GRB 200416A

P. A. Evans (U Leicester), V. D'Elia (SSDC), J.D. Gropp (PSU),
N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL)
and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels
Swift Observatory Team:

At 07:05:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200416A (trigger=966554).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 335.691, -7.530 which is 
   RA(J2000) = 22h 22m 46s
   Dec(J2000) = -07d 31' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 07:06:57.1 UT, 99.9 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 335.69906, -7.51816 which
is equivalent to:
   RA(J2000)  = 22h 22m 47.77s
   Dec(J2000) = -07d 31' 05.4"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 51 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 (6.54 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.2
(+3.00/-2.56) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 102 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	22:22:47.83 = 335.69929
  DEC(J2000) = -07:31:05.9  =  -7.51831
with a 90%-confidence error radius of about 0.75 arc sec. This position is 1.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.47 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.06. 

Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.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/)

E. Bissaldi (Politecnico and INFN Bari)
reports on behalf of the Fermi GBM Team:


"At 07:05:17.38 UT on 16 April 2020, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 200416A (trigger 608713522 /200416295),
which was also detected by the Swift/BAT (Evans et al. 2020, GCN 27591
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 ).
The trigger was initially misclassified as a particle event by the flight software.
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 92 degrees.

The GBM light curve shows a double-peaked emission episode
with a duration (T90) of about 9 s (50-300 keV).
The time-averaged spectrum from T0-2 s to T0+6 s is
adequately fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.87 +/- 0.15 and
the cutoff energy, parameterized as Epeak, is 74 +/- 6 keV.

The event fluence (10-1000 keV) in this time interval is
(1.43 +/-  0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band
is 6.5 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 64 +/- 9 keV, alpha = -0.66 +/- 0.24
and beta = -2.5 +/- 0.3.


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/"

P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team:

We have analysed 677 s of XRT data for GRB 200416A (Evans et al. GCN
Circ. 27591
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 ), from 84 s to 773 s after the  BAT trigger. The data
comprise 43 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The refined XRT position is RA, Dec = 335.6986, -7.5179 which is
equivalent to:

RA (J2000): 22 22 47.66
Dec(J2000): -07 31 04.3

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.9 (+/-0.5), followed by a break at T+167 s to an alpha
of 0.25 (+0.18, -0.25).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.86 (+0.22, -0.20). The
best-fitting absorption column is  9.6 (+6.3, -3.1) x 10^20 cm^-2,
consistent with the Galactic value of 6.5 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 3.6 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.6 (+6.3, -3.1) x 10^20 cm^-2
Galactic foreground: 6.5 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.86 (+0.22, -0.20)

The GRB entered Swift's Moon-proximity observing constraint shortly
after the trigger, and will not be observable until early on Monday
April 20th; observations are planned for that time. The light curve
appears to be in the plateau phase common to X-ray afterglows and is
expected to break to a steeper decay at some point within the next ~24
hours, so we do not attempt to predict the flux at T0+24 hours.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00966554.

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

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), P. A. Evans (U Leicester)
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL)
(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 200416A (trigger #966554)
(P. A. Evans et al., GCN Circ. 27591
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 ).  The BAT ground-calculated position is
RA, Dec = 335.691, -7.525 deg which is
   RA(J2000)  =  22h 22m 45.8s
   Dec(J2000) = -07d 31' 29.5"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 33%.

The mask weighted light curve shows multi-peaked structure. The
overall structure starts at ~T-2 s and lasts till ~T+6 s.
T90 (15-350 keV) is 5.04 +- 0.73 sec (estimated error including systematics).

The time-averaged spectrum from T-1.31 to T+4.69 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.76 +- 0.15.  The fluence in the 15-150 keV band is 8.7 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.05 sec in the 15-150 keV band
is 3.8 +- 0.5 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/966554/BA/

GRB 200416A: Swift/UVOT Detection

K. K. Simpson (PSU) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200416A
102 s after the BAT trigger (Evans et al., GCN Circ. 27591
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 ).
A source consistent with the XRT position
(Evans GCN Circ. 27594
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  22:22:47.84 = 335.69934 (deg.)
    Dec (J2000) = -07:31:06.0  =  -7.51833 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric
system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:

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

white              102          252          147         16.57 +/- 0.03
v                  644          664           19         17.05 +/- 0.32
b                  570          590           20         17.48 +/- 0.20
u                  314          564          246         16.44 +/- 0.04
w1                 694          714           20         16.59 +/- 0.23
m2                 668          688           19        >16.3
w2                 620          640           19        >17.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).