arXiv subjects

R. Soria

Publications and source records attributed to R. Soria.

98 records · Page 6Linked to original sources

arXiv2003

X-ray emission line gas in the LINER galaxy M81

We present the soft X-ray spectrum of the LINER galaxy M81 derived from a long observation with the XMM RGS. The spectrum is dominated by continuum emission from the active nucleus, but also contains emission lines from Fe L, and H-like and He-like N, O, and Ne. The emission lines are significantly broader than the RGS point-source spectral resolution; in the cross dispersion direction the emission lines are detected adjacent to, as well as coincident with, the active nucleus. This implies that they originate in a region of a few arc-minutes spatial extent (1 arc-minute ~ 1 kpc in M81). The flux ratios of the OVII triplet suggest that collisional processes are responsible for the line emission. A good fit to the whole RGS spectrum is obtained using a model consisting of an absorbed power law from the active nucleus and a 3 temperature optically thin thermal plasma. Two of the thermal plasma components have temperatures of 0.18+-0.04 keV and 0.64+-0.04 keV, characteristic of the hot interstellar medium produced by supernovae; the combined luminosity of the plasma at these two temperatures accounts for all the unresolved bulge X-ray emission seen in the Chandra observation by Tennant et al. (2001). The third component has a higher temperature (~1.7 keV), and we argue that this, along with some of the 0.64 keV emission, comes from X-ray binaries in the bulge of M81.

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arXiv2002

A High Resolution X-ray spectrum of the LINER Galaxy M81

We present the soft X-ray spectrum of the LINER galaxy M81 from a long observation with the XMM-Newton RGS. As well as continuum emission from the active nucleus, the spectrum shows emission lines from multi temperature collisionally ionized gas. The emission lines are significantly broader than the RGS point-source spectral resolution, and in the cross dispersion direction the emission lines are detected adjacent to, as well as coincident with, the active nucleus. This implies that they originate in a region of more than an arcminute (~ 1 kpc) spatial extent. A good fit to the whole RGS spectrum can be found using a model consisting of an absorbed power law from the active nucleus and a 3 temperature thermal plasma. Two of the thermal plasma components have temperatures of 0.18+-0.04 keV and 0.64+-0.04 keV, characteristic of the hot interstellar medium produced by supernovae; the combined luminosity of these two plasma components accounts for all the unresolved bulge X-ray emission seen in the Chandra observation by Tennant et al (2001). The third component has a higher temperature (~1.7 keV) and we propose X-ray binaries in the bulge of M81 as the most likely source of this emission.

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arXiv2002

Do NLS1s and ultrasoft AGN have irradiated, warped accretion disks?

When Beppo-SAX measured the 0.1--12 keV spectrum of RE J1034+396, observations in the optical, UV and EUV were also taken within a few weeks. This multiwavelength spectrum placed very strong constraints on its unusually hot big blue bump component, which has been attributed to a high (almost Eddington) rate of accretion onto a disk surrounding a low mass black hole. However, while a simple, geometrically-thin accretion disk provides a good fit to the UV to X-ray continuum, it leaves a residual flat and featureless component in the optical. We propose that the disk is actually flared or warped and that the central ionizing EUV/X-ray continuum is irradiating the outer parts of the disk and boosting the optical/UV continuum flux. The relatively narrow permitted lines may be due to a resulting disk wind. This physical interpretation may explain the link between ultrasoft X-ray excesses and broad line velocity in the AGN class as a whole. It may also have implications for the possible relationship between ultrasoft AGN and galactic black holes.

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arXiv2001

The 1998 outburst of XTE J1550-564: a model based on multiwavelength observations

The 1998 September outburst of the black-hole X-ray binary XTE J1550-564 was monitored at X-ray, optical and radio wavelengths. We divide the outburst sequence into five phases and discuss their multiwavelength properties. The outburst starts with a hard X-ray spike, while the soft X-ray flux rises with a longer timescale. We suggest that the onset of the outburst is determined by an increased mass transfer rate from the companion star, but the outburst morphology is determined by the distribution of specific angular momentum in the accreting matter. The companion in XTE J1550-564 is likely to be an active magnetic star, with a surface field strong enough to influence the dynamics of mass transfer. We suggest that its magnetic field can create a magnetic bag capable of confining gas inside the Roche lobe of the primary. The impulsive rise in the hard X-rays is explained by the inflow of material with low angular momentum onto the black hole, on a free-fall timescale, when the magnetic confinement breaks down. At the same time, high angular momentum matter, transferred via ordinary Roche-lobe overflow, is responsible for the formation of a disk.

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arXiv2001

An irradiated accretion disk in the narrow-line Seyfert 1 RE J1034+396?

We model the optical to X-ray continuum spectrum of the narrow-line Seyfert 1 galaxy RE J1034+396. We show that the flat optical spectrum is consistent with emission from an irradiated accretion disk. The X-ray emission can be modelled with a disk blackbody and a Comptonised component. The temperature at the inner edge of the disk T_{in} = (0.12 +/- 0.02) keV. Using this constraint, we show that the flat optical spectrum is consistent with emission from the irradiatively heated outer part of the accretion disk. We constrain the outer radius of the optically thick disk (R >~ 5 x 10^{16} cm) and the inner radius of the irradiation-dominated region (R >~ 5 x 10^{12} cm). Our optical and X-ray spectral fits indicate a mass 0.6 <~ M <~ 3 x 10^6 M_{sun}, and do not rule out a low (i.e. face-on) inclination angle for the system.

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arXiv2001

The central region of M31 observed with XMM-Newton. II. Variability of the individual sources

We present the results of a study of the variability of X-ray sources in the central 30' of the nearby Andromeda Galaxy (M31) based on XMM Performance Verification observations. Two observations of this field, with a total exposure time of about 50 ks, were performed in June and December of 2000. We found 116 sources brighter than a limiting luminosity of 6 x 10(35) erg/s (0.3--12 keV, d=760 kpc). For the ~60 brightest sources, we searched for periodic and non-periodic variability; at least 15% of these sources appear to be variable on a time scale of several months. We discovered a new bright transient source ~2.9' from the nucleus in the June observation; this source faded significantly and was no longer detected in December. The behaviour of the object is similar to a handful of Galactic LMXB transients, most of which are supposed to harbor black holes. We detected pulsations with a period of \~865 s from a source with a supersoft spectrum. The flux of this source decreased significantly between the two XMM observations. The detected period is unusually short and points to a rapidly spinning magnetized white dwarf. The high luminosity and transient nature of the source suggest its possible identification with classical or symbiotic nova, some of which were observed earlier as supersoft sources.

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arXiv2001

Radio Emission from the X-ray transient XTE J1550-564

We report multifrequency radio observations of XTE J1550-564 obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array at the time of its discovery and subsequent hard and soft X-ray outburst in 1998 September. A large radio flare was observed, peaking about 1.8 days after the X-ray flare. In addition, we present Australian Long Baseline Array images obtained shortly after the maximum of the radio flare which show evolving structure. The apparent separation velocity of the two outermost components is v>2c.

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arXiv2000

The central region of M31 observed with XMM-Newton (I. Group properties and diffuse emission)

We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30 arcmin of the nearby spiral galaxy M31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of 6 x 10^35 erg/s (0.3--12 keV, d = 760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below ~ 2.5 x 10^37 erg/s. We make use of hardness ratios for the detected sources in order to distinguish between classes of objects such as super-soft sources and intrinsically hard or highly absorbed sources. We demonstrate that the spectrum of the unresolved emission in the bulge of M31 contains a soft excess which can be fitted with a ~ 0.35-keV optically-thin thermal-plasma component clearly distinct from the composite point-source spectrum. We suggest that this may represent diffuse gas in the centre of M31, and we illustrate its extent in a wavelet-deconvolved image.

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