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

More documents

Recommendations

Info

Γ ∼ 1.5–1.8). From our observations of NGC 4697, we find that GC-LMXBs are bet- ter fit with higher temperatures and greater absorbing columns compared to the field-LMXBs. Similarly, we find a difference between X-ray fainter and brighter LMXBs. The fainter LMXBs tend to have smaller absorbing columns, while the brighter LMXBs tend to have a small excess in absorption, which may be due to accreting material. 7.1.4 Variability in Low-Mass X-Ray Binaries The study of variability plays a key role in understanding the behavior of Galactic LMXBs. Although we cannot study variability in the exquisite detail available for Milky Way LMXBs, we are beginning to probe variability of LMXBs in early-type galaxies (and other X-ray sources in the same FOV). Individual observations can reveal variability on timescales of minutes to hours. Although this has been traditionally probed with the Kolmogorov-Smirnov (KS) test, we have also developed a new method to detect flaring sources. This method has been applied to our observations of NGC 4697. Of the two most clearly flaring sources, one is a foreground star whose flare was also detected by the KS test. The other source is more interesting. Its flares, which were missed by the KS test, last for ∼ 70 s and are very super-Eddington for an NS (∼ 6 × 10 39 erg s −1 ). Although this source has no clear Galactic analog, we suggest it may be a microblazar, a microquasar observed along the jet axis. Our multi-epoch observations of NGC 4697 were planned to shed light on LMXB variability in elliptical galaxies over timescales of (11) days to (4.6) years. We deter- mine that 6.7 ± 1.0% of the Analysis Sample sources are variable between any two observations. There is a slight increase in the fraction of variable sources with the 280
variability timescale, but it is not found to be statistically significant. The fraction of variable sources is roughly consistent with those found in Centaurus A for a 0.5 year timescale (Kraft et al. 2001) and in NGC 4636 for a day timescale, but is lower than that found for a 3 year timescale in NGC 4636 (Posson-Brown et al. 2006). When we consider all five observations simultaneously, we find that ≈ 16 ± 4% of sources exhibit luminosity variability. Among these variable sources, we identify eleven transient candidates. If all LMXBs in NGC 4697 are long-term transients, they are on for ∼ 100 yr and have a duty cycle (∼ 7%) comparable to that derived from Galactic GCs (Heinke et al. 2003). We clearly identify a supersoft transient source with no optical counterpart. Our analysis indicates this source could be consistent with an accreting BH with a mass in the range of ∼(7 × 10 3 –10 6 ) M⊙; however, the origin of such a large BH outside of the center of a galaxy or of a GC is a formidable challenge to our current theories of BH formation. 7.1.5 Spectra of Diffuse Gas In NGC 4365 and NGC 4382, two X-ray faint, early-type Virgo Cluster galaxies, the diffuse gas produces less emission than the LMXBs. The gas from both galaxies were fit by relatively soft temperatures (kT ∼ 0.6 keV for NGC 4365 and kT ∼ 0.3 keV for NGC 4382) with subsolar heavy metal abundances. We note that the abundances were often poorly constrained due to the limited number of counts from the gas. In NGC 4365, there is some evidence that the temperature of the diffuse gas increases with increasing radius to kT ∼ 0.8 keV. On the other hand, NGC 1600 is an X-ray bright elliptical at the center of a group of galaxies. Although we expect the diffuse gas to dominate the X-ray emission, the LMXBs may account for ∼ 25–50% of the X-ray emission. Despite its greater 281
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 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 43 and 44:
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 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
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 87 and 88:
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
Page 107 and 108:
log I X (counts/sec/arcmin 2 ) 0.5
Page 109 and 110:
tion), and βouter = 0.36 +0.01 −
Page 111 and 112:
the east and northeast of NGC 1600.
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
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
Page 127 and 128:
jection to include the emission fro
Page 129 and 130:
Fig. 3.13.— Estimated gas and gra
Page 131 and 132:
ackground source population cannot
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 and 144:
the uncertainties quoted do not inc
Page 145 and 146:
to persistent rate for short flares
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
Page 155 and 156:
42:00.0 44:00.0 46:00.0 48:00.0 -5:
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 163 and 164:
Page 165 and 166:
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
Page 191 and 192:
Table 5.6—Continued Source LA LB
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 and 206:
Fig. 5.12.— X-ray color-color dia
Page 207 and 208:
5.9 Spectral Analysis We performed
Page 209 and 210:
some data loss, it allows for direc
Page 211 and 212:
for 2 dof and the f-test indicates
Page 213 and 214:
ple to LMXBs interior to that semi-
Page 215 and 216:
est-fit (χ 2 = 56.4 for 65 dof) by
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
Page 231 and 232:
dofs and the number of combinations
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
Page 243 and 244:
atio is expected only from the most
Page 245 and 246:
eak (Kim et al. 2006a). We find mar
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
Page 257 and 258: the QE degradation in the ACIS dete
Page 259 and 260: Table 6.3—Continued Galaxy NX LX,
Page 261 and 262: The positions of the GCs were used
Page 263 and 264: Fig. 6.2.— Scatter plot of GC gal
Page 265 and 266: Fig. 6.3.— Scatter plot of estima
Page 267 and 268: Fig. 6.5.— Scatter plot of estima
Page 269 and 270: isophote from the galaxy optical su
Page 271 and 272: 6.3.1 Luminosity and Mass Prior obs
Page 273 and 274: compare their χ 2 fits to test whi
Page 275 and 276: GCs without LMXBs; however, there a
Page 277 and 278: following dependence on GC properti
Page 279 and 280: of this probability with individual
Page 281 and 282: Fig. 6.9.— Identical to Figure 6.
Page 283 and 284: We used the indices from our best-f
Page 285 and 286: (20.3 for half-mass radius, both wi
Page 287 and 288: most are steeper than Z ∼0.4 . Ei
Page 289 and 290: Fig. 6.11.— (Left:) Two-dimension
Page 291 and 292: differently by the properties of th
Page 293 and 294: dependent IMF (Grindlay 1987), or e
Page 295 and 296: a 1.4M⊙ neutron star (NS). They s
Page 297: equivalent to a dependence on the b
Page 301 and 302: 7.2.1 X-ray Properties of the GC-LM
Page 303 and 304: of the metallicity dependence. As i
Page 305 and 306: Appendix A Encounter Rate Parameter
Page 307 and 308: Fig. A.1.— Dimensionless quantity
Page 309 and 310: and four; these positions do not in
Page 311 and 312: Table B.1—Continued RA Dec. d GC
Page 315 and 316: Table B.2. Optical Properties of Gl
Page 349 and 350:
Table B.2—Continued RA Dec. d GC
Page 351 and 352:
Page 353 and 354:
Page 355 and 356:
Page 357 and 358:
Page 359 and 360:
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Page 371 and 372:
Page 373 and 374:
Page 375 and 376:
Page 377 and 378:
Page 379 and 380:
Page 381 and 382:
Page 383 and 384:
Page 385 and 386:
Page 387 and 388:
Page 389 and 390:
Page 391 and 392:
Page 393 and 394:
Page 395 and 396:
Page 397 and 398:
Page 399 and 400:
Page 401 and 402:
Page 403 and 404:
Page 405 and 406:
Page 407 and 408:
Page 409 and 410:
Page 411 and 412:
Page 413 and 414:
Page 415 and 416:
Page 417 and 418:
Page 419 and 420:
Page 421 and 422:
investigations into improving the h
Page 423 and 424:
C.4 Sivakoff Signature Soy Sauce Sk
Page 425 and 426:
Blanton, E. L., Sarazin, C. L., & I
Page 427 and 428:
Frogel, J. A., Persson, S. E., Matt
Page 429 and 430:
Johnston, H. M. & Verbunt, F. 1996,
Page 431 and 432:
Makishima, K. et al. 2000, ApJ, 535
Page 433 and 434:
Porter, A. C. 1993, PASP, 105, 1250
Page 435:
Verner, D. A., Ferland, G. J., Kori
show all

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

Create successful ePaper yourself

Delete template?

Save as template?