ChandraLETG Observations of Supernova Remnant 1987A

Abstract

We discuss the results from deep Chandra LETG observations of the supernova remnant 1987A (SNR 1987A). We find that a distribution of shocks, spanning the same range of velocities (from ∼ 300 to 1700 km s −1 ) as deduced in the first part of our analysis (Zhekov et al. 2005, ApJ, 628, L127), can account for the entire X-ray spectrum of this object. The post-shock temperature distribution is bimodal, peaking at kT∼ 0.5 and ∼ 3 keV. Abundances inferred from the X-ray spectrum have values similar to those for the inner circumstellar ring, except that the abundances of nitrogen and oxygen are approximately a factor of two lower than those inferred from the optical/UV spectrum. The velocity of the X-ray emitting plasma has decreased since 1999, apparently because the blast wave has entered the main body of the inner circumstellar ring.

Chandra Observations of Supernova 1987A

“…The foreground column is fixed at N H = 2.35 × 10 21 cm −2 [10]. Metal abundances are fixed at values measured by Zhekov et al [13], which are generally consistent with the LMC abundances. Ionization timescales for the soft component (kT ∼ 0.3 keV) are high (n e t > 10 12 cm −3 s), indicating the hot gas is in collisional ionization equilibrium due to the shock interaction with dense CSM.…”

“…3b, [12]). The high-quality LETG spectrum showed that the continuous distribution of the shock temperature is represented by two dominant components (kT ∼ 0.5 and 2.5 keV) [13]. The LETG spectrum indicated LMC-like metal abundances with a moderate enhancement in N [13].…”

“…3). As the shock interacts with increasing amount of dense CSM, multiple components of hot optically thin plasma are required to adequately fit the observed X-ray [8,10,13]. In fact, a two-temperature NEI plane shock model fits the observed ACIS spectrum of SNR 1987A (Fig.…”

“…The high-quality LETG spectrum showed that the continuous distribution of the shock temperature is represented by two dominant components (kT ∼ 0.5 and 2.5 keV) [13]. The LETG spectrum indicated LMC-like metal abundances with a moderate enhancement in N [13]. X-ray line broadening measurements using the deep LETG observation indicated shock velocities of v ∼ 300−1700 km s −1 [12] which are significantly lower than that deduced from the HETG observation performed ∼5 yr earlier (v ∼ 3400 km s −1 , [6]).…”

“…We have thus been observing SN 1987A with Chandra since its launch in 1999, roughly twice a year, in order to monitor the earliest stages of the evolution of the X-ray remnant of SN 1987A. We here review previous results from our Chandra observations of SNR 1987A [2,6,7,8,9,10,12,13], and present some preliminary results from the latest Chandra observations.…”