Time resolved X-ray spectroscopy of NGC 4051

Katrien C. SteenbruggeSt John’s College, University of Oxford

Marjan Fenovic, Elisa Costantini, Jelle Kaastra (SRON) and Frank Verbunt (SIU)

NCG 4051

• Narrow line Seyfert 1• X-ray bright• Variable X-ray flux.• Distance of 18.6 Mpc

(Tully & Pierce 2000).

Observations I discuss:• LETGS 01 Jan. 2002

for 94 ks. • LETGS 23 July 2003

for 96 ks.

X-ray spectroscopy

• Possibility to detect variation in the absorber properties with changing flux.

• If ionization changes with flux, then the density of the outflow can be calculated.

• Hence, the distance of the absorber, the energy density and mass outflow can be calculated.

X-ray lightcurve

The flux decreases by a factor of 5 just before D.

Spectra were extracted for periods A, B, C and D.

X-ray continua

Between spectrum C and D, power-law photon index, becomes softer.

Temperature of black body decreases.

X-ray spectra

• The spectra are of rather low signal to noise.• Spectrum C: 4 absorption components are necessary: log ξ = 0.07-3.19.• Spectrum D: RRC of C V and C VI.

Radiative Recombination Continua

• Using emission measure, temperature and maximum broadening, a BH mass of 3x105 Msun and luminosity we derive a column density that is similar to the highest ionized absorber: ~1026 m-2.

• However, the ionization parameter log ξ ~ 1.6 is much lower than that of the highest ionized absorber.

RRC’s might be from the accretion disk.

Absorbers

• None of the 4 ionization parameters does react linearly to the decrease in flux by a factor of 5 between spectra C and D.

• One ionization parameter shows a 2.3σ change from logξ = 0.87 to 0.52 between spectrum C and D.

• The other 3 ionization parameters change less than 1σ between spectrum A, B, C and D.

Long term spectral results

• The column densities we measure are consistent as those measured from RGS spectrum (Ogle et al. 2004) except logξ > 3.

• The highest ionized absorber in our spectrum has the largest outflow velocity: 4670 km/s.

• HETG spectrum: the highest ionized absorber has the highest outflow velocity: 2340 km/s (Collinge et al. 2001).

• We do not detect a 2340 km/s absorber.This component is variable on years timescale.

Broad emission lines

• We detect broadened emission lines from C VI and O VII.

• C VI FWHM is ~2000 km/s, similar to the with of Hβ.

• O VII triplet FWHM is ~11000 km/s broader than the He II line of ~5000 km/s.

There is an ionization gradient in the broad line region.

Relativistic O VIIILyα line

• Detected in spectra A, B and C.

• Inclination angle is the same as found from XMM (Ogle et al. 2004) and for the narrow line region (Christopoulou et al. 1997).

Conclusions

• The spectrum has multiple components!

• The continuum shape does change with flux.

• In spectrum D we detect C V, C VI RRC.

• There are broad C VI and O VII, and relativistic O VIII Lyα lines present.

• The highest outflow component is variable on timescales of years.