GRB 210419A

S. Laha (GSFC/UMBC/CRESST), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR),
J. A. Kennea (PSU), K. L. Page (U Leicester) and D. M. Palmer (LANL)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 06:53:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210419A (trigger=1044032).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 86.862, -65.539 which is 
   RA(J2000) = 05h 47m 27s
   Dec(J2000) = -65d 32' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, no
obvious variation is visible in the immediately-available lightcurve. 

The XRT began observing the field at 06:55:49.0 UT, 127.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 86.85414,
-65.50357 which is equivalent to:
   RA(J2000)  = 05h 47m 24.99s
   Dec(J2000) = -65d 30' 12.9"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 128 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
https://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 (7.76 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.3
(+3.15/-2.74) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.57e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 136 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
0.075. 

This source lies within the current (Sector 37) field-of-view of TESS camera 4. 

Burst Advocate for this burst is S. Laha (sib.laha 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/)

R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:

We observed Swift GRB 210419A (Laha, et al., GCN 29828
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 ) with the LCO 1-m Sinistro instrument at the Siding Spring Observatory, Australia site, on April 19, from 08:33 to 08:57 UT (corresponding to 1.67 to 2.1 hours from the GRB trigger time) with the Bessel R and I filters.

We performed a series of 4x180s exposures in R and I. We do not detect any uncatalogued optical source in the coadded images within the XRT error region (Laha, et al., GCN 29828
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 ).  Using the USNO-B.1 catalog as reference, we calculate the following upper limits:

R>21.91

I>21.16

These magnitudes are not corrected for galactic extinction.

R.S. is funded by NSF AST grant #1831682

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

Using 2647 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 210419A, 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 = 86.85096, -65.50250 which is equivalent
to:

RA (J2000): 05h 47m 24.23s
Dec (J2000): -65d 30' 09.0"

with an uncertainty of 2.0 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.

V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, 
V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva,
D.Kuvshinov,  D. Cheryasov
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile 
(Observatorio Astronomico Felix Aguilar OAFA),

R. Rebolo, M. Serra 
(The Instituto de Astrofisica de Canarias),

D. Buckley 
(South African Astronomical Observatory),

O.A. Gres, N.M. Budnev, O.Ershova 
(Irkutsk State University, API),

A. Tlatov, D. Dormidontov 
(Kislovodsk Solar Station of the Pulkovo Observatory),

V. Yurkov, A. Gabovich, Yu. Sergienko 
(Blagoveschensk Educational State University)




MASTER-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 210419A ( S. Laha et al., GCN 29828
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 ) errorbox  58845 sec after notice time and 58929 sec after trigger time at 2021-04-19 23:15:50 UT, with upper limit up to  18.1 mag. Observations started at twilight.  The observations began at zenith distance = 43 deg. The sun  altitude  is -14.8 deg. 

The galactic latitude b = -31 deg., longitude l = 275 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1595763

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   59019 |         MASTER-OAFA |   C |   180 | 17.9 |        
   59305 |         MASTER-OAFA |   C |   180 | 18.1 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne
(U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi	(INAF-IASFPA) ,
M. Capalbi (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J.
D. Gropp (PSU) and S. Laha report on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 210419A (Laha et al. GCN
Circ. 29828
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 ), from 134 s to 64.1 ks after the  BAT trigger. The data
comprise 143 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 29830
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 ).

The late-time light curve (from T0+5.5 ks) can be modelled with a
power-law decay with a decay index of alpha=1.0 (+/-0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.71 (+0.11, -0.10). The
best-fitting absorption column is  1.4 (+0.4, -0.3) x 10^21 cm^-2, in
excess of the Galactic value of 7.8 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.60 (+0.29, -0.27)
and a best-fitting absorption column of 1.9 (+0.7, -0.6) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 2.6 x 10^-11 (4.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.9 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 7.8 x 10^20 cm^-2
Excess significance: 2.9 sigma
Photon index:	     2.60 (+0.29, -0.27)

If the light curve continues to decay with a power-law decay index of
1.0, the count rate at T+24 hours will be 4.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (2.1 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/01044032.

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

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), 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+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210419A (trigger #1044032)
(Laha et al., GCN Circ. 29828
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 ).  The BAT ground-calculated position is
RA, Dec = 86.912, -65.452 deg which is
   RA(J2000)  =  05h 47m 38.9s
   Dec(J2000) = -65d 27' 07.2"
with an uncertainty of 2.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 61%.

The BAT light curve showed a complex structure with a duration of about ~100 sec.
T90 (15-350 keV) is 64.43 +- 11.69 sec (estimated error including systematics).

The time-averaged spectrum from T+21.92 to T+95.01 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.17 +- 0.24.  The fluence in the 15-150 keV band is 7.8 +- 1.2 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+41.82 sec in the 15-150 keV band
is 0.6 +- 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/1044032/BA/

M. H. Siegel (PSU) and S. L. Laha (GSFC/UMBC/CRESST)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210419A
136 s after the BAT trigger (Laha et al., GCN Circ. 29828
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 ).
No optical afterglow consistent with the XRT position
(Osborne et al., GCN Circ 29830
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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           136          286          147         >18.1
u_FC               294          544          246         >17.9
white              136         1027          333         >18.1
v                  627         1079           58         >17.5
b                  550          746           39         >17.7
u                  294          721          265         >17.9
w1                 677          871           39         >17.8
m2                 651         1103           58         >18.3
w2                 119         1053           67         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.075 in the direction of the burst
(Schlegel et al. 1998).