Deep-survey constraints on X-ray outbursts from galactic nuclei

B. Luo, W. N. Brandt, A. T. Steffen, F. E. Bauer

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13 Scopus citations


Luminous X-ray outbursts with variability amplitudes as high as ∼ 1000 have been detected from a small number of galactic nuclei. These events are likely associated with transient fueling of nuclear supermassive black holes. In this paper we constrain X-ray outbursts with harder spectra, higher redshifts, and lower luminosities than have been studied previously. We performed a systematic survey of 24,668 optical galaxies in the Chandra Deep Fields to search for such X-ray outbursts; the median redshift of these galaxies is ∼0.8. The survey spans 798 days for the Chandra Deep Field-North, and 1828 days for the Chandra Deep Field-South. No outbursts were found, and thus we set upper limits on the rate of such events in the universe, which depend on the adopted outburst X-ray luminosity. For an outburst with X-ray luminosity ≳ 1043 ergs s_1 and a duration of 6 months, the upper limit on its event rate is ∼10-4 galaxy-1 yr-1, roughly consistent with theoretical predictions. Compared to previous survey results, our harder band and deeper survey suggests that the outburst rate may increase by a maximum factor of 10 when considering both obscured X-ray outbursts and redshift evolution from z ∼ 0 to z ∼ 0.8. Our results also suggest that the X-ray luminosity function for moderate-luminosity active galactic nuclei is not primarily due to stellar tidal disruptions.

Original languageEnglish (US)
Pages (from-to)122-132
Number of pages11
JournalAstrophysical Journal
Issue number1
StatePublished - Feb 10 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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