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MDM Observatory GRB Team

GRB 060526: Optical follow-up

GCN Circular #5175
GRB 060526: MDM-2.4m Observations
N. D. Morgan and X. Dai (Ohio State Univ.)

We observed GRB 060526 (GCN 5162, Campana et al. 2006) with MDM-2.4m for 
three epochs.  The afterglow is detected in all three observations.

Using USNO B-1 star as the reference (RA=15:31:18.6, DEC=+00 17 34.9, 
R2MAG=16.35, same one used in GCN5173 Khamitov et al. 2006), we get

Rc = 19.90 @ May 27, 03:33:00 UT
Rc = 19.98 @ May 27, 06:02:00 UT
Rc = 20.11 @ May 27, 09:49:00 UT

This message may be cited.

GCN Circular #5176
GRB 060526: Optical Flare
J. P. Halpern (Columbia U.), E. Armstrong (UCSD), & N. Mirabal (U. Michigan) 
report on behalf of the MDM Observatory GRB follow-up team:

"Using the MDM 1.3m telescope on Kitt Peak, we obtained a continuous R-band
time series of the afterglow of Swift GRB 060526 (Campana et al. GCN 5162), 
consisting of 40 10-minute exposures, from 11.0 to 18.2 hours after the burst.  
Preliminary photometry was performed using comparison stars in r' from the
SDSS calibration (Cool et al. GCN 5164).  In addition, wherever possible, we 
placed other GCN reported R-band photometry (Covino et al. GCN 5167; 
Khamitov et al. GCN 5173; Morgan & Dai GCN 5175) on a common scale using the 
SDSS r' magnitudes of their indicated comparison stars.  As a result, we find 
that a power-law decay index of -1.18 +/- 0.05 fitted to the Khamitov et al. 
data alone from 5.6 to 8.9 hours also fits the MDM light curve very well, until 
about 16 hours after the burst.  At that time, a flare began that had a rise 
time of about 40 minutes, followed by a slower decay, and had not yet returned 
to the extrapolated power law when the observations were terminated at twilight.
The peak of the flare occurred around May 27 09:06 UT, and reached about 0.3 
magnitudes above the extrapolation.

In combination with the multiple episodes of gamma-ray and X-ray emission
(Campana et al. GCNs 5163, 5168; Markwardt et al. GCN 5174) and the long
plateau in the early optical light curve (Rykoff et al. GCN 5166), these
results indicate the possibility of extended and complex activity from
GRB 060526 that warrants intensive monitoring.

A preliminary version of the MDM optical light curve and incorporated
GCN data is available at

The data contained in the figure are not yet suitable for publication."

(J2000) 15h 31m 18.36s, +00° 17′ 04.9″ (2.2′ × 2.2′)
MDM 1.3m MDM 1.3m

GCN Circular #5188
GRB 060526: Multiple Optical Flares
J. P. Halpern (Columbia U.), E. Armstrong (UCSD), & N. Mirabal (U. Michigan) 
report on behalf of the MDM Observatory GRB follow-up team:

"We have continued to observe the afterglow of Swift GRB 060526 (Campana 
et al. GCN 5162) in the R-band for four consecutive nights using the
MDM 1.3m.  In combination with the GCN reported R-band photometry of 
Khamitov et al. (GCNs 5173,5177,5183,5186), it is evident that there have
been at least four flares, by which we mean alternating positive and
negative deviations from a mean decay rate.  These are characterized
as increases and decreases of at least 0.3 mag in as short a time as
delta t = 0.04*(t-t0), where t0 is the burst time.  In view of these
flares, it is problematic to fit a small number of power-law segments
(as noted by Kann & Thoene GCN 5187).  Rather, we observe that the most 
recent point, r' = 22.87+/-0.07 on May 30 04:23 UT as calibrated with
Cool et al. (GCN 5164) data, falls only 0.25 mag below the -1.18 power
law originally fitted from 5.6 to 16 hours by Khamitov et al. (GCN 5173)
and Halpern et al. (GCN 5176).  Other details of the MDM optical light
curve and incorporated GCN data can be seen at:

This type of light curve is not uncommon in GRB afterglows (see, e.g.,
Stanek et al. astro-ph/0602495, and references therein), and is often
apparent when the source is well placed for long observing runs at
ground-based telescopes."

This decay curve is preliminary, not for publication.
Decay Curve
Expanded Decay Curve

Eve Armstrong
Nick Morgan
Xinyu Dai
Jules Halpern
Nestor Mirabal
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Last Modified: June 1, 2006