Ultraluminous Xray sources: highlights on NGC1313 X2 and M82 X1

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Ultraluminous X-ray sources highlights on
NGC1313 X-2 and M82 X-1
Paola Mucciarelli

• Department of Astronomy, University of Padova
• Department of Physics, University of Padova
• INAF-Astronomical Observatory of Padova

• In collaboration with
• Zampieri, Turolla, Treves, Falomo, Chieregato,
  Kaaret, di Stefano, Casella, Belloni Ranalli.

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Outline

• NGC1313 X-2
• X-ray spectrum
• Optical counterpart
• M82 X-1
• X-ray spectrum
• timing properties

PM, High energies in the Highlands 27 June - 1
July 2005
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NGC1313 X-2 introduction

• NGC1313 is a nearby spiral galaxy hosting two
  ULXs, NGC1313 X-1 and X-2, and the interacting
  supernova 1978K.
• NGC1313 X-2 is a well known ULX, variable on a
  timescale of months.
• Assuming that at maximum the source radiates at
  the Eddington limit, a mass of 50 M? is derived
  for the compact remnant.

NGC1313 X-1
NGC1313 X-2
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July 2005
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NGC1313 X-2 X-ray spectrum

• The XMM spectrum shows statistical evidence for a
  MCD component with kT0.2 keV
• (Miller et al. 2003 ,Zampieri et al. 2004)

Assuming that the temperature of the MCD
component represents the maximum temperature of a
standard accretion disk we obtain
MBH 90f4 M?

• f (1.6-1.7) color correction factor

PM, High energies in the Highlands 27 June - 1
July 2005
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NGC1313 X-2 photometry

• On the basis of a Chandra observation (19 ks)
  and accurate astrometry, we derived the source
  position with an uncertainty of 0.7?? (1?). In an
  ESO 3.6m R band image we identified object C as
  the optical counterpart (Zampieri et al., 2004).

Recently, we analyzed also archive ESO VLT (BVR)
band images. Thanks to the higher resolution of
these images, we were able to resolve object C in
two distinct point-like sources, C1 and C2,
separated by 0.7". Taking into account Galactic
absorption
C1 R23.5, (B-V)0-0.2 (V-R)0-0.2
C2 R23.4, (B-V)0gt1.9 (V-R)00.4

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July 2005
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NGC1313 X-2 results
C1
Colors consistent with a B4-O I or B9-O3 V. From
the bolometric magnitude we conclude that object
C1 is very likely a B0-B4 supergiant in NGC 1313
with L8x1037erg s-1. If C1 is the counterpart,
the ULX is an high mass X-ray binary where the
donor star is a supergiant of 20-25 M?.
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July 2005
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NGC1313 X-2 results
C2

• Non stellar colors
• B-V implies a spectral type later than M6 V or M2
  I
• V-R and R-I (Liu et al. 2005) imply a F2-G2 I or
  F0-G8V
• A reddened star? Not using Cardelli's extinction
  law.
• An AGN?

• A preliminary analysis of the optical spectrum of
  object C1C2 (both inside the slit) shows that no
  AGN-like emission lines are present.
• fX/fR 2000-3000, too high.
• Inferred column density higher than that derived
  from X-ray.

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July 2005
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M82 X-1 XMM spectrum
New XMM EPIC observation of 105 ks (75
ks flares free), taken on April 2004

• Strong contamination from the host starburst
  galaxy up to 2-3 keV (as noted by Strohmayer
  Mushotzky 2003) and from point sources (Matsumoto
  et al. 2001).

• Our best fit implies a MCD component with kT
  0.17 keV. If this component is due to an
  accretion disk, its temperature gives an estimate
  of the BH mass of about 200f4 M?.

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July 2005
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M82 X-1 XMM timing

• The PDS of a 66ks data segment reveals the
  presence of a QPO at 113 mHz with parameters
  similar to those of the 56 mHz QPO detected by
  Strohmayer Mushotzky 2003.
• The frequency of the QPO decreases by 10.8
  between the first and second part of the
  observation.
• The fractional rms is higher above 4 keV.

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July 2005
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M82 X-1 XMM timing

• 30 archive RXTE PDS were extracted in the 2-13keV
  energy range
• 7 show the presence of a single QPO at different
  frequencies

• The frequency distribution is suggestive of
• a harmonic 123 ratio.

The properties of the individual QPOs observed in
M82 X-1 (rms up to 18, Q greather than 4,
variability) are reminiscent of those of
low-frequency QPOs observed in Galactic BHCs.
Scaling the frequency inversely to the BH mass,
the observed frequency range would yield a MBH
anywere in the range of 10-1000M?.
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July 2005
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Conclusions
NGC1313 X-2

• Two optical counterparts are detected (on VLT
  images)inside the Chandra error box.
• C1 the scenario in Zampieri et al 2004 would be
  confirmed.
• C2 both cases are unlikely a supergiant in
  NGC1313 or an AGN.
• Follow up optical spectroscopy under optimal
  seeing conditions and with the slit along the
  line of conjunction C1-C2 is crucial to
  disentangle the emission from the two object.

M82 X-1

• The MCD temperature is suggestive of an IMBH with
  mass higher than 200 M?.
• The properties of the individual QPOs observed in
  M82 X-1 are reminiscent of those of low-frequency
  QPOs. Scaling the frequency inversely to the BH
  mass, the observed frequency range would yield to
  a MBH anywere in the range of 10-1000M?.

PM, High energies in the Highlands 27 June - 1
July 2005