GRB 190422A

M. J. Moss (George Washington University), S. D. Barthelmy (GSFC),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
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 22:55:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190422A (trigger=899979).  Swift did not slew until ~T+8 min 
due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 182.124, -60.238 which is 
   RA(J2000) = 12h 08m 30s
   Dec(J2000) = -60d 14' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of at least 220 sec, where data are currently
available. The peak count rate based on the available data
was ~2000 counts/sec (15-350 keV), at ~175 sec after the trigger. 

The XRT began observing the field at 23:04:18.5 UT, 529.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 182.03650, -60.22311 which is
equivalent to:
   RA(J2000)  = 12h 08m 08.76s
   Dec(J2000) = -60d 13' 23.2"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 165 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 in excess of the Galactic value (8.59 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 1.1
(+1.25/-0.89) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 531 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 none of
the XRT error circle. 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 large, but
uncertain, extinction expected. 

This source lies within the current (Sector 11) field-of-view of TESS camera 2. 

Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 
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/)

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

Using 1699 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 190422A, 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 = 182.03450, -60.22425 which is equivalent
to:

RA (J2000): 12h 08m 8.28s
Dec (J2000): -60d 13' 27.3"

with an uncertainty of 1.8 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.

D.N. Burrows (PSU), A. Tohuvavohu (PSU), A.P. Beardmore (U. Leicester),
P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), S. J.
LaPorte (PSU) and M.J. Moss report on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 190422A (Moss et al. GCN
Circ. 24147
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 ), from 536 s to 31.0 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Evans et al. (GCN Circ. 24151
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.7 (+1.8, -1.2). At T+895 s  the decay
flattens to an alpha of -0.4 (+0.4, -0.5) before breaking again at
T+3926 s to a final decay with index alpha=0.54 (+/-0.15).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+0.18, -0.17). The
best-fitting absorption column is  1.66 (+0.25, -0.23) x 10^22 cm^-2,
in excess of the Galactic value of 8.6 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 5.5 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.66 (+0.25, -0.23) x 10^22 cm^-2
Galactic foreground: 8.6 x 10^21 cm^-2
Excess significance: 5.7 sigma
Photon index:	     2.04 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
0.54, the count rate at T+24 hours will be 0.11 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-12 (1.4 x 10^-11) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00899979.

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

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
M. J. Moss (GWU), D. M. Palmer (LANL),
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 190422A (trigger #899979)
(Moss et al., GCN Circ. 24147
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 ).  The BAT ground-calculated position is
RA, Dec = 182.126, -60.167 deg which is
   RA(J2000)  =  12h 08m 30.3s
   Dec(J2000) = -60d 10' 02.6"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 82%.

The mask-weighted light curve shows a multi-peaked structure. The emission
started before the source entered the BAT FOV, and lasted until ~T+360 s.
The main peak occurred at ~ T+175 s. We cannot determine T90 since
the available data do not cover the entire burst emission.

The time-averaged spectrum from T+6.39 to T+359.48 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.76 +- 0.08.  The fluence in the 15-150 keV band is 6.5 +- 0.3 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T+174.47 sec in the 15-150 keV band
is 2.6 +- 0.2 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/899979/BA/

GRB 190422A: Swift/UVOT Upper Limits

K. K. Simpson (PSU) and M. J. Moss (George Washington University)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190422A
532 s after the BAT trigger (Moss et al., GCN Circ. 24147
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 ).
No optical afterglow consistent with the XRT position
(Evans et al. GCN Circ. 24151
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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           532          682          147         >18.8
white              532         7906          647         >18.8
v                  689         6879          352         >17.2
b                  788         7700          352         >18.3
u                  763         7495          352         >18.9
w1                 738         7289          352         >19.1
m2                 713         7084          352         >19.1
w2                 838         7995          438         >19.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.58 in the direction of the burst
(Schlegel et al. 1998).

R. Hamburg (UAH), C. Fletcher (USRA), and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 22:58:24.00 UT on 22 April 2019, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 190422A (trigger 577666709 / 190422957)
which was also detected by the Swift/BAT (Moss et al. 2019, GCN 24147
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 71
degrees.

The GBM light curve shows a complex lightcurve with one main peak
preceded and followed by weaker bursts of emission.
A duration (T90) is calculated to be about 212 s (50-300 keV).
The time-averaged spectrum from T0-21.5 s to T0+42.0 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.67 +/- 0.09 and
the cutoff energy, parameterized as Epeak, is 58 +/- 7 keV.
A Band function fits the spectrum equally well with
Epeak = 50 +/- 9 keV, alpha = -1.57 +/- 0.14 and
beta = -2.42 +/- 0.27.

The event fluence (10-1000 keV) in this time interval is
(4.8 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.54 s in the 10-1000 keV band
is 4.84 +/- 0.17 ph/s/cm^2."


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support
Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/