Gamma-ray Burst 240819A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #37203
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the SVOM/Eclairs GRB 240819A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021702
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 SVOM/Eclairs 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 #37206
A.Li (BNU), H. Sun, H. Q. Cheng, Z. X. Ling (NAOC, CAS), J. Q. Peng, J. Guan, C. K. Li, Y. Chen, S. M. Jia, W. W. Cui, H. Feng, D. W. Han, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, J. Zhang, S. N. Zhang, H. S. Zhao, X. F. Zhao (IHEP, CAS), J. Wang, L. P. Xin, Y. Liu, C. C. Jin, W. Yuan, C. Zhang (NAOC, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe and SVOM teams
We performed an observation of SVOM/Eclairs-triggered GRB 240819A with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2024-08-19T09:29:55 (UTC), and the exposure time is about 5.7 ks. FXT-A detected 3 uncatalogued sources in the 90% localization error circle (with a radius of 10.4 arcmin centered at RA, DEC = 310.909 deg, 49.589 deg), and two of them are also detected by FXT-B.
The following table lists the detailed information of the three X-ray sources detected by FXT-A. The positions are given with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The 0.5 - 10 keV flux is derived from FXT-A data; The uncertainties of flux are at the 90% confidence level.
```
Source name         | RA       | DEC     | Estimated Flux      |
                    | deg      | deg     | (erg/s/cm^2)        |

-----------------------------------------------------------------------------------

EP J204334.6+493448 | 310.8943 | 49.5800 | 7.5(+/-4.0) x 10^-14
EP J204347.6+493054 | 310.9483 | 49.5149 | 2.1(+/-0.6) x 10^-13 
EP J204244.0+494023 | 310.6835 | 49.6730 | 1.7(+/-0.5) x 10^-13 
-----------------------------------------------------------------------------------
```
The above observation was made with the EP-FXT instrument. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular #37207
S.Q. Jiang, J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), X. Liu, S.Y. Fu, Z.P. Zhu, S.Y. Gao, D. Xu, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration:
We observed the field of GRB 240819A detected by SVOM/Eclairs using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, US. Observations started at 09:41:45.015 UTC on 2024-08-19, i.e., 7.107 hr after the T0 of this GRB, and 16 x 240 s frames were obtained in R-band aiming to cover the whole SVOM/Eclairs error circle.
No new optical source is detected within the X-ray error circles provided by Swift/XRT (Evans et al., GCN37203) and EP/FXT (Li et al., GCN 37206), down to the following 3-sigma optical upper limits:
```
Source | R.A. | Dec. | Upper Limit (mag)
--------------------------------------------------------
XRT Source1          | 311.0531 | 49.6821 | R>19.0
XRT Source2*         | 310.9468 | 49.5141 | N/A
EP J204334.6+493448  | 310.8943 | 49.5800 | R>19.8
EP J204347.6+493054* | 310.9483 | 49.5149 | N/A
EP J204244.0+494023  | 310.6835 | 49.6730 | R>19.8
```
calibrated with PanSTARRS stars in the field and not corrected for Galactic extinction. The two sources marked with * are very likely an identical one detected by both Swift/XRT and EP/FXT, but not covered by TRT.
GCN Circular #37208
SVOM/ECLAIRs commissioning team: Alexis Coleiro (APC), St=C3=A9phane Schann= e, Fr=C3=A9d=C3=A9ric Chateau, Nicolas Dagoneau, Herv=C3=A9 Le Provost (CEA= ), Olivier Godet, Laurent Bouchet, Sebastien Guillot, Juliette Alaux (IRAP)= , Fr=C3=A9d=C3=A9ric Piron (LUPM), Karine Mercier, Marie-Claire Charmeau, S= tefano Crepaldi (CNES)
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (I= HEP), St=C3=A9phane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA)= , Zi-Gao Dai (USTC), Fr=C3=A9d=C3=A9ric Daigne (IAP), Jin-Song Deng (NAOC),= Andrea Goldwurm (APC), Diego G=C3=B6tz (CEA), Xu-Hui Han (NAOC), Cyril Lac= haud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Par= is), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV= )
report on behalf of the SVOM team:
GRB 240819A : An X-Ray Transient located on-board by SVOM/ECLAIRs.
During the commissioning phase, the SVOM/ECLAIRs telescope triggered and lo= cated an X-Ray Transient (sb24081901), hereafter GRB 240819A, at 2024-08-19= T02:35:21.2 UT (T0).
The following trigger information was received on the ground with low-laten= cy by the SVOM VHF Alert Network: The image SNR is 10.3, measured in the [8= -50] keV energy band, over a time window of 40.96 seconds, starting at T0.
The transient location is RA, Dec =3D 310.91, 49.59 (J2000). This is about= 9 degrees from the ECLAIRs optical axis, in the totally coded field of vie= w. The statistical uncertainty on this position is 8.0 arcminutes, to which= we recommend to add 10 arcminutes of systematic uncertainty. This location= was subsequently observed in X-rays by Swift (GCNC 37203) and Einstein Pro= be (GCNC 37206), and in the optical by the Thai Robotic Telescope network (= GCNC 37207).
We are confident of the reality of this transient, however its location 4= =C2=B0 above the galactic plane raises some doubts on its nature: an unknow= n galactic source or a GRB behind the galactic plane.
While the real-time alert was received within 1 minute of the trigger, we h= ave awaited the availability of the full X-band data to send this GCN, in o= rder to confirm the reality of the source with the full reconstructed sky i= mage.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission l= ed by the Chinese National Space Administration (CNSA, China), French Space= Agency (CNES, France) and the Chinese Academy of Sciences (CAS, China), wh= ich is dedicated to observing gamma-ray bursts and other transient phenomen= a in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNE= S and IRAP.
GCN Circular #37213
WeiKang Zheng and Alexei V. Filippenko (UCB),
SVOM JSWG: Jian-Yan Wei (NAOC, China), Bertrand Cordier (CEA, F),
Shuang-Nan Zhang (IHEP, CN), Stephane Basa (LAM, F), Jean-Luc Att=C3=A9ia
(IRAP, F), Arnaud Claret (CEA, F), Zi-Gao Dai (USTC, CN), Frederic Daigne
(IAP, F), Jin-Song Deng (NAOC, CN), Andrea Goldwurm (APC, F),
Diego G=C3=B6tz (CEA, F), Xu-Hui Han (NAOC, CN), Cyril Lachaud (APC, F),
En-Wei Liang (GXU, CN), Yu-Lei Qiu (NAOC, CN), Susanna Vergani
(Obs. Paris, F), Jing Wang (NAOC, CN), Chao Wu (NAOC, CN), Li-Ping Xin
(NAOC, CN), Bing Zhang (UNLV, CN)
report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to GRB 240819A from the SVOM/ECLAIRs
trigger sb24081901 (Coleiro et al., GCN 37208) starting at 03:49
UT, Aug 19th, ~1.23 hours after the trigger. Observations were
performed in 3x3 tiling mode and lasted for about 6 hours, a set
of clear (roughly R) filter images were obtained. The location of
the 4 X-ray sources, two from Swift XRT (Evans et al., GCN 37203)
and two additional ones from EP/FXT (Li et al., GCN 37206) were all
covered in our images. Preliminary analysis do not reveal any new
optical counterpart candidate within the X-ray error circles,
neither in single image, nor in the co-add images, consistent with
the reports from Jiang et al. (GCN 37207). The typical limiting
magnitude of our single clear image is about 19.5 mag calibrated to
the Pan-STARRS1 catalog.
GCN Circular #37217
S.Q. Jiang, Z.P. Zhu, X. Liu, J. An, S.Y. Fu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the Swift/XRT Source 1 (Evans et al., GCN37203), an X-ray afterglow candidate of GRB 240819A detected by SVOM/Eclairs (Coleiro et al., GCN 37208), using the 100C telescope of the JinShan project located at Altay, Xinjiang, China. Observations started at 20:16:17.46 UTC on 2024-08-20, i.e., 1.737 day after the T0 of this GRB, and a series of frames were obtained in the Sloan i- and z- bands.
No new optical source is detected within the Swift/XRT Source 1 error circle, down to the following 3-sigma optical upper limits:
```
-----------------------------------------------------------------
Tmid-T0(hr)  exp(s)   filter      UL(3-sigma)
-----------------------------------------------------------------
41.974        14x120      i           >20.6
42.663        22x120      z           >20.3
-----------------------------------------------------------------
```
calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction.
We acknowledge the excellent support from S.W. Luo, Z.K. Feng, Q.C. Zhao, M.M. Yang, and L.F. Huo for enabling these observations.
GCN Circular #37218
P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (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 SVOM/Eclairs-detected X-ray transient GRB 240819A (GCN 37208 Coleiro et al.), collecting 2.0 ks of Photon Counting (PC) mode data between T0+19.7 ks and T0+26.6 ks.
Two 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 1:
```
  RA (J2000.0):  311.0531  =  20:44:12.74
  Dec (J2000.0): +49.6821  =  +49:40:55.5
  Error: 6.6 arcsec (radius, 90% conf.)
  Count-rate: (3.4 [+2.0, -1.5])e-3 ct s^-1   
  Distance: 336 arcsec from SVOM/Eclairs position.
  Flux: (9.8 [+5.7, -4.2])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
```
Source 2:
```
  RA (J2000.0):  310.9464  =  20:43:47.14
  Dec (J2000.0): +49.5140  =  +49:30:50.3
  Error: 5.8 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.0111 [+0.0035, -0.0029] ct s^-1   
  Distance: 636 arcsec from SVOM/Eclairs position.
  Flux: (4.4 [+1.4, -1.1])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
```
Moreover Source 2, separated by 5.525" from EP J204347.6+493054 (GCN 37206 Li et al.), has not been detected from a previous observation performed by Swift at MJD 54638.495 with a 3 sigma upper limit of 2.9e-03 ct s^-1.
Swift will perform further ToO observations to assess the nature of this transient.
The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021702.
This circular is an official product of the Swift-XRT team.
GCN Circular #37311
Antonino D=E2=80=99Ai, Elena Ambrosi (INAF/IASF-PA) report on behalf of the Swift-XRT team:
Swift performed a second epoch follow-up observation for Source2 (D=E2=80= =99Avanzo et al., GCN 37218), the likely counterpart for the SVOM/Eclairs-detected X-ray transient GRB 240819A (Coleiro et al., GCN 37208). We collected 3.4 ks of Photon Counting (PC) mode data between T0+6.01 days and T0+7.67 days.=20
At the position of Source2 (previously detected at rate 11(+3.5, -2.9) x 10^-3 ct/sec), no source is detected with a 3-sigma upper limit of 3.5 x 10^-3 ct/sec.=20
The upper limit is evidence for the lightcurve fading of this source, confirming the afterglow association with GRB 240819A.
This circular is an official product of the Swift-XRT team.
GCN Circular #37325
SVOM/ECLAIRs commissioning team: Sebastien Guillot, Olivier Godet, Laurent = Bouchet, Juliette Alaux (IRAP), Tais Maiolino (LUPM), Floriane Cangemi (APC= ), St=C3=A9phane Schanne, Fr=C3=A9d=C3=A9ric Chateau, Nicolas Dagoneau, Her= v=C3=A9 Le Provost (CEA), Karine Mercier, Marie-Claire Charmeau, Stefano Cr= epaldi (CNES)
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (I= HEP), St=C3=A9phane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA)= , Zi-Gao Dai (USTC), Fr=C3=A9d=C3=A9ric Daigne (IAP), Jin-Song Deng (NAOC),= Andrea Goldwurm (APC), Diego G=C3=B6tz (CEA), Xu-Hui Han (NAOC), Cyril Lac= haud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Par= is), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV= )
report on behalf of the SVOM team:
Following the trigger of the X-ray transient, named GRB 240819A, by SVOM/EC= LAIRs (Coleiro, et al., GCN 37208) at 2024-08-19T02:35:21.2 UT (T0), furthe= r analyses of the X-band data from ECLAIRs indicate a rather soft event wit= h most photons below 40 keV (signal-to-noise of ~10 for events between 4 to= 40 keV; versus S/N < 4 for events above 40 keV). =20
In addition, observations by Swift-XRT at T0+0.23 days and T0+0.31 days (D'= Avanzo, et al., GCN 37218) and at T0+6.01 days (D=E2=80=99ai, et al. GCN 3= 7311) revealed a fading X-ray source from 11(+3.5, -2.9) x 10^-3 ct/sec to= a 3-sigma upper limit of 3.5 x 10^-3 ct/sec. Therefore, the X-ray afterglo= w of GRB 240819A is likely source 2 (from D=E2=80=99ai, et al. GCN 37311), = localized at RA=3D310.9464 (20:43:47.14) and Dec.=3D+49.5140 (+49:30:50.3) = with a 90% c.l. error circle of 5.8 arcseconds.
The identification of the fading afterglow and the spectral softness of the= event described above, are indicative of a likely X-Ray Flash (XRF, i.e., = a soft GRB with lower luminosity and located at a closer distance than typi= cal GRBs), rather than a Galactic transient.
We encourage deep optical follow-up observations to attempt the detection o= f a possible supernova that could be associated with this event. We caution= that, due to the low galactic latitude of the transient, a potential super= nova will undergo strong visible extinction (Av ~ 5).
GCN Circular #37396
R. Jayaraman (MIT), M.M. Fausnaugh (TTU), R. Vanderspek (MIT), and G. Mo (M= IT) report:
The Transiting Exoplanet Survey Satellite (TESS; Ricker et al. 2015) was ob= serving the entirety of the localization region for the transient GRB 24081= 9A (Coleiro et al., GCN 37208), which was later identified as an X-ray flas= h (Guillot et al., GCN 37325). TESS observed this region at a 200 second ca= dence continuously from 2.14 days before the trigger to 3.85 days after the= trigger. The GRB occurred during TESS observational Sector 82, and the loc= alization fell within Camera 3, CCD 2.
We performed forced difference-imaging photometry at the location of the co= nfirmed X-ray afterglow (D=E2=80=99Ai et al., GCN 37311) using the full-fra= me images from the publicly-available TICA data archived at MAST (https://a= rchive.stsci.edu/hlsp/tica). Our analysis routine is described in Fausnaugh= et al. 2023 (ApJ 956(2):108).=20
There was no source detected at the location from Swift-XRT. We find a 3-si= gma upper limit of 17.3 around the time of trigger in the TESS band at the = native 200 s cadence. Stacking to 30 minutes yields a deeper limit of 19.4.= These limits are consistent with the upper limits reported a few hours aft= er the burst (Zheng et al., GCN 37213).
This circular includes data collected with the TESS mission, obtained from = the MAST data archive at the Space Telescope Science Institute (STScI). Fun= ding for the TESS mission is provided by the NASA Explorer Program. STScI i= s operated by the Association of Universities for Research in Astronomy, In= c., under NASA contract NAS 5-26555.

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