A search for X-rays from the long-duration microlensing event MACHO-96-BLG-5

Yoshitomo Maeda, Aya Kubota, Yoshihito Kobayashi, Akiharu Itoh, Hideyo Kunieda, Yuichi Terashima, Yohko Tsuboi

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13 Citations (Scopus)


MACHO-96-BLG-5 was a microlensing event of exceptionally long duration, lasting ∼800 days, which is suggestive of a stellar-mass black hole for the lens. With a 9.8 ks Chandra ACIS-S observation, we detected no X-ray events associated with the position of MACHO-96-BLG-5. An upper limit is estimated as 4.6 counts at the 99% confidence level. By assuming an absorbed power law spectrum with a photon index Γ = 1.4-2.0, the upper limit on the 0.3-8 keV luminosity is estimated as (7-8) × 1029 ergs s-1 at an assumed distance of 1 kpc. The corresponding Eddington ratio is (8-9) × 10-10 for a black hole of 6 M. The luminosity is lower than observed for quiescent black hole binaries in our Galaxy and is consistent with a scenario, previously suggested by Bennett et al., in which the lens for MACHO-96-BLG-5 is an isolated stellar-mass black hole, although other possibilities are not ruled out.

Original languageEnglish
Pages (from-to)L65-L68
JournalAstrophysical Journal
Issue number1 II
Publication statusPublished - 2005 Sept 20
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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