TITLE: GCN CIRCULAR
NUMBER: 38404
SUBJECT: EP241126a: 1.6m Mephisto Optical Upper Limits
DATE: 24/12/01 15:38:10 GMT
FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn>
Xingzhu Zou, Helong Guo, Xinlei Chen, Yu Pan, Yaosong Yu, Guowang Du, Xufeng Zhu, Tao Wang, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of fast X-ray transient EP241126a (Hu et al., GCN 38335; Zheng et al., GCN 38339) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were carried out in the v and r bands, ~15.8 hours after the EP trigger. We do not detect the optical counterpart (Fu et al., GCN 38337; Li et al., GCN 38338; Geng et al., GCN 38357; Qiu et al., GCN 38378; Malesani et al., GCN 38385) in the stacked images (total exposure 420 sec in each band). The 3-sigma upper limits in v and r bands (mid-UT 2024-11-27T11:28:36) are 22.2 and 22.3 mag respectively, which is consistent with Lai et al. (GCN 38344).
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Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
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TITLE: GCN CIRCULAR
NUMBER: 38402
SUBJECT: LIGO/Virgo/KAGRA S241201ac: Identification of a GW compact binary merger candidate
DATE: 24/12/01 06:44:24 GMT
FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S241201ac during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-12-01 05:57:58.628 UTC (GPS time: 1417067896.628). The candidate was found by the cWB BBH [1] and GstLAL [2] analysis pipelines.
S241201ac 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/S241201ac
The classification of the GW signal, in order of descending probability, is BBH (97%), Terrestrial (3%), NSBH (<1%), or BNS (<1%).
Transient noise was present in the Virgo detector data at the time of the candidate, which may affect the parameters or the sky localization of the candidate.
Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] 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 4%.
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 [4], distributed via GCN notice about 28 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [4], 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 3425 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 9495 +/- 2984 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] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
View this GCN Circular online at https://gcn.nasa.gov/circulars/38402.
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TITLE: GCN CIRCULAR
NUMBER: 38401
SUBJECT: LIGO/Virgo/KAGRA S241130be: Updated Sky localization
DATE: 24/12/01 06:23:21 GMT
FROM: ethan.payne(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 S241130be (GCN Circular 38393). 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/S241130be
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 1069 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1226 +/- 321 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/38401.
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