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Chandra Detection of the Type Ibc SNe 2007uy and 2008D in NGC 2770

ATEL # 1368; David Pooley and Alicia Soderberg (on behalf of a large collaboration)
on 25 Jan 2008; 8:08 UT
Password Certification: dave pooley (dave@mit.edu)

Subjects: X-ray, Nova, Supernova

The Chandra X-ray Observatory performed a 17.9 ks ACIS-S3 observation of the field of SNe 2008D (associated with XRB 010809; Berger & Soderberg, GCN 7159, ATEL #1353; Kong & Maccarone, ATEL #1355) and 2007uy (Nakano et al., IAUC 8908) starting at 2008 Jan 19 20:41 UT.

In a 1'x1' box around SN 2008D, four X-ray sources are detected, including SN 2008D at R.A. = 09:09:30.625, Decl. = +33:08:20.16 (J2000) with an error circle of 0.19" radius, in agreement with the radio (Soderberg, GCN 7178), optical (Deng & Shu, GCN 7160), and UVOT (Kong et al., GCN 7170; Immler et al., GCN 7168) positions. Ten counts are detected from 2008D in the 0.5--8 keV band, the lowest at ~0.9 keV and the highest at ~3.2 keV. Spectral analysis was performed in Sherpa using Cash statistics with two models, an absorbed power law (PL) and an absorbed thermal bremsstrahlung (TB). The best-fit parameters are:

PL: nH = 1.3(+1.0/-1.3)e22 cm^-2 , Photon Index = 3.6(+1.7/-1.4)
TB: nH = 1.0(+0.7/-0.5)e22 cm^-2 , kT = 1.2(+1.9/-0.5) keV

The PL model gave an unabsorbed 0.5-8 keV flux of 2.8e-14 erg/cm^2/s, and the TB gave 1.2e-14 erg/cm^2/s.

Fixing the column at 6e21 cm^-2 (Kong & Maccarone, ATEL 1355), the best-fit PL photon index is 2.4(+0.7/-0.6) with an unabsorbed flux of 0.9e-14 erg/cm^2/s, and the best-fit TB temperature is kT = 1.8(+2.3/-0.7) keV with an unabsorbed flux of 0.8e-14 erg/cm^2/s.

At a distance of 27 Mpc, the X-ray luminosity of SN 2008D is 2e39 erg/s at ~10 days after the X-ray burst. This is at least a factor of 100 less luminous than GRB afterglows on the same timescale, including sub-energetic bursts similar to GRB-SNe 1998bw and 2006aj, but it is comparable to optically selected SNe Ibc.

K-S analysis of the photon arrival times gives only a 3.1% chance of being consistent with a constant count rate. (Note: all of the above fluxes are time-averaged over the 17.9 ks observation.)

The positions and spectral parameters of the three other sources (X1, X2, X3) are listed below.

Src RA (J2000) Dec (J2000) err Cts nH Phot.Ind. Fx
X1 09:09:31.800 +33:08:05.03 0.05 166 1.6(+0.9/-0.8) 1.4(+0.2/-0.2) 10.8
X2 09:09:31.215 +33:08:21.83 0.09 41 6.5(+3.3/-2.6) 2.5(+0.7/-0.6) 3.9
X3 09:09:30.686 +33:08:05.79 0.19 11 0.3(+3.2/-0.3) 1.1(+0.9/-0.5) 0.7
Notes: err is the radius of the position error circle in arcsec. Cts is the number of detected counts in the 0.5-8 keV band. nH is in units of 10^21 cm^-2. Phot.Ind. is the best-fit PL photon index. Fx is the unabsorbed luminosity in units of 10^-14 erg/cm^2/s.

These sources are within the PSF of the Swift XRT (and therefore contaminate the Swift X-ray light-curve).

In addition, SN 2007uy and three other sources are detected in NGC 2770. Their parameters are given below.

Src RA (J2000) Dec (J2000) err Cts nH Phot.Ind. Fx
07uy 09:09:35.273 +33:07:09.09 0.36 5 0.2(+2.8/-0.2) 1.8(+1.2/-0.8) 0.2
X4 09:09:36.962 +33:06:33.97 0.27 12 4.6(+5.2/-1.8) 1.6(+1.0/-0.9) 1.0
X5 09:09:33.092 +33:07:18.83 0.28 7 4.1(+5.6/-4.1) 2.4(+1.5/-1.2) 0.5
X6 09:09:36.170 +33:07:08.12 0.33 6 0.2(+4.7/-0.2) 0.5(+1.0/-0.7) 0.6
The columns are the same as above.

The Chandra position of SN 2007uy agrees with the radio (Soderberg, ATEL #1350) and optical (Nakano et al., IAUC 8908) positions.

None of the sources besides SN 2008D show evidence for short-term variability.

True-color images can be found at:
http://www.astro.wisc.edu/~pooley/sn2008d.png (60"x60")
http://www.astro.wisc.edu/~pooley/sn2007uy.png (80"x80")
(0.5-1.2 keV in red, 1.2-2.5 keV in green, 2.5-6 keV in blue)

A plot of the photon distribution of SN 2008D produced by ACIS Extract can be found at:
http://www.astro.wisc.edu/~pooley/sn2008d-photon_dist.png


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