S. Zane, G. RamsayMSSL, University College of London, UK

M. JimenezMIT, Cambridge, USA

J.W. den HerderSpace Research Organization of the Netherlands C.J. HaileyColumbia Astrophysics Laboratory

Martin Still & Patricia Boyd NASA/Goddard Space Flight Center

XMM-NewtonXMM-Newton Observations of Observations of HER-X1HER-X1“Interacting Binaries: Probing Accretion, Evolution and Outcome”

3-10 July 2004, Cefalu, Italy

Her X-1 is an eclipsing binary system: NS + A/F star.

Pspin ~1.24 s , Porbital ~1.7 d

X-ray intensity varies on a period of 35 d. “Main-on” ~ 10 d; “short-on” ~ 5 d, separation period ~ 10 d of lower intensity.

Main-on broadband spectrum: bb at ~0.1 keV + PL + exponential cut-off at higher energies. Low NH ~1019 cm-2.

Also: I) a Gaussian feature at ~1 keV; ii) a Fe line at ~6.4 keV; iii) a cyclotron absorption line at ~40 keV (B ~3 x1012 G) (see e.g. McCray et al. 1982, Oosterbroek et al.1997, Dal Fiume et al. 1997).

Spectra taken outside the main-on are fitted by adding one or more partial covering absorbtion components (NH ~1022-1023 cm-2) to the model above.

35 d cycle: Occultation phases of the NS by a (tilted, warped) precessing accretion disk (Gerend & Boynton 1976, Coburn et al. 2000).

Exceptions to the 35 d cycle in 4 occasions : 1983, 1993, 1999.... and 2004 ! “Anomalous Low States (ALS)”

XMM-Newton Observations of HER-XMM-Newton Observations of HER-X1 X1 From Jan 2001 to Mar 2003: Her X-1 was observed at 15 different epochs during the 35 d cycle

Ramsay et al, 2002, MNRAS, 337, 185Jimenez-Garate et al, 2002, ApJ, 578, 391Zane et al, 2004, MNRAS, 350, 506 Preliminary results from the ALS.

The RXTE/ASM (2-10) keV lc of Her X-1: the thick lines indicate the XMM-Newton observations

Rev Exp. Time 35 orb

763 12.8 ks 0.79 0.51-0.59

764 12.8 ks 0.84 0.67-0.76

767 6.7 ks 0.01 0.18-0.24

770 6.0 ks 0.19 0.72-0.81

780 4.1 ks 0.75 0.46-0.58

781 4.5 ks 0.62 0.62-0.75

+Since Feb. 2004: 6 new observations during the ALS.

Spin Resolved Light Curves: 2-10 keV and 0.3-0.7 keV (Best fit P computed at each

35)

1) Confirm the slow-down trend monitored by BeppoSax and Chandra (Oosterbroek et al, 2000, Burwitz et al, 2002)

2) Spin modulation is weak or absent in the low states3) During the states of higher intensity: a substructure in the soft X-ray.

Separate peaks which reflect the structure seen at higher energies.

Beyond ~2 keV, all energy bands are consistent with being in phase each other. Turn over in the relative phasing of soft/ hard photons evident after ~2 keV.

Ct/

sC

t/s

2-10 keV

0.3-0.7 keV

HST image of the bow-shock nebula around RX J1856.5-3754 (van Kerkwick & Kulkarni 2001)

The Soft/Hard light curve The Soft/Hard light curve shiftshift

Crosscorrelation of the bands (0.3-0.7) and (2-4) keV: = 80° ± 20° at 35 = 0.60 = 130° ± 20° at 35 = 0.02 = 160° ± 20° at 35 = 0.17 = 340° ± 20° at 35 = 0.26

Hard/soft phase shift expected if soft photons result from reprocessing of hard X-rays in the inner part of the accretion disk.

If a non-tilted disk intercepts and reprocesses the NS beam, directed and reflected components will be shifted by = 180°. ~250° observed in the past during the main-on was associated with evidence of a tilt angle.

derived from EPIC data is very different from past main-on observations. Also, it changes dramatically in the other two states.

First observation of a substantial, continuous change in the tilt of the disk !

Pulse-averaged X-ray Pulse-averaged X-ray SpectraSpectra

Spectra at the three 35 are consistent with a single input emission model (BB + PL + gaussian lines) and an absorption component associated with the intervening matter.

PL index ~0.8-0.9 in the (2-12) keV.

Substructure of the soft emission: at 35 =0.17, 0.60 we require two blackbodies, with T~0.1-0.2 keV and T~0.06 keV.

Around ~1 keV we include a set of lines/edges modeling the most prominent ones resolved, at the same 35, by RGS.

6.4 keV Fe line: changes over the 35 d 6.4 keV Fe line: changes over the 35 d cyclecycle

Possible reasons:

1) an array of Fe K fluorescence lines for all charge states from Fe I-Fe XIII to Fe XXIII;

2) Comptonization from a hot corona ( 1) for a narrower range of charge states centered FeXX

3) Keplerian broadening

At 35= 0.17: V ~13000 km/s R~4x108

cm for M=1.4 M* ~ magnetospheric radius for B ~1012 G.

Change in line width: the FWHM is a factor 5-10 larger when the source is “on” (~20-50 eV at 35=0.26,0.6 to ~300 at 35=0.17).

Change in line center: Probably near neutral Fe (Fe XIV or

colder) in the low state and short-on.

Main-on line energies correspond to Fe XX- Fe XXI

(MOS: 6.52±0.03 keV; PN:6.50±0.02 keV)

EW

(e

V)

E (

ke

V)

Sig

ma

(e

V)

No

rm

OR….

The region emitting Fe KThe region emitting Fe K lines is likely to be lines is likely to be different for lines observed at different beat different for lines observed at different beat phasesphases

Main on: norm. and EW are correlated with the soft X-ray emission

Low state: line is >5 weaker and modulated with the orbital phase. - Correlation with the fast rising UVW1: disc origin scenario?

Low state: Evidence for a new feature at ~7 keV (in addition to that at 6.4 keV)Signature of the hot corona?

Evolution of the 7 keV line along the 35d cycle

7 keV line confirmed by Chandra at 35 = 0.44, 0.46(Jimenez et al)

35 = 0.02

35 = 0.79

E (

ke

V)

EW

(e

V)

No

rm

Constraint on the region emitting the 7 Constraint on the region emitting the 7 keV line: a widely extended photo keV line: a widely extended photo ionized plasma?ionized plasma?

Good Candidate predicted by illuminated disk models: “Accretion disk corona” : r ~108- 1010 cm, n ~ 1015 - 1016 cm-3

Model predictions: a) A spatially extended photo ionized layer on the top of a Shakura-Sunyaev disk, b) more external layers (Corona) where the Compton temperature goes up to few x106 K (Jimenez-Garate et al, 2001)

1) Upper limit:• 7 keV log >3.3• = Lx/(nr2) = ionization parameter• Lx= 1.6 x1037 erg/s

nr2 > 8x1033 cm-1

2) Lower limit:• Simplest single -T plasma: • L line = 7.7x1031 erg/s• T = 230 eV

n2V >3 x1055 cm-3 (EM)

3) R > R Alfven = 3.6 107 cm

Upper limit

Lower limit

RGS Spectra, Low and short on RGS Spectra, Low and short on statestate Jimenez-Garate et al, ApJ, 578, 391Jimenez-Garate et al, ApJ, 578, 391

Low and short-on states:

• Faint PL continuum;

• Narrow emission lines from: C VI, N VI, N VII, O VII, O VIII, Ne IX (NeX?);

• No velocity broadening (within the resolution);

• Weak RRCs of OVII and NVII photo ionized gas;

• From helium-like emission of Ne IX, O VII, N VI: G=(f+i)/r ~4 photo ionized gas.

The narrow line emission region: photo ionized disk atmosphere or illuminated face of the donor HZ?

1) Thermal and ionization balance upper limit on the e density;

2) EM from line fluxes lower limits on the e density;

3) He line ratios and UV photo excitation calculations upper limits to the radius enclosing the region;

Confidence limits (90%) on density and location of the narrow line emission region, obtained from spectroscopic analysis and modelling. The limits shown correspond to O VII, and similar limits with N VI and Ne IX can be set

Fe line at 7 keV: signature of the hottest layers of the corona

Narrow lines detected with RGS: photo ionized layers just above the disk

Low Emission detected with high resolution spectroscopy during the Low State may originate in the illuminated accretion disk atmosphere (blue) and hot corona (pink)

Feb 2004: HerX-1 entered its 4th ALS…

…Which is still going on!

XTE lc from April 15 to Jun 21, in 5 days average

There were two periods of increased apparent activity, but it does not look definitive now

ALS Spectra similar to those of the “standard” low state

Also RGS spectra qualitatively similar;No pulsations detected;

Work in progress…

E (

ke

V)

EW

(e

V)

Sig

ma

(e

V)

EW

(e

V)

No

rmE

(k

eV

)N

orm

Fe

K

no

rma

liza

tio

n

Summary:Summary: XMM spectra consistent with obscuration model by a precessing disk

Low State identified with illuminated accretion disk atmosphere and hot corona from high resolution spectroscopy.

Detection of a Fe line at 7 keV during the low state: signature of the hottest layers of the corona

RGS: narrow line emission during the low state. Photo ionized layers above the disk

35 d variability of the ~6.4 keV Fe line. Emitting regions probably different during low and high state.

UV modulation along the orbital period in both OM filters.

Before the ALS: spin-down and change in the hard/soft phase shift was the inner disk changing?

Spectra taken during the ALS remarkably similar to those taken during the standard low state