TITLE: GCN CIRCULAR
NUMBER: 40876
SUBJECT: Fermi Gamma-ray Burst Monitor trigger 772981768/250630548 is not a GRB
DATE: 25/06/30 14:44:50 GMT
FROM: Peter Veres at University of Alabama in Huntsville <veresp(a)gmail.com>
Peter Veres (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"The Fermi Gamma-ray Burst Monitor (GBM) trigger 772981768/250630548 at 13:09:23.19 UT
on 30 June 2025, tentatively classified as a GRB, is in fact not due
to a GRB. This trigger is likely due to Local Particles."
View this GCN Circular online at https://gcn.nasa.gov/circulars/40876.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40875
SUBJECT: GRB 250628B: SVOM/VT optical upper limit
DATE: 25/06/30 09:34:49 GMT
FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn>
H. L. Li, Y. L. Qiu, L. P. Xin, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), D. Dornic (CPPM),J-G. Ducoin(CPPM)report on behalf of the SVOM/VT team.
SVOM/VT performed ToO follow-up observations on the GRB 250628B (SVOM burst-id sb25062804, Dornic et al., GCN 40862) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started on 2025-06-28T20:33:10 UT, ie. 4.06 hours after the SVOM T0 time.
No uncatalogued sources are detected in single or stacked images at the position of the Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00021/) and EP (Zhang et al., GCN 40874), compared to the Legacy survey. The 3 sigma upper limit magnitudes are derived as below:
Mid_time | Band | Exposure Time | Upper limit (AB)
5.8 hour VT_B 50*70 sec 23.6 mag
5.8 hour VT_R 49*70 sec 23.4 mag
Also no apparent variation is found for the catalogued sources that lie within the errorbox of the Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00021/) and EP (Zhang et al., GCN 40874).
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40875.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40874
SUBJECT: GRB 250628B: EP-FXT counterpart detection
DATE: 25/06/30 06:04:47 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
W. J. Zhang, X. Mao (NAO, CAS), Y. C. Fu (BNU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250628B (SVOM/sb25062804, Dornic et al. GCN #40862) at 2025-06-28T18:51:59 (UTC), about 140 minutes after the SVOM/ECLAIRs trigger, with an exposure time of ~5000s. Five uncatalogued sources are detected within the ECLAIRs error circle. Preliminary analysis of these sources has been conducted automatically, and the details are listed below.
Source 1: EPF_J221230.7-453117
RA (J2000): 333.1278
Dec (J2000): -45.5213
Flux: 6.57 x 10^-14 erg/s/cm2 (FXT-A observed, 0.5-10 kev)
Flux_err: 2.48 x 10^-14 erg/s/cm2 (1 sigma)
Source 2: EPF_J221214.3-453344
RA (J2000): 333.0595
Dec (J2000): -45.5621
Flux: 2.13 x 10^-13 erg/s/cm2 (FXT-A observed, 0.5-10 kev)
Flux_err: 4.30 x 10^-14 erg/s/cm2 (1 sigma)
Source 3: EPF_J221327.1-453729
RA (J2000): 333.3628
Dec (J2000): -45.6247
Flux: 1.89 x 10^-13 erg/s/cm2 (FXT-A observed, 0.5-10 kev)
Flux_err: 4.06 x 10^-14 erg/s/cm2 (1 sigma)
Source 4: EPF_J221218.2-453223
RA (J2000): 333.0758
Dec (J2000): -45.5397
Flux: 9.71 x 10^-14 erg/s/cm2 (FXT-A observed, 0.5-10 kev)
Flux_err: 2.74 x 10^-14 erg/s/cm2 (1 sigma)
Source 5: EPF_J221226.9-453909
RA (J2000): 333.1120
Dec (J2000): -45.6525
Flux: 4.23 x 10^-14 erg/s/cm2 (FXT-B observed, 0.5-10 kev)
Flux_err: 1.54 x 10^-14 erg/s/cm2 (1 sigma)
Note: Sources 1-3 were simultaneously detected by both FXT-A and FXT-B, while Source 4 and Source 5 were individually detected by FXT-A and FXT-B, respectively.
The position uncertainties of the sources are about 10 arcsec in radius (90% C.L. statistical and systematic).
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).
View this GCN Circular online at https://gcn.nasa.gov/circulars/40874.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40873
SUBJECT: LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
DATE: 25/06/29 16:37:41 GMT
FROM: John Veitch at U of Glasgow <john.veitch(a)ligo.org>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S250629bs (GCN Circular 40869). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S250629bs
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 2998 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4847 +/- 1746 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040
View this GCN Circular online at https://gcn.nasa.gov/circulars/40873.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40872
SUBJECT: GRB 250627A: Insight-HXMT detection
DATE: 25/06/29 15:49:05 GMT
FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn>
Chen-Wei Wang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2025-06-27T16:46:23 (T0), Insight-HXMT/HE detected the short burst GRB 250627A, which is also detected by SVOM/GRM (Wang et al., GCN #40871).
The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 0.9 +0.1/-0.2 s.
The 1s peak rate, measured from T0+0.175 s, is 7839 cnts/sec.
The total counts from this burst is 8292 counts.
The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250627A.png
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40872.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40871
SUBJECT: GRB 250627A: SVOM/GRM detection of a short burst
DATE: 25/06/29 14:35:58 GMT
FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn>
SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a hard short burst GRB 250627A (SVOM trigger reference: sb25062711) at 2025-06-27T16:46:23 UTC (T0).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.9 +0.2/-0.4 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250627A.png
In addition, ECLAIRs was collecting data at the time of this burst and also detected this burst in the energy range of above 50 keV, although this burst is outside ECLAIRs FOV.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn)
View this GCN Circular online at https://gcn.nasa.gov/circulars/40871.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40870
SUBJECT: LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
DATE: 25/06/29 13:31:48 GMT
FROM: Aditya Vijaykumar <aditya.vijaykumar(a)ligo.org>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250629ae (GCN Circular 40867). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S250629ae
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 2834 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 7075 +/- 2116 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040
View this GCN Circular online at https://gcn.nasa.gov/circulars/40870.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40869
SUBJECT: LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
DATE: 25/06/29 13:05:07 GMT
FROM: rodrigo.cuzinatto(a)unifal-mg.edu.br
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250629bs during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-06-29 12:13:04.377 UTC (GPS time: 1435234402.377). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], and MBTA [4] analysis pipelines.
S250629bs is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.3e-08 Hz, or about one in 8 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250629bs
The classification of the GW signal, in order of descending probability, is BBH (94%), Terrestrial (6%), BNS (<1%), or NSBH (<1%).
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [5] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [5] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.
The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin.
Two sky maps are available at this time and can be retrieved from the GraceDB event page:
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [6], distributed via GCN and SCiMMA notices about 23 seconds after the candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [6], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 3008 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1811 +/- 561 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018
[3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008
[4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234
[5] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[6] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
View this GCN Circular online at https://gcn.nasa.gov/circulars/40869.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40868
SUBJECT: LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
DATE: 25/06/29 12:55:27 GMT
FROM: rodrigo.cuzinatto(a)unifal-mg.edu.br
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250628am during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-06-28 18:23:19.785 UTC (GPS time: 1435170217.785). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines.
S250628am is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.7e-14 Hz, or about one in 1e6 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250628am
The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.
The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin.
Two sky maps are available at this time and can be retrieved from the GraceDB event page:
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 32 seconds after the candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 427 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1112 +/- 273 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018
[3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008
[4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234
[5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a
[6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023
[7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
View this GCN Circular online at https://gcn.nasa.gov/circulars/40868.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…
TITLE: GCN CIRCULAR
NUMBER: 40867
SUBJECT: LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
DATE: 25/06/29 06:56:02 GMT
FROM: 林峻哲Lin, Chun-Che <lupin(a)phys.ncku.edu.tw>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250629ae during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-06-29 05:50:36.925 UTC (GPS time: 1435211454.925). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], and PyCBC Live [5] analysis pipelines.
S250629ae is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-08 Hz, or about one in 11 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250629ae
The classification of the GW signal, in order of descending probability, is BBH (98%), Terrestrial (2%), NSBH (<1%), or BNS (<1%).
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [6] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [6] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.
The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin.
Two sky maps are available at this time and can be retrieved from the GraceDB event page:
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [7], distributed via GCN and SCiMMA notices about 40 seconds after the candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [7], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 3184 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4550 +/- 1295 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018
[3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008
[4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234
[5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a
[6] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[7] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
View this GCN Circular online at https://gcn.nasa.gov/circulars/40867.
---
To unsubscribe, open this link in a web browser:
https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…