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

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4.4.2 CXOU J124839.0−054750 (Source C) By itself, the flare in observation 0784 of source C is highly significant. The com- bination of a similar flare in observation 4727 makes it the most probable (99.995%) flaring source in this chapter. There is no clear optical counterpart for source C. The nearest globular cluster is 1. ′′ 8 away. Given the rms of 0. ′′ 4 for X-ray/optical matches, we do not think this is a likely match. At this source’s radius from the center of NGC 4697 (48 ′′ ), one only expects ∼0.3 background sources at this flux level. There are 18 other sources as bright as source C and interior to it. Therefore, there is only a 1.6% probability the source is a background AGN from the X-ray data alone. The source is even less likely to be an AGN given the lack of an optical detection. We have estimated the 50% completeness limit near the source to be 24.9 in the z-band. Since, the X-ray flux in the 0.5–8.0 keV band is 4.2 × 10 −15 ergs s −1 cm −2 , log(FX/Fopt) is greater than 0.5. If we relax this to log(FX/Fopt) > 0.25 (z > 24.3), and look at GOODS X-ray selected sources (Treister et al. 2004), only 9.6% of the sources have log(FX/Fopt) > 0.25. Combining the expected X-ray background with the results for obscured AGN in the GOODS fields, we estimate that there is a 0.15% probability source C is an AGN. The flare behavior of source C has no clear analog in our own Galaxy. Its peak luminosity of 5.5 +11.2 − 2.3 × 10 39 ergs s −1 (8 times the Eddington luminosity of a helium- burning NS) is clearly super-Eddington for an NS. These flares are not type I X-ray bursts. Since NGC 4697 is an elliptical galaxy, this source is unlikely to be an HMXB like LMC X−4 or V4641 Sgr. The outburst need not exceed the Eddington limit by much if the compact object is a 10 M⊙ BH. The flare timescale is similar to rapid transients seen in the BH XRBs, GRS1915+105 and V4641 Sgr. Compared to GRS1915+105, the ratio of flare rate 126
to persistent rate for short flares is too high, and the recurrence timescale too long, arguing against accretion behavior like that in GRS1915+105. The rapid transient in V4641 Sgr, seen at the tail of a flare event with the Rossi X-Ray Timing Explorer (RXTE; Wijnands & van der Klis 2000), has the correct duration and peak luminosity (assuming a distance of ∼10 kpc, Orosz et al. 2001); however, its quiescent luminosity is too low compared to source C by more than a factor of 10. The activity in V4641 Sgr has been attributed to super-Eddington accretion onto a black hole with the formation of an extended envelope (Revnivtsev et al. 2002). This variability might look like source C if it occurred during a long-term luminous stage, as has been seen in GRS1915+105. Since its behavior is most like LMC X−4, one might suggest that they have a similar phenomenology. That is, the flare might be due to density inhomogeneities in the accretion columns on a neutron star polar caps (Moon et al. 2003). This would require that source C have a large magnetic field. Since most Galactic LMXBs do not appear to have strong fields, it is thought that magnetic fields in NS binaries decay with time or as a result of accretion (Bhattacharya & Srinivasan 1995). Since an NS in NGC 4697 is unlikely to be newly formed, a strong magnetic field in an NS binary could only occur if accretion causes the magnetic field decay in LMXBs and millisecond pulsars, and if the neutron star in this binary has only recently begun to accrete from its donor. One possibility is that source C (and possibly sources A and B as well) are related to Galactic microquasar sources. Microquasars are XRBs with accreting BHs that produce relativistic jets (e.g., Mirabel & Rodríguez 1999). In most of the known Galactic examples, we are observing the sources at a large angle from the jet axis (see, however, Orosz et al. 2001). The very high luminosity of source C might be 127
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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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Page 95 and 96: Fig. 3.3.— Histogram of the obser
Page 97 and 98: chip. The number of ULX candidates
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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
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Page 117 and 118: 04:55 -5:05:00 05 -5:05:10 15 -5:05
Page 119 and 120: for the spectrum: “Field” impli
Page 121 and 122: 90% confidence level errors. Bracke
Page 123 and 124: we adopted the power-law model as o
Page 125 and 126: sources could be a non-trivial sour
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Page 129 and 130: Fig. 3.13.— Estimated gas and gra
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Page 133 and 134: NGC 1600 that has a small spatial s
Page 135 and 136: (HMXBs). LMC X-4, an HMXB pulsar, h
Page 137 and 138: searched for the shortest time tn o
Page 139 and 140: with NGC 4697. Columns (1)-(4) list
Page 141 and 142: duration, ∆tflat, beginning at a
Page 143: the uncertainties quoted do not inc
Page 147 and 148: Chapter 5 Multi-Epoch Chandra X-ray
Page 149 and 150: the field, these different populati
Page 151 and 152: luminous (MB < −20) elliptical (E
Page 153 and 154: 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
Page 169 and 170: ate from Observation 0784 alone (Pa
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
Page 185 and 186: dependence are allowed to vary. Var
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 &
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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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