GRB 100526A

L. Vetere (PSU), S. Campana (INAF-OAB), J. R. Cummings (NASA/UMBC),
J. M. Gelbord (PSU), D. Grupe (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), W.B Landsman (GSFC), J. Mao (INAF-OAB),
F. E. Marshall (NASA/GSFC), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), T. A. Pritchard (PSU),
B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU), M. A. Stark (PSU)
and E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 16:26:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100526A (trigger=423181).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 230.785, +25.639 which is 
   RA(J2000) = 15h 23m 08s
   Dec(J2000) = +25d 38' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, there is
no obvious variation in the immediately-available lightcurve. 

The XRT began observing the field at 16:28:36.0 UT, 145.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 230.7684, +25.6310 which is equivalent to:
   RA(J2000)  = 15h 23m 04.41s
   Dec(J2000) = +25d 37' 51.6"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 61 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 2.71e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 151 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.04. 

Burst Advocate for this burst is L. Vetere (vetere AT astro.psu.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

V.Yurkov, Yu.Sergienko, D.Varda, A.Garusina Blagoveschensk Educational State 
University, Blagoveschensk

E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina, 
D.Kuvshinov, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov, D.Zemnukhov, 
M. Kornilov
Sternberg Astronomical Institute, Moscow State University

A. Tlatov, A.V. Parhomenko, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov Ural State University, 
Kourovka

K.Ivanov, S.Yazev, N.M.Budnev, E.Konstantinov, V.Lenok
Irkutsk State University

MASTER  robotic telescope (MASTER-Net: http://observ.pereplet.ru, 200 mm, 
FOV=8 square degrees (testing mode)) and  Very Wide Field Camera (D=50 
mm, 1000 square  degrees, 11 Mpx, 36" per pix, mounted on telescope) 
located at Blagoveschensk   was ponted to the  GRB 100526A (L. Vetere et 
al. gcn 10797
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 ) 21 min after burst. For the unknown reason any of our 
observatories hasn't received socket alert on this burst (we have
received only auxiliary packages).

We have a number images with  60-s exposition.
We haven't found optical transient within Swift-XRT error-box.
The 3-sigma unfiltred upper limit has been about 17.0 mag on single and 
18.2 mag on 10 images coadd.

http://observ.pereplet.ru/images/GRB100526A/grb100526.jpeg


The message may be cited.

mailto: lipunov@sai.msu.ru

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1199 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 100526A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 230.76903, +25.63234 which is equivalent
to:

RA (J2000): 15h 23m 4.57s
Dec (J2000): +25d 37' 56.4"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU), L. Vetere (PSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+303 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 100526A (trigger #423181)
(Vetere, et al., GCN Circ. 10797
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 ).  The BAT ground-calculated position is
RA, Dec = 230.792, 25.623 deg which is 
   RA(J2000)  =  15h 23m 10.2s 
   Dec(J2000) = +25d 37' 24.4" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 26%.
 
The mask-weighted light curve shows a few overlapping peaks starting at
~T-70 sec, peaking around T-20 and at ~T+75 sec, and ending at ~T+115 sec.
T90 (15-350 keV) is 102 +- 8.5 sec (estimated error including systematics).
 
The time-averaged spectrum from T-33.2 to T+80.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.83 +- 0.17.  The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+69.90 sec in the 15-150 keV band
is 0.7 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/423181/BA/

L. Vetere (PSU) reports on behalf of the Swift-XRT team:

We have analysed 1.6 ks of XRT data for GRB 100526A (Vetere et al. GCN  
Circ. 10797
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 ),
from 151 s to 5.0 ks after the BAT trigger. The data comprise 234 s in  
Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. The  
enhanced XRT
position for this burst was given by Beardmore et al. (GCN. Circ 10800).

The 0.3-10 keV light curve shows a multiple peak structure, with the  
main spike at about
T+200, followed by a fast decay with of alpha=3.24 (+/-0.08), followed  
by a break at
T+732 s to an alpha of 0.8 (+/-0.4).

A spectrum formed from the WT mode data can be fitted with an absorbed  
power-law
with a photon spectral index of 2.97 (+/-0.08). The best-fitting  
absorption column is 3.21
(+0.18, -0.17) x 10^21 cm^-2, in excess of the Galactic value of 3.8 x  
10^20 cm^-2
(Kalberla et al. 2005). The PC mode spectrum has a photon index of  
2.45 (+0.24, -0.22)
and a best-fitting absorption column of 1.8 (+0.6, -0.5) x 10^21  
cm^-2. The counts to
observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from  
this spectrum is
3.3 x 10^-11 (5.9 x 10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of  
0.8, the count rate
at T+24 hours will be 0.011 count s^-1, corresponding to an observed  
(unabsorbed)
0.3-10 keV flux of 3.7 x 10^-13 (6.7 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00423181.

This circular is an official product of the Swift-XRT team.

D. Xu (Weizmann Inst.), D. Malesani (DARK/NBI), P. Jakobsson (Univ. 
Iceland), T. Augusteijn (NOT), A. Thygesen (NOT)
report on behalf of a larger collaboration:

We observed the field of GRB 100526A (Vetere et al., GCN 10797
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 ) with 
the NOT equipped with ALFOSC in the R and i filters. Observations 
started on May 26 at 22:43 and 23:10 UT in R and i, respectively (6.282 
and 6.742 hr after the GRB), and were affected by the closeby Moon (47 
deg away).

We do not detect any new object within the refined XRT error circle 
(Beardmore et al, GCN 10800
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 ) in both R and i bands. The limiting 
magnitude is R(Vega) ~ 23.8, calibrated against the SDSS catalog.

[GCN OPS NOTE(27may10): Per author's request, Augusteijn was added
to the author list.]

D. A. Perley (UC Berkeley) reports on behalf of a larger collaboration:

We imaged the field of GRB 100526A (Vetere et al., GCN 10797
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 ) with the 
Near-InfraRed Imager (NIRI) on Gemini-North starting at 08:29 UT on 
2010-05-27.  We obtained 18 exposures of 60 seconds each in K-band and 
H-band.

At the edge of the XRT error circle (Beardmore et al., GCN 10800
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 ) we 
clearly detect a source with no SDSS counterpart in the K-band image. 
It is also present, but much fainter, in H-band.  The position (J2000) is:

RA  =  15:23:04.480
Dec = +25:37:55.23
(+/- 0.4")

Preliminary photometry relative to a single 2MASS star in the field 
(2MASS 1523017+2538260) gives:

K = 19.09 +/- 0.13  (t_mid = 16.21 hours)
H = 21.15 +/- 0.17  (t_mid = 16.75 hours)

This is an extremely red color, corresponding to a spectral slope of 
beta~5.5.  If this object is confirmed as the afterglow (rather than a 
host or background galaxy), its flux and color are reminiscent of GRB 
070306 (Jaunsen et al. 2008) at similar times.  That object had a visual 
extinction of A_V~5.5 mag and is among the most heavily extinguished 
afterglows known.  The large inferred XRT absorption column (Vetere et 
al., GCN 10804
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 ) of this event is also consistent with a highly 
dust-extinguished event at low to moderate redshift.

We thank Richard McDermid and the Gemini staff for acquiring these 
observations.

T. A. Pritchard (PSU) and Vetere (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100526A
151 s after the BAT trigger (Vetere et al., GCN Circ. 10797
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 ).
No optical afterglow consistent with the enhanced XRT position
(A. P. Beardmore et al.,GCN Circ. 10800) is detected in the initial
UVOT exposures.

Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC)
exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
--------------------------------------------------------------
white (FC)         151          301          147         >21.1
u (FC)             310          559          246         >20.1
white              151         7321          783         >22.4
v                  640         6296          313         >20.3
b                  565         7116          491         >21.5
u                  310         6911          717         >21.3
w1                 690         6706          471         >20.9
m2                4865         6501          393         >20.6
w2                 791         7374          263         >20.6

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998)

D. Shakhovkoy, V. Rumyantsev (CrAO), A. Pozanenko (IKI)  report on behalf of
larger GRB  follow-up collaboration:

We observed the field of the Swift GRB 100526A (Vetere et al. GCN  10797
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 )
with AZT-11 telescope of CrAO between (UT) May 26  21:34 -- 22:36 under
mean  seeing of about 3 arcsec. No objects is detected in enhanced XRT error
circle (Beardmore et al. GCN 10800
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 ).

The upper limit in a stacked image based on USNO-B1.0 star  1156-0223950 
(assuming R=18.44)  is following:

T0+      Filter,   Exposure, mag.
(mid, d)              (s)

0.2354   R       20x180    > 21.4

D. A. Perley, J. S. Bloom, and S. B. Cenko (UC Berkeley) report:

We re-observed the field of GRB 100526A (Vetere et al., GCN 10797
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 ) with 
NIRI on Gemini-North between 08:30 and 09:00 UT on 2010-06-24 UT.  We 
acquired 27 images of 60 seconds each in K-band.

Comparison to our previous K-band imaging of this field (Perley et al., 
GCN 10806
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 ) shows the infrared counterpart to have faded significantly. 
A source is still detected at high significance at the afterglow 
position.  Using the same 2MASS reference star as for our previous 
epoch, we measure a magnitude of:

K = 21.2 +/- 0.2   (t_mid = 27.7 days)

This corresponds to a decay index (t^-alpha) of only alpha~0.5 from our 
previous epoch, which is much slower than expected for a late-time 
afterglow, and suggests that the current epoch is likely host-galaxy 
dominated.

A comparison image is posted to:
http://lyra.berkeley.edu/~dperley/100526a/100526a_niri.png