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

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5.8 Hardness Ratios The spectral properties of sources can be crudely characterized by hardness ratios or X-ray colors (e.g., Paper I; Paper II). We defined hardness ratios of H21 ≡ (M − S)/(M + S), H31 ≡ (H − S)/(H + S), and H32 ≡ (H − M)/(H + M), where S, M, and H are the total counts in the soft (0.3–1 keV), medium (1–2 keV), and hard (2–6 keV) bands (Sivakoff et al. 2004). Hardness ratios without superscripts are the measured values; we use the superscript 0 to indicate the intrinsic hardness ratios, correcting for Galactic absorption and QE degradation in the Chandra ACIS detectors. The counts in each band are corrected assuming the best-fit Chandra X-ray spectrum of the inner resolved sources (a < aeff: Table 5.5, row 3). Since the different observations had different QE degradations, we adopted the following technique for correcting the observed counts in a band. Let Ni,j,k be the net counts for source i in band j during observation k, and let Cj,k be the absorption and degradation correction to counts for observation k in band j. (The QE degradation was assumed to be independent of position on the detector and thus the same for all sources within a given observation.) The combined correction for source i in band j is given by 〈Ci,j〉 ≡ (Cj,kNi,j,k)/ Ni,j,k, where the sums are only performed over observations k k where Ni,j,k > 0. We require that Ni,j,k > 0 because there is no correction to the source hardness when a source is not emitting at a detectable level. Having determined the appropriate correction, the corrected number of counts for source i in band j is N 0 i,j = 〈Ci,j〉 k Ni,j,k, where the sum is now over all observations. The corrected band counts are then used to calculate the corrected hardness ratios. We also combined Monte Carlo simulations of the observed counts in the source and background apertures with the count corrections to calculate the 1σ confidence intervals for the hardness ratios. (When no counts are observed, we set the expected number of counts in the 186
Fig. 5.12.— X-ray color-color diagrams H 0 31 vs. H 0 21 (left) and H 0 32 vs. H 0 21 (right) for the combined counts from all observations for the Analysis Sample sources. Here, H 0 21 ≡ (M 0 −S 0 )/(M 0 +S 0 ), H 0 31 ≡ (H 0 −S 0 )/(H 0 +S 0 ), and H 0 32 ≡ (H 0 −M 0 )/(H 0 + M 0 ), where S 0 , M 0 , and H 0 are the counts in the soft (0.3–1 keV), medium (1–2 keV), and hard (2–6 keV) bands, corrected for the effect of Galactic absorption and QE degradation according to the best-fit spectra of resolved sources. The area of each circle is proportional to the observed number of net counts. The solid curve and large diamonds show the hardness ratios for power-law spectral models; the diamonds indicate values of the power-law photon number index from Γ = 0 (upper right) to 3.2 (lower left) in increments of 0.4. The model underwent the same correction as the sources. The 1σ error bars at the upper left illustrate the median of the uncertainties. Monte Carlo simulations to 0.653. This is the average expectation for the Poisson distribution for expected numbers of counts between 0 and 1.841, which are the 1σ confidence intervals on a measurement of zero counts.) X-ray color-color diagrams of the combined intrinsic hardness ratios of the Analysis Sample sources are shown in Figure 5.12. The values of the hardness ratios and their 1σ errors are listed in columns (5)–(7) of Table 5.7. Harder sources tend to lie in the upper right of Figure 5.12a. Extra absorption tends to push objects to the right in Figure 5.12b. 187 The majority of sources have hardness ratios consistent with power-law indices of
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LOW-MASS X-RAY BINARIES, DIFFUSE GA
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smaller GCs are more likely to cont
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GO2-3099X, GO3-4099X, AR3-4005X, GO
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her room (my apologies to her offic
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US Court expert from India), for al
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Table of contents Abstract ii Ackno
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5.2.1 Chandra X-ray Observatory . .
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List of Figures 1.1 Hubble Tuning F
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List of Tables 1.1 Galactic Low-Mas
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Chapter 1 General Introduction 1.1
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Fig. 1.1.— Hubble Tuning Fork, co
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2000). In most HMXBs, the accreted
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not get a complete picture of the L
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this, the result of dynamical inter
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is the Advanced CCD Imaging Spectro
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Chapter 2 Chandra Observations of L
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keV (Sarazin et al. 2000, 2001). Wi
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agreed with positions from the USNO
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24:00 22:00 7:20:00 18:00 16:00 18:
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Table 2.1. Discrete X-ray Sources i
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Table 2.1—Continued Source d Coun
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Table 2.2—Continued Source d Coun
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optical/IR positions of R.A. = 12 h
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log N(>L) 2.0 1.5 1.0 0.5 0.0 NGC 4
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luminosity function for luminositie
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H31 1.0 0.5 0.0 -0.5 -1.0 NGC 4365
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2.4.5 Variability We searched for v
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Number 10 8 6 4 2 NGC 4365 Optical
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LMXBs has an effective radius of 12
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component (“MEKAL”) was used fo
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Table 2.4. X-ray Spectral Fits of N
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Fig. 2.9.— Top panels: Cumulative
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we extended the spectrum down to 0.
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We also examined whether the unreso
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esolved sources in the galaxy. This
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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—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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Page 157 and 158: Fig. 5.3.— Adaptively smoothed Ch
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Page 161 and 162: Table 5.1—Continued Source R.A. D
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Page 171 and 172: Table 5.2. : Optical Properties of
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Page 197 and 198: Fig. 5.8.— Cumulative luminosity
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Page 201 and 202: Fig. 5.10.— Cumulative luminosity
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Page 207 and 208: 5.9 Spectral Analysis We performed
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Page 221 and 222: Table 5.10. Possible Flaring Source
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Page 229 and 230: Fig. 5.17.— Percentage of Analysi
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Page 235 and 236: of states as transient candidates.
Page 237 and 238: Long-Term Hardness Ratio Variabilit
Page 239 and 240: In the final observation, there wer
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Page 251 and 252: 6.2 Sample 6.2.1 Galaxy Sample Tabl
Page 253 and 254: 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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