arXiv subjects

Marina Orio

Publications and source records attributed to Marina Orio.

At least 37 records · Page 2Linked to original sources

arXiv2016

Multi-mission observations of the old nova GK Per during the 2015 outburst

The remarkable old nova and an intermediate polar (IP) - GK Per was observed with Swift, the Chandra HETG and NuSTAR during its recent dwarf nova (DN) outburst in March - April 2015. Monitoring the outburst, we noticed several processes occurring on different time scales, such as: the slow evolution of the very soft X-ray emission (below 0.6 keV) during the first two weeks of the outburst and the very fast saturation of the X-ray flux above 1 keV. The Swift UVOT lights curves also showed different behaviour, depending on the filter. The broad band X-ray spectra revealed the presence of at least three different emitting sources. The white dwarf (WD) spin was observed even in the very hard X-ray range of NuSTAR, indicating that the modulation is not due to absorption, in contrast to a typical IP. It is also supported by the similarity of the on-pulse and off-pulse X-ray spectra. We propose that the scenario when the inner accretion disk pushed towards the WD by the increased accretion obscures the lower WD pole can work also for GK Per.

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arXiv2015

Suzaku observation of the classical nova V2491 Cyg in quiescence

We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. A very soft blackbody-like component peaking at 0.5 keV indicates that either we observe remaining, localized hydrogen burning on the surface of the white dwarf, or accretion onto a magnetized polar cap. In the second case, V2491 Cyg is a candidate "soft intermediate polar". We obtained the best fit for the X-ray spectra with several components: two of thermal plasma, a blackbody and a complex absorber. The later is typical of intermediate polars. The X-ray light-curve shows a modulation with a $\sim$38 min period. The amplitude of this modulation is strongly energy dependent and reaches maximum in the 0.8--2.0 keV range. We discuss the origin of the X-ray emission and pulsations, and the likelihood of the intermediate polar scenario.

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arXiv2013

X-ray observations of VY Scl type nova-like binaries in the high and low state

Four VY Scl-type nova-like systems were observed in X-rays both during the low and the high optical states. They are BZ Cam, MV Lyr, TT Ari, and V794 Aql. Using archival ROSAT, Swift and SUZAKU observations we found that the X-ray flux for BZ Cam is higher during the low state, but there is no supersoft X-ray source (SSS) that would indicate the thermonuclear burning predicted in a previous article. The X-ray flux is lower by a factor 2-10 in the low than the high state in other systems, and does not reflect the drop in $\dot{M}$ inferred from optical and UV data. The best fit model for the X-ray spectra is a collisionally ionized plasma model. The X-ray flux may originate in a shocked wind or in accretion onto polar caps in intermediate polar systems that continues even during the low state.

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arXiv2013

X-Ray Grating Observations of Recurrent Nova T Pyxidis During The 2011 Outburst

The recurrent nova T Pyx was observed with the X-ray gratings of Chandra and XMM-Newton, 210 and 235 days, respectively, after the discovery of the 2011 April 14 outburst. The X-ray spectra show prominent emission lines of C, N, and O, with broadening corresponding to a full width at half maximum of ~2000-3000 km/s, and line ratios consistent with high-density plasma in collisional ionization equilibrium. On day 210 we also measured soft X-ray continuum emission that appears to be consistent with a white dwarf (WD) atmosphere at a temperature ~420,000 K, partially obscured by anisotropic, optically thick ejecta. The X-ray continuum emission is modulated with the photometric and spectroscopic period observed in quiescence. The continuum at day 235 indicated a WD atmosphere at a consistent effective temperature of 25 days earlier, but with a lower flux. The effective temperature indicates a mass of ~1 solar mass. The conclusion of partial WD obscuration is supported by the complex geometry of non-spherically-symmetric ejecta confirmed in recent optical spectra obtained with the Southern African Large Telescope (SALT) in November and December of 2012. These spectra exhibited prominent [O III] nebular lines with velocity structures typical of bipolar ejecta.

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arXiv2013

On the nature of CP Pup

We present new X-ray and optical spectra of the old nova CP Pup (nova Pup 1942) obtained with Chandra and the CTIO 4m telescope. The X-ray spectrum reveals a multi-temperature optically thin plasma reaching a maximum temperature of 36$^{+19}_{-16}$ keV absorbed by local complex neutral material. The time resolved optical spectroscopy confirms the presence of the $\sim$1.47 hr period, with cycle-to-cycle amplitude changes, as well as of an additional long term modulation which is suggestive either of a longer period or of non-Keplerian velocities in the emission line regions. These new observational facts add further support to CP Pup as a magnetic cataclysmic variable (mCV). We compare the mCV and the non-mCV scenarios and while we cannot conclude whether CP Pup is a long period system, all observational evidences point at an intermediate polar (IP) type CV.

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arXiv2013

Building galaxies, stars, planets and the ingredients for life between the stars. A scientific proposal for a European Ultraviolet-Visible Observatory (EUVO)

The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950A-3000A) spectral range that is unobservable from the ground. A versatile space observatory with UV sensitivity a factor of 50-100 greater than existing facilities will revolutionize our understanding of the Universe. Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the star-disk interaction that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by the UV field, providing unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Earth's atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. A 50-100 times improvement in sensitivity would enable the observation of the key atmospheric ingredients of Earth-like exoplanets (carbon, oxygen, ozone), provide crucial input for models of biologically active worlds outside the solar system, and provide the phenomenological baseline to understand the Earth atmosphere in context. In this white paper, we outline the key science that such a facility would make possible and outline the instrumentation to be implemented.

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arXiv2013

The Hot and Energetic Universe: End points of stellar evolution

White dwarfs, neutron stars and stellar mass black holes are key laboratories to study matter in most extreme conditions of gravity and magnetic field. The unprecedented effective area of Athena+ will allow us to advance our understanding of emission mechanisms and accretion physics over a wide range of mass accretion rates, starting from lower and sub-luminous quiescent X-ray binaries up to super-Eddington ultra-luminous sources. Athena+ will measure stellar black hole spins in a much higher number of binaries than achievable now, opening the possibility to study how spin varies with black hole history. The high throughput and energy resolution of the X-IFU will be instrumental in establishing how disc wind properties depend on accretion state, in determining wind launching mechanism and in quantifying the impact of the wind induced mass loss on binary evolution and environment. Triggers and high quality optical and radio data originating from large wide field contemporaneous instruments will provide essential complementary information on jet launching mechanisms and on the physics of rotation powered pulsars, for instance. In addition, Athena+ will furnish multiple, independent measurements of the neutron star mass/radius relation in a wide range of environments and conditions so as to constrain the debated equation of state.

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arXiv2013

The multiple periods and the magnetic nature of CP Pup

Fast cadence time resolved spectra taken at the CTIO-4m telescope with the RC-spectrograph during 2 consecutive nights revealed a long term modulation of the binary radial velocity. Chandra hard X-ray spectra taken with the HETGS instrument showed features typically observed in magnetic white dwarfs (WD). Here, we present the new data and suggest that CP Pup is possibly a long orbital period intermediate polar.

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arXiv2012

Bright radio emission from an ultraluminous stellar-mass microquasar in M31

A subset of ultraluminous X-ray sources (those with luminosities < 10^40 erg/s) are thought to be powered by the accretion of gas onto black holes with masses of ~5-20 M_solar, probably via an accretion disc. The X-ray and radio emission are coupled in such Galactic sources, with the radio emission originating in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium precludes determining the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source whose peak luminosity can exceed 10^39 erg/s in the nearby galaxy, M31. The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a stellar mass black hole. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.

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arXiv2012

Observations of Classical and Recurrent Novae with X-ray Gratings

X-ray grating spectra have opened a new window on the nova physics. High signal-to-noise spectra have been obtained for 12 novae after the outburst in the last 13 years with the Chandra and XMM-Newton gratings. They offer the only way to probe the temperature, effective gravity and chemical composition of the hydrogen burning white dwarf before it turns off. These spectra also allow an analysis of the ejecta, which can be photoionized by the hot white dwarf, but more often seem to undergo collisional ionization. The long observations required for the gratings have revealed semi-regular and irregular variability in X-ray flux and spectra. Large short term variability is especially evident in the first weeks after the ejecta have become transparent to the central supersoft X-ray source. Thanks to Chandra and XMM-Newton, we have discovered violent phenomena in the ejecta, discrete shell ejection, and clumpy emission regions. As expected, we have also unveiled the white dwarf characteristics. The peak white dwarf effective temperature in the targets of our samples varies between ~400,000 K and over a million K, with most cases closer to the upper end, although for two novae only upper limits around 200,000 K were obtained. A combination of results from different X-ray satellites and instruments, including Swift and ROSAT, shows that the shorter is the supersoft X-ray phase, the lower is the white dwarf peak effective temperature, consistently with theoretical predictions. The peak temperature is also inversely correlated with t(2) the time for a decay by 2 mag in optical. I strongly advocate the use of white dwarf atmospheric models to obtain a coherent physical picture of the hydrogen burning process and of the surrounding ejecta.

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arXiv2011

X-ray and UV emission from the recurrent nova RS Ophiuchi in quiescence: Signatures of accretion and shocked gas

RS Ophiuchi is a recurrent nova system that experiences outbursts every ~20 years, implying accretion at a high rate onto a massive white dwarf. However, previous X-ray observations of the system in quiescence have detected only faint emission that is difficult to reconcile with the high accretion rate predicted by nova theory for such frequent outbursts. Here, we use new Chandra and XMM-Newton observations obtained 537 and 744 days after the 2006 outburst to constrain both the accretion rate onto the white dwarf and the properties of the nova ejecta at these times. We detect low level UV variability with the XMM-Newton Optical Monitor on day 744 that is consistent with accretion disk flickering, and use this to place a lower limit on the accretion rate. The X-ray spectra in both observations are well described by a two component thermal plasma model. The first component originates in the nova shell, which can emit X-rays for up to a decade after the outburst. The other component likely arises in the accretion disk boundary layer, and can be equally well fit by a single temperature plasma or a cooling flow model. Although the flux of the single temperature model implies an accretion rate that is 40 times lower than theoretical predictions for RS Oph, the best fit cooling flow model implies Mdot < 1.2x10^-8 M_sol/yr 537 days after the outburst, which is within a factor of 2 of the theoretical accretion rate required to power an outburst every 20 years. Furthermore, we place an upper limit on the accretion rate through an optically thick region of the boundary layer of 2.0x10^-8 M_sol/yr. Thus, the X-ray emission in quiescence is consistent with the accretion rate expectations of nova theory. Finally, we discuss the possible origins of the low temperature associated with the accretion component, which is a factor of 10 lower than in T CrB, an otherwise similar recurrent nova.

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arXiv2010

A decline and fall in the future of Italian Astronomy?

On May 27th 2010, the Italian astronomical community learned with concern that the National Institute for Astrophysics (INAF) was going to be suppressed, and that its employees were going to be transferred to the National Research Council (CNR). It was not clear if this applied to all employees (i.e. also to researchers hired on short-term contracts), and how this was going to happen in practice. In this letter, we give a brief historical overview of INAF and present a short chronicle of the few eventful days that followed. Starting from this example, we then comment on the current situation and prospects of astronomical research in Italy.

astro-ph.IM↗

arXiv2007

X-ray Spectroscopy of the 2006 Outburst of RS Oph

We present the X-ray grating spectra of the recurrent nova RS Ophiuchi during its 2006 outburst, obtained with the XMM-Newton and Chandra observatories. Two weeks after optical maximum, the X-ray spectrum was hard and dominated by emission lines of H-like and He-like ions. The X-ray luminosity was 2.4 x 10^36 erg s^-1 in the 0.33-10 keV range. The spectra indicate a collisionally dominated plasma with a broad range of temperatures. All the lines are blue-shifted, with the velocity shift increasing with lower ionization state and longer wavelength. Two weeks later, the spectrum was still dominated by emission lines, although the line ratios present indicate cooling. During this observation, a soft X-ray flare occurred in which a new system of higher velocity emission lines appeared in the soft end of the spectrum. The dominant component during the third month was the supersoft continuum with the broad absorption features of a hot white dwarf atmosphere. A preliminary model fit indicates a white dwarf temperature slightly exceeding 800,000 K. The X-ray luminosity reached at least 9 x 10^37 erg s^-1 in the 0.2-1 keV range, while the intrinsic nebular absorption decreased by a factor of five since the first observation. The spectral fits indicate a massive white dwarf, with a mass of at least 1.2 M_\odot. Therefore, RS Oph may be an important type Ia supernova progenitor. We show that the data are consistent with mass loss ending before day 54 after the outburst, and nuclear burning ending around day 69. A rapid decay in X-ray luminosity followed after week 10. The X-ray luminosity 5, 7 and 8 months after optical maximum dropped by more than two orders of magnitude. The spectra do not appear to consistent with emission from an accretion disk.

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arXiv2005

Analysis of a XMM-Newton Spectrum of the Extremely Hot White Dwarf in Nova V4743 Sgr

Classical novae occur in close binary systems (main-sequence star + white dwarf). V4743 Sgr is a very fast nova exhibiting a X-ray spectrum which is consistent with a view on the optically thick atmosphere of an extremely hot white dwarf (WD). It exhibits strong absorption features of the C V, C VI, N VI, N VII, and O VII resonance lines indicating an effective temperature of about 610 kK. We present preliminary results of a spectral analysis by means of line-blanketed non-LTE atmosphere models of a XMM-Newton RGS-1 spectrum of V4743 Sgr, taken about half a year after its outburst.

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arXiv2004

Chandra observations of the recurrent nova IM Nor

The recurrent nova IM Nor was observed twice in X-rays with Chandra ACIS-S, 1 and 6 months after the optical outburst. It was not detected in the first observation, with an upper limit on the X-ray luminosity in the 0.2-10 keV range L(x) < 4.8 x 10^(30) x (d/1 kpc)^2 erg s^(-1) (where d is the distance to the nova). Five months later, a hard X-ray source with L(x) = (1.4-2.5) x 10^(32) x (d/1 kpc)^2 erg s^(-1) was detected. The X-ray spectrum appears to be thermal, but we cannot rule out additional components due to unresolved emission lines. A blackbody component is likely to contribute to the observed spectrum, but it has bolometric luminosity L$_{\rm bol} = 2.5 x 10^(33) x (d/1 kpc)^2 erg s^(-1), therefore it is not sufficiently luminous to be due to a central white dwarf which is still burning hydrogen on the surface. An optical spectrum, taken 5 months post-outburst, indicates no intrinsic reddening of the ejecta. Therefore, we conclude that the shell had already become optically thin to supersoft X-rays, but nuclear burning had already turned off, or was in the process of turning off at this time. We discuss why this implies that recurrent novae, even the rare ones with long optical decays like IM Nor, indicating a large envelope mass, are not statistically significant as type Ia SN candidates.

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arXiv2004

Spectral Analysis of Super Soft X-ray Sources: V4743 Sagittarii

Half a year after its outburst, the nova V4743 Sgr evolved into the brightest super-soft X-ray source in the sky with a flux maximum around 30A, exhibiting resonance lines of C V, C VI, N VI, N VII, and O VII. We present preliminary results of an analysis of the XMM-Newton RGS spectra by means of NLTE model-atmosphere techniques.

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arXiv2004

X Ray Observations of Classical and recurrent Novae in Outburst

I review X-ray observations of classical and recurrent novae in outburst. Significant X-ray flux is emitted by the nova shell, with a peak luminosity up to 10**35 erg/cm**2/s in the 0.2-10 keV range.In recurrent nova systems, or in novae hosting a red giant, the source of X-rays may be previous circumstellar matter shocked by the nova wind. However, for most classical novae, X-rays originate inside the nebula ejected in the outburst. The data indicate a very high fraction of shocked material, and a non-smooth, varying wind outflow. A nebular emission line spectrum is also observed at late phases. In about half of the observed novae, the central white dwarf appears as a very luminous supersoft X-ray source for 1 to 9 years after the outburst. It is the best type of object to study the characteristics of shell hydrogen burning on white dwarfs in single degenrate systems. The available statistics indicate that the duration of the supersoft X-ray phase is peaked around 2 years. Recently, ``template grating spectra'' with high S/N have been obtained for V4743 Sgr. The X-ray light curve of this nova reveals a rich and complex power spectrum, with signatures of non-radial g-mode oscillations of the white dwarf. The oscillations and the spectra allow to determine the properties of the shell hydrogen burning white dwarf.

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arXiv2004

A New View of the Supersoft X-Ray Source Cal 87 Observed with XMM-Newton

Cal 87 was observed with XMM-Newton in April of 2003. The source shows a rich emission line spectrum, where lines can be identified if they are red-shifted by 700-1200 km/s. These lines seem to have been emitted in a wind from the system. The eclipse is observed to be shifted in phase by 0.03 phi(orb), where phi(orb) is the phase of the optical light curve.

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