GRB 150222A

M. G. Bernardini (INAF-OAB), S. D. Barthelmy (GSFC),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), A. Melandri (INAF-OAB), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 16:56:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150222A (trigger=632180).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 198.774, -12.137 which is 
   RA(J2000) = 13h 15m 06s
   Dec(J2000) = -12d 08' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of about 15 sec.  The peak count rate
was ~6000 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 16:58:13.6 UT, 92.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 198.7865,
-12.1517 which is equivalent to:
   RA(J2000)  = 13h 15m 08.76s
   Dec(J2000) = -12d 09' 06.3"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 68 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.31 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.9
(+2.52/-2.21) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 96 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
0.05. 

Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini 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.)

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

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

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

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

V.Krushinsky, I.Zalozhnih,  A. Popov
Ural Federal University, Yekaterinburg, Kourovka

D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Tunka was pointed to the  GRB150222A  58 sec after notice time 
and 76 sec after trigger time at 2015-02-22 16:57:57 UT in two 
polarizations. On our first (10s 
exposure)  set we haven`t found optical transient  within SWIFT error-box 
(Bernardini  et. al GCN 17486
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 ).
The 5-sigma upper limit has been about 15.5 mag
The observations  made on high zenith distance (z=75 d).
The message may be cited.

A. Klotz, D. Turpin (IRAP-CNRS-OMP), D. Macpherson (UWA/ICRAR), D. 
Coward (UWA),
M. Boer, B. Gendre, K. Siellez, H. Dereli, O. Bardho (UNS-CNRS-OCA),
A. Williams (PO-UWA), R. Martin (PO-UWA)
report:

We imaged the field of GRB 150222A detected by SWIFT
(trigger 632180) with the Zadko robotic telescope (D=100cm)
located at the observatory - Gingin, Australia.

The observations started 55s after the GRB trigger
(42s after the notice). The elevation of the field increased from
51 degrees above horizon and weather conditions
were very good.

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect any OT at the XRT position
(Bernardini et al. GCNC 17486) with a limiting magnitude of:
t0+55s to t0+115s : Rlim = 18.5

The second image is 30.0s exposure in tracking mode:
t0+134s to t0+164s : Rlim = 19.8

We co-added a series of exposures:
t0+134s to t0+834s : Rlim = 21.5

Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.

E. Mazaeva (IKI), A. Volnova (IKI), E. Klunko (ISTP), I. Korobtsev 
(ISTP), M. Eselevich (ISTP), A. Pozanenko (IKI) report on behalf of 
larger GRB follow-up collaboration:

We observed the field of GRB 150222A  (Bernardini  et al., GCN 17486
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 ) 
with AZT-33IK telescope of Sayan observatory (Mondy)  starting on Feb., 
22 (UT) 17:48:56. We obtained 37 images in R-filter of 120 s exposure. 
Within the Swift-XRT error circle (Bernardini  et al., GCN 17486
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 ) we 
marginally detected optical  source with a magnitude of R=22.15+/-0.25 
at 0.06201 days after trigger (mid time). Photometry of the source is 
based on nearby USNO-B1.0 (R2) stars. At this time we cannot confirm 
variability or fading nature of the source.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),  W. H. Baumgartner (GSFC/UMBC),
M. G. Bernardini (INAF-OAB), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-60 to T+117 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150222A (trigger #632180)
(Bernardini, et al., GCN Circ. 17486
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 ).  The BAT ground-calculated position is
RA, Dec = 198.787, -12.151 deg which is
    RA(J2000)  =  13h 15m 09.0s
    Dec(J2000) = -12d 09' 02.0"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 48%.

The mask-weighted light curve shows a double-peaked structure, with a first peak 
from T+0 to T+3 sec and a second, larger peak from T+3 to T+18 sec, followed by 
lower level emission out to ~T+40 sec.
T90 (15-350 keV) is 15.90 +- 7.32 sec (estimated error including systematics).

The time-averaged spectrum from T-0.14 to T+28.11 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.61 +- 0.08.  The fluence in the 15-150 keV band is 2.2 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+5.62 sec in the 15-150 keV band
is 4.7 +- 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/632180/BA/

D. Malesani (DARK/NBI), V. D'Elia (INAF/OAR and ASI/ASDC), P. D'Avanzo 
(INAF/OABr), A. Melandri (INAF/OABr), S. Covino (INAF/OABr), V. Lorenzi 
(INAF/TNG), Albar Garcia de Gurtubai Escudero (INAF/TNG), report on 
behalf of the CIBO collaboration:

We observed the field of GRB 150222A (Bernardini et al., GCN 17486
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 ) with 
the 3.6m TNG telescope equipped with the DOLoRes camera. Observations 
consisted of 4 images in the I band for a total of 20 min exposure. The 
seeing was poor (3.2").

No object is detected within the (currently unenhanced) XRT position, 
down to a limiting magnitude I > 22.3 (calibrated against nearby USNO 
stars). The mean time of the observation was 2015 Feb 23.055 UT, that is 
8.4 hr after the GRB.

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

Using 3503 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 150222A, 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 = 198.78648, -12.15200 which is equivalent
to:

RA (J2000): 13h 15m 8.75s
Dec (J2000): -12d 09' 07.2"

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.

A. Nicuesa Guelbenzu (TLS Tautenburg), P. Wiseman (MPE Garching), and J.
Greiner (MPE Garching) report:

We observed the field of GRB 150222A (Swift trigger 632180; Bernardini et
al., GCN 17486
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 03:39:15 UT on February 23, about 10 hours after
the GRB trigger. Inside the enhanced X-ray error circle (Beardmore et al.,
GCN 17494
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 ) we detect a faint source at coordinates RA, DEC (J2000) =
13:15:08.75, -12:09:06.2 with an error of 0".5.

At a mean time of February 23, at 04:39:07 UT, we measure the following
preliminary AB magnitude:


g' = 24.8 +/- 0.2.
r' = 24.6 +/- 0.3.

At present we cannot decide if this is the afterglow. Observations are
ongoing.

Magnitudes are calibrated against GROND zeropoints (g'r'i'z')
and are not corrected for the Galactic extinction
in the direction of the burst.

C. Pagani (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), M.
de Pasquale (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows
(PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and M. G.
Bernardini (INAF-OAB) report on behalf of the Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 150222A (Bernardini et al.
GCN Circ. 17486
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 ), from 76 s to 44.7 ks after the  BAT trigger. The data
comprise 221 s in Windowed Timing (WT) mode (the first 10 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN Circ. 17494
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.95 (+/-0.03). Some flaring activity is observed 
between T+250 s and T+650 s.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.51 (+0.12, -0.11). The
best-fitting absorption column is  4.7 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 3.3 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.45 (+0.19, -0.18)
and a best-fitting absorption column of 5.8 (+1.0, -0.9) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.4 x 10^-11 (7.9 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.8 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 3.3 x 10^20 cm^-2
Excess significance: 10.0 sigma
Photon index:	     2.45 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
0.95, the count rate at T+24 hours will be 9.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.3 x
10^-13 (7.8 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/00632180.

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

N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150222A
96 s after the BAT trigger (Bernardini et al., GCN Circ. 17486
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 ).
No optical afterglow consistent with the XRT position (Beardmore et
al. GCN Circ. 17494
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 ) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            96          246          147         >20.8
u_FC               308          558          246         >20.7
white               96         6906          746         >21.3
v                  639         5881          274         >19.9
b                  564         6702          452         >20.9
u                  308         6496          678         >20.8
w1                 689         6292          432         >20.0
m2                 836         6086          413         >20.4
w2                1019         6994          297         >20.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).

Antonio de Ugarte Postigo (IAA-CSIC, DARK/NBI), Christina Thoene (IAA-CSIC), 
and Victor Casanova (IAA-CSIC) report on behalf of a larger collaboration:

We observed the field of GRB 150222A (Bernardini et al., GCN 17486
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 ) with the 
1.5 m telescope at Sierra Nevada Observatory (Granada, Spain). 
Observations consisted of 34x300s in I-band and ranged from 2:46 to 5:44 UT 
(mid epoch at 4:15 UT, or 11.31 hr after the burst trigger). Observing conditions 
were poor, with a seeing of 2.9". We do not detect the optical counterpart 
candidate reported by Mazaeva et al. (GCN 17489
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 ) and Nicuesa Guelbenzu et al.
(GCN 17495
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 ) or any other object within the enhanced XRT error circle (Beardmore
et al. GCN 17494
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 ). The 3-sigma limit of the combined image is I(Vega) = 22.5 mag,
as compared with USNOB-1.0 stars.
 
Considering an optical decay slope of alpha ~ 1.1 (where F_nu ~ t^(-alpha)) 
between the epochs of Mazaeva et al. and Nicuesa Guelbenzu et al., and a typical 
GRB colour, our observation is consistent with the expected brightness and is also 
consistent with the non-detections reported by other groups (Ivanov et al. GCN 
17487
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 ; Klotz et al. GCN 17488
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 ; Malesani et al. GCN 17493
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 ; Kuin et al. GCN 17499
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 )

A. Nicuesa Guelbenzu (TLS Tautenburg), P. Wiseman, P. Schady and J. 
Greiner (all MPE Garching) report on behalf of the GROND team:

We continued to observe the field of GRB 150222A (Swift trigger 632180; 
Bernadini et al., GCN 17486
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 ) for a second night, simultaneously in 
g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at 
the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).

Observations began at 06:25:38 UT on February 24, ~34 hours after the 
GRB trigger. They were performed at an average seeing of 1.3" and at an 
average airmass of 1.1//.
In 106 min of total exposures in g'r'i'z', we detect a source in all 
optical bands towards the north-eastern edge of the the 1.7" enhanced 
Swift-XRT error circle (Beardmore et al., GCN 17494
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 ) , at a position 
consistent with that reported in Nicuesa Guelbenzu et al. (GCN 17495
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 ).
In 115 min of total NIR exposures in the JHK bands, no source is 
detected within the enhanced XRT error circle.

We detect no fading of the source between the two epochs, and therefore 
suggest that this is not the afterglow, but could be the host galaxy 
instead, unless we caught an afterglow plateau phase.

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

We observed the field of the Swift GRB GRB 150222A (Bernardini et al., 
GCN 17486
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 ) with ZTSh telescope of CrAO observatory starting on
Feb. 22 (UT) 23:19:54. We took several images in R-filter of 120 s 
exposure under non-optimal weather conditions and mean seeing of 4". 
Within enhanced  XRT position (Beardmore et al., GCN 17494
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 ) we detect a 
source in coordinates (J2000) 13 15 08.74 -12 09 07.2 with uncertainty 
of 0.4 arcsec in both coordinates. The source position is coincident 
with the optical afterglow candidate (Nicuesa Guelbenzu et al., GCNs 
17495
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 , GCN 17506
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 ).  Photometry of the source in a combined image is 
following

Date       UT start,  t-t0     Filter   Exp.    OT   OT_err UL(3sigma)
                       (mid, days)        (s)

2015-02-22 23:19:54   0.2913   R        34*120  23.0 0.3    23.3

The photometry is based on USNO-B1.0  star 0778-0337957 (J2000) 13 15 
05.41 -12 08 17.5 assuming R2=15.31

Taking into account photometry of the source r' = 24.6+/-0.3 at ~0.42 
days reported by Nicuesa Guelbenzu et al. (GCN 17495
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 ) one could suggest 
the source is the optical afterglow of GRB 150222A.

The source reported in GCN 17489
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  (Mazaeva et al) is clearly visible in 
coordinates (J2000) 13 15 08.30 -12 08 57.5 with uncertainty of 0.4 
arcsec in both coordinates. A photometry of the source is R=22.12+/-0.12.