7-6:

http://www.phys.unsw.edu.au/~jw/paper.html

Morning- Readings


Authors: Smith, R.K., Bautz, M.W., Bookbinder, J., Garcia, M.R., Guainazzi, M., Kilbourne, C.A.
Title: Predicted X-ray backgrounds for the international X-ray observatory.
constellationx.nasa.gov/resources/Published.../IXO-bkgnd-SPIE.pdf

This paper is in my g-mail, search "ptak spie background" if more bibliographic info is needed.

Notes:


" The background that will be observed by IXO’s X-ray detectors naturally separates into two components: (1) a Cosmic
X-ray Background (CXB), primarily due to unresolved point sources at high energies (E>2 keV), along with Galactic
component(s) at lower energies that are generated in the disk and halo as well as the Local Bubble and charge exchange
in the heliosphere, and (2) a Non-X-ray Background (NXB) created by unvetoed particle interactions in the detector
itself."

" These two components have distinct effects on observations. The CXB is a sum of power-law, thermal, and charge
exchange components that will be focused and vignetted by the IXO mirrors. The NXB, in contrast, is due to particle,
not photon, interactions (although there will be some fluorescence features induced by particle interactions), and so
will not show the same effects of vignetting or trace the effective area response of the satellite."

exosphere- uppermost layer of the Earth's atmosphere (wikipedia)







Summary:

This paper summarizes the radiation background that IXO will be exposed to in it's orbit around the Earth. The background is made up of two components: the cosmic X-Ray background and the non-cosmic X-ray background. The cosmic x-ray background is made up of power-law, thermal, and charge exchange components. The non-cosmic X-ray background, on the other hand, is made up of particle interations on the telescope itself.
The cosmic x-ray backgroun is made up of local, galactic, and extra-galactic sources.

-----> Side note: Andy mentioned that O I is neutral oxygen, O II is once ionized oxygen, O III is twice ionized... O VII is helium-like, and O VIII is hydrogen-like

IXO was planned to be set in orbit in the L2 orbit, or a LaGrangian point

http://en.wikipedia.org/wiki/Lagrangian_point

A LaGrangian point is a point in a 3 body system in a which a 3rd body of low mass relative to the other bodies can orbit and experience no net force. This is pretty cool. JWST (James Webb .... Telescope) was also set to go into an L2 orbit, according to http://www.stsci.edu/jwst/overview/design/orbit

--back to reading
Components of the local cosmic background:

Solar Wind Charge Exchange:
Features line features, and not contiuum
"Solar Wind Charge Exchange (SWCX) itself arises from the Earth’s exosphere and the Solar system’s heliosphere3.
The SWCX component creates low energy (E<1.5 keV) emission lines due to electron cascades following transfers from
neutral material either in the Earth’s exosphere or the heliosphere onto highly ionized solar wind ions. "



Local Hot Bubble:
Also has line features

Modelled as a 10^6 K plasma

keyword: look direction--> which direction you look
galactic lattitude--> lattitude in galactic coordinates, in which Earth is at the origin, and the equator is in the galactic plane of the Milky Way.

Galactic Halos--> http://www.daviddarling.info/encyclopedia/G/galhalo.html


Extra-galactic background is primarily a continuum source. It is generaly agreed upon that the primary source of the extra-galactic background is unresolved AGN

The paper quotes many different flux units, including

erg/cm2/s/arcmin2. I suppose arcmin is dimensionless, so it doesn't change the dimensions. Is this and erg/cm^2/s ?


--The Non- X-Ray Background

No X-Ray detectors have orbited at an L2 orbit, so the expected particle interactions have to be estimated.

XMM Newton has a large eliptical orbit, while Swift has a Low Earth Orbit. As a result, Swift's background is 3-4 times less that of Newton because it is shielded by the Earth's magnetosphere.


Key idea: orbit location can play a big factor in the background. IXO was set to be in an L2 orbit. I bet this will be assumed when we determine background in the future.

Section 3.2 gives a description of the known energetic particles at L2.

The stages of the solar cycle significantly influence background. Solar maximum increases the size of the heliosphere, which can deflect more galactic cosmic rays, but it can also produce more local solar wind.


What does a count rate of 0.17 * 10^-2 cts/s/arcmin^2 indicate? Is this a lot of counts? Small?


Some Solar Wind info:

"In general the solar wind average 1-10 particles/cm3, with a velocity of 400 km/s and a thermal energy of only a few eV. However, at times the thermal energy can increase to keV (although the density is then
only ~0.1 particles/cm3)."


" As a result, it is difficult to estimate what effect this will have on individual observations; obviously, during times of high incident solar
particle flux no data will be used, and the satellite might even be put in safe mode."



To model the expected non x-ray background, the author made modifications to background counts for existing satellites. For the XMS detector on IXO, NXB per unit area "is assumed to be four times that seen in the Suzaku XRS." This appears to be the same ratio commented on earlier between Suzaku and XMM.

The paper also mentions that "The Suzaku XIS background does correlate well with the Earth’s magnetic field coefficient of rigidity (COR)"
looking this up, I find
http://en.wikipedia.org/wiki/Rigidity_%28electromagnetism%29

This paper gives information on anti-coincidence counting

irs.inms.nrc.ca/publications/articles/pdf/BaergMunzenmayerEtAl-1976.pdf


if I need the reference.


For the WFI detector, the model for non-cosmic X-ray background is from the Suzaku, Chandra, and XMM-Newton CCD's.
Questions:

Why does the fraction AGN output to the X-ray background decrease as the flux-limit increases? figure 2. This does not make sense to me.

What is a GEANT simulation?

Are cosmic X-rays shielded from the detector?

Why in Figure 8 is the non cosmic background a straight line? Wouldn't it depend on the chemical makeup of the detector?

Connections to what I am currently doing:



-------------------------------------------------------------------

Fundamental Questions in Astrophysics: Guidelines for ... - tiera.ru

Now, reading



The absorption-dominated model for the X-ray spectra of type I active
galaxies: MCG–6-30-15

L. Miller,1 T. J. Turner2,3 and J. N. Reeves4
1 Department of Physics, Oxford University, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH
2 Department of Physics, University of Maryland Baltimore County, Baltimore, MD 21250, USA
3 Astrophysics Science Division, NASA/GSFC, Greenbelt, MD 20771, USA
4 Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 8EH
Accepted 2009 July 17. Received 2009 July 17; in original form 2009 May 24


This Galaxy, MCG-6-30-15 is a prime example of a galaxy which shows broad, redwing broadening, particularly below 6.4 the Fe k-alpha 6.4 keV line

"MCG–6-30-15 is the archetypal example of a type I active galaxy showing broad ‘red-wing’ emission in its X-ray spectrum at energies below the 6.4 keV Fe Kα emission line and a continuum excess above 20 keV."


It looks like this is related to the GR effects Andy was talking about with the Fe K-alpha line.

Summary- The author notes two groups with competing theories for the development of the "red-wing" emission, one (Miller et al.) pointing to clumpy absorping material, while the other, Thompson et al, argued this could not be true unless the global covering factor was very low.

Quasar- wikipedia

An AGN which is very far away. It is the active region of the accretion disk surroinding a black hole. Quasar's are extremely luminous. They can emit up to 1000 times the energy output of the Milky Way.

Occultation (wikipedia)- The occurance of an object being out of view to an observer because of another object coming into the line of sight between the observer and object. It is similar to a transit, except in a transit, the object blocking the view is smaller than the more distant object. In an occultation, the blocking object is "larger" (angular wise) than the more distant object. Planets transit stars, stars occult planets.


-bound-free transitions
see this paper for some helping on understanding bound-bound, bound-free transitions
www.astro.umd.edu/~miller/teaching/astr601/lecture21.pdf and
http://en.wikipedia.org/wiki/Atomic_spectral_line

a bound-bound transition is a transition of an electron from one bound energy state of an atomic to another, say from 2s to 2p, 2s to 3s

a bound-free transition is a transition of an electron from a bound energy to being free from the atom (it is ionized!)



Yes, this article discusses the relativistic effects on the Iron K-alpha line
"This effect is often called 'blurring.'

global covering factor --> the fraction of the sky covered by the absorber as seen from the ionizing source.

Miller et al. created a model to describe 'blurring' that based on absorption by clumpy material. He analyzed data from chandra, XMM, and Suzaku, on the energy range frmo 0.5 keV to 40 keV.


Point of paper:
so
"here we also test a model, suggested by MTR but not tested at that
time, in which the spectrum and its variability are shaped by such
high-opacity, clumpy absorption."

Recent paper about hard x-ray excess (x-ray excess)

http://arxiv.org/abs/1103.1238

http://hesperia.gsfc.nasa.gov/sftheory/xray.htm

X-Ray energies range from about 1 keV to 100 keV
1 to 10 keV ~ soft x-rays
10 keV-100 keV~ hard x-rays

"More relevant to the distinction are the instruments required to observe them and the physical conditions under which the x-rays are produced"


information on NuStar
http://hesperia.gsfc.nasa.gov/sftheory/xray.htm

Definition of covering factor, Cf, in the paper

Cf is the fraction of the source covered by the absorber, as seen by the observer

Cg is the fraction of the sky covered by the absorber, as seen by the source.

Should this be the same?

to get a feel for magnitudes

Fe-K alpha line flux is 2.54 * 10^-4 photons/s/cm^2

Reynolds chose a column density of 2*10^24 and a Photon Index of 2.2. Both of these numbers seem higher than what I have seen.


CONCEPTS TO READ ABOUT: scattering, cross sections, opacity

http://en.wikipedia.org/wiki/Opacity_%28optics%29

opacity tells you you how impenetrabile a given medium is to radiation, most commonly electromagnetic radiation.

Opaque (let's nothing through)
opacity can depend on the wavelength of radiation coming through

For example, the atmosphere is essentially opaque to x-rays, and some microwaves, I think, but it lets a lot of other e&m radiation through, namely visible.

THINK ABOUT WAVES, in particular boundaries, (reflection, transmission, absorption, scattering(new))

from the xspec website, about the phabs multiplicative model:

phabs

A photoelectric absorption using cross-sections set by the xsect command. The relative abundances are set by the abund command.

HUGE!

CROSS-SECTIONS WIKIPEDIA

This paper looked at the range of energies of 0.5 keV to 50 keVs, across multiple data sets from several telescopes. How could they do this? How do they know calibrations, background cancelling, and other factors were the same?

order of magnitude feel: normalization for the powerlaw was 0.01695

On page 4, he discusses estimating systematic errors to be 0.03

"...we likewise adopt here a systematic fractional error of 0.03, a likely lower limit to the calibration uncertainty given cross-instrument comparisons that show energy-dependent differences of 5-20 per cent (Stuhlinger 2007)."

POSSIBLE TO DO

I could try and replicate the values on page 4, for the galaxy MCG6-30-15, using the values on the bottom of page 4...see if MCG6-30-15 is on the xassist website


??-- This paper talks about a "mean continuum flux incident of the absorber of 0.0383 +- 0.0012 photons*s^-1*cm^-2*keV^-1 at 1 keV. I don't quite understand why energy is in the units. Do these units say "photons per second per cm^2 per keV deposited by the photon?" Is this saying that not all of the energy of the photon is deposited into the detector? Is this related to effective area? "


"optical depth to Comtpon scattering in this absorber would be tau_C approximately equal to 1.5"

?? what is tau_C ?



This paper discussed a way to model the red-wing broadening of the Fe-K alpha line in the galaxy MGC6-30-15. It used models very similar to the phabs model in xspec. It discussed two separate papers which used different models. One, by Miller et al, proposed that the broadening of the iron line can be described by interaction with clumpy material. Another group, Reynold et al, proposed that the wing is caused by relativistic effects. The paper used many concepts related to absorption, cross-sections, viewing angle, composition, and flux. I did not understand a lot of the significance of the motivation behind the models or even what their models even mean. However, it is related to the broadening of the iron-line, which is a very important feature which is to be investigated by con-x. Andy said that this line could be either caused by relativistic effects or absorption and a narrow line. This paper must be hitting at this point, so I SHOULD GET A GOOD UNDERSTANDING OF THIS PAPER!

-------------------------------------------

Another key concept Andy has discussed is degeneracy in models, especially when you have large error bars.

---------------------------------------

now, my goal is to model "Take a simple power-law only model, run fakeit a larger number times, get the error on photon index, then plot the histogram of photon index best-fit values. From that histogram see where the 90% of the value are. "


To do this,

1. Make a python program to drive xspec
2. make run_fakeit program for a powerlaw
3. make a program that can pluck out the best fit value of photon index
4. plot a hisogram of the different values of the photon index

The main step I do not know how to do is plot a histogram. Maybe I make a list, where each value in the list is a given energy. From this list, I make a plot, for a given coordinate (x,y), x corresponds to the energy, and y corresponds to the number of times x shows up in the list, I think simply list.count(x). I do not know how to make a plot of this. --> LOOK AT PH 265 notes


It looks like matplotlib will be exceptionally useful, I should learn how to use it:

http://matplotlib.sourceforge.net/


OTHER TO DO:

go to Andy's long-term plan e-mail, try making the loop he made for driving xspec work.