EVIDENCE OF ACCRETION-GENERATED X-RAYS IN THE YOUNG ...

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as the Grating Element Support Structure (GESS), which places the gratings behind the HRMA when in use. The GESS supports a system of 180 grating modules, each of which has three grating facets that each contain 80 grating elements. In the case of LETG, the grating elements are triangular in shape and are composed of individual fine gold wires supported by coarser gold wires. Due to the triangular shape of the coarse support structure, the dispersed spectrum of an X-ray target is star-shaped at zeroth-order. 3.2.3 HRC The High Resolution Camera (HRC) is one of two primary imaging instruments on the integrated Science Instrument Module (SIM) of Chandra. This camera is an imaging-optimized microchannel plate (MCP) detector (as opposed to the traditional CCD detector). The HRC, like ACIS, is composed of two sets of detectors. The HRC-I has the largest field of view of any of the science instruments (30 0 by 30 0 ), and is optimized for imaging. HRC-S is optimized for spectroscopic work, has a field of view of 6 0 by 30 0 ,andisusedinconjunctionwiththeLETG. A MCP works on the basis of photoemission. The HRC consists of two MCPs, each with millions of angled channels that are on the order of 10 microns in diameter. As an incoming X-ray photon intercepts the MCP, the photon enters a microchannel and, due to the angle of the channels, strikes the channel wall, which results in the ejection of an electron. Due to the bias charge between the two plates, the electron is accelerated down the channel, striking the wall again and releasing more electrons. This cascade e↵ect continues through the channel, and a shower of several million 39
electrons eventually exits the output microchannel plate where they are intercepted by an array of detectors that record both the position and charge of an incoming signal. As multiple photons strike the MCP and the resulting electron showers are recorded by the position-charge detectors, an image is built up. 3.2.4 ACIS The other workhorse detector of CXO is the Advanced CCD Imaging Spectrometer (ACIS). ACIS consists of 10 1024x1024 pixel CCDs, four of which are arranged in a 2x2 fashion (ACIS-I) and are used primarily for X-ray imaging. The remaining six CCDs (ACIS-S) are arranged in a horizontal row below ACIS-I and can be used for imaging or for X-ray spectroscopy when used in conjunction with one of the grating systems. Two of the ACIS-S CCDs (labeled “S1” and “S3”) are back-illuminated while the remaining eight ACIS CCDs are front-illuminated. “Back-illuminated” and “front-illuminated” refer to how CCDs detect incoming photons. In traditional CCDs, the gate structures (discussed below) are mounted on the illuminated side of the CCD. Incoming photons can be reflected or absorbed by the gates and internal wiring of the chip before reaching the depletion layer (where the photons are “detected”). This can dramatically reduce the quantum e ciency of the chip. Back-illuminated CCDs have improved quantum e ciency since they are illuminated from the side opposite the gates and the chip substrate above the depletion has been dramatically thinned such that the substrate layer is essentially transparent to the incoming photons. Thus, the two back-illuminated ACIS-S CCDs have higher quantum e ciency in regard to the lower-energy (0.3⇠4.0 keV) photon range and have slightly better spectral resolution 40
Page 1 and 2: EVIDENCE OF ACCRETION-GENERATED X-R
Page 3 and 4: 4.3.2. Spectral Modeling . . . . .
Page 5 and 6: the first time through a telescope,
Page 7 and 8: List of Tables Table Page 1. 2002-2
Page 9 and 10: 19. Correlation Between Changes in
Page 11 and 12: on Earth, nay, the entire solar sys
Page 13 and 14: known as a molecular cloud. These s
Page 15 and 16: internal pressure will be overcome.
Page 17 and 18: With advancements in telescope and
Page 19 and 20: the circumstellar disk, such as the
Page 21 and 22: perturbations or disk instabilities
Page 23 and 24: CHAPTER II ERUPTING YOUNG STARS 2.1
Page 25 and 26: (1997). Once the TTS spectral class
Page 27 and 28: Annu. Rev. Astro. Astrophys. 1996.3
Page 29 and 30: FUors have typical accretion rates
Page 31 and 32: and radiative equilibrium and that
Page 33 and 34: CHAPTER III X-RAY ASTRONOMY: A TOOL
Page 35 and 36: of the X-ray luminosity (LX) totheb
Page 37 and 38: filtered light curves (which had la
Page 39 and 40: 3.1.4 Gleaning Other Information fr
Page 41 and 42: Fig. 9a ~6.4 keV ~6.7 keV Figure 8:
Page 43 and 44: 34 Figure 9: Schematic of the Chand
Page 45 and 46: Figure 10: Schematic of the Chandra
Page 47: Top View Rowland Circle Grating fac
Page 51 and 52: one to e↵ectively determine the e
Page 53 and 54: pixels or pixel columns. • Parame
Page 55 and 56: deal of built-in flexibility in how
Page 57 and 58: accrete most of their mass (Hartman
Page 59 and 60: 4.2 Observations & Data Reduction O
Page 61 and 62: were grouped into energy bins with
Page 63 and 64: Since V1647 Ori was imaged with bot
Page 65 and 66: 4.3 Results 4.3.1 Short-Term and Lo
Page 67 and 68: overall X-ray light curve, the soft
Page 69 and 70: Count Rate (cts/s) Count Rate (cts/
Page 75 and 76: The highest measured X-ray mean cou
Page 77 and 78: during short-term variability, howe
Page 79 and 80: Change in Mean Hardness Ratio 1 0.5
Page 81 and 82: These results suggest that we can i
Page 83 and 84: Table 3. Model Fits for 2008-2009 C
Page 85 and 86: For the CXO observations of V1647 O
Page 87 and 88: normalized counts s −1 keV −1
Page 89 and 90: Determining a robust model for the
Page 91 and 92: April 4 XMM observation (109 eV) an
Page 93 and 94: s −1 ) Log Observed Flux (ergs cm
Page 95 and 96: tures of a few million Kelvin (kTX
Page 97 and 98: 2004 March, especially if the large
Page 99 and 100:
and AK =0.5on2004Feburary18,allofwh
Page 101 and 102:
In order to test whether CXO would
Page 103 and 104:
• and X-ray luminosities that are
Page 105 and 106:
With V1647 Ori being observed inten
Page 107 and 108:
level approximately one year after
Page 109 and 110:
of an object in which this process
Page 111 and 112:
eduction. In §3, we discuss the re
Page 113 and 114:
Table 5. Chandra ACIS Observations
Page 115 and 116:
5.3 Results from X-ray Observations
Page 117 and 118:
y an intervening column of hydrogen
Page 119 and 120:
Table 6. Best-Fit Models for EX Lup
Page 121 and 122:
component plasma, subject to a sing
Page 123 and 124:
does require a third, heavily-absor
Page 125 and 126:
5.3.3 The Temporal Evolution of the
Page 127 and 128:
Figure 29 shows the three CXO spect
Page 129 and 130:
From 2008 June to August, the plasm
Page 131 and 132:
June, however, the X-ray flux from
Page 133 and 134:
to test this light curve for possib
Page 135 and 136:
We note that in the above analysis,
Page 137 and 138:
5.5 Discussion & Conclusions The op
Page 139 and 140:
CHAPTER VI DISCUSSION AND CONCLUSIO
Page 141 and 142:
sensitive line diagnostics that wou
Page 143 and 144:
Bell, K. R., Lin, D. N. C., & Ruden
Page 145 and 146:
Hartmann, L. & Kenyon, S. J. 1996,
Page 147 and 148:
Orlando, S., Peres, G., & Reale, F.
Page 149:
Venkat, V. & Anandarao, B. G. 2011,
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