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GCN Circular 19250

Subject
GRB 160327A: Continued RATIR Optical and NIR Observations
Date
2016-04-01T19:20:19Z (8 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (GSFC/STScI),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
Jos�� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes��s Gonz��lez (UNAM),
Carlos Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC),
John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 160327A (Racusin, et al., GCN 19235) for a
third epoch with the Reionization and Transients Infrared Camera (RATIR;
www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio
Astron��mico Nacional on Sierra San Pedro M��rtir from 2016/04 1.22 to
2016/04 1.41 UTC (115.97 to 120.62 hours after the BAT trigger), obtaining
a total of 3.18 hours exposure in the r and i bands and 1.34 hours exposure
in the Z, Y, J, and H bands.

We are able to detect two of the three sources identified by the GTC (de
Ugarte Postigo, et al., GCN 19245).  The afterglow (GTC source #1 and
Golkhou, et al., GCN 19236) is detected in our night 2 observations on 28
March (Golkhou, et al., GCN 19243) but not on 1 April.  The GTC source #2
is detected on 28 March and 1 April and is the dominant source in terms of
brightness.  We do not detect GTC source #3 on either night.

In comparison with the SDSS DR9 and 2MASS catalogs, we obtain the following
detections and upper limits (3-sigma):

Afterglow (GTC Source #1):

 28 March                 1 April
r > 24.37               r > 24.41
i = 24.20 +/- 0.31      i > 24.38
Z = 22.98 +/- 0.28      Z > 23.15
Y > 22.85               Y > 22.91
J > 22.67               J > 22.61
H > 22.21               H > 22.23

GTC Source #2:

 28 March                 1 April
r = 23.84 +/- 0.22      r > 24.42
i = 23.33 +/- 0.14      i = 23.57 +/- 0.17
Z = 22.57 +/- 0.20      Z = 22.71 +/- 0.25
Y = 22.83 +/- 0.35      Y > 22.73
J = 22.43 +/- 0.29      J > 22.60
H = 21.75 +/- 0.24      H > 22.24

GTC Source #3:

 28 March                 1 April
r > 24.37               r > 24.41
i > 24.34               i > 24.39
Z > 23.19               Z > 23.11
Y > 22.86               Y > 22.76
J > 22.66               J > 22.6
H > 22.21               H > 22.25

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

In addition to our first night observations (Golkhou, et al., GCN 19236),
which show the afterglow peaking and then fading, our observations on 28
March and 1 April confirm the fading of the afterglow.  The above
photometric analysis, based on PSF fitting, may still suffer from modest
contamination between sources.  More detailed analyses are under way.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.
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