1. ANDICAM Observations of GRBs
Bethany E. Cobb
Yale University

2. SMARTS 1.3m Service/queue telescope On-site observer
Interruptible queue allows for target-of-opportunity observations
Observing time available > 80 total hours this semester
ANDICAM simultaneous optical/NIR imaging
FOV:
6’x6’optical
2.4’x2.4’ NIR

3. SMARTS GRB Observing Program
Program Goals:
1) RAPID FOLLOW-UP
 Afterglow detection
2) LONG-TERM FOLLOW-UP
 SNe detection
~17 months of observations (as of 4/15/05)
total # of GRBs: 63
total # observed: 25
SWIFT-era observations (~4 months, since late December 2004)
# of GRBs: 33 (3 HETE, 3 INTEGRAL, 27 SWIFT)
# observed: 12

4. SWIFT large # of GRBs detected (2/week) 3’ error in GRB position
X-ray afterglow detection localizes GRB to 6” !!

5. 1) Rapid Observing Protocol
GRB detected by SWIFT/HETE/INTEGRAL
Burst alert received by software
If GRB is observable at CTIO, the observers are alerted
Observations begin as soon as possible with predetermined observing scripts
BVRIJHK imaging performed, 2-3 minutes in each band

6. 1) Rapid Observing Results
# of observed SWIFT bursts with afterglow = 6
# of afterglows detected = 3
GRB
t = 16.1 hours
GRB
t = 63.7 hours

7. 2) Long-Term Observing Protocol
GRB detected by SWIFT/HETE/INTEGRAL
Nightly observations spaced out over a few weeks (as SNe should peak around ~20 days)
Image differencing performed (using ISIS) to locate SN brightening
Observations scheduled in the nightly queue
Deep I/J imaging performed
GRBs with reported redshift > 0.3 are not pursued

8. 2) Long-Term Observing Results
# GRBs observed long-term: 14 (7 of those pre-SWIFT)
# of SNe detected: 1  GRB /SN 2003lw (z=0.1055)
I magnitude of host =
/- 0.01
ΔI = / mag
J magnitude of host =
/- 0.03
ΔJ = / mag
Days After GRB
Cobb et al. (2004)

9. GRB and SN 2003lw

10. GRB and SN 2003lw
 ISIS kernel-convolved image subtraction
host
SN 2003lw
Cobb et al. (2004)

11. GRB & GRB
Compare GRB /SN 1998bw and GRB /SN 2003lw:
Both LOW-ENERGY GRBs
Neither GRB had an observed optical afterglow
Late-time lightcurve of both GRBs dominated by SN light
Both Type Ic SN (spectroscopically identified)
Both peculiar SN
SN have similar peak magnitude but different shape
SN 1998bw (line)
SN 2003lw (points)

12. Program Summary/Future
Over ~17 months of observations have observed 25 GRB,
detected 3 afterglows and 1 SN
Plans for the future:
Observe more GRBs!
Improve response times (where possible)
Learn from initial batch of SWIFT bursts how
to optimize our response to future bursts

14. GRB 031203, SN 2003lw  Comparison of 2003lw and 1998bw
Cobb et al. 2004, ApJ, 608, L93
Galama et al. 1998, Nature, 395, 670
Prochaska et al. 2004, ApJ, in press
Malesani et al. 2004, ApJ, 609, L5
 Comparison of 2003lw and 1998bw
SN 1998bw (line)
SN 2003lw (points)
Galactic extinction assumed to be E(B-V) = 0.78
If a higher extinction is assumed, SN 2003lw is ~0.5 mag brighter than SN 1998bw

15. Importance of a Well-Sampled LC
Gal-Yam et al. 2004
J-band: 3 points
Cobb et al. 2004
J-band 23 points
I-band 31 points!
I-band: 8 points
Thomsen et al. 2004

16. Observing Script Example
30 minute standard script N E
R (30s)
J (10s x 3 dithers )
B (45s)
K (15s x 3 dithers)
V (30s)
H (10s x 3 dithers)
I (45s)
Y (15s x 3 dithers)
Offset telescope DEC+00:00:05
Offset telescope RA+00:00:01
DEC-00:00:10
repeat
Observations are FLEXIBLE e.g. highly reddened bursts will be observed with a “reddened” script that focuses on the redder wavebands

17. IR Reduction
To produce a single master IR image (from 12/18 single IR frames in a given filter):
Flat-field each frame
Sky subtraction: 4/6 dither position A frames  median combine to produce sky frame A  subtract scaled sky frame A from each dither position A frame (repeat for dither positions B and C)
Align all sky subtracted frames: remove background with precor leaving only stars  crossdrizzle to cross-correlate the position of the stars  shiftfind calculates offset  imshift shifts each frame
Combine aligned frames to produce master IR image