GRB 240419B

S. Dichiara (PSU), J.D. Gropp (PSU), R. Gupta (NASA/GSFC),
F. E. Marshall (NASA/GSFC), M. J. Moss (GSFC),
P. T. O'Brien (U Leicester), M. H. Siegel (PSU) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 12:22:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240419B (trigger=1223072).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 325.877, +4.234 which is 
   RA(J2000) = 21h 43m 30s
   Dec(J2000) = +04d 14' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex structure lasted 
for ~40 seconds and returned to background before showing three bright pulses at 
~100 seconds for a total duration of 160 seconds.  The peak count rate
was ~2049 counts/sec (15-350 keV), at ~119 sec after the trigger. 

The XRT began observing the field at 12:25:20.7 UT, 148.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 325.89615, 4.23548 which
is equivalent to:
   RA(J2000)  = 21h 43m 35.08s
   Dec(J2000) = +04d 14' 07.7"
with an uncertainty of 3.5 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 https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 6.84
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 7.01e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 158 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
0.077. 

Burst Advocate for this burst is S. Dichiara (sbd5667 AT psu.edu). 
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/)

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

Using 1231 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 240419B, 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 = 325.89679, +4.23479 which is equivalent
to:

RA (J2000): 21h 43m 35.23s
Dec (J2000): +04d 14' 05.2"

with an uncertainty of 2.5 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.

V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik,  D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(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. Gress, N.M. Budnev, O.Ershova
(Irkutsk State University, API),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez
(INAOE, Guillermo Haro Astrophysics Observatory),

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

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

MASTER-Amur robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Blagoveshchensk State Pedagogical University) was pointed to the Swift GRB 240419B ( S. Dichiara et al., GCN 36180
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 ) errorbox  24752 sec after notice time and 24919 sec after trigger time at 2024-04-19 19:18:11 UT, with upper limit up to  15.6 mag. Observations started at twilight.  The observations began at zenith distance = 69 deg. The sun  altitude  is -11.0 deg. 

The galactic latitude b = -35 deg., longitude l = 61 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2427564

We obtain a following upper limits.  

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

   25009 |         MASTER-Amur |   C |   180 | 15.1 |        
   25009 |         MASTER-Amur |   C |   180 | 15.6 |        
Filter C is a clear (unfiltred) band. 


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

Daniele B. Malesani (DAWN/NBI and Radboud Univ.) and David Jones (NOT) report on behalf of a larger collaboration.

We observed the field of GRB 240419B (Dichiara et al., GCN 36180
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 ) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out straddling the morning twilight, at airmass ~2, and the seeing was about 1.7".

An object consistent with the X-ray localization error circle (Osborne et al., GCN 36186
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 ) is detected in our images. Its coordinates are (J2000):

RA = 21:43:35.289
Dec = +04:14:05.30

Calibrating against nearby point-like sources from the Pan-STARRS catalog, we measure the following AB magnitudes:

r = 22.01 +- 0.10  (Apr 20.214 UT, or 0.698 days after the trigger);
z = 20.81 +- 0.19  (Apr 20.222 UT, or 0.701 days after the trigger).

This object is not visible in the Legacy Survey images, which are deeper than ours, and we thus conclude that it is the optical afterglow of GRB 240419B. We note however the presence of a fainter (r ~ 23.2), distinct source visible in the Legacy Survey, approximately 2.5" to the west of the afterglow. Given the relatively large offset, the relation of this object with the GRB is unclear.

J.P. Osborne (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), C. Salvaggio (INAF-OAB), J. D. Gropp (PSU), S. Dichiara
(PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 7.5 ks of XRT data for GRB 240419B, from 141 s to 52.1
ks after the  BAT trigger. The data comprise 282 s in Windowed Timing
(WT) mode (the first 6 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+4.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.02 (+0.12, -0.11).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.95 (+/-0.05). The
best-fitting absorption column is  1.21 (+0.16, -0.15) x 10^21 cm^-2,
in excess of the Galactic value of 6.8 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.08 (+0.20, -0.19)
and a best-fitting absorption column of 1.2 (+/-0.5) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.2 x 10^-11 (4.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.2 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 6.8 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index:	     2.08 (+0.20, -0.19)

If the light curve continues to decay with a power-law decay index of
1.02, the count rate at T+24 hours will be 10.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.2 x
10^-13 (4.2 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/01223072.

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

S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.),
A. A. Breeveld (UCL-MSSL), N. P. M. Kuin (UCL-MSSL) and S. Dichiara (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240419B
159 s after the BAT trigger (Dichiara et al., GCN Circ. 36180
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 ).
No optical afterglow consistent with either the enhanced XRT position
(Osborne et al., GCN Circ. 36186
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 ) or the NOT optical afterglow position
(Malesani et al., GCN Circ. 36191
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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) exposures and subsequent exposures are:

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

white_FC           159          308          147         >20.3
u_FC               317          567          246         >19.5
white              159          790          186         >20.4
v                  647          667           19         >17.3
b                  572          765           39         >18.6
u                  317          741          265         >19.5
w1                 696          716           19         >17.5
m2                 672          691           19         >17.2
w2                 623          643           19         >17.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.077 in the direction of the burst
(Schlegel et al. 1998).

N. Higuchi, Y. Kubo, S. Joshima, H. Hagio, I. Takahashi, M. Sasada, M. Niwano, S. Hayatsu, H. Seki, Y. Yatsu and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 240419B (Dichiara et al., GCN 36180
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 ) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. 

The observation started at 2024-04-19 17:46:23 UT (5.4 hrs after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the enhanced Swift/XRT error region (Osborne et al., GCN 36186
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 ), despite the detection report of Daniele et al., (GCN 36191
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 ). We obtained the 5-sigma limits of the stacked images as follows.

T0+[hrs] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
6.4 | 2024-04-19 18:44:10.13 | 3660 | g'>18.6, Rc>18.8, Ic>18.4
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time

We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire).

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC),(i.e. the Swift-BAT team):

Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 240419B (trigger #1223072)
(Dichiara, et al., GCN Circ. 36180
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 ).  The BAT ground-calculated position is
RA, Dec = 325.853, 4.299 deg which is
   RA(J2000)  =  21h 43m 24.7s
   Dec(J2000) = +04d 17' 58.2"
with an uncertainty of 3.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 43%.

The BAT light curve shows a complex structure with a duration of ~ 150 sec.
T90 (15-350 keV) is 132.16 +- 26.29 sec (estimated error including systematics).

The time-averaged spectrum from T-3.3 to T+159.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.92 +- 0.09.  The fluence in the 15-150 keV band is 4.1 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+116.36 sec in the 15-150 keV band
is 2.4 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1223072