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

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1.2–2.0. On average, these sources tend to lie to the right of the power-law curve, which might indicate some extra absorption is occurring. A few sources occupy very different positions in the hardness ratio planes. Sources 81, 96, 105, 112, 123, 134, 146, 148, 153, and 158 are harder than the typical source in NGC 4697. Both their spectral properties and tendency to occur farther away from the center of NGC 4697 suggest that these very hard sources may be unrelated, strongly absorbed AGNs. Sources 11, 19, 25, 78, 84, 94, 110, 121, and 156 are softer than the typical source in NGC 4697. Sources 84 and 156 both have optical counterparts; the former is an extended object much redder than a typical GC, while the latter is a star. Sources 19, 25, 78, and 110 have little if any emission above 1 keV and are all SSs. Based on its H32 color, Source 150 may be strongly absorbed or have a very atypical spectrum. As with luminosity, we used the Spearman’s ρ test to search for a correlation between merged hardness ratio and galactocentric semimajor distance, a. We display the hardness ratios of Analysis Sample sources versus spatial position in the bottom frames of Figure 5.11. If we use the entire Analysis Sample, we find 1.8σ, 2.2σ, and 1.8σ significant correlations of H 0 21, H 0 31, and H 0 32, respectively, with distance. In each case, the sense of the correlation is that harder sources are found at larger a. These correlation become insignificant (< 1σ) when only sources with a < 220 ′′ are considered. The Wilcoxon rank-sum comparison of a < 220 ′′ and a > 220 ′′ significantly detected sources reproduces the effects seen by the Spearman’s ρ test. However, we believe that the correlation at larger distances is due to the increasing dominance of hard background AGNs, as opposed to LMXBs intrinsic to NGC 4697. Scaling the expected number of sources unrelated to NGC 4697 with the area in each region, we expect ∼12/97 and ∼17/29 Analysis Sample sources are unrelated to NGC 4697 for a < 220 ′′ and a > 220 ′′ , respectively. 188
5.9 Spectral Analysis We performed an analysis of the spectra of sources in the 0.5–10.0 keV band, extracting the spectra and response files separately for each observation of each source. The background spectra for each source were determined locally, using the same nearby regions as discussed in § 5.4. Note that the response files for each separate observation and source include the varying effects of absorption by the contaminant which produces the QE degradation in the ACIS detectors. Since the majority of our sources are too faint for spectral analysis, we co-added the spectra and responses of groups of sources for each observation. We only included sources whose total count rate was determined at the 3σ level. We also excluded the sources discussed individually in § 5.9.5 and 5.10.2. All of the spectra were grouped to have at least 25 counts per spectral bin prior to background correction to enable our use of χ 2 statistics. The use of a minimum number of counts per spectral bin and the restricted energy range in the spectrum can result in some excluded bins, although those bins have some photons in the allowed energy range. Unless otherwise noted, the individual observations were required to have the same spectral shape, but their normalizations were allowed to vary. The spectra of Galactic LMXBs can be complex. High luminosity LMXBs, like those seen in NGC 4697, have often been modeled with multi-component models that may include combinations of an isothermal blackbody, a multi-color disk blackbody, a Comptonized power-law, or more complicated models (White et al. 1995). For our observations, there are two complicating factors. First, we are looking at a collection of sources, each of which is likely to have a slightly different spectrum. Second, our spectra, even when co-added, have a much lower signal-to-noise ratio than that for a Galactic LMXB. Therefore, we have only attempted to fit simple 189
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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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Although Chandra is known to encoun
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Page 157 and 158: Fig. 5.3.— Adaptively smoothed Ch
Page 159 and 160: 1 × 10 −5 count s −1 arcsec
Page 161 and 162: Table 5.1—Continued Source R.A. D
Page 167 and 168: source list against which to regist
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Page 171 and 172: Table 5.2. : Optical Properties of
Page 173 and 174: actually be an AGN. Sources 79, 80,
Page 175 and 176: two potential GC counterparts. We l
Page 177 and 178: Table 5.3—Continued X-ray Source
Page 179 and 180: Fig. 5.6.— Color (G475−Z850) -
Page 181 and 182: mass segregation of GCs with the sa
Page 183 and 184: Table 5.4. Fits to the Expected Num
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Page 187 and 188: NGC 4697 to convert the observed so
Page 189 and 190: Table 5.6—Continued Source LA LB
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Page 193 and 194: Table 5.7. Combined Luminosities &
Page 195 and 196: Table 5.7—Continued Source Not De
Page 197 and 198: Fig. 5.8.— Cumulative luminosity
Page 199 and 200: LF, there are enough datapoints tha
Page 201 and 202: Fig. 5.10.— Cumulative luminosity
Page 203 and 204: Fig. 5.11.— Merged luminosities (
Page 205: Fig. 5.12.— X-ray color-color dia
Page 209 and 210: some data loss, it allows for direc
Page 211 and 212: for 2 dof and the f-test indicates
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Page 217 and 218: 5.10.1 Intraobservation Variability
Page 219 and 220: Fig. 5.14.— Binned lightcurve usi
Page 221 and 222: Table 5.10. Possible Flaring Source
Page 223 and 224: Fig. 5.16.— Cumulative lightcurve
Page 225 and 226: pairs of observations. In Figure 5.
Page 227 and 228: Table 5.11—Continued Source PL,AB
Page 229 and 230: Fig. 5.17.— Percentage of Analysi
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Page 233 and 234: Table 5.12—Continued Source Obs.S
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
Page 241 and 242: limits). The 0.3-10 keV X-ray lumin
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Page 247 and 248: LMXBs in Galactic GCs (Heinke et al
Page 249 and 250: in the field of the Milky Way and a
Page 251 and 252: 6.2 Sample 6.2.1 Galaxy Sample Tabl
Page 253 and 254: Table 6.2. Properties of Chandra Ob
Page 255 and 256: 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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