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ANDICAM Observations of GRBs. Bethany E. Cobb Yale University. 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:
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- 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
- 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
- large # of GRBs detected (2/week)
- 3’ error in GRB position
- X-ray afterglow detection localizes GRB to 6” !!
- 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
# of observed SWIFT bursts with afterglow = 6
# of afterglows detected = 3
GRB 050401
t = 16.1 hours
GRB 050401
t = 63.7 hours
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
2) Long-Term Observing Results
# GRBs observed long-term: 14 (7 of those pre-SWIFT)
# of SNe detected: 1 GRB 031203/SN 2003lw (z=0.1055)
I magnitude of host =
19.21 +/- 0.01
ΔI = 0.22 +/- 0.03 mag
J magnitude of host =
18.29 +/- 0.03
ΔJ = 0.29 +/- 0.04 mag
0 20 40 60 80 100
Days After GRB
Cobb et al. (2004)
- Compare GRB 980425/SN 1998bw and GRB 031203/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)
- 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
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
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
E
Observing Script Example
30 minute standard script
repeat
Observations are FLEXIBLE e.g. highly reddened bursts will be observed with a “reddened” script that focuses on the redder wavebands
- 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
