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Chandra Monitoring of X-Ray Evolution of SNR 1987A

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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Chandra Monitoring of X-Ray Evolution of SNR 1987A

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  1. 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)

  2. 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)

  3. SNR 1987A: Physical Picture Optical/Soft X-rays Hard X-rays Radio ? NS/BH Artistic presentation of SN 1987A (SAO/CXC) Cf. Michael et al. 1998

  4. SNR 1987A: ACIS Images 2000–2008 N E 1 arcsec 2008-1-10 (7626)

  5. SNR 1987A: X-Ray & Radio Light Curves

  6. SNR 1987A: X-Ray & Radio Light Curves

  7. SNR 1987A: X-Ray & Radio Light Curves (Zhekov+ 06,08) (Haberl+ 06; Heng+ 08) (Haberl+ 06; Heng+ 08)

  8. 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.

  9. SNR 1987A: X-ray Radial Expansion 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.

  10. SNR 1987A: X-Ray Spectral Evolution 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 2008 Jan Park+ 2006 Dewey+ 2008, Zhekov+ 2008

  11. 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

  12. Ring-like morphology withasymmetric 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 SUMMARY

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