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),
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Department of Astronomy & Astrophysics
The Pennsylvania State University
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)
=> Core-collapse explosion => neutron star?
confirming explosive nucleosynthesis
=> ADS: ~1000 (~1/week) refereed papers (since 1987)
- Monitoring: ACIS, twice a year, separated by ~6 months
- Spectroscopy: HETG/LETG
16 ACIS monitoring (Penn State/Colorado)
4 HETG/LETG deep spectroscopy (Penn State/Colorado/MIT)
1 HRC imaging (CfA/Sydney/Penn State/Colorado)
Artistic presentation of SN 1987A (SAO/CXC)
Cf. Michael et al. 1998
(Haberl+ 06; Heng+ 08)
- 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
Racusin et al. 2008
X-ray radius vs time.
Broadband deconvolved image for each epoch
is 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.
Soft component: kTs ~ 0.3 keV
net ~ 1013 cm-3 s
Hard component: kTh ~ 1.9 keV
net ~ 2 x 1011 cm-3 s
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+ 2008
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
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