The X-Ray Universe 2008, Granada, Spain, May 28, 2008

Chandra Monitoring of X-Ray Evolution of SNR 1987A

Sangwook Park

Department of Astronomy & Astrophysics

The Pennsylvania State University

with

D. N. Burrows, J. L. Racusin (Penn State),

S. A. Zhekov, R. McCray (Colorado),

B. M. Gaensler, C.-Y. Ng (Sydney), &

L. Staveley-Smith (Western Australia)

SN 1987A in Her Uniqueness• Brightest supernova observed by mankind since 1604 (J. Kepler)

• Distance: 50 kpc, in the LMC

• Age: 21 years old as of Jan 2008

• Type II SN

• Progenitor: Blue supergiant (Sk -69 202, B3 I)

• Neutrino burst

=> Core-collapse explosion => neutron star?

• Most intensively studied SN of all time:

– Optical/UV: HST and many ground-based

– Radio: initial detection, turned on again in ~1990

– X-ray: no initial detection, turned on in ~1990

– Gamma-ray: detected decay lines from 56Co decay of 56Ni,

confirming explosive nucleosynthesis

=> ADS: ~1000 (~1/week) refereed papers (since 1987)

Chandra observations since 1999: - Monitoring: ACIS, twice a year, separated by ~6 months- Spectroscopy: HETG/LETG - As of 2008-4, 21 Chandra observations performed: 16 ACIS monitoring (Penn State/Colorado) 4 HETG/LETG deep spectroscopy (Penn State/Colorado/MIT) 1 HRC imaging (CfA/Sydney/Penn State/Colorado)

SNR 1987A: Physical Picture

Cf. Michael et al. 1998Artistic presentation of SN 1987A (SAO/CXC)

Optical/Soft X-rays

Hard X-rays

Radio

?NS/BH

N

E

2008-1-10 (7626)

SNR 1987A: ACIS Images 2000–2008

1 arcsec

SNR 1987A: X-Ray & Radio Light Curves

SNR 1987A: X-Ray & Radio Light Curves

SNR 1987A: X-Ray & Radio Light Curves

(Zhekov+ 06,08)

(Haberl+ 06; Heng+ 08)

(Haberl+ 06; Heng+ 08)

SNR 1987A: X-Ray & Radio Light Curves

- Soft X-ray light curve continues a rapid increase (f ~ t7): a current (last 2 yr) rate of ~35% /yr.

As of 2008-1, f (0.5-2 keV) = 4.1 x 10-12 erg/cm2/s, Lx = 2.7 x 1036 erg/s.

- Hard X-ray light curve increases with a lower rate of ~20% /yr (f ~ t4).

As of 2008-1, f (3-10 keV) = 5.2 x 10-13 erg/cm2/s, Lx = 1.6 x 1035 erg/s.

- Cross-comparisons among different X-ray instruments are consistent.

- Radio emission shows an evolution of the spectral index: currently S ~ -0.8.

Radio light curves are flatter than X-rays: ~ t2.6 (9 GHz), ~ t2.2 (1.4 GHz).

An upper limit (~50% of the 3-10 keV flux) for the contribution from synchrotron emission

in the observed hard X-ray flux is estimated based on a simple extrapolation of the radio

fluxes (assuming S ~ -0.8 and no spectral break), and SRCUT/PL model fits of the latest

ACIS spectrum.

SNR 1987A: X-ray Radial ExpansionRacusin et al. 2008

X-ray radius vs time. Broadband deconvolved image for each epochis deprojected (43 deg) and fitted to a model (a torus + 4 lobes) in order to estimate the radius of the SNR as a function of time. Estimated overall expansion velocity is ~3500 km/s (w/ poor fit). The expansion slows down to ~1700 km/s since d ~ 6000.

SNR 1987A: X-Ray Spectral Evolution 2008 Jan

Soft component: kTs ~ 0.3 keV

net ~ 1013 cm-3 s

Hard component: kTh ~ 1.9 keV

net ~ 2 x 1011 cm-3 s

ns/nh ~ 100

Overall softening of spectrum.Abundances fixed at values obtained from

the LETG/HETG data (Zhekov et al. 2008):

N = 0.56 O = 0.08 Ne = 0. 29 Mg = 0.28

Si = 0.33 Si = 0.30 Fe = 0.19

Dewey+ 2008, Zhekov+ 2008Park+ 2006

SNR 1987A: Dispersed Spectrum (2007)Dewey+ 2008; Zhekov+ 2008

Deep HETG (355 ks) & LETG (285 ks)

observations in 2007.

Two characteristic shock model fit:

kT ~ 0.5 and 2 keV.

- Soft kT is constant (~0.5 keV).

- Hard kT decreases (2.7 -> 1.9 keV).

Bulk gas velocities measured by the line

widths are v ~ 150-700 km/s, while

v ~ 500-1000 km/s as derived from

the fitted electron temperatures.

Do lower bulk motion velocities imply a

contribution from the reflecte shock?

kT ~ 1.9 keV

kT ~ 0.5 keV

SUMMARYRing-like morphology with asymmetric intensity

Developments of X-ray spots

=> becomes a complete ring as the blast wave arrives the inner ring

Steep brightening in soft X-rays

=> Now ~24 x brighter than 2000: Lx (0.5-2keV) = 2.7 x 1036 ergs/s

A rapid brightening (~ t7): The shock continues interacting w/ a steep density increase.

Radial expansion: v ~ 7800 km/s to 1700 km/s at day ~6000

Slower brightening in hard X-rays: ~6 x brighter than 2000.

Synchrotron emission? But, steeper than radio light curves (f ~ t4 vs t2.6).

Shock-CSM interaction: spectral softening and distribution of shock velocity

Soft comp kT ~ 0.3-0.5 keV (constant)

Hard comp kT ~ 1.9 keV (decreasing)

Low bulk velocities: reflected shock?

Little changes in metal abundances.

The complex shock structure by interacting with inner ring: Careful analysis with more data is required with upcoming Chandra monitoring with the HETG.

The origin of hard X-ray emission: hot gas vs synchrotron? We need to watch continuous evolution in both X-ray and radio emission.

Searching for the embedded neutron star