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Browsing by Author "Irwin, J. A."

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    Classifying X-Ray Sources in External Galaxies from X-Ray Colors
    (2003-10-01) Prestwich, A. H.; Irwin, J. A.; Kilgard, R. E.; Krauss, M. I.; Zezas, A.; Primini, F.; Kaaret, P.; Boroson, B.; University of Alabama Tuscaloosa
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    Deep spectroscopy of the M-V similar to-14.8 host galaxy of a tidal disruption flare in A1795
    (Oxford University Press, 2014) Maksym, W. P.; Ulmer, M. P.; Roth, K. C.; Irwin, J. A.; Dupke, R.; Ho, L. C.; Keel, W. C.; Adami, C.; University of Alabama Tuscaloosa; Northwestern University; University of Michigan System; University of Michigan; Eureka Scientific; Peking University; Carnegie Institution for Science; UDICE-French Research Universities; Aix-Marseille Universite
    A likely tidal disruption of a star by the intermediate-mass black hole (IMBH) of a dwarf galaxy was recently identified in association with Abell 1795. Without deep spectroscopy for this very faint object, however, the possibility of a more massive background galaxy or even a disc-instability flare from a weak active galactic nucleus (AGN) could not be dismissed. We have now obtained 8 h of Gemini spectroscopy which unambiguously demonstrates that the host galaxy is indeed an extremely low mass (M-star similar to 3 x 10(8) M-circle dot) galaxy in Abell 1795, comparable to the least massive galaxies determined to host IMBHs via other studies. We find that the spectrum is consistent with the X-ray flare being due to a tidal disruption event rather than an AGN flare. We also set improved limits on the black hole mass (log[M-lozenge/M-circle dot] similar to 5.3-5.7) and infer a 15 yr X-ray variability of a factor of greater than or similar to 10(4). The confirmation of this galaxy-black hole system provides a glimpse into a population of galaxies that is otherwise difficult to study, due to the galaxies' low masses and intrinsic faintness, but which may be important contributors to the tidal disruption rate.
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    Deep spectroscopy of the M-V similar to-14.8 host galaxy of a tidal disruption flare in A1795
    (Oxford University Press, 2014) Maksym, W. P.; Ulmer, M. P.; Roth, K. C.; Irwin, J. A.; Dupke, R.; Ho, L. C.; Keel, W. C.; Adami, C.; University of Alabama Tuscaloosa; Northwestern University; University of Michigan System; University of Michigan; Eureka Scientific; Peking University; Carnegie Institution for Science; UDICE-French Research Universities; Aix-Marseille Universite
    A likely tidal disruption of a star by the intermediate-mass black hole (IMBH) of a dwarf galaxy was recently identified in association with Abell 1795. Without deep spectroscopy for this very faint object, however, the possibility of a more massive background galaxy or even a disc-instability flare from a weak active galactic nucleus (AGN) could not be dismissed. We have now obtained 8 h of Gemini spectroscopy which unambiguously demonstrates that the host galaxy is indeed an extremely low mass (M-star similar to 3 x 10(8) M-circle dot) galaxy in Abell 1795, comparable to the least massive galaxies determined to host IMBHs via other studies. We find that the spectrum is consistent with the X-ray flare being due to a tidal disruption event rather than an AGN flare. We also set improved limits on the black hole mass (log[M-lozenge/M-circle dot] similar to 5.3-5.7) and infer a 15 yr X-ray variability of a factor of greater than or similar to 10(4). The confirmation of this galaxy-black hole system provides a glimpse into a population of galaxies that is otherwise difficult to study, due to the galaxies' low masses and intrinsic faintness, but which may be important contributors to the tidal disruption rate.
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    The remarkable stability of probable black hole low-mass X-ray binaries in nearby galaxies
    (Blackwell, 2006) Irwin, J. A.; University of Michigan System; University of Michigan; University of Alabama Tuscaloosa
    The most luminous X-ray sources in nearby elliptical galaxies are likely black hole low-mass X-ray binaries (BHLMXBs). In the Milky Way, such systems are always transient, and with the exception of GRS 1915+105 have burst durations on the order of weeks or months. However, the low duty cycle of short-duration outburst BHLMXBs makes it improbable that any one source would be caught in an outburst during a single snapshot observation. Long-duration outburst BHLMXBs, although much rarer, would be detectable in a series of snapshot observations separated by several years. Our analysis of multi-epoch Chandra observations of the giant elliptical galaxies NGC 1399 and M87 separated by 3.3 and 5.3 yr, respectively, finds that all 37 luminous (>8 x 10(38) erg s(-1)) X-ray sources that were present in the first epoch observations were still in outburst in all of the following observations. Many of these probable long-duration outburst BHLMXBs reside within globular clusters of the galaxies. Conversely, no definitive short-duration outburst BHLMXBs were detected in any of the observations. This places an upper limit on the ratio of short-to-long-duration outbursters that is slightly lower, but consistent with what is seen in the Milky Way. The fact that none of the luminous sources turned off between the first and last epochs places a 95 per cent lower limit of 50 yr on the mean burst duration of the long-duration outburst sources. The most likely scenario for the origin of these sources is that they are long-period (> 30 d) black hole binaries with a red giant donor, much like GRS 1915+105. However, unlike GRS 1915+105, most of the sources show only modest variability from epoch to epoch.