Download Chandra Observations of Low Mass X

Chandra Observations of
Low Mass X-ray Binaries,
ULXs, and Globular Clusters
in Elliptical Galaxies
Craig Sarazin
University of Virginia
Chandra Observations of Early Type Galaxies
and Collaborators
NGC 4697 – E6 – Sarazin, Irwin, & Bregman 2000, 2001
NGC 4365 – E3 – Sivakoff, Sarazin, & Irwin 2003
NGC 4649 (M60) – E2 – Randall, Sarazin, & Irwin 2003
NGC 1553 - S0 – Blanton, Sarazin, & Irwin 2003
NGC 4382 (M80) – S0 – Sivakoff, Sarazin, & Irwin 2003
NGC 1291 – Sa bulge - Irwin, Sarazin, & Bregman 2002
NGC 1600 – E3 - Sivakoff, Sarazin, & Carlin 2003
NGC 533 – E3 – Carlin, Sarazin, & Sivakoff 2003
Definition of ULXs
Because of interest in connection to IMBHs, take a
conservative definition:
LX > 2 x 1039 erg/s, broad-band (0.3-10 keV)
Macc ≳ 20 M → not a stellar black hole or NS
if Eddington limited
(Irwin et al. 2004)
NGC 4697
E6
Nearest optically luminous, X-ray faint elliptical
Chandra X-ray Image of NGC 4697
~ 90 % of X-ray flux resolved into point sources
Most of X-rays from X-ray faint ellipticals
= point sources
Point Sources
Low Mass X-ray Binaries (LMXBs)
Wavelet detection (CIAO WAVDETECT)
Significance Threshold < 10-6
(< 1 spurious source per galaxy)
Flux SNR > 3 s
Limits ≳ 3 x 10-4 cts/sec
≳ 11 counts
(LX ≳ 5 x 1037 ergs/sec)
50 – 300 LMXBs / galaxy
(~10 BG sources)
Total X-ray Spectrum of LMXBs
LMXBs
Hard Spectrum
Bremsstrahlung kTbrem ~ 7 keV, or
Power-law, G ~ 1.5 (Sarazin et al. 2000; Irwin et
al. 2003)
X-ray Spectra of Bright LMXBs
in Early-Type Galaxies
Exception: sources with 1039 ≤ LX ≤ 2 x 1039
have softer spectra (Irwin et al. 2003)
High/soft state in BH binaries?
X-ray “Colors”
H21 = (M – S)/(M + S)
H31 = (H – S)/(H + S)
S = soft band counts, 0.3 – 1 keV
M = medium band counts, 1 – 2 keV
H = hard band counts, 2 – 10 keV
H31
X-ray Colors – NGC 4697
H21
X-ray Colors – NGC 4697
G = photon index
0.0
H31
1.2
2.0
3.2
H21
X-ray Colors – NGC 4697
AGN?
Supersoft
sources
LMXBs
AGN?
LMXB?
Supersoft Sources
0 – 5 found per galaxy
No X-rays hn  1 keV
(see also Di Stefano et al., also quasi-soft
sources)
kTeff ≈ 70 (40 – 100) eV
LX = 1 – 4 x 1038 ergs/s (0.3 – 10 keV)
Lbol ≈ 0.3 – 2 x 1039 ergs/s > LEdd (1.4 M WD)
Not accreting WDs!
Are E galaxy supersofts accreting,
intermediate mass BHs?
Variable Sources
During Chandra
observations
~ 10 hours
Doing repeat
Chandra
observations
(NGC 4697, 5 obs.,
t ~ min → 5 years)
Spatial Distribution of LMXBs
distribution LMXBs ≳ distribution stars
Luminosity Function of LMXBs
NGC 4697
Broken Power-Law?
broken power-law
power-law
fit by broken power-law
(Sarazin et al. 2000)
Broken Power-Law?
Lb
BHs?
Mainly NSs?
Lb ≈ 3 x 1038 ergs/s ≈ LEddington (1.4 M NS)
Cutoff Power-Law?
Lcutoff ≈ 1039 ergs/s ≈ LEdd (largest stellar BH)
(Sivakoff et al. 2003; Jordan et al 2004)
LMXBs and Globular Clusters (GCs)
High fraction of
LMXBs are in GCs
20 - 70%
But, most areas of most
galaxies lack GC
catalogs (require HST
observations)
also, NGC 1399 (Angelini
et al. 2001), NGC 4472
NGC
(Kundu et al. 2002),
4365
M87 (Jordan et al. 2004)
o = LMXBs
o = GC
LMXBs
LMXBs and GC – Virgo Survey
Lack of HST GC catalogs for nearby ellipticals
HST Cycle 11 Large Project: ACS Virgo Cluster
Survey (PI: Coté) → GCs
Chandra Cycles 4 & 5 Virgo Cluster Survey
HST Cycle 13 Fornax Cluster Survey
(PI: Jordan)
~100 elllipticals with LMXBs and GC
LMXBs and Globular Clusters (GCs)
Fraction LMXBs in GCs ~ 20 - 70%
Fraction of optical stars in GCs ~ 0.1 %
Optical stars in GCs ~ 500 x more likely to be in
LMXB than field stars (same true for Galaxy,
M31)
LMXBs made by stellar interactions in GCs
(Clark 1975; Fabian et al. 1975; Hills 1976)
Are All LMXBs Made in GCs?
LX(LMXBs) ∝ Number of GCs (not galaxy luminosity)
(Grindlay 1984; Sarazin et al. 2001; White et al. 2002;
Irwin et al. 2003)
Fraction LMXBs in GCs vs. Hubble Type
Sp bulges
fraction LMXBs in
GCs
10%
S0
E
18% 47%
cD
70%
SN ≡ No. GCs/
galaxy optical
luminosity
1.2
2.6
5.4
13
fraction GCs with
LMXBs
3%
3%
4%
4%
Two populations: GC LMXBs and field LMXBs?
LMXBs vs. GC Properties
LMXBs prefer brighter GCs (Kundu et al. 2002;
Sarazin et al. 2003)
Probability of LMXB ∝ Lopt ∝ number of
possible donor stars
LMXBs vs. GC Properties (cont.)
LMXBs prefer red GCs
Due to:
Younger GCs?
More metal-rich GCs?
More metal-rich (Kundu et
al. 2003)
LMXBs vs. GC Properties (cont.)
LMXBs prefer dense GCs?
M87 (Jordan et al. 2004)
ProbX ∝ n✳ N✳ / σ (not just N✳)
∝ rate of exchange or tidal interactions
LMXBs made by stellar interactions in GCs
LMXBs vs. GC Properties (cont.)
No strong differences in X-ray
properties of LMXB in GCs
vs. field, but
Luminous LMXBs avoid GCs?
BH hard to retain in GCs?
True in our Galaxy?
(Portegies Zwart & McMillan
2000)
Spatial Distribution of LMXBs and GCs
In E galaxies, GCs are “missing” from inner regions
Due to:
didn’t form in inner regions?
were destroyed in inner regions?
Destroyed → leave stars behind
LMXBs = detectable population from GCs
Spatial distribution of LMXBs, GCs, and stars
information on destruction of GCs,
fraction of LMXBs made in GCs
Do Early-Type Galaxies
Contain ULXs?
E/S0s have many sources with LX < 2 x 1039 erg/s
(0.3-10 keV) (Colbert & Ptak 2002)
but . . .
N(LX > 2 x 1039 erg/s) ≈ N(BG sources)
Density ≈ constant on sky
(Irwin et al. 2004)
Do Early-Type Galaxies
Contain ULXs?
No evidence for real ULXs in E/S0s ?
(Irwin et al. 2004)
Do Early-Type Galaxies
Contain ULXs?
NGC 720, NGC 1407: Distances poorly known,
could be < 2 x 1039
some are BG AGN
(Arp et al. 2004)
NGC 1600: 21 ULXs, expect
10 BG sources (but
cosmic variance?)
NGC 1399: two ULXs in
GCs, one marginal,
NGC1600
multiple sources?
(Sivakoff et al. 2004)
Spiral Galaxy ULXs and Star Clusters
Many ULXs in star forming galaxlies associated
with young and intermediate age star clusters
Examples:
Antennae (Zezas, Fabbiano, et al., Clark et al.)
M82-X7 in cluster MGC-11 (Kaaret et al. 2001)
Are ULXs in or just near to young clusters?
IMBHs or runaway binaries with lower mass
BHs?
Conclusions: LMXBs, ULXs, and
GCs in X-ray Faint Ellipticals
 Most of X-ray emission is from LMXBs, large populations
hard integrated spectrum
some supersoft sources → IMBHs
 Luminosity function: “Eddington break” Lb or high
luminosity cutoff
BHs vs. NSs? Stellar BHs vs. IMBHs
 High fraction of LMXBs in GCs
fraction increases Hubble sequence
Sp bulges → S0 → E → cD
 No real ULXs in early-type galaxies?
Associated with star formation only?
 New window on stellar evolution in ellipticals
1st detections of NSs and stellar BHs in bright E’s
Proof that Es once had many OB stars