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: 6’x6’optical 2.4’x2.4’ NIR
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
SWIFT large # of GRBs detected (2/week) 3’ error in GRB position X-ray afterglow detection localizes GRB to 6” !!
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
1) Rapid Observing Results # 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)
GRB 031203 and SN 2003lw
GRB 031203 and SN 2003lw ISIS kernel-convolved image subtraction host SN 2003lw Cobb et al. (2004)
GRB 980425 & GRB 031203 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)
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
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
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
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
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