GRB 190220A

V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), S. J.
LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), A.P.
Beardmore (U. Leicester), P.A. Evans (U. Leicester) and K.L. Page
report on behalf of the Swift-XRT team:

We have analysed 6.9 ks of XRT data for GRB 190220A (Page et al. GCN
Circ. 23908
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 ), from 68 s to 80.7 ks after the  BAT trigger. The data
comprise 67 s in Windowed Timing (WT) mode (the first 8 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 Evans et
al. (GCN Circ. 23912
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 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.4 (+0.3, -0.4), followed by a break at T+173 s to an
alpha of 1.10 (+/-0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.69 (+0.25, -0.23). The
best-fitting absorption column is  3.9 (+1.5, -1.2) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 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 4.7 x 10^-11 (6.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.9 (+1.5, -1.2) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 3.7 sigma
Photon index:	     1.69 (+0.25, -0.23)

If the light curve continues to decay with a power-law decay index of
1.10, the count rate at T+24 hours will be 1.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.1 x
10^-14 (1.2 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/00889785.

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

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
K. L. Page (U Leicester), 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+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 190220A (trigger #889785)
(Page et al., GCN Circ. 23908
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 ).  The BAT ground-calculated position is
RA, Dec = 330.128, -76.669 deg which is
  RA(J2000)  =  22h 00m 30.7s
  Dec(J2000) = -76d 40' 10.1"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 46%.

The mask-weighted light curve shows a single-pulse structure that starts
at ~T0, peaks at ~T+2 s, and ends at ~T+12 s. T90 (15-350 keV)
is 10.0 +- 2.0 sec (estimated error including systematics).

The time-averaged spectrum from T-0.12 to T+11.88 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.79 +- 0.77,
and Epeak of 40.3 +- 6.7 keV (chi squared 60.03 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 8.9 +- 1.0 x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+1.88 sec in the 15-150 keV band is
2.6 +- 0.4 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.03 +- 0.13 (chi squared 70.39 for 57 d.o.f.).  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/889785/BA/

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

Using 749 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 190220A, 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 = 330.16376, -76.68124 which is equivalent
to:

RA (J2000): 22h 00m 39.30s
Dec (J2000): -76d 40' 52.5"

with an uncertainty of 1.5 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.

K. L. Page (U Leicester), N. J. Klingler (PSU),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. H. Siegel (PSU)
and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 02:59:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190220A (trigger=889785).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 330.142, -76.691 which is 
   RA(J2000) = 22h 00m 34s
   Dec(J2000) = -76d 41' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 10 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 03:00:55.5 UT, 80.8 seconds after
the BAT trigger. The position determined from promptly downlinked data
differs significantly from the on-board position, suggesting that the
XRT may have centroided on a cosmic ray; the initial XRT position
notice should be treated with caution. Using promptly downlinked data
we find an uncatalogued, fading X-ray source located at RA, Dec 330.16325,
-76.68047 which is equivalent to:
   RA(J2000)  = 22h 00m 39.18s
   Dec(J2000) = -76d 40' 49.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 41 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 (1.10 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 4.9
(+3.65/-3.07) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 86 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	22:00:39.14 = 330.16309
  DEC(J2000) = -76:40:50.4  = -76.68067
with a 90%-confidence error radius of about 0.66 arc sec. This position is 3.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.29 with a 1-sigma error of about  0.16. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.13. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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/)