Gamma-ray Burst 240513A

(All information courtesy of the instrument teams.)

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Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 13 May 24 10:13:16 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     737277727
GRB_RA:          144.750d {+09h 39m 00s} (J2000),
                 145.024d {+09h 40m 06s} (current),
                 144.189d {+09h 36m 45s} (1950)
GRB_DEC:         -26.170d {-26d 10' 11"} (J2000),
                 -26.281d {-26d 16' 50"} (current),
                 -25.943d {-25d 56' 35"} (1950)
GRB_ERROR:       2.21 [deg radius, statistical only]
GRB_DATE:        20443 TJD;   134 DOY;   24/05/13
GRB_TIME:        26522.55 SOD {07:22:02.55} UT
GRB_PHI:         160.80 [deg]
GRB_THETA:        18.95 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        50.75d {+03h 23m 00s}  +18.56d {+18d 33' 23"}
SUN_DIST:        101.78 [deg]   Sun_angle= -6.3 [hr] (East of Sun)
MOON_POSTN:      123.31d {+08h 13m 14s}  +25.07d {+25d 04' 26"}
MOON_DIST:        55.47 [deg]
MOON_ILLUM:      30 [%]
GAL_COORDS:      257.83, 19.40 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      157.75,-37.64 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240513307/quicklook/glg_lc_medres34_bn240513307.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240513307/quicklook/glg_locplot_all_bn240513307.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice has human-in-the-loop processing.

GCN Circular #36455
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

GCN Circular #36457
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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB240513.31 (trigger No 737277727,09h 39m 00.00s , -26d 10m 12.0s, R=2.21) errorbox 24416 sec after notice time and 34691 sec after trigger time at 2024-05-13 17:00:14 UT, with upper limit up to 18.8 mag. Observations started at twilight. The observations began at zenith distance = 6 deg. The sun altitude is -14.9 deg.
The galactic latitude b = 20 deg., longitude l = 258 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2454488
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   34722 | 2024-05-13 17:00:14 |         MASTER-SAAO | (09h 34m 08.08s , -27d 10m 41.6s) |   C |    60 | 18.6 |        
   34722 | 2024-05-13 17:00:14 |         MASTER-SAAO | (09h 36m 15.82s , -27d 23m 44.0s) |   C |    60 | 17.7 |        
   34801 | 2024-05-13 17:01:33 |         MASTER-SAAO | (09h 43m 04.51s , -27d 11m 59.9s) |   C |    60 | 18.6 |        
   34801 | 2024-05-13 17:01:34 |         MASTER-SAAO | (09h 45m 12.36s , -27d 25m 02.9s) |   C |    60 | 17.5 |        
   35066 | 2024-05-13 17:05:58 |         MASTER-SAAO | (09h 24m 59.70s , -25d 18m 20.2s) |   C |    60 | 18.8 |        
   35066 | 2024-05-13 17:05:58 |         MASTER-SAAO | (09h 26m 59.64s , -25d 31m 25.3s) |   C |    60 | 17.7 |        
   35146 | 2024-05-13 17:07:18 |         MASTER-SAAO | (09h 33m 52.55s , -25d 17m 57.1s) |   C |    60 | 18.7 |        
   35146 | 2024-05-13 17:07:18 |         MASTER-SAAO | (09h 35m 52.62s , -25d 31m 02.4s) |   C |    60 | 17.7 |        
   35225 | 2024-05-13 17:08:38 |         MASTER-SAAO | (09h 41m 45.50s , -25d 17m 46.0s) |   C |    60 | 18.7 |        
   35225 | 2024-05-13 17:08:38 |         MASTER-SAAO | (09h 43m 45.66s , -25d 30m 51.2s) |   C |    60 | 17.8 |        
   35305 | 2024-05-13 17:09:57 |         MASTER-SAAO | (09h 50m 35.56s , -25d 16m 18.3s) |   C |    60 | 18.6 |        
   35305 | 2024-05-13 17:09:57 |         MASTER-SAAO | (09h 52m 35.78s , -25d 29m 23.4s) |   C |    60 | 17.6 |        
   35385 | 2024-05-13 17:11:17 |         MASTER-SAAO | (09h 33m 05.72s , -23d 22m 13.4s) |   C |    60 | 18.7 |        
   35385 | 2024-05-13 17:11:17 |         MASTER-SAAO | (09h 35m 04.15s , -23d 35m 17.3s) |   C |    60 | 17.8 |        
   35464 | 2024-05-13 17:12:36 |         MASTER-SAAO | (09h 41m 52.20s , -23d 23m 12.5s) |   C |    60 | 18.8 |        
   35464 | 2024-05-13 17:12:36 |         MASTER-SAAO | (09h 43m 50.71s , -23d 36m 16.4s) |   C |    60 | 18.0 |        
   36212 | 2024-05-13 17:25:04 |         MASTER-SAAO | (09h 34m 19.25s , -27d 11m 32.3s) |   C |    60 | 18.6 |        
   36212 | 2024-05-13 17:25:04 |         MASTER-SAAO | (09h 36m 24.48s , -27d 24m 30.6s) |   C |    60 | 17.9 |        
   36292 | 2024-05-13 17:26:24 |         MASTER-SAAO | (09h 43m 19.56s , -27d 10m 15.7s) |   C |    60 | 18.6 |        
   36292 | 2024-05-13 17:26:24 |         MASTER-SAAO | (09h 45m 24.71s , -27d 23m 15.3s) |   C |    60 | 17.7 |        
   36372 | 2024-05-13 17:27:44 |         MASTER-SAAO | (09h 24m 59.15s , -25d 17m 48.5s) |   C |    60 | 18.6 |        
   36372 | 2024-05-13 17:27:44 |         MASTER-SAAO | (09h 27m 02.00s , -25d 30m 47.5s) |   C |    60 | 17.7 |        
   36451 | 2024-05-13 17:29:03 |         MASTER-SAAO | (09h 33m 53.45s , -25d 17m 18.4s) |   C |    60 | 18.7 |        
   36451 | 2024-05-13 17:29:03 |         MASTER-SAAO | (09h 35m 56.23s , -25d 30m 18.6s) |   C |    60 | 17.9 |        
   36531 | 2024-05-13 17:30:23 |         MASTER-SAAO | (09h 41m 46.96s , -25d 16m 06.3s) |   C |    60 | 18.7 |        
   36531 | 2024-05-13 17:30:23 |         MASTER-SAAO | (09h 43m 49.86s , -25d 29m 07.4s) |   C |    60 | 17.8 |        
   36611 | 2024-05-13 17:31:43 |         MASTER-SAAO | (09h 50m 35.13s , -25d 17m 35.3s) |   C |    60 | 18.6 |        
   36611 | 2024-05-13 17:31:43 |         MASTER-SAAO | (09h 52m 38.19s , -25d 30m 36.4s) |   C |    60 | 17.8 |        
   36690 | 2024-05-13 17:33:02 |         MASTER-SAAO | (09h 33m 13.04s , -23d 21m 49.0s) |   C |    60 | 18.7 |        
   36690 | 2024-05-13 17:33:02 |         MASTER-SAAO | (09h 35m 14.19s , -23d 34m 49.8s) |   C |    60 | 17.9 |        
   36770 | 2024-05-13 17:34:22 |         MASTER-SAAO | (09h 41m 47.34s , -23d 22m 39.0s) |   C |    60 | 18.8 |        
   36770 | 2024-05-13 17:34:22 |         MASTER-SAAO | (09h 43m 48.36s , -23d 35m 39.8s) |   C |    60 | 17.8 |        
   36850 | 2024-05-13 17:35:42 |         MASTER-SAAO | (09h 27m 17.67s , -29d 05m 23.3s) |   C |    60 | 18.7 |        
   36850 | 2024-05-13 17:35:42 |         MASTER-SAAO | (09h 29m 24.78s , -29d 18m 25.1s) |   C |    60 | 17.8 |        
   36930 | 2024-05-13 17:37:02 |         MASTER-SAAO | (09h 36m 29.72s , -29d 04m 55.8s) |   C |    60 | 18.8 |        
   36930 | 2024-05-13 17:37:02 |         MASTER-SAAO | (09h 38m 36.91s , -29d 17m 58.0s) |   C |    60 | 17.8 |        
   37009 | 2024-05-13 17:38:21 |         MASTER-SAAO | (09h 44m 39.29s , -29d 04m 54.1s) |   C |    60 | 18.8 |        
   37009 | 2024-05-13 17:38:21 |         MASTER-SAAO | (09h 46m 46.37s , -29d 17m 56.5s) |   C |    60 | 17.9 |        
   37168 | 2024-05-13 17:41:00 |         MASTER-SAAO | (09h 34m 20.69s , -27d 10m 19.6s) |   C |    60 | 18.6 |        
   37168 | 2024-05-13 17:41:00 |         MASTER-SAAO | (09h 36m 25.11s , -27d 23m 21.5s) |   C |    60 | 17.7 |        
   37248 | 2024-05-13 17:42:20 |         MASTER-SAAO | (09h 43m 19.18s , -27d 09m 20.1s) |   C |    60 | 18.7 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 13 May 24 17:54:10 UT
NOTICE_TYPE:     Fermi-LAT Offline Position
TRIGGER_NUM:     240513307
GRB_RA:          163.400d {+10h 53m 36s} (J2000),
                 163.692d {+10h 54m 46s} (current),
                 162.801d {+10h 51m 12s} (1950)
GRB_DEC:         -27.500d {-27d 30' 00"} (J2000),
                 -27.630d {-27d 37' 47"} (current),
                 -27.234d {-27d 14' 00"} (1950)
GRB_ERROR:       24.00 [arcmin radius, 90% containment, statistical only]
GRB_DATE:        20443 TJD;   134 DOY;   24/05/13
GRB_TIME:        26522.00 SOD {07:22:02.00} UT
TRIGGER_ID:      0x0
MISC:            0x40000000
SUN_POSTN:        51.07d {+03h 24m 16s}  +18.63d {+18d 38' 02"}
SUN_DIST:        118.11 [deg]   Sun_angle= -7.5 [hr] (East of Sun)
MOON_POSTN:      127.55d {+08h 30m 12s}  +24.05d {+24d 03' 06"}
MOON_DIST:        62.33 [deg]
MOON_ILLUM:      33 [%]
GAL_COORDS:      273.18, 28.48 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      176.71,-31.63 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi LAT Offline position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        It is the result of human-in-the-loop processing.  
COMMENTS:        This is a human generated position of a LAT ground detection.
COMMENTS:        This source corresponds to GBM trigger.

GCN Circular #36462
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).
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.
GCN Circular #36464
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.
GCN Circular #36478
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.
GCN Circular #36479
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) and AstroSat CZTI (Joshi et al. 2024, GCN 36455). 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/"
GCN Circular #36504
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; Fermi-LAT detection: Cutini et al., GCN 36462; Fermi-GBM observation: Bissaldi & Meegan, GCN 36479) 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, 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.
GCN Circular #36506
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.
GCN Circular #36533
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, 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=3D163.4548, -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.

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Jochen Greiner, last update: 22-May-2024 [Disclaimer]