GRB 240516A

T. M. Parsotan (GSFC), 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 03:36:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240516A (trigger=1228797).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 212.770, -63.505 which is 
   RA(J2000) = 14h 11m 05s
   Dec(J2000) = -63d 30' 17"
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 20 sec.  The peak count rate
was ~1400 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 03:38:50.4 UT, 142.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 212.8071, -63.4878 which is equivalent to:
   RA(J2000)  = 14h 11m 13.70s
   Dec(J2000) = -63d 29' 16.1"
with an uncertainty of 6.1 arcseconds (radius, 90% containment). This
location is 85 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of	2 seconds with the White filter
starting 150 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. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. Results from the list of sources generated on-board are not
available at this time. No correction has been made for the large, but
uncertain, extinction expected. 

Burst Advocate for this burst is T. M. Parsotan (parsotat AT umbc.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/)

Y. Julakanti, B. P. Gompertz, A. Kumar, J. Lyman, R. Starling, K. Ackley, M. J. Dyer, K. Ulaczyk, F. Jimenez-Ibarra, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration:

The Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022) performed a targeted observation in response to Swift detected GRB 240516A (Parostan et al. GCN 36493
Loading...
 
 ) also detected by Fermi/GBM (trigger number 737523389) at 2024-05-16 UT 08:29:06 (4.9 hours after trigger). The observation consisted of 3x90s exposures in the GOTO L-band (400-700 nm).

Images were processed immediately after acquisition using the GOTO pipeline. No optical counterpart is detected within the Swift/XRT 90% localisation region to a 3-sigma limiting magnitude of L > 20.3 (AB).

Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).

S. Bala (USRA), S. Dalessi (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 03:36:24.84 UT on 16 May 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240516A (trigger 737523389/240516150).
which was also detected by Swift BAT (T. M. Parsotan et al. 2024, GCN 36493
Loading...
 
 ).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 47 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 46 s (50-300 keV). The time-averaged spectrum
from T0+1.0 to T0+45.1 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.69 +/- 0.09 and the cutoff energy,
parameterized as Epeak, is 528 +/- 72 keV.

The event fluence (10-1000 keV) in this time interval is
(1.12 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.7 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 490 +/- 107 keV, alpha = -0.7 +/- 0.1 and beta = -2.1 +/- 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/"

K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 240516A. Following the
prompt detection of an X-ray source reported in GCN Circ. 36493
Loading...
 
 
(Parsotan et al.), Swift passed into the South Atlantic Anomaly, and so
no further data were collected until 1.6 ks after the BAT trigger.
Combining all the Photon Counting (PC) mode data collected after this
time (6.7 ks, from 1.6 to 45.5 ks post-trigger), the source is no
longer detected, with a 3-sigma upper limit of 2.2 x 10^-3 count s^-1.

Assuming a typical GRB spectrum with a photon spectral index of 1.9 and
the Galactic absorption column of 1.29 x 10^22 cm^-2 (Willingale et al.
2013), the counts to observed (unabsorbed) 0.3-10 keV flux conversion
deduced from this spectrum is 5.6 x 10^-11 (1.0 x 10^-10) erg cm^-2
count^-1. The observed (unabsorbed) flux upper limit for the X-ray
source is thus 1.2 x 10^-13 (2.2 x 10^-13) erg cm^-2 s^-1.

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

J. Joshi (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 240516A which was also detected by Swift-BAT (Parsotan et al., GCN Circ. 36493
Loading...
 
 ) and Fermi-GBM (Fermi GBM team, GCN Circ. 36499
Loading...
 
 ).

The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2024-05-16 03:36:35.02 UTC. The measured peak count rate associated with the burst is 181 (+32, -25) counts/s above the background in the combined data of all quadrants, with a total of 2323 (+336, -367) counts. The local mean background count rate was 1420 (+4, -4) counts/s. We measure a T90 of 22 (+2, -2) s from the cumulative Veto light curve.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb

S. Chastain (UNM), J. K. Leung (U. Toronto/HUJI), G. E. Anderson (Curtin University), 
A. Gulati (U. Sydney), L. Rhodes (U. Oxford), 
A. J. van der Horst (GWU) on behalf of the PanRadio GRB collaboration

The Australia Telescope Compact Array (ATCA) performed observations
of the long GRB 240516A detected by Swift-BAT (Parsotan et al., GCN 36493
Loading...
 
 ),
Fermi-GBM (S. Bala et al., GCN 26499
Loading...
 
 ), and AstroSat CZTI (Joshi et al., GCN 36503
Loading...
 
 )
at 5.5, 9, 17 and 19 GHz as part of the Large ATCA "PanRadio GRB"
follow-up programme C3542 (PI. Anderson). ATCA start observing on
2024-05-16 at 13:24 UT (~10 hours post-burst) and continued to observe  
until 21:00 UT on 2024-05-16. In our preliminary analysis, we find 
no radio source coincident with the Swift XRT uncataloged source
(Parsotan et al., GCN 36493
Loading...
 
 ) with 3 sigma upper limits of 
186, 126, 276 and 381 microJy/beam at 5.5, 9.0, 17 and 19 GHz, respectively.

We thank the CSIRO Space and Astronomy staff for supporting these 
observations. We acknowledge the Gomeroi people as the traditional
owners of the Observatory site. The Australia Telescope Compact Array is
part of the Australia Telescope National Facility 
(https://ror.org/05qajvd42) which is funded by the Australian Government
for operation as a National Facility managed by CSIRO.

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

Using the data set from T-200 to T+200 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 240516A (trigger #1228797)
(Parsotan et al., GCN Circ. 36493
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 212.784, -63.495 deg which is
   RA(J2000)  =  14h 11m 08.3s
   Dec(J2000) = -63d 29' 41.7"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 45%.

The mask-weighted light curve shows a single-peaked, FRED-like structure
that starts at ~T-5 s, peaks at ~T-2 s, and ends at ~T+15 s. In addition,
there are some weak tail emissions that last till ~T+110 s.
T90 (15-350 keV) is 94.69 +- 34.00 sec (estimated error including
systematics).

The time-averaged spectrum from T-4.75 to T+112.50 sec is best fit by
a simple power-law model.  The power law index of the time-averaged
spectrum is 1.09 +- 0.19.  The fluence in the 15-150 keV band
is 2.0 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured
from T-2.20 sec in the 15-150 keV band is 1.1 +- 0.3 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/1228797

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

The Swift/UVOT began settled observations of the field of GRB 240516A
150 s after the BAT trigger (Parsotan et al., GCN Circ. 36493
Loading...
 
 ).
No optical afterglow consistent with the XRT position
(Parsotan et al., GCN Circ. 36493
Loading...
 
 ) 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 initial exposures are:

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

white_FC          151          153            2          >17.8
white             150          1689           90         >19.9
v                 5228         5427           197        >18.9
m2                5432         5632           197        >18.9
w1                5638         5838           197        >19.1
u                 5843         5948           104        >19.1

        
We note that the first orbit of data only contained observations in the
white filter. The other filters are from a later orbit of data.

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 2.390 in the direction of the burst
(Schlegel et al. 1998).