GRB 180222A

S. A. Sebzda (PSU) and J. K. Cannizzo (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180222A
83 s after the BAT trigger (Cannizzo et al., GCN Circ. 22433
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 ).
No optical afterglow consistent with the XRT position
(Cannizzo et al. GCN Circ. 22433
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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            83          233          147         >20.6
u_FC               295          545          246         >19.5
white               83         1196          353         >21.6
v                  624         1073           58         >18.0
b                  551         1171           58         >18.6
u                  295         1146          285         >19.7
w1                 673         1122           58         >18.0
m2                 649         1097           58         >18.0
w2                 600         1221           78         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.68 in the direction of the burst
(Schlegel et al. 1998).

A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB),
J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU),
P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), J.P. Osborne (U.
Leicester) and J.K. Cannizzo report on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 180222A (Cannizzo et al. GCN
Circ. 22433
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 ), from 82 s to 24.2 ks after the  BAT trigger. The data
comprise 54 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. 22435
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.25 (+0.19, -0.18).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.7 (+0.6, -0.5). The
best-fitting absorption column is  1.7 (+0.9, -0.8) x 10^22 cm^-2, in
excess of the Galactic value of 6.6 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 5.4 x 10^-11 (9.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1.7 (+0.9, -0.8) x 10^22 cm^-2
Galactic foreground: 6.6 x 10^21 cm^-2
Excess significance: 2.3 sigma
Photon index:	     1.7 (+0.6, -0.5)

If the light curve continues to decay with a power-law decay index of
2.25, the count rate at T+24 hours will be 1.1 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.7 x
10^-17 (9.7 x 10^-17) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00811235.

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

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),  J. K. Cannizzo (NASA/UMBC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+423 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180222A (trigger #811235)
(Cannizzo, et al., GCN Circ. 22433
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 ).  The BAT ground-calculated position is
RA, Dec = 256.537, -36.819 deg which is
  RA(J2000)  =  17h 06m 08.8s
  Dec(J2000) = -36d 49' 08.2"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 98%.

The mask-weighted light curve consists of a single FRED pulse beginning at ~T-8 sec,
peaking at T+0 sec and decaying to background by T+60 sec. T90 (15-350 keV) is 
64.0 +- 22.6 sec (estimated error including systematics).

The time-averaged spectrum from -15.1 to 48.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.40 +- 0.21.  The fluence in the 15-150 keV band is 7.9 +- 1.0 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+8.44 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/811235/BA/

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

Using 2537 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 180222A, 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 = 256.54179, -36.81207 which is equivalent
to:

RA (J2000): 17h 06m 10.03s
Dec (J2000): -36d 48' 43.4"

with an uncertainty of 6.8 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.

S.Mereghetti (IASF-Milano), D.Gotz (CEA, Saclay), C.Ferrigno, E.Bozzo, 
V.Savchenko (ISDC, Versoix), L. Ducci (IAAT, Germany and ISDC, Versoix) 
and J.Borkowski (CAMK, Torun) on behalf of the IBAS Localization Team 
report:

a gamma ray burst lasting about 20 s has been detected by IBAS in the
IBIS/ISGRI data at 13:10:02  UT of February 22, 2018

The refined coordinates (J2000) are:

R.A.= 256.5418 deg
DEC.= -36.8016  deg

with an uncertainty of  1.5   arcmin (90% c.l.).

The burst had a peak flux of about 1 counts/cm2/s (20-200 keV, 1-s 
integration time) and a fluence in the same energy range of about 6e-7 
erg/cmq.

This burst was also detected by the Swift/BAT (Cannizzo et al., GCN 
22433
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 ).

A plot of the light curve will  be posted at
http://ibas.iasf-milano.inaf.it/IBAS_Results.html

J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU),
A. Y. Lien (GSFC/UMBC), Z. Liu (NAOC/U. Leicester),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 13:10:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180222A (trigger=811235).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 256.571, -36.803, which is 
   RA(J2000)  =  17h 06m 17s
   Dec(J2000) = -36d 48' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single FRED-like peak
with a duration of about 25 sec.  The peak count rate
was ~1400 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 13:11:22.7 UT, 79.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 256.54119, -36.80929 which
is equivalent to:
   RA(J2000)  = 17h 06m 09.89s
   Dec(J2000) = -36d 48' 33.4"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 88 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 (6.65 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 7.9
(+11.04/-4.96) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 82 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 97% of
the XRT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the large, but uncertain, extinction
expected. 

Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.nasa.gov). 
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.)