Mass Measurements of Black Holes in X-Ray Transients: is there a Mass Gap?
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Mass Measurements of Black Holes in X-Ray Transients: is there a Mass Gap?
Will M. FarrNorthwestern University, CIERA
(See Kreidberg, Bailyn, WMF, Kalogera, arXiv:1205.1805)
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The Mass Gap• Strange, because
main-sequence mass distribution rising at low M. (Özel, et al (2010))
• Not expected in evolutionary theory (Freyer & Kalogera (2001))
• Provides a clue about SNe? (Belczynski, et al (2011))
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Mass Gap History I: Bailyn, et al (1996)
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Özel, et al (2010)
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Farr, et al (2011)
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A Systematic Effect?
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Mass Measurements (A Theorist’s Perspective)
• Uncertainties in inclination can have a large effect on mass.
• Uncertainties in mass ratio are relatively unimportant.
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Measuring Inclinations• Measure inclination by
looking at ellipsoidal variations in light from secondary.
• Any additional non-stellar light (NSL) reduces variation => lower inclination.
• Lower inclination => higher masses.
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Cantrell, et al (2010): A0620
• Measurements of inclination bimodal
• Lower in active state than passive
• Can we model the NSL that is contaminating the active phase?
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Modeling the Active State
• The NSL is mostly due to the disk, and is therefore correlated in time.
• Produce synthetic NSL, and examine star-only fits to inclination
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Inclination Corrections
Generate a fitting formula for inclination correction based on synthetic A0620 NSL.
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Adjust NSL Fraction• Different spectral
types• Different mass ratios• Different inclinations
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Corrected Masses
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Which Systems Could Matter for Mass Gap?
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Corrected Mass Distribution
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Corrected Minimum Mass
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Why You Should Trust J0422+32’s Correction• One of smallest and coolest (M type) secondaries
in sample.• Sometimes observed to have no ellipsoidal
variations (Reynolds, et al (2007)).• Very faint in quiescence: R ~ 21.• Points toward ease of NSL distortion.• Distortion may not mimic A0602, though?• Further observations warranted.
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4U 1543-47 Could Still Contribute
• Very low inclination: small changes mean a lot.• Conflicting inclination measurements (Orosz, et al
(1998) vs. Orosz, et al (2002)).• Small ellipsoidal variations => precise
observations required.• Data currently in the pipeline---stay tuned!
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Conclusions• Previous studies found
strong evidence for a mass gap from 3 to 5 MSun.
• Careful study of effects of NSL suggest that inclinations may be systematically underestimated.
• Applying sensible correction to data eliminates mass gap.
• Other properties of distribution remain unchanged.