Thermal Emission and Radioactive Lines, but No Pulsar, in the Broadband X-Ray Spectrum of Supernova 1987A. (arXiv:2103.02612v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Alp_D/0/1/0/all/0/1">Dennis Alp</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Larsson_J/0/1/0/all/0/1">Josefin Larsson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fransson_C/0/1/0/all/0/1">Claes Fransson</a>
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 ${sim}$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
non-thermal X-ray emission and place constraints on non-thermal components, but
cannot firmly exclude an underlying power law. Radioactive lines show a
$^{44}$Ti redshift of $670^{+520}_{-380}$ km s$^{-1}$, $^{44}$Ti mass of
$1.73_{-0.29}^{+0.27}times{}10^{-4}$ solar masses, and $^{55}$Fe mass of
$<4.2times{}10^{-4}$ solar masses. The 35-65 keV luminosity limit on the
compact object is $2times{}10^{34}$ 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.
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 ${sim}$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
non-thermal X-ray emission and place constraints on non-thermal components, but
cannot firmly exclude an underlying power law. Radioactive lines show a
$^{44}$Ti redshift of $670^{+520}_{-380}$ km s$^{-1}$, $^{44}$Ti mass of
$1.73_{-0.29}^{+0.27}times{}10^{-4}$ solar masses, and $^{55}$Fe mass of
$<4.2times{}10^{-4}$ solar masses. The 35-65 keV luminosity limit on the
compact object is $2times{}10^{34}$ 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.
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