Solid State Astrophysicsand/with the RGS

Frits PaerelsColumbia Astrophysics Laboratory

XMM-Newton 20th Anniversary SymposiumGSFC, October 21-22, 2019

courtesy of Steve Kahn, Andy Rasmussen, Jean Cottam, John Peterson, Josh Spodek, Masao Sako, Marcela Stern, Todd Decker, Bill Craig, Jay Bixler, Chris Mauche, Chuck Hailey; Bert Brinkman, Jan Willem den Herder, Cor de Vries, Ton den Boggende, Rolf

Mewe, Jelle Kaastra; Christian Erd; and Herr Bräuniger, Herr Burkert

1. Test Early, Test Often

first representative test: Electro-Optical Bread Board (EOBB, 12/1993):8 flight-grade replicated gratings

in flight-design mounting, correctly alignedbehind four mirror shells, at Panter Long Beam

8 gratings, 4 mirror shellsReflection Grating Module in “6 o’clock position”

RGS at Panter: EOBB

PSF formation by a grazing incidence mirror in

(small angle)

out: narrow ‘fan’-shaped beam;fan is perpendicular to the mirror;

fan width reflects slope error distributionrough mirror surface

a narrow mirror sector contributes a narrow fan-shaped spot to the PSF

RGS at Panter: EOBB

In the “6 o’clock” or “noon” positions wrt. to the mirror, thegratings make a narrow spot in dispersed light,

perpendicular to the dispersion direction.At EOBB, we had effective resolving power ~ 3000!

Sample RGS EOBB image:Al Kα m = −1

You can kind of see theindividual gratings

The spot is roughly elliptical,as expected

(mirror dominates over grating flatness and alignment errors);

but fuzzier than expected!

And what is this??

The secondary spot was always there in orders m ≠ 0,at wavelength slightly shorter than Kα

We tried everything: rogue reflections? reflection off the ‘ribs’?Maybe double ionization? Read Handbuch der Physik on X-rayspectroscopy? (desperate form of lab astrophysics!!)

Heinrich Bräuniger alterted us to ‘satellite lines’ listed in HdP-but to us, that suggested “satellite lines”in highly ionized plasmas, which alwaysappear at longer wavelengths than their‘parent line’…

Also note these large scattering wings:sign of unauthorized tinkering with manufacturingprocess by vendor(byproduct: a very nicescalar theory of scatteringapplied to diffraction gratings, worked out bySteve Kahn)

Finally, Bill Craig and I scanned the source radiation with a monochromator:the lines are indeed intrinsic to the source! Likely mechanism: excitation in oxides!

2. The ISM

this ‘chemical shift’ must also be happening inmolecules in interstellar space, and in dust particles

(silicates, oxides, C compounds)! Resolvable with RGS and Chandra!

X0614+091 Chandra LETGS

1s-2p in atomic O (not consistent with lab data!)

1s-2p in oxide variability in appearance of Fe L

FP et al., ApJ, 2001

photoelectric absorption by isolated atom

free electron

free electron wave function

photon

p = �k; k � n�/a

E� = � + n2 h2

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‘XAFS’

3. Finally, the Solid State: Absorption by Astrophysical Dust

atom surrounded by other atoms, inregular structure (‘short-range order’)

free electronphoton

a

scattered electron wave function

XAFS example: Cu K edge

dedicated RGS observation ofSco X-1: O K edge

(de Vries & Costantini 2009):amorphous water ice XAFS !??

atomic absorption model

Si K edge in GX5-1/ Chandra HETGS

Sascha Zeegers et al. 2019

XAFS probes short range order!Not the full crystal lattice!(that’s IR)

0.26 0.28 0.30 0.32 0.34Energy [keV]

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Nor

mal

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Abs

orpt

ion

[Uni

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] Instrument1ES 1553

Try the interstellar Carbon K edge!G

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et a

l. 20

13

1ES1553+113Chandra LETGS

work with John Staunton(Columbia); in progress

Graphene XAFS