The Supernova Remnant G284.3$-$1.8 and Its Relation to the Gamma-ray Binary 1FGL J1018.6$-$5856

TL;DR

The paper investigates whether the supernova remnant G284.3-1.8 and the gamma-ray binary 1FGL J1018.6-5856 originate from a single supernova event. Using Suzaku XIS spectroscopy, the authors determine Mg-rich ejecta abundances and an X-ray absorbing column consistent with a common distance to both objects, supported by $^{12}$CO data from NANTEN that places the SNR at about $3~ ext{kpc}$. The Mg/Ne and Si/Mg mass ratios, together with stellar-model comparisons, point to a Ne-burning shell intrusion and favor a neutron-star remnant, aligning with neutron-star–driven emission scenarios for the gamma-ray binary. Taken together, the results support a plausible common-origin scenario, albeit with observational tests needed to confirm the binary’s compact object and to reconcile distance measurements.

Abstract

G284.3$-$1.8 is a supernova remnant with a radio shell and thermal X-ray emission. Located near its center is the gamma-ray binary 1FGL J1018.6$-$5856, although the physical association between the two systems is not clear yet. Our X-ray spectroscopy with Suzaku reveals that G284.3$-$1.8 and 1FGL J1018.6$-$5856 have compatible absorption column densities of $N_\mathrm{H} = 6\textrm{--}7 \times 10^{21}~\mathrm{cm}^{-2}$, indicating that the two systems have similar distances. The actual distance is determined as $3~\mathrm{kpc}$ using $\mathrm{^{12}CO}$ ($J=1\textrm{--}0$) data obtained with NANTEN. The X-ray spectrum of G284.3$-$1.8 shows a strong K-shell emission line of Mg, confirming that the earlier claim that the SNR is one of the few Mg-rich SNRs. Comparing recent stellar models taking into account the "shell merger" processes, we find that the obtained Mg-to-Ne mass ratio of $M_\mathrm{Mg}/M_\mathrm{Ne} = 0.73^{+0.07}_{-0.03}$ and Si-to-Mg mass ratio of $M_\mathrm{Si}/M_\mathrm{Mg} = 0.44\pm0.03$ suggest a supernova explosion that would have left a neutron star. The characteristics of 1FGL J1018.6$-$5856, on the other hand, are better explained with a model in which its compact object is neutron star. The present results, therefore, would suggest a possible scenario where G284.3$-$1.8 and 1FGL J1018.6$-$5856 are both remnants of a common supernova explosion although further observational tests are necessary.

Figures (8)

• Figure 1: Suzaku XIS3 image of G284.3$-$1.8 in the 0--12 keV energy band (color scale) from obsID 407069010,overlaid with the Molonglo Observatory Synthesis Telescope (MOST) radio contours at 843 MHz (cyan). The color bar shows X-ray surface brightness in the logarithmical scale. The source region is shown by a solid box. The ${ {\newline}_{\hbox{$\m@th$}} ^{\hbox{$\m@th55$}} \mathrm{Fe} }$ calibration source (green dashed circles) and the emission region of the gamma-ray binary 1FGL J1018.6$-$5856 and another point-like source (magenta dashed circles) were excluded from the region. Alt text: X-ray image of the region toward the SNR G284.3$-$1.8 obtained with Suzaku XIS.
• Figure 2: NXB-subtracted Suzaku FI (XIS0+3) X-ray spectrum of G284.3$-$1.8 in the 0.7-10 keV band. The best-fit plasma model (red), and the background model (FE ; cyan, GRXE ; magenta, CXB ; blue). Alt text: X-ray spectrum of the SNR G284.3$-$1.8 in obtained with Suzaku XIS and the best-fit model.
• Figure 3: Velocity channel map of $\mathrm{^{12}CO}$ ($J$=1--0) emission obtained with NANTEN (magenta contours) overlaid on 843 MHz continuum emission obtained with MOST (color). The black circle indicates the rough location of the G284.3$-$1.8. Alt text: Velocity channel map of the $\mathrm{^{12}CO}$ ($J$=1--0) line emission produced from the NANTEN data. The overlaid contours are 843 MHz continuum image with MOST.
• Figure 4: (a) Integrated intensity distribution of the associated cloud in $\mathrm{^{12}CO}$ ($J=1\textrm{--}0$) overlaid with black contours outlining $\mathrm{^{12}CO}$ ($J=1\textrm{--}0$) emission in the galactic coordinates. The black circle indicates the position of the G284.3$-$1.8. (b) Velocity-galactic latitude diagram of the associated cloud. (c) Galactic longitude-velocity diagram of the associated cloud. Only the color bar in (a) has a column density of molecular hydrogen. The unit of the color bar in (a) has been converted to the molecular hydrogen column density using the conversion factor derived by Okamoto2017. Alt text: Integrated intensity distribution of the $\mathrm{^{12}CO}$ ($J=1\textrm{--}0$) emission associated with the SNR G284.3$-$1.8 in the Galactic coordinate (a), velocity-Galactic latitude diagram (b), and Galactic longitude-velocity diagram (c).
• Figure 5: NXB-subtracted Suzaku XIS (XIS0+3) X-ray spectrum of 1FGL J1018.6$-$5856 in the 0.7-10 keV band. Alt text: X-ray spectrum of the gamma-ray binary 1FGL J1018.6$-$5856 obtained with Suzaku XIS.