GCN Circular 10903
Subject
GRB 090709A: Host galaxy detection
Date
2010-06-29T04:44:26Z (15 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, S. B. Cenko, and J. S. Bloom (UC Berkeley) report:
We observed the field of GRB 090709A (Morris et al., GCN 9625) using
NIRI on Gemini-North on the night of 2010-06-23 between 11:54 and 14:46
UT, under good conditions. Our co-added stack contains a total of 146
images of 60 seconds each (2.43 hours of imaging) in the K' filter. The
3-sigma limiting magnitude of the stack is K' ~ 23.7. (Calibration of
the field was established relative to several 2MASS stars in the image.)
Matching our image directly to early-time PAIRITEL imaging (Morgan et
al., GCN 9635), we detect a faint, extended source slightly offset (0.6
arcsec) from the position of the IR afterglow. The orientation of the
offset is along the apparent direction of extension of the source (E-W).
Aperture photometry within a 1.0 arcsec aperture centered on the
object gives a magnitude of K' = 22.0 +/- 0.2 mag. The chance
probability for this alignment is approximately one percent (Bloom et
al. 2002, AJ 123:1111, Djorgovski et al. 1995, ApJL 438:L13).
We therefore associate this object with the host galaxy of GRB 090709A.
The detection of a host galaxy confirms the extragalactic,
cosmological nature of this event (de Luca et al. 2010, MNRAS 402:1870;
Cenko et al. 2010, AJ 140:224). We note that deep optical imaging of
this field by the GTC (Castro-Tirado et al., GCN 9655) detected no
object at this position to a limit of i' > 25.5, suggesting that the
host galaxy may be internally dust-reddened. The infrared afterglow
also showed evidence of strong reddening (Cenko et al. 2010), and
foreground extinction in this direction is low; E(B-V) = 0.09 mag.
Additional imaging is encouraged to test this hypothesis.
An image of the field is posted to:
http://lyra.berkeley.edu/~dperley/090709a/090709a_niri.png
We are happy to thank Marie Lemoine-Busserolle, Matthew Dillman, and
Andrew Stephens for their support during our classical NIRI run.