January 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 36987] GRB 250119B: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Jan '25

19 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38979 SUBJECT: GRB 250119B: Fermi GBM Final Real-time Localization DATE: 25/01/19 08:37:41 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 08:27:01 UT on 19 Jan 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250119B (trigger 758968026.673982 / 250119352). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 306.7, Dec = 21.2 (J2000 degrees, equivalent to J2000 20h 26m, 21d 11'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 106.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250119352/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250119352/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250119352/… View this GCN Circular online at https://gcn.nasa.gov/circulars/38979. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36986] LIGO/Virgo/KAGRA S250119ag: Identification of a GW compact binary merger candidate
by GCN Circulars 19 Jan '25

19 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38978 SUBJECT: LIGO/Virgo/KAGRA S250119ag: Identification of a GW compact binary merger candidate DATE: 25/01/19 03:18:08 GMT FROM: Zhi-Chao Zhao <zhaozc(a)cau.edu.cn> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250119ag during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-01-19 02:51:38.775 UTC (GPS time: 1421290316.775). The candidate was found by the CWB [1], CWB-BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250119ag is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.3e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250119ag The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object 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. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN notice about 28 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN notice about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 622 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2613 +/- 626 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. (2023) arXiv:2305.05625 [4] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [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/38978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36985] GRB 250119A: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Jan '25

19 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38977 SUBJECT: GRB 250119A: Fermi GBM Final Real-time Localization DATE: 25/01/19 02:10:06 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 01:59:27 UT on 19 Jan 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250119A (trigger 758944772.334442 / 250119083). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 204.1, Dec = 43.1 (J2000 degrees, equivalent to J2000 13h 36m, 43d 06'), with a statistical uncertainty of 23.4 degrees. The angle from the Fermi LAT boresight is 90.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250119083/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250119083/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250119083/… View this GCN Circular online at https://gcn.nasa.gov/circulars/38977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36984] GRB 250118A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38976 SUBJECT: GRB 250118A: Fermi GBM Final Real-time Localization DATE: 25/01/18 18:41:33 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 18:31:11 UT on 18 Jan 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250118A (trigger 758917876.966464 / 250118772). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 263.8, Dec = 38.8 (J2000 degrees, equivalent to J2000 17h 35m, 38d 47'), with a statistical uncertainty of 10.7 degrees. The angle from the Fermi LAT boresight is 14.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250118772/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250118772/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250118772/… View this GCN Circular online at https://gcn.nasa.gov/circulars/38976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36983] LIGO/Virgo/KAGRA S250118dp: Identification of a GW compact binary merger candidate
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38975 SUBJECT: LIGO/Virgo/KAGRA S250118dp: Identification of a GW compact binary merger candidate DATE: 25/01/18 17:37:47 GMT FROM: julio.martins(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250118dp during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-01-18 17:05:23.221 UTC (GPS time: 1421255141.221). The candidate was found by the CWB [1], CWB-BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250118dp is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.6e-25 Hz, or about one in 1e17 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250118dp The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), BNS (<1%), or Terrestrial (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object 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. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. 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 notice about 30 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [8], distributed via GCN notice 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 1136 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2125 +/- 569 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. (2023) arXiv:2305.05625 [4] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [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/38975. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36982] LIGO/Virgo/KAGRA S250118t: Updated Sky localization
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38974 SUBJECT: LIGO/Virgo/KAGRA S250118t: Updated Sky localization DATE: 25/01/18 13:46:50 GMT FROM: Soichiro Morisaki at U. of Tokyo <soichiro.morisaki(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 S250118t (GCN Circular 38971). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250118t For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 2332 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6631 +/- 2213 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. (2023) arXiv:2307.13380 View this GCN Circular online at https://gcn.nasa.gov/circulars/38974. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36981] LIGO/Virgo/KAGRA S250118az: Identification of a GW compact binary merger candidate
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38973 SUBJECT: LIGO/Virgo/KAGRA S250118az: Identification of a GW compact binary merger candidate DATE: 25/01/18 06:23:53 GMT FROM: Zhi-Chao Zhao <zhaozc(a)cau.edu.cn> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250118az during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-01-18 05:58:02.472 UTC (GPS time: 1421215100.472). The candidate was found by the CWB-BBH [1], GstLAL [2], MBTA [3], PyCBC Live [4], and SPIIR [5] analysis pipelines. S250118az is an event of interest because its false alarm rate, as estimated by the online analysis, is 9.8e-09 Hz, or about one in 3 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250118az 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 the lighter compact object 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. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 19%. 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 notice about 29 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [7], distributed via GCN notice 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 1219 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1336 +/- 410 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] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [2] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [3] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [4] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [5] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [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/38973. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36980] EP250108a / AT2025kg: GMG Optical Observations
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38972 SUBJECT: EP250108a / AT2025kg: GMG Optical Observations DATE: 25/01/18 04:40:23 GMT FROM: Fei-Fan Song at Yunnan Observatories <songfeifan(a)ynao.ac.cn> F.-F. Song, R.-Z. Li, B.-T. Wang, J. Mao, K.-X. Lu and J.-M. Bai (YNAO) report: We observed the field of EP 250108a (Li et al., GCN 38861, T0 at 2025-01-08T12:30:28.34 UTC) using the GMG-2.4m telescope at the Lijiang Observatory. The observations were made three times, starting at 2025-01-15T14:26:43, 2025-01-16T12:33:50 and 2025-01-16T12:38:36, respectively. The optical counterpart of EP 250108a (Eyles-Ferris, GCN 38878; Zhu et al., GCN 38885; Malesani et al., GCN 38902; Kumar et al., GCN 38907; Zhu et al, GCN 38908; L. Izzo, GCN 38912; Zou et al., GCN 38914; Moskvitin et al., GCN 38925) was detected. The preliminary analysis results are shown as follows: +---------------+----------+--------------+--------------+ | Tmid-T0 [h] | Filter | Mag | 5-sigma UL | +===============+==========+==============+==============+ | 170.10 | r | 20.75 ± 0.16 | 21.1 | +---------------+----------+--------------+--------------+ | 192.09 | g | 20.78 ± 0.09 | 21.7 | +---------------+----------+----------+------------------+ | 192.17 | r | 20.28 ± 0.07 | 21.6 | +---------------+----------+--------------+--------------+ The given magnitudes are derived based on calibrating against Pan-STARRS1 field stars. We acknowledge the staff at the Lijiang Observatory for conducting the observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/38972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36979] LIGO/Virgo/KAGRA S250118t: Identification of a GW compact binary merger candidate
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38971 SUBJECT: LIGO/Virgo/KAGRA S250118t: Identification of a GW compact binary merger candidate DATE: 25/01/18 03:12:05 GMT FROM: Lijing Shao at Peking University <lshao(a)pku.edu.cn> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250118t during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-01-18 02:32:25.941 UTC (GPS time: 1421202763.941). The candidate was found by the CWB-BBH [1], GstLAL [2], MBTA [3], and PyCBC Live [4] analysis pipelines. S250118t is an event of interest because its false alarm rate, as estimated by the online analysis, is 4e-10 Hz, or about one in 79 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250118t 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 the lighter compact object 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. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 4%. Three sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [6], distributed via GCN notice about 27 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [6], distributed via GCN notice about 31 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [6], distributed via GCN notice 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 2393 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 8129 +/- 2357 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] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [2] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [3] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [4] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [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/38971. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36978] EP250108a / AT2025kg: VLA radio upper limit
by GCN Circulars 18 Jan '25

18 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38970 SUBJECT: EP250108a / AT2025kg: VLA radio upper limit DATE: 25/01/18 03:08:32 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> We observed the position of AT2025kg (Eyles-Ferris, GCN 38878; Zhu et al., GCN 38885; Malesani et al., GCN 38902; Kumar et al., GCN 38907; Zhu et al., GCN 38908, Levan et al., GCN 38909; Izzo, GCN 38912; Zou et al., GCN 38914), the optical counterpart to Fast X-ray Transient EP250108a (Li et al. GCN 38861) with the Karl G. Jansky Very Large Array (VLA) under program 25A-374 (PI: Perley) beginning on 2025 January 15 at 00:21 UT (6.5 days post discovery) at a mean frequency of 10 GHz. Based on preliminary analysis, we do not detect any radio emission at or near the position of AT2025kg to a 3-sigma limit of 16.5 microJy. At a redshift of z=0.176 (Zhu et al., GCN 38908), the VLA observation corresponds to a 10 GHz upper limit of < 2E28 erg/s/Hz. This is consistent with previous observations of luminous fast blue optical transients: for example, at 10 days post discovery, AT2020xnd was 4E28 erg/s/Hz (e.g., Ho et al. 2022, ApJ, 932, 116), but AT2018cow was over an order of magnitude less luminous (Margutti et al. 2019, ApJ, 872, 18). This luminosity limit is two orders of magnitude lower than a typical GRB radio afterglow, but is consistent with the luminosities of sub-energetic GRBs at a similar epoch (e.g., Margutti et al. 2014, ApJ, 797, 107; Laskar et al. 2023, ApJ, 946, 23). Additional followup is planned. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/38970. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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