12' Chandra Directors Office

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Our Local ULX? IC 10 X-1 and NGC 300 X-1
A.H. Prestwich (CfA) S. Carpano (ESA) R. E.
Kilgard (Weslayan) A.M.T. Pollock (ESA) T. P
Roberts M.J. Ward (Durham) With special
thanks to Ramesh Narayan, Jeff McClintock
Vicky Kalogera
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Our Local ULX, Prestwich, Carpano et al.
IC 10 X-1 and NGC 300 X-1

• IC 10 X-1
• Brightest X-ray source in Local Group Galaxy IC
  10, Lx2?1038 ergs/s
• IC 10 our local group starburst
• dwarf galaxy
• low metalicity (Z0.2Z?)
• Optical counterpart luminous WR star (Bower
  Brandt 2004, Clark Crowther 2004)

IC 10, BVH? composite Local Group Survey Massey
et al

• NCC 300 X-1
• Brightest X-ray source in NGC 300, Lx2?1038
  ergs/s
• Counterpart identified by Carpano et al to be WR
  star

Both sources thought to be rare example of He
star ?CC predicted by van den Heuvel Loore
1973(Cyg X-3 only galactic example) also
candidates for ULX?
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Our Local ULX, Prestwich, Carpano et al.
Discovery of Eclipses

• IC 10
• 90 ks Chandra observation split into 2?45 ks,
  separated by 2 days
• Evidence for eclipses.but how many cycles?
  (Wang et al 2005)
• Monitored with SWIFT XRT for 10 days (1 ks per
  orbit)
• Peak in the periodogram at 34.4 hours

• NCC 300 X-1
• SWIFT TOO awarded to S. Carpano, period 33 hours.

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Our Local ULX, Prestwich, Carpano et al.
Mass Limits

• IC 10
• Spectroscopy of the He II 4686 A line shows
  evidence for a 750 kms-1 velocity shift
• Assume this is due to radial velocity

• The Mass Function
• depends on observables radial velocity (K2) and
  period (P)
• is the MINIMUM mass for compact object
• f(M)7.8M?
• Assume i90 deg, and donor mass 20-35M?,
• compact object mass 26-35M?
• Using an indirect argument Carpano et al (2007)
  estimate the black hole mass in NGC 300 X-1 gt13M?
• THE MOST MASSIVE STELLAR BLACK HOLES KNOWN!

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Our Local ULX, Prestwich, Carpano et al.
Accretion Mechanism - wind or Roche Lobe
Overflow?

• Keplers Law, assuming i90
• aseparation between BH and donor
• IF donor fills Roche Lobe and accretion is via
  RLOF
• Roche Lobe radiusdonor radius, use standard
  values for WR stars
• Use Eggleton (1983) approximation for separation
  in term of mass ratio, and assume donor mass 35M?

For any reasonable values of M1 (1-1000M?), the
period should be a few hours! The observed
period is INCONSITENT with RLOF
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Our Local ULX, Prestwich, Carpano et al.
Do the theorists understand how to make a gt20M?
Black Hole?

• MZAMS vs Mfinal for SINGLE star
• Maximum remnant 27 M?, if metallicity low
• ZIC10 0.2 Z?
• Mass transfer from donor may increase remnant
  mass, but probably not significant for IC 10 X-1
  and NGC 300 X-1
• Conclude
• BH masses consistent with theoretical
  expectations if metallicity low
• Close to the maximum theoretical BH mass

Belczynski, Sadawski Rasio 2004
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Our Local ULX, Prestwich, Carpano et al.
X-ray spectroscopy and the Connection with
ULX (work in progress, wild speculation)

• Chandra spectrum of IC 10 X-1 fit by power law,
  ?1.98
• ??2162.5 for 175 DOF (reduced ?20.92)
• Evidence for thermal residuals (WIP)
• NGC 300 X-1 X-ray spectrum very similar
• Are IC 10 X-1 and NGC 300 X-1 BHB in the hard
  (formerly low/hard) state? Possibly close to
  intermediate.
• Consistent with X-ray spectrum
• Consistent with X-ray luminosity. If BH
  mass20-35M?, Lx2.6-4.5?1038 ergs s-1 for 10
  Eddington
• If accretion rate increases to Eddington,
  Lx3-5?1039 ergs s-1

Close to modest ULX, may get higher luminosities
if accretion super-Eddington
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Our Local ULX, Prestwich, Carpano et al.
Summary and Conclusions

• SWIFT observations of IC 10 X-1 and NGC 300 X-1
  show they are eclipsing binaries, periods 34
  hours.
• Periods inconsistent with Roche Lobe Overflow
• Archival optical spectra SWIFT period can be
  used to constrain the mass of the BH in IC 10 X-1
• F(M)7.8 M?
• M 20-35 M?
• Mass of BH in NGC 300 X-1 similar
• If confirmed, these are the most massive stellar
  BH known! Consistent (just!) with theoretical
  expectations if metallicity low
• Are IC 10 X-1 and NGC 300 X-1 BHB in the hard
  (formerly low/hard) accretion state? If so,
  transition to the high state/super-Eddington
  would turn them into ULXs
• Do these objects make up some of the ULX
  population?
• Consistent with ULX association with star
  formation
• Formed by normal stellar evolutionary processes
• Rare (Ergma Yungelson 1998)
• Consistent with picture of ULXs as super
  accretion sources (talks by Roberts and Soria
  this conference)

CXC