Chandra observation of the shell of Nova Persei 1901 (GK Persei): Detection of localized nonthermal X-ray emission from a miniature supernova remnant

Abstract

I present data on the shell of classical Nova Persei (1901) obtained by the Advanced CCD Imaging Spectrometer S3 detector on board the Chandra X-Ray Observatory. The X-ray nebula is affected mostly by the complex interstellar medium around the nova and has not developed a regular shell. The X-ray nebula is lumpy and asymmetric, with the bulk of the emission coming from the southwestern quadrant. The brightest X-ray emission is detected as an arc that covers the region from the west to the south of the central source. Part of this feature, which is cospatial with the brightest nonthermal radio emission region, is found to be a source of nonthermal (synchrotron) X-ray emission with a power-law photon index of 2.3(-0.9)(+1.5) and alpha = 0.68(-0.15)(+0.03) at about a flux of 1.7 x 10(-13) ergs cm(-2) s(-1). This confirms that the shell is a site of particle acceleration, mainly in the reverse shock zone. There are strong indications for nonlinear diffusive shock acceleration occurring in the forward shock/transition zone with an upper limit on the nonthermal X-ray flux of 1.0 x 10(-14) ergs cm(-2) s(-1). The total X-ray spectrum of the nebula consists of two prominent components of emission (other than the resolved synchrotron X-ray emission). The component dominant below 2 keV is most likely a nonequilibrium ionization thermal plasma of kT(s) = 0: 1 0: 3 keV with an X-ray flux of 1: 6; 10(-11) ergs cm(-2) s(-1). There is also a higher temperature, kTs 0: 5 2: 6 keV, embedded, N-H (4.0-22.0) x 10(22) cm(-2) emission component prominent above 2 keV. The unabsorbed X-ray flux from this component is 1.5 x 10(-10) ergs cm(-2) s(-1). The X-ray-emitting plasma is of solar composition except for enhancement in the elemental abundances (mean abundances over the remnant) of Ne/Ne-circle dot and N/N-circle dot in the ranges 13-21 and 1-5, respectively. A distinct emission line of neon, He-like Ne IX, is detected, which reveals a distribution of several emission knots/blobs and shows a conelike structure with wings extending toward the northwest and southeast at expansion velocities similar to 2600 km s(-1) in the X-ray wavelengths. The emission measures yield an average electron density in the range 0.6-11.2 cm(-3) for both of the components (filling factor 1). The electron density increases to higher values similar to 300 cm(-3) if the filling factor is decreased substantially. The mass in the X-ray-emitting nebula is (2.1 +/- 38.5) x 10(-4) M-circle dot. The X-ray luminosity of the forward shock similar to 4.3 x 10(32) ergs s(-1) indicates that it is adiabatic. The shocked mass, the X-ray luminosity, and comparisons with other wavelengths suggest that the remnant has started cooling and most likely is in a Sedov phase.