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

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Fig. 2.10.— Top panels: Cumulative X-ray spectra of the unresolved emission in the inner effective radius of NGC 4365 (left) and inner two effective radii of NGC 4382 (right) with 1 σ error bars overlayed by the solid histograms of the best-fit model spectra (Table 2.3, row 13, Table and 2.4, row 11). Bottom panels: Contribution to χ 2 with the sign indicating the sign of the residual. MEKAL-only fits are consistent with previous ROSAT measurements from Davis & White (1996). The fits to the unresolved emission using only a soft MEKAL model showed large residuals at high energies. Of course, the unresolved emission includes unresolved point sources, as well as diffuse gas, and the unresolved point sources will have a hard spectrum if they are like the resolved sources. Thus, we added a hard component to the fit with the same spectral shape as the best-fit model for the source. This produced a dramatic reduction in χ 2 by 37 for 1 less dof, clearly indicating that values from single temperature fits, like in Davis & White (1996), may be suspect. Allowing the power-law index to vary did not improve the fit significantly. Therefore, we adopted the model with a power-law index of 1.67, a MEKAL temperature of 0.56 +0.05 −0.08 keV, and an abundance in solar units of 0.35 (row 13) as our best-fit model for unresolved emission (Figure 2.10). Although the line emission strength from heavy elements is well constrained, minimal emission from hydrogen leads to poorly constrained (>0.08) abundances. These best-fit values are consistent with some of the soft temperatures and abundances found from two-temperature fits to ASCA observations (Buote & Fabian 1998). 50
We also examined whether the unresolved emission’s spectrum changed with radius. The unresolved spectrum between one and three effective radii had 1155 net counts. We first fitted this spectrum with the best-fit model for unresolved emission (row 14). Then, we allowed the soft component model to vary in the fit. This produced a much better fit (∆χ 2 = −37) with a statistically significant higher temperature (row 15). This suggests that there is a positive radial gradient in the temperature of the gas. If there is a significant gradient, this would also affect the spectra in the inner parts of the galaxy. We would be observing both cooler gas located near the center of the galaxy, and hotter gas at larger radii seen in projection against the center. Thus, we tried fitting the emission from the inner effective radius with two soft components and a hard component; that model did not improve on the single soft+hard model spectral fit we report in Table 2.3. A temperature gradient may exist in the diffuse gas; however, deeper observations of NGC 4365 are necessary to do a more detailed deprojection. In addition to a possible temperature gradient in the diffuse emission, the spectral fits of the sources and unresolved emission point to a possible change in the unresolved sources with respect to radius. In the resolved sources, the model fluxes for sources in the inner effective radius and sources between one and three effective radii are about the same. The correction for increased contribution by background sources based on the luminosity function we fitted earlier suggests that the flux from resolved sources between one and three effective radii should be ∼0.9 times the flux from resolved sources in the inner effective radius. The luminosity function of background sources in a particular field can differ from an average field either by total number of sources or by having a brighter than expected background source in the field. Source 69 is a very hard and bright source that might be such an unusually bright AGN. This 51
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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
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 and 24: 2000). In most HMXBs, the accreted
Page 25 and 26: not get a complete picture of the L
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 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
Page 53 and 54: H31 1.0 0.5 0.0 -0.5 -1.0 NGC 4365
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: we extended the spectrum down to 0.
Page 71 and 72: esolved sources in the galaxy. This
Page 73 and 74: temperature ∼0.3 keV. Matsumoto e
Page 75 and 76: log I X (counts/sec/arcmin 2 ) -1.0
Page 77 and 78: ∼45% of the counts are resolved i
Page 79 and 80: Chapter 3 Chandra Observations of D
Page 81 and 82: noninteracting members (de Vaucoule
Page 83 and 84: used for spectroscopic analysis. We
Page 85 and 86: 02:00.0 03:00.0 04:00.0 05:00.0 06:
Page 89 and 90: Table 3.1—Continued d a Count Rat
Page 91 and 92: We also attempted detections in mul
Page 93 and 94: sociated with extended X-ray or opt
Page 95 and 96: Fig. 3.3.— Histogram of the obser
Page 97 and 98: chip. The number of ULX candidates
Page 99 and 100: these luminosities among previously
Page 101 and 102: to 2-6 keV. Since the 6-10 keV rang
Page 103 and 104: absorption and varying power-law in
Page 105 and 106: counts occur within ∼ 4 ks. Sourc
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Page 109 and 110: tion), and βouter = 0.36 +0.01 −
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Page 113 and 114: group, we assumed that they were at
Page 115 and 116: the group gas than we calculate fro
Page 117 and 118: 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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