Browsing by Author "Carrasco, Eleazar R."

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    The Cheshire Cat Gravitational Lens: The Formation of a Massive Fossil Group
    (2015-06-20) Irwin, Jimmy A.; Dupke, Renato; Carrasco, Eleazar R.; Maksym, W. Peter; Johnson, Lucas; White, Raymond E. III; University of Alabama Tuscaloosa
    The Cheshire Cat is a relatively poor group of galaxies dominated by two luminous elliptical galaxies surrounded by at least four arcs from gravitationally lensed background galaxies that give the system a humorous appearance. Our combined optical/X-ray study of this system reveals that it is experiencing a line of sight merger between two groups with a roughly equal mass ratio with a relative velocity of ∼1350 km s−1 . One group was most likely a lowmass fossil group, while the other group would have almost fit the classical definition of a fossil group. The collision manifests itself in a bimodal galaxy velocity distribution, an elevated central X-ray temperature and luminosity indicative of a shock, and gravitational arc centers that do not coincide with either large elliptical galaxy. One of the luminous elliptical galaxies has a double nucleus embedded off-center in the stellar halo. The luminous ellipticals should merge in less than a Gyr, after which observers will see a massive 1.2–1.5 × 1014 M⊙ fossil group with an Mr = −24.0 brightest group galaxy at its center. Thus, the Cheshire Cat offers us the first opportunity to study a fossil group progenitor. We discuss the limitations of the classical definition of a fossil group in terms of magnitude gaps between the member galaxies. We also suggest that if the merging of fossil (or nearfossil) groups is a common avenue for creating present-day fossil groups, the time lag between the final galactic merging of the system and the onset of cooling in the shock-heated core could account for the observed lack of well-developed cool cores in some fossil groups.
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    DISCOVERY OF THE CANDIDATE OFF-NUCLEAR ULTRASOFT HYPER-LUMINOUS X-RAY SOURCE 3XMM J141711.1+522541
    (IOP Publishing, 2016-04-10) Lin, Dacheng; Carrasco, Eleazar R.; Webb, Natalie A.; Irwin, Jimmy A.; Dupke, Renato; Romanowsky, Aaron J.; Ramirez-Ruiz, Enrico; Strader, Jay; Homan, Jeroen; Barret, Didier; Godet, Olivier; University System Of New Hampshire; University of New Hampshire; Centre National de la Recherche Scientifique (CNRS); Universite de Toulouse; Universite Toulouse III - Paul Sabatier; University of Alabama Tuscaloosa; University of Michigan System; University of Michigan; Eureka Scientific; California State University System; San Jose State University; University of California System; University of California Santa Cruz; Michigan State University; Massachusetts Institute of Technology (MIT)
    We report the discovery of an off-nuclear ultrasoft hyper-luminous X-ray source candidate 3XMM J141711.1 + 522541 in the inactive S0 galaxy SDSS. J141711.07+522540.8 (z = 0.41827, dL = 2.3 Gpc) in the Extended Groth Strip. It is located at a projected offset of similar to 1.'' 0 (5.2 kpc) from the nucleus of the galaxy and was serendipitously detected in five XMM-Newton observations in 2000 July. Two observations have enough counts and can be fitted with a standard thermal disk with an apparent inner disk temperature kT(MCD) similar to 0.13 keV and a 0.28-14.2 keV unabsorbed luminosity LX similar to 4 x 10(43) erg s(-1) in the source rest frame. The source was still detected in three Chandra observations in 2002 August, with similarly ultrasoft but fainter spectra (kT(MCD) similar to 0.17 keV, LX similar to 0.5 x 10(43) erg s(-1)). It was not detected in later observations, including two by Chandra in 2005 October, one by XMM-Newton in 2014 January, and two by Chandra in 2014 September-October, implying a long-term flux variation factor of > 14. Therefore the source could be a transient with an outburst in 2000-2002. It has a faint optical counterpart candidate, with apparent magnitudes of m(F606W) = 26.3 AB mag and m(F814W) = 25.5 AB mag in 2004 December (implying an absolute V-band magnitude of similar to-15.9 AB mag). We discuss various explanations for the source and find that it is best explained as a massive black hole (BH) embedded in the nucleus of a possibly stripped satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. The BH mass is similar to 10(5)M circle dot, assuming the peak X-ray luminosity at around the Eddington limit.
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    A likely decade-long sustained tidal disruption event
    (Nature Portfolio, 2017-02-02) Lin, Dacheng; Guillochon, James; Komossa, S.; Ramirez-Ruiz, Enrico; Irwin, Jimmy A.; Maksym, W. Peter; Grupe, Dirk; Godet, Olivier; Webb, Natalie A.; Barret, Didier; Zauderer, B. Ashley; Duc, Pierre-Alain; Carrasco, Eleazar R.; Gwyn, Stephen D. J.; University System Of New Hampshire; University of New Hampshire; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of California System; University of California Santa Cruz; University of Alabama Tuscaloosa; Seoul National University (SNU); Morehead State University; Centre National de la Recherche Scientifique (CNRS); Universite de Toulouse; Universite Toulouse III - Paul Sabatier; New York University; CEA; UDICE-French Research Universities; Universite Paris Cite; Universite Paris Saclay; National Research Council Canada
    Multiwavelength flares from tidal disruption and accretion of stars can be used to find and study otherwise dormant massive black holes in galactic nuclei(1). Previous well-monitored candidate flares were short-lived, with most emission confined to within similar to 1 year(2-5). Here we report the discovery of a well-observed super-long (> 11 years) luminous X-ray flare from the nuclear region of a dwarf starburst galaxy. After an apparently fast rise within similar to 4 months a decade ago, the X-ray luminosity, though showing a weak trend of decay, has been persistently high at around the Eddington limit (when the radiation pressure balances the gravitational force). The X-ray spectra are soft - steeply declining towards higher energies and can be described with Comptonized emission from an optically thick low-temperature corona, a super-Eddington accretion signature often observed in accreting stellar-mass black holes(6). Dramatic spectral softening was also caught in one recent observation, implying either a temporary transition from the super-Eddington accretion state to the standard thermal state, or the presence of a transient highly blueshifted (similar to 0.36c) warm absorber. All these properties in concert suggest a tidal disruption event with an unusually long super-Eddington accretion phase that has never before been observed.
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    A luminous X-ray outburst from an intermediate-mass black hole in an off-centre star cluster
    (Nature Portfolio, 2018-06-14) Lin, Dacheng; Strader, Jay; Carrasco, Eleazar R.; Page, Dany; Romanowsky, Aaron J.; Homan, Jeroen; Irwin, Jimmy A.; Remillard, Ronald A.; Godet, Olivier; Webb, Natalie A.; Baumgardt, Holger; Wijnands, Rudy; Barret, Didier; Duc, Pierre-Alain; Brodie, Jean P.; Gwyn, Stephen D. J.; University System Of New Hampshire; University of New Hampshire; Michigan State University; Universidad Nacional Autonoma de Mexico; California State University System; San Jose State University; University of California System; University of California Santa Cruz; Eureka Scientific; University of Alabama Tuscaloosa; Massachusetts Institute of Technology (MIT); Universite de Toulouse; Universite Toulouse III - Paul Sabatier; Centre National de la Recherche Scientifique (CNRS); University of Queensland; University of Amsterdam; CNRS - National Institute for Earth Sciences & Astronomy (INSU); UDICE-French Research Universities; Universites de Strasbourg Etablissements Associes; Universite de Strasbourg; National Research Council Canada
    A unique signature for the presence of massive black holes in very dense stellar regions is occasional giant-amplitude out-bursts of multi-wavelength radiation from tidal disruption and subsequent accretion of stars that make a close approach to the black holes(1). Previous strong tidal disruption event (TDE) candidates were all associated with the centres of largely isolated galaxies(2-6). Here, we report the discovery of a luminous X-ray outburst from a massive star cluster at a projected distance of 12.5 kpc from the centre of a large lenticular galaxy. The luminosity peaked at similar to 10(43) erg s(-1) and decayed systematically over 10 years, approximately following a trend that supports the identification of the event as a TDE. The X-ray spectra were all very soft, with emission confined to be less than or similar to 3.0 keV, and could be described with a standard thermal disk. The disk cooled significantly as the luminosity decreased-a key thermal-state signature often observed in accreting stellar-mass black holes. This thermal-state signature, coupled with very high luminosities, ultrasoft X-ray spectra and the characteristic power-law evolution of the light curve, provides strong evidence that the source contains an intermediate-mass black hole with a mass tens of thousand times that of the solar mass. This event demonstrates that one of the most effective means of detecting intermediate-mass black holes is through X-ray flares from TDEs in star clusters.
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    Multiwavelength follow-up observations of the tidal disruption event candidate 2XMMi J184725.1-631724
    (Oxford University Press, 2017-11-16) Lin, Dacheng; Strader, Jay; Carrasco, Eleazar R.; Godet, Olivier; Grupe, Dirk; Webb, Natalie A.; Barret, Didier; Irwin, Jimmy A.; University System Of New Hampshire; University of New Hampshire; Michigan State University; Centre National de la Recherche Scientifique (CNRS); Universite de Toulouse; Universite Toulouse III - Paul Sabatier; Morehead State University; University of Alabama Tuscaloosa; Seoul National University (SNU)
    The ultrasoft X-ray flare 2XMMi J184725.1-631724 was serendipitously detected in two XMM-Newton observations in 2006 and 2007, with a peak luminosity of 6 x 10(43) erg s(-1). It was suggested to be a tidal disruption event (TDE) because its position is consistent with the centre of an inactive galaxy. It is the only known X-ray TDE candidate whose X-ray spectra showed evidence of a weak steep power-law component besides a dominant supersoft thermal disc. We have carried out multiwavelength follow-up observations of the event. Multiple X-ray monitorings show that the X-ray luminosity has decayed significantly after 2011. Especially, in our deep Chandra observation in 2013, we detected a very faint counterpart that supports the nuclear origin of 2XMMi J184725.1-631724 but had an X-ray flux a factor of similar to 1000 lower than in the peak of the event. Compared with follow-up ultraviolet (UV) observations, we found that there might be some enhanced UV emission associated with the TDE in the first XMM-Newton observation. We also obtained a high-quality UV-optical spectrum with the Southern Astrophysical Research (SOAR) Telescope and put a very tight constraint on the persistent nuclear activity, with a persistent X-ray luminosity expected to be lower than the peak of the flare by a factor of > 2700. Therefore, our multiwavelength follow-up observations strongly support the TDE explanation of the event.
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    Using Strong Gravitational Lensing to Identify Fossil Group Progenitors
    (IOP Publishing, 2018-04-01) Johnson, Lucas E.; Irwin, Jimmy A.; White, Raymond E., III; Wong, Ka-Wah; Maksym, W. Peter; Dupke, Renato A.; Miller, Eric D.; Carrasco, Eleazar R.; University of Alabama Tuscaloosa; Seoul National University (SNU); Minnesota State Colleges & Universities; Minnesota State University Mankato; Eureka Scientific; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of Michigan System; University of Michigan; Massachusetts Institute of Technology (MIT)
    Fossil galaxy systems are classically thought to be the end result of galaxy group/cluster evolution, as galaxies experiencing dynamical friction sink to the center of the group potential and merge into a single, giant elliptical that dominates the rest of the members in both mass and luminosity. Most fossil systems discovered lie within z < 0.2, which leads to the question, what were these systems' progenitors? Such progenitors are expected to have imminent or ongoing major merging near the brightest group galaxy that, when concluded, will meet the fossil criteria within the look forward time. Since strong gravitational lensing preferentially selects groups merging along the line of sight, or systems with a high mass concentration like fossil systems, we searched the CASSOWARY survey of strong-lensing events with the goal of determining whether lensing systems have any predisposition to being fossil systems or progenitors. We find that similar to 13% of lensing groups are identified as traditional fossils while only similar to 3% of nonlensing control groups are. We also find that similar to 23% of lensing systems are traditional fossil progenitors compared to similar to 17% for the control sample. Our findings show that strong-lensing systems are more likely to be fossil/pre-fossil systems than comparable nonlensing systems. Cumulative galaxy luminosity functions of the lensing and nonlensing groups also indicate a possible, fundamental difference between strong-lensing and nonlensing systems' galaxy populations, with lensing systems housing a greater number of bright galaxies even in the outskirts of groups.