$ and $γ> 0.025$. It is further shown that variable NL AGN and GAL sources occupying the same parameter space in $A$ and $γ$ are very likely to correspond to obscured or low luminosity AGN. Our samples are, however, small, and we expect to revisit these results using larger samples with longer light curves obtained as part of our ongoing survey.

astro-ph.GA↗

arXiv2014

The ASTRO-H X-ray Astronomy Satellite

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of Delta E < 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.

astro-ph.IM↗

arXiv2014

GAMMA-LIGHT: High-Energy Astrophysics above 10 MeV

High-energy phenomena in the cosmos, and in particular processes leading to the emission of gamma- rays in the energy range 10 MeV - 100 GeV, play a very special role in the understanding of our Universe. This energy range is indeed associated with non-thermal phenomena and challenging particle acceleration processes. The technology involved in detecting gamma-rays is challenging and drives our ability to develop improved instruments for a large variety of applications. GAMMA-LIGHT is a Small Mission which aims at an unprecedented advance of our knowledge in many sectors of astrophysical and Earth studies research. The Mission will open a new observational window in the low-energy gamma-ray range 10-50 MeV, and is configured to make substantial advances compared with the previous and current gamma-ray experiments (AGILE and Fermi). The improvement is based on an exquisite angular resolution achieved by GAMMA-LIGHT using state-of-the-art Silicon technology with innovative data acquisition. GAMMA-LIGHT will address all astrophysics issues left open by the current generation of instruments. In particular, the breakthrough angular resolution in the energy range 100 MeV - 1 GeV is crucial to resolve patchy and complex features of diffuse sources in the Galaxy as well as increasing the point source sensitivity. This proposal addresses scientific topics of great interest to the community, with particular emphasis on multifrequency correlation studies involving radio, optical, IR, X-ray, soft gamma-ray and TeV emission. At the end of this decade several new observatories will be operational including LOFAR, SKA, ALMA, HAWK, CTA. GAMMA-LIGHT will "fill the vacuum" in the 10 MeV-10 GeV band, and will provide invaluable data for the understanding of cosmic and terrestrial high-energy sources.

astro-ph.IM↗

arXiv2014

Persistent C II Absorption in the Normal Type Ia Supernova 2002fk

We present well-sampled $UBVRIJHK$ photometry of SN 2002fk starting 12 days before maximum light through 122 days after peak brightness, along with a series of 15 optical spectra from -4 to +95 days since maximum. Our observations show the presence of C II lines in the early-time spectra of SN 2002fk, expanding at ~11,000 km s$^{-1}~$ and persisting until ~8 days past maximum light with a velocity of $\sim$9,000 km s$^{-1}~$. SN 2002fk is characterized by a small velocity gradient of $\dot v_{Si~II}=26$ km s$^{-1}$ day$^{-1}$, possibly caused by an off-center explosion with the ignition region oriented towards the observer. The connection between viewing angle of an off-center explosion and the presence of C II in the early time spectrum suggests that the observation of C II could be also due to a viewing angle effect. Adopting the Cepheid distance to NGC 1309 we provide the first $H_{0}$ value based on near-IR measurements of a Type Ia supernova between 63.0$\pm$ 0.8 ($\pm$ 2.8 systematic) and 66.7$\pm$1.0 ($\pm$ 3.5 systematic) km/s/Mpc, depending on the absolute magnitude/decline rate relationship adopted. It appears that the near-IR yields somewhat lower (6-9 %) $H_0$ values than the optical. It is essential to further examine this issue by (1) expanding the sample of high-quality near-IR light curves of SNe in the Hubble flow, and (2) increasing the number of nearby SNe with near-IR SN light curves and precise Cepheid distances, which affords the promise to deliver a more precise determination of $H_0$.

astro-ph.HE↗

arXiv2014

Magnetic Field Amplification and Flat Spectrum Radio Quasars

We perform time-dependent, spatially-resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts for light-travel-time effects and is applied to flares observed in the flat spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/γ-ray correlation at some times, but orphan optical flares at other times. Changes in both the magnetic field and the particle acceleration efficiency are explored as causes of flares. Generally, external Compton emission appears to describe the available data better than a synchrotron self-Compton scenario, and in particular orphan optical flares are difficult to produce in the SSC framework. X-ray soft-excesses, γ-ray spectral hardening, and the detections at very high energies of certain FSRQs during flares find natural explanations in the EC scenario with particle acceleration change. Likewise, optical flares with/without γ-ray counterparts can be explained by different allocations of energy between the magnetization and particle acceleration, which may be related to the orientation of the magnetic field relative to the jet flow. We also calculate the degree of linear polarization and polarization angle as a function of time for a jet with helical magnetic field. Tightening of the magnetic helix immediately downstream of the jet perturbations, where flares occur, can be sufficient to explain the increases in the degree of polarization and a rotation by >= 180 degree of the observed polarization angle, if light-travel-time effects are properly considered.

astro-ph.HE↗

arXiv2013

A Time Resolved Study of the Broad Line Region in Blazar 3C 454.3

We present multi-epoch optical observations of the blazar 3C 454.3 (z = 0.859) from 2008 August through 2011 December, using the SMARTS Consortium 1.5m+RCSpectrograph and 1.3m+ANDICAM in Cerro Tololo, Chile. The spectra reveal that the broad optical emission lines Mg II, H-beta and H-gamma are far less variable than the optical or gamma-ray continuum. Although, the gamma-rays varied by a factor of 100 above the EGRET era flux, the lines generally vary by a factor of 2 or less. Smaller variations in the gamma-ray flux did not produce significant variation in any of the observed emission lines. Therefore, to first order, the ionizing flux from the disk changes only slowly during large variations of the jet. However, two exceptions in the response of the broad emission lines are reported during the largest gamma-ray flares in 2009 December and 2010 November, when significant deviations from the mean line flux in H-gamma and Mg II were observed. H-gamma showed a maximum 3-sigma and 4-sigma deviation in each flare, respectively, corresponding to a factor of 1.7 and 2.5 increase in flux. Mg II showed a 2-sigma deviation in both flares; no variation was detected in H-beta during either flare. These significant deviations from the mean line flux also coincide with 7mm core ejections reported previously (Jorstad et al. 2012). The correlation of the increased emission line flux with mm core ejections, and gamma-ray, optical and UV flares suggests that the broad line region extends beyond the gamma-emitting region during the 2009 and 2010 flares.

astro-ph.CO↗

arXiv2013

The Impact of Bound Stellar Orbits and General Relativity on the Temporal Behavior of Tidal Disruption Flares

We have carried out general relativistic particle simulations of stars tidally disrupted by massive black holes. When a star is disrupted in a bound orbit with moderate eccentricity instead of a parabolic orbit, the temporal behavior of the resulting stellar debris changes qualitatively. The debris is initially all bound, returning to pericenter in a short time ~ the original stellar orbital timescale. The resulting fallback rate can thus be much higher than the Eddington rate. Furthermore if the star is disrupted close to the hole, in a regime where general relativity is important, the stellar and debris orbits display general relativistic precession. Apsidal precession can make the debris stream cross itself after several orbits, likely leading to fast debris energy dissipation. If the star is disrupted in an inclined orbit around a spinning hole, nodal precession reduces the probability of self-intersection, and circularization may take many dynamical timescales, delaying the onset of flare activity. An examination of the particle dynamics suggests that quasi-periodic flares with short durations, produced when the center of the tidal stream passes pericenter, may occur in the early-time light curve. The late-time light curve may still show power-law behavior which is generic to disk accretion processes. The detection triggers for future surveys should be extended to capture such "non-standard" short-term flaring activity before the event enters the asymptotic decay phase, as this activity is likely to be more sensitive to physical parameters such as the black hole spin.

astro-ph.HE↗

arXiv2012

The ASTRO-H X-ray Observatory

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.

astro-ph.IM↗

arXiv2011

A study of the color diversity around maximum light in Type Ia supernovae

From a sample of 12 well-observed Type Ia supernovae, we find clear evidence of correlations between early phase (U-B), (V-R), and (V-I) colors and the velocity shifts of the [Fe II] λ7155 and [Ni II] λ7378 nebular lines measured from late-phase spectra. As these lines are thought to trace the ashes of the initial deflagration process, our findings provide additional support to the new paradigm of off-center explosions in Type Ia supernovae, and we interpret these correlations as viewing angle effects in the observed colors. We also show that the nebular velocity shifts are related to the strength and width of the Ca II H&K and IR-triplet lines near-maximum light. The evidence presented here implies that the viewing angle must be taken into account when deriving extinction values and distances in future cosmological studies based on Type Ia supernovae.

astro-ph.CO↗

arXiv2011

Discovery and Characterization of an Extremely Deep-Eclipsing Cataclysmic Variable: LSQ172554.8-643839

We report the discovery of an eclipsing cataclysmic variable with eclipse depths > 5.7 mag, orbital period 94.657 min, and peak brightness V~18 at J2000 position 17h 25m 54s.8, -64d 38' 39". Detected by visual inspection of images from Yale University's QUEST camera on the ESO 1.0-m Schmidt telescope at La Silla, we obtained light curves in B, V, R, I, z and J with the SMARTS 1.3-m and 1.0-m telescopes at Cerro Tololo and spectra from 3500 to 9000 Angstrom with the SOAR 4.3-m telescope at Cerro Pachon. The optical light curves show a deep, 5-min eclipse immediately followed by a shallow 38-min eclipse and then sinusoidal variation. No eclipses appear in J. During the deep eclipse we measure V-J > 7.1, corresponding to a spectral type M8 or later secondary, consistent with the dynamical constraints. The estimated distance is 150 psec. The spectra show strong Hydrogen emission lines, Doppler broadened by 600 - 1300 km/s, oscillating with radial velocity that peaks at mid deep eclipse with semi-amplitude 500 +/- 22 km/s. We suggest that LSQ172554.8-643839 is a polar with a low-mass secondary viewed at high inclination. No known radio or x-ray source coincides with the new object's location.

astro-ph.SR↗

arXiv2010

Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State

Using Suzaku and the Rossi X-ray Timing Explorer, we have conducted a series of four simultaneous observations of the galactic black hole candidate Cyg X-1 in what were historically faint and spectrally hard low states. Additionally, all of these observations occurred near superior conjunction with our line of sight to the X-ray source passing through the dense phases of the focused wind from the mass donating secondary. One of our observations was also simultaneous with observations by the Chandra-High Energy Transmission Grating. These latter spectra are crucial for revealing the ionized absorption due to the secondary's focused wind. Such absorption is present and must be accounted for in all four spectra. These simultaneous data give an unprecedented view of the 0.8-300 keV spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet models of black hole hard states. Three models fit the spectra well: coronae with thermal or mixed thermal/non-thermal electron populations, and jets. All three models require a soft component that we fit with a low temperature disk spectrum with an inner radius of only a few tens of GM/c^2. All three models also agree that the known spectral break at 10\,keV is not solely due to the presence of reflection, but each gives a different underlying explanation for the augmentation of this break. Thus whereas all three models require that there is a relativistically broadened Fe line, the strength and inner radius of such a line is dependent upon the specific model, {thus making premature line-based estimates of the black hole spin in the Cyg X-1 system. We look at the relativistic line in detail, accounting for the narrow Fe emission and ionized absorption detected by HETG. Although the specific relativistic parameters of the line are continuum-dependent, none of the broad line fits allow for an inner disk radius that is >40 GM/c^2.

astro-ph.HE↗

arXiv2010

The Sudden Death of the Nearest Quasar

Galaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light echo in `Hanny's Voorwerp', but whose present-day radiative output is lower by at least 2 and more likely by over 4 orders of magnitude. This extremely rapid shutdown provides new insights into the physics of accretion in supermassive black holes, and may signal a transition of the accretion disk to a radiatively inefficient state.

astro-ph.CO↗

arXiv2010

The ASTRO-H Mission

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of Delta E ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be pursued.

astro-ph.IM↗

arXiv2010

Black hole growth and host galaxy morphology

We use data from large surveys of the local Universe (SDSS+Galaxy Zoo) to show that the galaxy-black hole connection is linked to host morphology at a fundamental level. The fraction of early-type galaxies with actively growing black holes, and therefore the AGN duty cycle, declines significantly with increasing black hole mass. Late-type galaxies exhibit the opposite trend: the fraction of actively growing black holes increases with black hole mass.

astro-ph.CO↗