GRB 240513A

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 240513A which was also detected by Fermi (Trigger Num. 737277727).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2024-05-13 07:22:02.65 UTC. The measured peak count rate associated with the burst is 648 (+161, -104) counts/s above the background in the combined data of three quadrants (out of four), with a total of 623 (+121, -101) counts. The local mean background count rate was 238 (+4, -7) counts/s. Using cumulative rates, we measure a T90 of 6.4 (+0.1, -0.4) s.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2024-05-13 07:22:05.69 UTC. The measured peak count rate associated with the burst is 505 (+68, -73) counts/s above the background in the combined data of all quadrants, with a total of 1322 (+297, -319) counts. The local mean background count rate was 1255 (+6, -5) counts/s. We measure a T90 of 6.6 (+3.4, -3.4) 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. Cutini (INFN Perugia), E. Bissaldi (Politecnico and INFN Bari), R. Gupta (NASA/GSFC) and N. Di Lalla (Stanford University) report on behalf of the Fermi-LAT Collaboration:

On May 13, 2024 Fermi-LAT detected high-energy emission from GRB 240513A, which was also detected by Fermi-GBM (trigger 737277727 / 240513307) and AstroSat CZTI (GCN #36455
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 ).

The best LAT on-ground location is found to be

RA, Dec = 163.4, -27.5 (J2000)

with an error radius of 0.4 deg (90 % containment, statistical error only). This was 34 deg from the LAT boresight at the time of the GBM trigger:

T0 = 07:22:02.55 UT.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-100 s after the GBM trigger is (1.7 +/- 0.6) E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.3 +/- 0.4. The highest-energy photon is a 0.8 GeV event which is observed about 5 seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini@pg.infn.it).

The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

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

Swift has initiated a series of observations, tiled on the sky, of the
Fermi/LAT GRB 240513A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00125

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. Tohuvavohu (U. Toronto),
D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester),
J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 240513A in a series of observations tiled
on the sky. The total exposure time is 5.1 ks, distributed over 7
tiles; the maximum exposure at a single sky location was 1.6 ks. The
data were collected between T0+46.1 ks and T0+80.7 ks, and are entirely
in Photon Counting (PC) mode. 

Three uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit or shows definitive signs of fading.
Therefore, at the present time we cannot identify which, if any, is the
afterglow. Details of these sources are given below:

Source 2:
  RA (J2000.0):  163.8237  =  10:55:17.69
  Dec (J2000.0): -27.6225  =  -27:37:20.9
  Error: 9.7 arcsec (radius, 90% conf.)
  Count-rate: (8.6 [+4.8, -3.5])e-3 ct s^-1   
  Distance: 1422 arcsec from Fermi/LAT position.

Source 4:
  RA (J2000.0):  163.9338  =  10:55:44.10
  Dec (J2000.0): -27.5934  =  -27:35:36.2
  Error: 7.6 arcsec (radius, 90% conf.)
  Count-rate: (7.4 [+4.8, -3.4])e-3 ct s^-1   
  Distance: 1736 arcsec from Fermi/LAT position.

Source 6:
  RA (J2000.0):  163.4544  =  10:53:49.05
  Dec (J2000.0): -27.4116  =  -27:24:41.7
  Error: 5.1 arcsec (radius, 90% conf.)
  Count-rate: 0.0224 [+0.0072, -0.0060] ct s^-1   
  Distance: 362 arcsec from Fermi/LAT position.
  Flux: (1.64 [+0.53, -0.44])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Two catalogued sources were also detected.

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00125.

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

E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:


"At 07:22:02 UT on 13 May 2024, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 240513A (trigger 737277727 / 240513307),
which was also detected by the Fermi/LAT (Cutini et al. 2024, GCN 36462
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 )
and AstroSat CZTI (Joshi et al. 2024, GCN 36455
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 ).
The GBM on-ground location is consistent with the LAT position.

The angle from the Fermi LAT boresight at the GBM trigger time is 34 degrees.

The GBM light curve consists of two emission episodes
with a duration (T90) of about 7 s (50-300 keV).
The time-averaged spectrum from T0-0.3 s to T0+6.5 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.87 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 1700 +/- 400 keV.

The event fluence (10-1000 keV) in this time interval is
(3.93 +/- 0.17)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.8 s in the 10-1000 keV band
is 4.1 +/- 0.2 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/"

A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 240513A
(AstroSat CZTI detection: Joshi et al., GCN 36455
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 ;
Fermi-LAT detection: Cutini et al., GCN 36462
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 ;
Fermi-GBM observation: Bissaldi & Meegan, GCN 36479
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 ) 
triggered Konus-Wind at T0=26527.128 s UT (07:22:07.128).

The burst light curve shows a multipeaked structure
which started at ~T0-5.3 s and had a total duration of ~7.8 s.
KW triggered on the second of two emission episodes
reported in GCN 36479
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 , this episode had a total duration of ~2.6 s.
The emission is seen up to ~6 MeV. 

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240513_T26527/

As observed by Konus-Wind, the burst
had a fluence of 3.42(-0.39,+2.50)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0-0.066 s,
of 5.12(-0.78,+2.09)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Since the brightest part of the burst emission
was detected before the trigger, the spectral analysis
was performed using the KW 3-channel light curve data.

Modelling the KW 3-channel time-integrated spectrum
(measured from T0-5.339 s to T0+2.512 s)
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep),
yields alpha = -1.00(-0.22,+0.26) and Ep = 732(-249,+745) keV.

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

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

Swift has initiated a ToO observation of the Fermi/LAT GRB 240513A. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021692

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Fermi/LAT event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

A. Melandri (INAF-OAR) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 240513A in a series of observations tiled on the sky. 

Three uncatalogued X-ray sources were reported in GCN 36478
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 , of which one ("Source #6”) is fading with 2.7-sigma significance, and is therefore likely the GRB afterglow.  

The position of this source is RA, Dec=163.4548, -27.4114 which is equivalent to:

RA (J2000): 10:53:49.16
Dec(J2000): -27:24:41.3

with an uncertainty of 5.1 arcsec (radius, 90% confidence).  

The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_curves/00021687/

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