Browsing by Author "Romanowsky, Aaron J."

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    The Megasecond Chandra X-Ray Visionary Project Observation of NGC 3115. II. Properties of Point Sources
    (2015-07-20) Lin, Dacheng; Irwin, Jimmy A.; Wong, Ka-Wah; Jennings, Zachary G.; Homan, Jeroen; Romanowsky, Aaron J.; Strader, Jay; Sivakoff, Gregory R.; Brodie, Jean P.; Remillard, Ronald A.; University of Alabama Tuscaloosa
  • Thumbnail Image
    Item
    The Megasecond Chandra X-Ray Visionary Project Observation of NGC 3115. III. Luminosity Functions of LMXBS and Dependence on Stellar Environments
    (2015-07-20) Lin, Dacheng; Irwin, Jimmy A.; Wong, Ka-Wah; Jennings, Zachary G.; Homan, Jeroen; Romanowsky, Aaron J.; Strader, Jay; Brodie, Jean P.; Sivakoff, Gregory R.; Remillard, Ronald A.; University of Alabama Tuscaloosa
  • Thumbnail Image
    Item
    The Sluggs Survey: HST/ACS Mosaic Imaging of the NGC 3115 Globular Cluster System
    Jennings, Zachary G.; Strader, Jay; Romanowsky, Aaron J.; Brodie, Jean P.; Arnold, Jacob A.; Lin, Dacheng; Irwin, Jimmy A.; Sivakoff, Gregory R.; Wong, Ka-Wah; University of Alabama Tuscaloosa
    We present Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) g and z photometry and half-light radii Rh measurements of 360 globular cluster (GC) candidates around the nearby S0 galaxy NGC 3115. We also include Subaru/Suprime-Cam g, r, and i photometry of 421 additional candidates. The well-established color bimodality of the GC system is obvious in the HST/ACS photometry. We find evidence for a “blue tilt” in the blue GC subpopulation, wherein the GCs in the blue subpopulation get redder as luminosity increases, indicative of a mass–metallicity relationship. We find a color gradient in both the red and blue subpopulations, with each group of clusters becoming bluer at larger distances from NGC 3115. The gradient is of similar strength in both subpopulations, but is monotonic and more significant for the blue clusters. On average, the blue clusters have ∼10% larger Rh than the red clusters. This average difference is less than is typically observed for early-type galaxies but does match that measured in the literature for the Sombrero Galaxy (M104), suggesting that morphology and inclination may affect the measured size difference between the red and blue clusters. However, the scatter on the Rh measurements is large. We also identify 31 clusters more extended than typical GCs, which we term ultra-compact dwarf (UCD) candidates. Many of these objects are actually considerably fainter than typical UCDs. While it is likely that a significant number will be background contaminants, six of these UCD candidates are spectroscopically confirmed as NGC 3115 members. To explore the prevalence of low-mass X-ray binaries in the GC system, we match our ACS and Suprime-Cam detections to corresponding Chandra X-ray sources. We identify 45 X-ray–GC matches: 16 among the blue subpopulation and 29 among the red subpopulation. These X-ray/GC coincidence fractions are larger than is typical for most GC systems, probably due to the increased depth of the X-ray data compared to previous studies of GC systems.
  • Thumbnail Image
    Item
    Ultraluminous X-ray bursts in two ultracompact companions to nearby elliptical galaxies
    (Nature Portfolio, 2016-10-20) Irwin, Jimmy A.; Maksym, W. Peter; Sivakoff, Gregory R.; Romanowsky, Aaron J.; Lin, Dacheng; Speegle, Tyler; Prado, Ian; Mildebrath, David; Strader, Jay; Liu, Jifeng; Miller, Jon M.; University of Alabama Tuscaloosa; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of Alberta; California State University System; San Jose State University; University of California System; University of California Santa Cruz; University System Of New Hampshire; University of New Hampshire; Michigan State University; Chinese Academy of Sciences; National Astronomical Observatory, CAS; University of Chinese Academy of Sciences, CAS; University of Michigan System; University of Michigan
    A flaring X-ray source was found near the galaxy NGC 4697 (ref. 1). Two brief flares were seen, separated by four years. During each flare, the flux increased by a factor of 90 on a timescale of about one minute. There is no associated optical source at the position of the flares(1), but if the source was at the distance of NGC 4697, then the luminosities of the flares were greater than 10(39) erg per second. Here we report the results of a search of archival X-ray data for 70 nearby galaxies looking for similar flares. We found two ultraluminous flaring sources in globular clusters or ultracompact dwarf companions of parent elliptical galaxies. One source flared once to a peak luminosity of 9 x 10(40) erg per second; the other flared five times to 10(40) erg per second. The rise times of all of the flares were less than one minute, and the flares then decayed over about an hour. When not flaring, the sources appear to be normal accreting neutron-star or black-hole X-ray binaries, but they are located in old stellar populations, unlike the magnetars, anomalous X-ray pulsars or soft gamma repeaters that have repetitive flares of similar luminosities.