PhD Thesis (PDF) - Department of Astronomy - University of Virginia

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Much of the work in this thesis concerns the LMXBs in relatively nearby early- type galaxies. The work was made possible by the high spatial resolution and high sensitivity of the Chandra X-ray Observatory. Prior to the launch of Chandra, LMXBs were mainly studied in our galaxy (the Milky Way) and in the companion galaxies (the Large and Small Magellanic Clouds, and the Andromeda galaxy, M31). Studies of LMXBs in the Milky Way and in E/S0s are very complementary. Galactic LMXBs can be studied in great detail during both active (LX 10 36 ergs s −1 ) and quiescent ( 10 34 ergs s −1 ) states across all wavelengths. Optical/IR studies of individual LMXBs can provide important information about the donor star. Radio observations can detect the presence of jets, allowing the study of the connection between accretion physics and jet formation. Detailed variability and spectral studies can allow the orbital parameters to be derived, which allows the masses of the compact object and donor star to be determined. The X-ray spectra and time variability can be measured in great detail, which gives information on the accretion physics. All of this can provide a detailed understanding of the formation and evolution of a small sample of Galactic LMXBs. However, there are several limitations in studying Galactic LMXBs. Many are observed through the extinction of the Galactic disk, which can make it difficult to detect the systems optically. As a result, distances are known for only a small subset of Galactic LMXBs, which implies that their luminosities and other properties are poorly known. The absorption columns vary from source to source, and in many cases is not known for a given LMXB. It is difficult to observe the whole Galaxy at once, so one may miss interesting sources, and we cannot have a complete census of the LMXB population of the Milky Way at a single instance. Perhaps most importantly the size of the observed sample of Galactic LMXBs is very limited, particularly if one considers the more luminous sources. With so few sources, we may 6
not get a complete picture of the LMXB phenomena, and may completely miss rare but very powerful types of LMXBs. For observations of nearby E/S0 galaxies, we typically can only detect bright active LMXBs ( 10 37 ergs s −1 ), and these LMXBs cannot be studied in as great a level of detail as in the Milky Way. However, there are distinct advantages to E/S0 observations. All LMXBs in a given E/S0 share a common Galactic absorption column and a common distance, which makes it easy to determine accurate luminosities. In most cases, nearby E/S0 galaxies fit within the field-of-view (FOV) of a Chandra observation, and thus all of the LMXBs in a given galaxy can be observed at the same time. Thus, the instantaneous luminosity function (LF) of LMXBs can be easily determined. Furthermore, individual E/S0s often have 50–200 sources brighter than ∼ 5×10 37 ergs s −1 , as opposed to the small number of bright sources in the Galaxy. There are ∼30 early-type galaxies with good Chandra observations. Thus, it is much easier to study the properties of the population of LMXBs in external galaxies, and to do statistical studies. Moreover, there is a much greater chance of detecting rare but luminous states of these systems. 1.4 The Galactic Connection Between Low-Mass X-ray Binaries and Globular Clusters Except for some galactic nuclei, the stellar densities in the field in galaxies are quite low. For example, the local stellar mass density near the Sun is ∼ 0.1 M⊙ pc −3 (Binney & Merrifield 1998). At such low densities, individual stars in galaxies do not interact with one another, either physically (collisions or tidal interactions) or even gravitationally, unless they are formed together in a binary system. Thus, in the field 7
Page 1 and 2: LOW-MASS X-RAY BINARIES, DIFFUSE GA
Page 3 and 4: smaller GCs are more likely to cont
Page 5 and 6: GO2-3099X, GO3-4099X, AR3-4005X, GO
Page 7 and 8: her room (my apologies to her offic
Page 9 and 10: US Court expert from India), for al
Page 11 and 12: Table of contents Abstract ii Ackno
Page 13 and 14: 5.2.1 Chandra X-ray Observatory . .
Page 15 and 16: List of Figures 1.1 Hubble Tuning F
Page 17 and 18: List of Tables 1.1 Galactic Low-Mas
Page 19 and 20: Chapter 1 General Introduction 1.1
Page 21 and 22: Fig. 1.1.— Hubble Tuning Fork, co
Page 23: 2000). In most HMXBs, the accreted
Page 27 and 28: this, the result of dynamical inter
Page 29 and 30: is the Advanced CCD Imaging Spectro
Page 31 and 32: Chapter 2 Chandra Observations of L
Page 33 and 34: keV (Sarazin et al. 2000, 2001). Wi
Page 35 and 36: agreed with positions from the USNO
Page 37 and 38: 24:00 22:00 7:20:00 18:00 16:00 18:
Page 39 and 40: Table 2.1. Discrete X-ray Sources i
Page 41 and 42: Table 2.1—Continued Source d Coun
Page 43 and 44: Table 2.2. Discrete X-ray Sources i
Page 45 and 46: Table 2.2—Continued Source d Coun
Page 47 and 48: optical/IR positions of R.A. = 12 h
Page 49 and 50: log N(>L) 2.0 1.5 1.0 0.5 0.0 NGC 4
Page 51 and 52: luminosity function for luminositie
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Page 55 and 56: 2.4.5 Variability We searched for v
Page 57 and 58: Number 10 8 6 4 2 NGC 4365 Optical
Page 59 and 60: LMXBs has an effective radius of 12
Page 61 and 62: component (“MEKAL”) was used fo
Page 63 and 64: Table 2.4. X-ray Spectral Fits of N
Page 65 and 66: Fig. 2.9.— Top panels: Cumulative
Page 67 and 68: we extended the spectrum down to 0.
Page 69 and 70: We also examined whether the unreso
Page 71 and 72: esolved sources in the galaxy. This
Page 73 and 74: temperature ∼0.3 keV. Matsumoto e
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log I X (counts/sec/arcmin 2 ) -1.0
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∼45% of the counts are resolved i
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Chapter 3 Chandra Observations of D
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noninteracting members (de Vaucoule
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used for spectroscopic analysis. We
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02:00.0 03:00.0 04:00.0 05:00.0 06:
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Table 3.1. Discrete X-ray Sources i
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Table 3.1—Continued d a Count Rat
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We also attempted detections in mul
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sociated with extended X-ray or opt
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Fig. 3.3.— Histogram of the obser
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chip. The number of ULX candidates
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these luminosities among previously
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to 2-6 keV. Since the 6-10 keV rang
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absorption and varying power-law in
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counts occur within ∼ 4 ks. Sourc
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log I X (counts/sec/arcmin 2 ) 0.5
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tion), and βouter = 0.36 +0.01 −
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the east and northeast of NGC 1600.
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group, we assumed that they were at
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the group gas than we calculate fro
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04:55 -5:05:00 05 -5:05:10 15 -5:05
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for the spectrum: “Field” impli
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90% confidence level errors. Bracke
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we adopted the power-law model as o
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sources could be a non-trivial sour
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jection to include the emission fro
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Fig. 3.13.— Estimated gas and gra
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ackground source population cannot
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NGC 1600 that has a small spatial s
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(HMXBs). LMC X-4, an HMXB pulsar, h
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searched for the shortest time tn o
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with NGC 4697. Columns (1)-(4) list
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duration, ∆tflat, beginning at a
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the uncertainties quoted do not inc
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to persistent rate for short flares
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Chapter 5 Multi-Epoch Chandra X-ray
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the field, these different populati
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luminous (MB < −20) elliptical (E
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Although Chandra is known to encoun
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42:00.0 44:00.0 46:00.0 48:00.0 -5:
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Fig. 5.3.— Adaptively smoothed Ch
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1 × 10 −5 count s −1 arcsec
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Table 5.1—Continued Source R.A. D
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source list against which to regist
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ate from Observation 0784 alone (Pa
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Table 5.2. : Optical Properties of
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actually be an AGN. Sources 79, 80,
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two potential GC counterparts. We l
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Table 5.3—Continued X-ray Source
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Fig. 5.6.— Color (G475−Z850) -
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mass segregation of GCs with the sa
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Table 5.4. Fits to the Expected Num
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dependence are allowed to vary. Var
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NGC 4697 to convert the observed so
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Table 5.6—Continued Source LA LB
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Table 5.6—Continued Source LA LB
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Table 5.7. Combined Luminosities &
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Table 5.7—Continued Source Not De
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Fig. 5.8.— Cumulative luminosity
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LF, there are enough datapoints tha
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Fig. 5.10.— Cumulative luminosity
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Fig. 5.11.— Merged luminosities (
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Fig. 5.12.— X-ray color-color dia
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5.9 Spectral Analysis We performed
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some data loss, it allows for direc
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for 2 dof and the f-test indicates
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ple to LMXBs interior to that semi-
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est-fit (χ 2 = 56.4 for 65 dof) by
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5.10.1 Intraobservation Variability
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Fig. 5.14.— Binned lightcurve usi
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Table 5.10. Possible Flaring Source
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Fig. 5.16.— Cumulative lightcurve
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pairs of observations. In Figure 5.
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Table 5.11—Continued Source PL,AB
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Fig. 5.17.— Percentage of Analysi
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dofs and the number of combinations
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Table 5.12—Continued Source Obs.S
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of states as transient candidates.
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Long-Term Hardness Ratio Variabilit
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In the final observation, there wer
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limits). The 0.3-10 keV X-ray lumin
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atio is expected only from the most
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eak (Kim et al. 2006a). We find mar
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LMXBs in Galactic GCs (Heinke et al
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in the field of the Milky Way and a
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6.2 Sample 6.2.1 Galaxy Sample Tabl
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Table 6.2. Properties of Chandra Ob
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identification of point sources, AC
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the QE degradation in the ACIS dete
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Table 6.3—Continued Galaxy NX LX,
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The positions of the GCs were used
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Fig. 6.2.— Scatter plot of GC gal
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Fig. 6.3.— Scatter plot of estima
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Fig. 6.5.— Scatter plot of estima
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isophote from the galaxy optical su
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6.3.1 Luminosity and Mass Prior obs
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compare their χ 2 fits to test whi
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GCs without LMXBs; however, there a
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following dependence on GC properti
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of this probability with individual
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Fig. 6.9.— Identical to Figure 6.
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We used the indices from our best-f
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(20.3 for half-mass radius, both wi
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most are steeper than Z ∼0.4 . Ei
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Fig. 6.11.— (Left:) Two-dimension
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differently by the properties of th
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dependent IMF (Grindlay 1987), or e
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a 1.4M⊙ neutron star (NS). They s
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equivalent to a dependence on the b
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variability timescale, but it is no
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7.2.1 X-ray Properties of the GC-LM
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of the metallicity dependence. As i
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Appendix A Encounter Rate Parameter
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Fig. A.1.— Dimensionless quantity
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and four; these positions do not in
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Table B.1—Continued RA Dec. d GC
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Table B.2. Optical Properties of Gl
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investigations into improving the h
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C.4 Sivakoff Signature Soy Sauce Sk
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Blanton, E. L., Sarazin, C. L., & I
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Frogel, J. A., Persson, S. E., Matt
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Johnston, H. M. & Verbunt, F. 1996,
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Makishima, K. et al. 2000, ApJ, 535
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Porter, A. C. 1993, PASP, 105, 1250
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Verner, D. A., Ferland, G. J., Kori
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