Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49 (2009)
Soria, Roberto, Hau, George K. T., Graham, Alister W., Kong, Albert K. H., Kuin, N. Paul M., Li, I-Hui, ...
The existence of black holes of masses ~ 10^3-10^4 Msun has important implications for the formation and evolution of star clusters and galaxies. The strongest candidate so far is the hyperluminous...
Ultraluminous X-ray Source Correlations with Star-Forming Regions (2009)
Swartz, Douglas A., Tennant, Allyn F., Soria, Roberto
Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u-g, g-r and r-i colors are used to determine whether Ultraluminous X-ray sources (ULXs) are predominantly associated with...
A census of X-ray nuclear activity in nearby galaxies (2009)
Zhang, Wei Ming, Soria, Roberto, Zhang, Shuang Nan, Swartz, Douglas A., Liu, JiFeng
We have studied the X-ray nuclear activity of 187 nearby (distance < 15 Mpc) galaxies observed with Chandra/ACIS. We found that 86 of them have a point-like X-ray core, consistent with an accreting...
The ULX NGC 1313 X-2 : an optical study revealing an interesting behavior (2009)
Grisé, Fabien, Pakull, Manfred W., Soria, Roberto, Motch, Christian
We present a summary of our ongoing efforts to study one of the brightest ultraluminous X-ray source, NGC 1313 X-2. Despite a large coverage in the X-rays, much of the information we have about the...
Different types of ultraluminous X-ray sources in NGC 4631 (2009)
We have re-examined the most luminous X-ray sources in the starburst galaxy NGC 4631, using XMM-Newton, Chandra and ROSAT data. The most interesting source is a highly variable supersoft ULX. We...
Soria, Roberto, Risaliti, Guido, Elvis, Martin, Fabbiano, Giuseppina, Bianchi, Stefano, Kuncic, Zdenka
Based on our long (~ 300 ks) 2007 XMM-Newton observation of the Seyfert galaxy NGC 1365, we report here on the spectral and timing behaviour of two ultraluminous X-ray sources, which had previously...
How rapidly do neutron stars spin at birth? (2008)
Soria, Roberto, Perna, Rosalba, Pooley, David, Stella, Luigi
We have studied the X-ray properties of ageing historical core-collapse supernovae in nearby galaxies, using archival data from Chandra, XMM-Newton and Swift. We found possible evidence of a young...
Black hole masses and accretion states in ULXs (2008)
Soria, Roberto, Kuncic, Zdenka
We summarize indirect empirical arguments used for estimating black hole (BH) masses in ultraluminous X-ray sources (ULXs). The interpretation of the X-ray data is still too model-dependent to...
The oldest X-ray supernovae: X-ray emission from 1941C, 1959D, 1968D (2008)
Soria, Roberto, Perna, Rosalba
We have studied the X-ray emission from four historical Type-II supernovae (the newly-discovered 1941C in NGC 4631 and 1959D in NGC 7331; and 1968D, 1980K in NGC 6946), using Chandra ACIS-S imaging....
Do Ultraluminous X-Ray Sources Exist in Dwarf Galaxies? (2008)
Swartz, Douglas A., Soria, Roberto, Tennant, Allyn F.
A thorough search for Ultraluminous X-ray source candidates within the Local Volume is made. The search spatially matches potential ULXs detected in X-ray images or cataloged in the literature with...
Perna, Rosalba, Soria, Roberto, Pooley, Dave, Stella, Luigi
Traditionally, studies aimed at inferring the distribution of birth periods of neutron stars are based on radio surveys. Here we propose an independent method to constrain the pulsar spin periods at...
Is Gx 339-4 A Black Hole Candidate? Optical Spectroscopy And Photometry (2007)
Roberto Soria, Kinwah WU, Helen M. JOHNSTON
. We carried out spectroscopic and photometric observations of the candidate black-hole binary GX 339\Gamma4 during its low-hard and high-soft X-ray states. We have found that the emission lines from...
Characteristic temperatures and spectral appearance of ULX disks (2007)
Soria, Roberto, Wu, Kinwah, Kuncic, Zdenka
A standard disk around an accreting black hole may become effectively optically-thin and scattering dominated in the inner region, for high accretion rates (as already predicted by the...
On the Nature of Ultra-Luminous X-ray Sources from Optical/IR Measurements (2007)
Cropper, Mark, Copperwheat, Christopher, Wu, Kinwah, Soria, Roberto
We present a model for the prediction of the optical/infra-red emission from ULXs. In the model, ULXs are binary systems with accretion taking place through Roche lobe overflow. We show that...
Discovery of a Transient X-ray Source in the Compact Stellar Nucleus of NGC 2403 (2007)
Yukita, Mihoko, Swartz, Douglas A., Soria, Roberto, Tennant, Allyn F.
We report the discovery of an X-ray source coincident with the nuclear star cluster at the dynamical center of the nearby late-type spiral galaxy NGC 2403. The X-ray luminosity of this source varies...
Quasi-Periodic Variability in NGC 5408 X-1 (2007)
Strohmayer, Tod E., Mushotzky, Richard F., Winter, Lisa, Soria, Roberto, Uttley, Phil, Cropper, Mark
We report the discovery with XMM-Newton of quasiperiodic variability in the 0.2 - 10 keV X-ray flux from the ultraluminous X-ray source NGC 5408 X-1. The average power spectrum of all EPIC-pn data...
Recipes for ULX formation: necessary ingredients and garnishments (2006)
I summarize the main observational features that seem to recur more frequently in the ULX population. I speculate that two of the most important physical requirements for ULX formation are low metal...
Soft-excess in ULX spectra: the chilled-disk scenario (2006)
Soria, Roberto, Goncalves, Anabela, Kuncic, Zdenka
Soft X-ray spectra of ULXs show small deviations from a power-law model, that can be attributed to reprocessing in a fast, ionized outflow, or to thermal emission from a cool disk. If it is thermal...
A ULX associated with a cloud collision in M99 (2006)
Soria, Roberto, Wong, Diane Sonya
The Sc galaxy M99 in the Virgo cluster has been strongly affected by tidal interactions and recent close encounters, responsible for an asymmetric spiral pattern and a high star formation rate. Our...
Dwarf Galaxies of the Local Group (2006)
Di Stefano, Rosanne, Soria, Roberto, Primini, F. A., Kong, Albert
XMM-Newton and Chandra have ushered in a new era for the study of dwarf galaxies in the Local Group. We provide an overview of the opportunities, challenges, and some early results. The large number...
On the weakness of disc models in bright ULXs (2006)
Goncalves, Anabela C., Soria, Roberto
It is sometimes suggested that phenomenological power-law plus cool disc-blackbody models represent the simplest, most robust interpretation of the X-ray spectra of bright ultraluminous X-ray sources...
A ULX microquasar in NGC 5408? (2006)
Soria, Roberto, Fender, Rob, Hannikainen, Diana, Read, Andrew, Stevens, Ian
We studied the radio source associated with the ultraluminous X-ray source in NGC 5408 (L_X ~ 10^{40} erg/s). The radio spectrum is steep (index ~ -1), consistent with optically-thin synchrotron...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the X-ray luminosity of the nuclear SMBH of a sample of quiescent early-type galaxies, and the inflow rate of the hot gas, feeding the SMBH. We have also studied the additional...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
Our X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, as well as in a larger sample from the literature, confirmed (Paper I) that the Bondi accretion rate of...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the X-ray luminosity of the nuclear SMBH of a sample of quiescent early-type galaxies, and the inflow rate of the hot gas, feeding the SMBH. We have also studied the additional...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
Our X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, as well as in a larger sample from the literature, confirmed (Paper I) that the Bondi accretion rate of...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the X-ray luminosity of the nuclear SMBH of a sample of quiescent early-type galaxies, and the inflow rate of the hot gas, feeding the SMBH. We have also studied the additional...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
Our X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, as well as in a larger sample from the literature, confirmed (Paper I) that the Bondi accretion rate of...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the X-ray luminosity of the nuclear SMBH of a sample of quiescent early-type galaxies, and the inflow rate of the hot gas, feeding the SMBH. We have also studied the additional...
Accretion and nuclear activity of quiescent supermassive black holes I: x-ray study (2006)
Soria, Roberto, Fabbiano, Giuseppina F., Graham, Alister W., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the nuclear activity in a sample of six quiescent early-type galaxies, with new Chandra data and archival HST optical images. Their nuclear sources have X-ray luminosities...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the X-ray luminosity of the nuclear SMBH of a sample of quiescent early-type galaxies, and the inflow rate of the hot gas, feeding the SMBH. We have also studied the additional...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina F., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
Our X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, as well as in a larger sample from the literature, confirmed (Paper I) that the Bondi accretion rate of...
Accretion and nuclear activity of quiescent supermassive black holes I: x-ray study (2006)
Soria, Roberto, Fabbiano, Giuseppina F., Graham, Alister W., Baldi, Alessandro, Elvis, Martin S., Jerjen, Helmut, ...
We have studied the nuclear activity in a sample of six quiescent early-type galaxies, with new Chandra data and archival HST optical images. Their nuclear sources have X-ray luminosities...
Soria, Roberto, Graham, Alister W., Fabbiano, Giuseppina, Baldi, Alessandro, Elvis, Martin, Jerjen, Helmut, ...
Our X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, and in a larger sample from the literature, confirmed (Soria et al., Paper I) that the Bondi accretion...
Accretion and nuclear activity of quiescent supermassive black holes. I: X-ray study (2005)
Soria, Roberto, Fabbiano, Giuseppina, Graham, Alister W., Baldi, Alessandro, Elvis, Martin, Jerjen, Helmut, ...
We have studied the nuclear activity in a sample of six quiescent early-type galaxies, with new Chandra data and archival HST optical images. Their nuclear sources have X-ray luminosities ~ 10^{38} -...
Optical and Infrared Signatures of ULX's (2005)
Copperwheat, Christopher, Cropper, Mark, Soria, Roberto, Wu, Kinwah
We have constructed a model to describe the optical emission from ultra-luminous X-ray sources (ULXs). We assume a binary model with a black hole accreting matter from a Roche lobe filling companion...
Bhardwaj, Anil, Branduardi-Raymont, Graziella, Elsner, Ronald F., Gladstone, G. Randall, Ramsay, Gavin, Rodriguez, Pedro, ...
During November 26-29, 2003 XMM-Newton observed soft (0.2-2 keV) X-ray emission from Jupiter for 69 hours. The low-latitude X-ray disk emission of Jupiter is observed to be almost uniform in...
Runaway core collapse and cluster survival: where are the parent clusters of ULXs? (2005)
Accreting intermediate-mass black holes (IMBHs) have been proposed as an explanation for ultraluminous X-ray sources (ULXs). Runaway core collapse inside a massive cluster is a possible mechanism for...
Detection of the Tip of Red Giant Branc in NGC 5128 (2004)
Soria, Roberto, Mould, Jeremy R., Watson, Alan M., Gallagher, John S. III, Ballester, Gilda E., Burrows, Christopher J., ...
We present a color-magnitude diagram of more than 10,000 stars in the halo of galaxy NGC 5128 (Centaurus A), based on WFPC2 images through the V and I filters. The position of the red-giant branch...
The star-forming environment of a ULX in NGC 4559: an optical study (2004)
Soria, Roberto, Cropper, Mark, Pakull, Manfred, Mushotzky, Richard, Wu, Kinwah
We have studied the candidate optical counterparts and the stellar population in the star-forming complex around a bright ULX in NGC4559, using HST/WFPC2, XMM-Newton/OM, and ground-based data. We...
Classifying the zoo of ultraluminous X-ray sources (2004)
Soria, Roberto, Cropper, Mark, Motch, Christian
Ultraluminous X-ray sources (ULXs) are likely to include different physical types of objects. We discuss some possible subclasses, reviewing the properties of a sample of ULXs recently observed by...
A variable ultra-luminous X-ray source in the colliding galaxy NGC 7714 (2004)
Soria, Roberto, Motch, Christian
We studied the colliding galaxy NGC 7714 with two XMM-Newton observations, six months apart. The galaxy contains two bright X-ray sources: we show that they have different physical nature. The...
A ULX in NGC 4559: a "mini-cartwheel" scenario? (2003)
Soria, Roberto, Cropper, Mark, Pakull, Manfred
We have studied an ultraluminous X-ray source (ULX) in NGC 4559 with XMM-Newton, and its peculiar star-forming environment with HST/WFPC2. The X-ray source is one of the brightest in its class (L_x ~...
Probable intermediate mass black holes in NGC4559: XMM-Newton spectral and timing constraints (2003)
Cropper, Mark, Soria, Roberto, Mushotzky, Richard F., Wu, Kinwah, Markwardt, Craig B., Pakull, Manfred
We have examined X-ray and optical observations of two ultra-luminous X-ray sources, X7 and X10 in NGC4559, using XMM-Newton, Chandra and HST. The UV/X-ray luminosity of X7 exceeds 2.1e40 erg/s in...
Constraints on AGN accretion disc viscosity derived from continuum variability (2003)
Starling, Rhaana L. C., Siemiginowska, Aneta, Uttley, Phil, Soria, Roberto
We estimate a value of the viscosity parameter in AGN accretion discs for the PG quasar sample. We assume that optical variability on time-scales of months to years is caused by local instabilities...
Properties of discrete X-ray sources in the starburst spiral galaxy M83 (2003)
We have identified 127 discrete sources in a Chandra observation of M83, with a detection limit of ~ 3 x 10^{36} erg/s in the 0.3-8.0 keV band. We discuss the individual properties of about 20 bright...
A second glance at SN 2002ap and the M74 field with XMM-Newton (2003)
Soria, Roberto, Pian, Elena, Mazzali, Paolo
We have re-observed the field of M74 in January 2003 with XMM-Newton, 11 months after the X-ray detection of SN 2002ap. From a comparison of the two XMM-Newton observations we obtain more accurate...
X-ray properties of spiral galaxies (2002)
X-ray studies of nearby spiral galaxies with star formation allow us to investigate temperature and spatial distribution of the hot diffuse plasma, and to carry out individual and statistical studies...
XMM-Newton observations of the spiral galaxy M74 (NGC 628) (2002)
Soria, Roberto, Kong, Albert K. H.
The face-on spiral galaxy M74 (NGC 628) was observed by XMM on 2002 February 2. In total, 21 sources are found in the inner 5' from the nucleus (after rejection of a few sources associated to...
We have studied the face-on, barred spiral M83 (NGC 5236) with Chandra. Eighty-one point sources are detected (above 3.5-sigma) in the ACIS S3 image: 15 of them are within the inner 16 arcsec region...
State transitions in LMC X-3 (2002)
Soria, Roberto, Page, Mat, Wu, Kinwah
We carried out a multiwavelenght study of the black-hole candidate LMC X-3 with XMM-Newton. The system showed a transition to a low-hard state, in which the X-ray spectrum was well fitted by a simple...
Chandra has resolved the starburst nuclear region of the face-on grand-design spiral M83. Eighty-one point sources are detected above 3.5 sigma in the ACIS S3 image, and 15 of them are within the...
Low and High Angular Momentum Accretion Flows in BHCs: Case Study of XTE J1550-564 (2001)
Soria, Roberto, Wu, Kinwah, Hannikainen, Diana, McCollough, Mike, Hunstead, Richard
The 1998 outburst of XTE J1550-564 started with a hard X-ray spike, rising in less than a day and declining after 3-4 days; at the same time, the soft X-ray flux was rising with a longer timescale (~...
Formation of optical lines in black-hole binaries (2001)
Wu, Kinwah, Soria, Roberto, Johnston, Helen, Hunstead, Richard
The HI Balmer emission lines of black-hole binaries show double-peaked profiles during the high-soft state and the quiescent state. In the high-soft state the profiles are asymmetric with a stronger...
The optical emission lines as a probe of state transitions in black-hole candidates (2001)
Optical spectroscopic studies of emission lines in black-hole candidates can help us investigate state transitions in those systems. Changes in the optical line profiles reflect changes in the...
XMM-Newton EPIC and RGS observations of LMC X-3 (2000)
Wu, Kinwah, Soria, Roberto, Page, Mathew, Sakelliou, Irini, Kahn, Steven, De Vries, Cor
We report the results of preliminary analysis of the XMM_Newton EPIC and RGS observations of the candidate black-hole binary LMC X-3 between February and June 2000. The observations covered both the...
XMM-Newton Optical Monitor observations of LMC X-3 (2000)
Soria, Roberto, Wu, Kinwah, Page, Mathew, Sakelliou, Irini
We study the optical counterpart of the black-hole X-ray binary LMC X-3, by using XMM-Newton/OM observations carried out during a low-hard X-ray state. We derive a better constraint for the...
Wu, Kinwah, Soria, Roberto, Hunstead, Richard W., Johnston, Helen M.
We have carried out observations of the X-ray transient GX339-4 during its high-soft and low-hard X-ray spectral states. Our high-resolution spectroscopic observation in 1999 April suggests that the...
Optical Spectroscopy of GRO J1655-40 (1999)
Soria, Roberto, Wu, Kinwah, Hunstead, Richard
We have obtained optical spectra of the soft X-ray transient GRO J1655-40 during different X-ray spectral states (quiescence, high-soft and hard outburst) between 1994 Aug and 1997 Jun....
Optical Spectroscopy of GX339-4 During the High-Soft and Low-Hard States (Paper I) (1999)
Soria, Roberto, Wu, Kinwah, Johnston, Helen
We carried out spectroscopic observations of the candidate black-hole binary GX339-4 during its low-hard and high-soft X-ray states, in 1997 and 1998 respectively. We have found that the spectrum is...
A Study of the New X-ray Transient RXTE J2123-058 during its Post-Outburst State (1999)
Soria, Roberto, Wu, Kinwah, Galloway, Duncan
We carried out I, R, V and B photometric observations of the neutron star X-ray binary RXTE J2123-058 shortly after the end of the X-ray outburst in mid-1998. We adopt the low mass binary model to...
The Optical Counterpart of the X-ray Transient RX J0117.6-7330: Spectroscopy and Photometry (1998)
We conducted spectroscopic and photometric observations of the optical counterpart of the X-ray transient RX J0117.6-7330 in the Small Magellanic Cloud, during a quiescent state. The primary star is...
Measuring the Motion of the Black Hole in GRO J16550-40 (1998)
Soria, Roberto, Wickramasinghe, Dayal T., Hunstead, Richard W., Wu, Kinwah
We report optical spectroscopic observations of the Low Mass X-ray Binary GRO J1655-40 during outbursts in August-September 1994 and in June 1996. The spectra show emission and absorption lines from...