GRB 110530A

P. D'Avanzo (INAF-OAB), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), S. Campana (INAF-OAB),
V. D'Elia (ASDC), J. M. Gelbord (PSU), B. Gendre (ASDC),
C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
V. Mangano (INAF-IASFPA), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), P. T. O\'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-OAB/IASFPA),
M. H. Siegel (PSU), C. A. Swenson (PSU) and T. N. Ukwatta (MSU) report
on behalf of the Swift Team:

At 15:31:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110530A (trigger=454473).  Swift slewed after 11 minutes
because of an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 282.045, +61.932, which is 
   RA(J2000)  =  18h 48m 11s
   Dec(J2000) = +61d 55' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 20 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 15:38:16.7 UT, 434.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 282.06718, 61.92861 which is equivalent
to:
   RA(J2000)  = 18h 48m 16.12s
   Dec(J2000) = +61d 55' 43.0"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 39 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 5.65
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 437 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	18:48:16.35 = 282.06814
  DEC(J2000) = +61:55:45.1  =  61.92920
with a 90%-confidence error radius of about 0.71 arc sec. This position is 2.8
arc sec. from the center of the XRT error circle. The estimated magnitude is
20.31 with a 1-sigma error of about  0.18. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.06. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.it). 
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.)

Y. Yatsu, K.Kawakami, Y. Aoki, K. Tokoyoda, M. Hayashi, S. Song,
R. Usui, and N. Kawai (Tokyo Tech)  report on behalf of the MITSuME
collaboration:

We observed GRB110530A (D'Avanzo et al, GCN12046
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 )
with the optical three color (g, Rc, and Ic) CCD camera attached
to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.
The follow-up observation was started at 15:31:02, ~2min after the BAT trigger.
And we detected a very faint object within the XRT error circle in R-band.
The measured R-band magnitude is shown below.

T0+[s]   MID-UT   T-EXP[sec]    g'             Rc           Ic
-----------------------------------------------------------------------
125    15:39:42          660           ---   18.84 +/- 0.65   ---
-----------------------------------------------------------------------
T0+ : Elapsed time after the burst [sec]
T-EXP: Total Exposure time [sec]

Photometric results and are listed below. We used GSC2.3 catalog for
flux calibration.

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
P. D'Avanzo (INAF-OAB), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 110530A (trigger #454473)
(D'Avanzo, et al., GCN Circ. 12046
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 ).  The BAT ground-calculated position is
RA, Dec = 282.045, 61.953 deg, which is 
   RA(J2000)  =  18h 48m 10.8s 
   Dec(J2000) = +61d 57' 11.2" 
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 98%.
 
The mask-weighted light curve shows a single pulse starting at ~T-50 sec
with a slow rise, peaking at ~T+2 sec, and ending at ~T+15 sec.
T90 (15-350 keV) is 19.6 +- 3.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-4.5 to T+17.4 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.06 +- 0.24.  The fluence in the 15-150 keV band is 3.3 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.01 sec in the 15-150 keV band
is 0.4 +- 0.1 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/454473/BA/

K.Ivanov, O. Gres, V.A.Poleshchuk, S.Yazev, N.M.Budnev, 
O.Chuvalaev
Irkutsk State University

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


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

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

V.Yurkov, Yu.Sergienko, I.Kudelina
Blagoveschensk Educational State University, Blagoveschensk

  MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Tunka(Siberia) was pointed to the  GRB 110530A (D'Avanzo et 
al, GCN12046
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 )  12 sec s after notice time and 73 sec after GRB time at
2011-05-30 15:32:15.215 UT. On our first (10s exposure) set 
we haven`t found optical transient  within 
SWIFT error-box.
The 5-sigma upper limit has been about 15.2 mag (Polarization + R band).

The OT appears at 15:42:14 UT  (t_start-t_triger = 673 s, Exp_time=130s). 
Mag ~18.3 (R).

After that we see OT on our images in different filters 
(R,I,Unfiltered,R+P).
20 min ago (2011-05-30 17:44:42):  R ~19.5+-0.5.

The reduction is continued.

This message may be cited.

[GCN OPS NOTE(30may11):  Per author's request, the subject line
was changed from "110521" to "110530".]

Vladimir Lipunov.

The GCN Circular N 12050 correct subject is:

GRB 110530A: MASTER OT observations

I am sorry.

M. Andreev, A. Sergeev, I. Sokolov (Terskol Branch of Institute of 
Astronomy), Yu. Bronich (IC AMER of NASU),  A.Pozanenko (IKI) on behalf of 
larger GRB follow up collaboration report:

We observed the optical afterglow  of the Swift   GRB 110530A (D'Avanzo et 
al, GCN 12046
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 ) with Zeiss-2000 and Zeiss-600 telescopes of Mt.Terskol 
observatory. Optical afterglow is detected in a stacked images. The 
photometry is based on the star USNO-B1.0 1519-0265568 (RA=18 48 15.86, 
Dec=+61 56 15.0) assuming R=16.08  is following

UT (mid time), Exposure,   Filter,     OT

18:00              12 x 30 s    R(gunn)  20.32 +/- 0.08
18:58              24 x 150 s  R           20.6   +/- 0.2

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 110530A (D'Avanzo et al., GCNC 12046)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2011-05-30 15:41:32 UT (~11 min after
the burst). We detected the previously reported afterglow
(Yatsu et al., GCNC 12048) in Rc and Ic bands.


Photometric results and are listed below. We used GSC2.3 catalog for
flux calibration.

#T0+[day]  MID-UT    T-EXP[sec]   g'    Rc  Rc_err   Ic  Ic_err
----------------------------------------------------------------------
0.06460    17:04:03    5520.0   >20.3  19.8   0.2   19.6   0.2
----------------------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

A. De Cia, P. Vreeswijk (U. of Iceland), D. Xu (Weizmann Inst.),
J. Telting (NOT) and P. Jakobsson (U. of Iceland)

report on behalf of a larger collaboration:

We observed the field of D'Avanzo et al. (GCN 12046
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 ) with the
2.5m NOT telescope at Roque de los Muchachos Observatory (La
Palma, Spain) equipped with ALFOSC, starting at 22:18 UT (6.8h
after the burst). The optical afterglow is detected, within the
XRT error circle reported by D'Avanzo et al., at R ~ 21.3,
calibrated against the USNO-B1.0 1519-0265568 star (R2=16.08)
also adopted by Andreev et al. GCN 12052
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 .

Preliminary reduction of the subsequent spectroscopic
observations does not show any evident absorption lines, given
the poor S/N. A rough limit on the source redshift z<2.7 may be
placed by the non-detection of Lyman alpha absorption in the
spectra.

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

Using 8011 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 110530A, 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 = 282.06843, +61.92897 which is equivalent
to:

RA (J2000): 18h 48m 16.42s
Dec (J2000): +61d 55' 44.3"

with an uncertainty of 1.4 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.

L.P. Xin, Y.L. Qiu, J.Y. Wei, J. Wang, J.S. Deng, 
C. Wu, X. H. Han on behalf of EAFON report:

We began to observe GRB 110530A (D'Avanzo et al, GCN 12046
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 ) 
with Xinglong TNT telescope at 15:33:15(UT), 133 sec after 
the burst. The optical afterglow is clearly detected in all images.
The brightness is 20.7 mag in R band relative to the reference star
of Andreev et al. (GCN Circ. 12052
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 ) at the mean time of 10000 sec 
after the burst. 

More observations are encouraged. 

This message may be cited.
.

F. E. Marshall (NASA/GSFC) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110530A
438 s after the BAT trigger (D'Avanzo et al., GCN Circ. 12046
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 ).
A fading source consistent with the enhanced XRT position
(Evans et al., GCN Circ. 12055
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 ) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  18:48:16.40 = 282.06833 (deg.)
    Dec (J2000) = +61:55:44.9  =  61.92913 (deg.)
with an estimated uncertainty of 0.65 arc sec. (radius, 90% confidence).

Preliminary detections using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag
white              438         1015          295         20.31 +/- 0.10
white             7070         8315         1042         21.52 +/- 0.21

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).

P. D'Avanzo (INAF-OAB) reports on behalf of the Swift-XRT team:

We have analysed 12 ks of XRT data for GRB 110530A (D'Avanzo  et al.
GCN Circ. 12046
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 ), from 446 s to 43.1 ks after the  BAT trigger. The
data comprise 29 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN. Circ 12055).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.81 (+0.05, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.30 (+0.09, -0.17). The
best-fitting absorption column is  2.8 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 5.6 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.7 x 10^-11 (7.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.8 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 5.6 x 10^20 cm^-2
Excess significance: 9.2 sigma
Photon index:	     2.30 (+0.09, -0.17)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00454473.

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

M. Andreev, A. Sergeev, I. Sokolov (Terskol Branch of Institute of 
Astronomy), Yu. Bronich (IC AMER of NASU),  A. Pozanenko (IKI) on behalf of 
larger GRB follow up collaboration report:

We observed the optical afterglow  of the Swift   GRB 110530A (D'Avanzo et 
al, GCN 12046
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 ) with Zeiss-2000 telescope of Mt.Terskol observatory On May, 
31 between (UT) 21:41-22:11.  At  the place of optical afterglow we detect 
extended object (elongated from SE to NW) with brightness R(gunn) ~ 22.7 
calibrated against  the star USNO-B1.0 1519-0265568 (RA=18 48 15.86, Dec=+61 
56 15.0) and assuming R=16.08.

Coordinates of South-East part of the extended object are  (J2000) 18 48 
16.27   +61 55 45.3  which is ~2" apart from position of the optical 
afterglow (J2000) 18 48 16.39   +61 55 45.16  obtained in our first epoch 
observations (Andreev et al. GCN 12052
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 ). The accuracy of  astrometry  is 
about 0.7" in both coordinates. One can suggest  the extended object might 
be a bright host of GRB 110530A.
The finding chart can be found at 
http://grb.rssi.ru/GRB110530A/grb110530_2m110531.jpg

A. Volnova (SAI MSU),   E. Klunko (ISTP),  A. Pozanenko (IKI) on behalf of 
larger GRB follow up collaboration report:

We observed the optical afterglow  of the Swift   GRB 110530A (D'Avanzo et 
al, GCN 12046
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 ) with AZT-33IK telescope of Sayan observatory (Mondy) on May, 
30 between (UT) 16:06:01 - 19:14:06 (i.e. t0+0.0243 d -- t0+0.1549 days 
after burst trigger). We took several series of 60 s exposures in R. Optical 
afterglow is detected in single images in the beginning of the observations 
while in the end we stacked images in 180 - 300 s combined exposures. The 
photometry is based on the USNO-B1.0 1519-0265568 star (RA=18 48 15.86, 
Dec=+61 56 15.0) assuming R=16.08.   In particular, the photometry

UT (mid time), Exposure,   Filter,     OT
18:04               5x60          R           20.25 +/- 0.06
18:54               5x60          R           20.58 +/- 0.07

coincide with the photometry reported earlier (Andreev et al., GCN 12052
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 ).

Preliminary light curve can be found at

http://grb.rssi.ru/GRB110530A/GRB110530A_AZT33IK_lc.png

One can note a non-monotonous light curve decay with possible rebrightening 
at  0.03 d and 0.53 d and general power law decay index of about 0.9.