Thermal Emission and Radioactive Lines, but No Pulsar, in the Broadband X-Ray Spectrum of Supernova 1987A

Abstract

Supernova 1987A offers a unique opportunity to study an evolving supernova in unprecedented detail over several decades. The X-ray emission is dominated by interactions between the ejecta and the circumstellar medium, primarily the equatorial ring (ER). We analyze 3.3 Ms of NuSTAR data obtained between 2012 and 2020, and two decades of XMM-Newton data. Since ∼2013, the flux below 2 keV has declined, the 3–8 keV flux has increased but has started to flatten, and the emission above 10 keV has remained nearly constant. The spectra are well described by a model with three thermal shock components. Two components at 0.3 and 0.9 keV are associated with dense clumps in the ER, and a 4 keV component may be a combination of emission from diffuse gas in the ER and the surrounding low-density H ii region. We disfavor models that involve nonthermal X-ray emission and place constraints on nonthermal components, but cannot firmly exclude an underlying power law. Radioactive lines show a 44 Ti redshift of 670 − 380 + 520 km s − 1 , 44 Ti mass of 1.73 − 0.29 + 0.27 × 10 − 4 M ⊙ , and 55 Fe mass of < 4.2 × 10 − 4 M ⊙ . The 35–65 keV luminosity limit on the compact object is 2 × 10 34 erg s−1, and < 15 % of the 10–20 keV flux is pulsed. Considering previous limits, we conclude that there are currently no indications of a compact object, aside from a possible hint of dust heated by a neutron star in recent ALMA images.

Spectral Evolution of the X-Ray Remnant of SN 1987A: A High-Resolution $Chandra$ HETG Study

“…A detailed analysis of the contribution of the Galactic NH towards total absorption column density is beyond the scope of our work. While this issue was similarly outlined by Alp et al (2021) in relation to their analysis of the XMM-Newton data of SNR 1987A, we note that the total columns (Galactic + LMC) are generally consistent between either values of the Galactic column, and thus that the best-fit parameters in our spectral…”

“…This is consistent with previous analyses of the X-ray emission from SNR 1987A between 2004 and 2007 (Zhekov et al 2006;Dewey et al 2008;Zhekov et al 2009), where X-ray emission from these trace elements were negligible. This is also noted with XMM-Newton data from 2012 -2017 (Alp et al 2021). Thus, we set the abundances of all trace elements with vpshock (version ATOMDB v3.0.9) to zero, using the XSPEC command NEI_TRACE_ABUND.…”

“…We tie NH,LMC among all the fitted spectra, assuming no temporal variation in the LMC column for SNR 1987A. We obtain a best-fit total absorption column density, NH = N H,Gal + NH,LMC = 2.17 (Alp et al 2021). We note that more recent HI surveys have suggested much higher N H,Gal values towards LMC, i.e., ∼ (2.5 -4) × 10 21 cm −2 (Kalberla et al 2005;Willingale et al 2013;HI4PI Collaboration et al 2016).…”

“…These multi-wavelength observations show that the remnant of SN 1987A is now entering a new phase, where the blast wave has started probing outside the ER, while the reverse shock may be closing in on the metal-rich ejecta towards the center. Recently, NuSTAR observations of SNR 1987A have showed evidence for hard X-ray emission up to E ∼ 20 keV (Greco et al 2021;Alp et al 2021). While its origins are still unclear, either nonthermal (Greco et al 2021) or thermal (Alp et al 2021) origins have been suggested.…”

“…Recently, NuSTAR observations of SNR 1987A have showed evidence for hard X-ray emission up to E ∼ 20 keV (Greco et al 2021;Alp et al 2021). While its origins are still unclear, either nonthermal (Greco et al 2021) or thermal (Alp et al 2021) origins have been suggested.…”