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GCN Circular 7216

Subject
SNe 2008D and 2007uy: Chandra Detections
Date
2008-01-25T13:58:13Z (16 years ago)
From
Dave Pooley at UW,Madison <dave@astro.wisc.edu>
David Pooley and Alicia Soderberg report on behalf of a large collaboration:
the Chandra X-ray Observatory performed a 17.9 ks ACIS-S3 observation
of the field of SNe 2008D (associated with XRB 080109; 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.

A Kolmogorov-Smirnov 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 is in agreement 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 of the fields 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

[GCN OPS NOTE(25jan08): Per author's request, the "010809" string in the
first sentence was changed to "080109".  Line breaks were also added.]
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