Chandra Observation of SN 2005kd: Very Luminous and Hard X-ray Emission
ATel #1023; D. Pooley (UC Berkeley), S. Immler (NASA/USRA/GSFC), and A. V. Filippenko (UC Berkeley)
on 8 Mar 2007; 08:01 UT
Credential Certification: dave pooley (dave@mit.edu)
Subjects: X-ray, Supernovae
We report on a Chandra Director's Discretionary Time observation of the type IIn SN 2005kd (IAUC 8630 ) which was performed on 2007-03-04.61 (UT). In the 3.0 ks ACIS-S3 observation, we detect 66 counts from the location of the SN. The X-ray emission is extremely hard. We fit an absorbed power-law model to the extracted spectrum, constraining the total column density to be at least equal to the Galactic value of 1.49e21 cm^-2 (Dickey & Lockman 1990). The best-fit parameters are: no additional column above the Galactic value, and a power-law photon index of -0.2 (+0.3/-0.4). Based on this fit, the unabsorbed 0.5-8 keV X-ray luminosity (for a distance of 64.2 Mpc) is 2.7e41 erg/s. We note that this is one of the highest X-ray luminosities recorded for a SN.
The hardness of the X-ray spectrum is reminiscent of SN 2001em (Pooley & Lewin, 2004, IAUC 8323 ), which had a best-fit photon index of 1.1. Restricting the power law model of SN 2005kd to have a photon index >= 1 results in a best-fit model with a total column of 9.1e21 cm^-2 and photon index of 1. The unabsorbed X-ray luminosity for this model is 2.2e41 erg/s, similar to the above value.
The detected count rate indicates that the spectrum may be slightly piled up, which could affect the determination of the photon index (biasing it to harder values). However, the amount of pileup is low (< 5%), which should not strongly affect the analysis. Nevertheless, we applied the "jdpileup' model to our spectral fits in Sherpa. In this case, the best-fit model again has no additional column above the Galactic value, and the photon index is -0.14 (+0.30/-0.34). The unabsorbed X-ray luminosity for this model is 2.6e41 erg/s.
These results seem to indicate that the extremely high X-ray luminosity is robustly determined and that the X-ray spectrum is intrinsically hard.
We thank Harvey Tananbaum and the Chandra staff for executing this observation.
A long XMM-Newton TOO observation is planned for late March under the identifier 410581101. Details can be found at http://xmm.esac.esa.int/external/xmm_sched/sched_obs_srch_frame.shtml.
