LIGO/Virgo/KAGRA S240915b
GCN Circular 37512
Subject
LIGO/Virgo/KAGRA S240915b: Identification of a GW compact binary merger candidate
Date
2024-09-15T00:59:52Z (9 months ago)
From
Gungwon Kang at Chung-Ang University <gungwon.kang@ligo.org>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S240915b during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-09-15 00:13:57.715 UTC (GPS time: 1410394455.715). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines.
S240915b is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S240915b
The classification of the GW signal, in order of descending probability, is BBH (86%), NSBH (14%), Terrestrial (<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%. [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 13%.
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 29 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 71 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 865 +/- 185 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
GCN Circular 37513
Subject
LIGO/Virgo/KAGRA S240915b: Updated Sky localization and EM Bright Classification
Date
2024-09-15T03:20:38Z (9 months ago)
From
Aaron Zimmerman at U. of Texas at Austin <aaron.zimmerman@utexas.edu>
Via
Web form
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 S240915b (GCN Circular 37512). 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/S240915b
Based on posterior support from parameter estimation [1], under the assumption that the candidate S240915b is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass above one solar mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] HasRemnant is assumed to be zero when the heavier component mass is below 1 solar mass. 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 2%.
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 19 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis):
icrs; ellipse(07h36m, -49d55m, 3.88d, 1.60d, 23.49d)
Marginalized over the whole sky, the a posteriori luminosity distance estimate is 872 +/- 149 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
[2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
GCN Circular 37520
Subject
LIGO/Virgo/KAGRA S240915b: Coverage and upper limits from MAXI/GSC observations
Date
2024-09-16T06:13:06Z (9 months ago)
From
Motoko Serino at Aoyama Gakuin U. <serino@phys.aoyama.ac.jp>
Via
Web form
H. Nishikawa, S. Sugita, M. Serino, Y. Kawakubo, H. Hiramatsu, Y. Kondo (AGU)
H. Negoro, M. Nakajima, K. Takagi (Nihon U.),
N. Kawai, T. Mihara, (RIKEN),
report on behalf of the MAXI team:
We examined MAXI/GSC all-sky X-ray images (2-20 keV)
after compact binary merger candidate S240915b at 2024-09-15 00:13:57.715 UTC (GCN 37512, 37513).
At the trigger time of S240915b, the high-voltage of MAXI/GSC was off,
and it was turned on at T0+707 sec (+11.8 min).
The first one-orbit (92 min) scan observation with GSC after the event covered 100%
of the 90% credible region of the Bilby skymap from 01:17:12 to 01:19:17 UTC (T0+3795 to T0+3920 sec).
No significant new source was found in the region in the one-orbit scan observation.
A typical 1-sigma averaged upper limit obtained in one scan observation
is 20 mCrab at 2-20 keV.
If you require information about X-ray flux by MAXI/GSC at specific coordinates,
please contact the submitter of this circular by email.
GCN Circular 37528
Subject
LIGO/Virgo/KAGRA S240915b: NED Galaxies in the Localization Volume
Date
2024-09-16T15:31:50Z (9 months ago)
From
David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>
Via
Web form
David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)
On behalf of the NASA/IPAC Extragalactic Database (NED) Team.
We spatially cross-matched the LVK S240915b-4-Update sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 121 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:
Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S240915b/4
Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S240915b/4/20
The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic followup observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D*P_SFR; and specific star formation rate, P_3D*P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.
| objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV|m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1|
|-------------------------|--------------|--------------|-------|-----------|-----------|-------|---------|------------|------------|------------|------------|--------|----------|
|WISEA J073837.61-485525.6| 114.65613| -48.92356| G| 990.52| null| null| null| 13.601| 0.191| 11.276| 0.007|4.71e-07| 2.84e-08|
|WISEA J073404.99-500810.2| 113.52088| -50.13622| G| 738.22| null| null| null| 13.598| 0.227| 13.757| 0.025|2.92e-06| 9.98e-09|
|WISEA J074722.25-511232.2| 116.84267| -51.20906| G| 607.13| null| null| null| 13.676| 0.198| 10.126| 0.005|1.28e-07| 8.45e-09|
|WISEA J073722.17-492211.0| 114.34246| -49.36983| G| 514.22| null| null| null| 13.562| 0.185| 10.176| 0.006|1.77e-07| 7.95e-09|
|WISEA J073605.42-501521.8| 114.02258| -50.25611| G| 613.50| null| null| null| 13.559| 0.184| 12.527| 0.015|9.74e-07| 7.11e-09|
|WISEA J073845.34-492641.5| 114.68892| -49.44489| G| 868.41| null| null| null| 13.568| 0.205| 14.020| 0.024|1.85e-06| 6.86e-09|
|WISEA J074200.71-490215.9| 115.50304| -49.03778| G| 941.86| null| null| null| 13.450| 0.172| 12.141| 0.009|2.65e-07| 6.68e-09|
|WISEA J071925.06-480802.0| 109.85429| -48.13372| G| 861.77| null| null| null| 12.678| 0.145| 11.747| 0.007|1.55e-07| 4.50e-09|
|WISEA J074607.32-492655.0| 116.53050| -49.44867| IrS| 765.32| null| null| null| 12.806| 0.088| 11.475| 0.023|1.46e-07| 4.39e-09|
|WISEA J073308.99-485029.3| 113.28758| -48.84156| G| 587.29| null| null| null| 13.265| 0.178| 10.500| 0.007|9.69e-08| 4.22e-09|
|WISEA J073337.19-494213.1| 113.40496| -49.70361| G| 657.33| null| null| null| 13.726| 0.222| 13.827| 0.025|1.61e-06| 4.11e-09|
|WISEA J074747.05-512246.8| 116.94600| -51.37967| G| 579.13| null| null| null| 13.326| 0.175| 10.131| 0.005|6.24e-08| 3.73e-09|
|WISEA J074517.88-493623.3| 116.32454| -49.60650| G| 573.90| null| null| null| 13.737| 0.209| 11.226| 0.006|1.34e-07| 2.87e-09|
|WISEA J073444.72-500022.6| 113.68633| -50.00622| G| 604.99| null| null| null| 13.645| 0.202| 13.712| 0.025|9.97e-07| 2.39e-09|
|WISEA J073552.84-510713.6| 113.97008| -51.12044| G| 657.12| null| null| null| 13.405| 0.162| 12.733| 0.023|3.03e-07| 2.10e-09|
|WISEA J071622.35-481344.8| 109.09296| -48.22925| G| 742.68| null| null| null| 13.041| 0.150| 12.265| 0.007|1.49e-07| 1.99e-09|
|WISEA J074831.90-510452.3| 117.13300| -51.08128| G| 677.56| 0.79| null| null| 12.733| 0.118| 12.161| 0.020|1.54e-07| 1.95e-09|
|WISEA J074140.07-484512.7| 115.41704| -48.75350| G| 923.13| null| null| null| 13.292| 0.177| 13.023| 0.020|1.74e-07| 1.88e-09|
|WISEA J073615.34-504822.7| 114.06396| -50.80628| G| 678.69| null| null| null| 13.879| 0.266| 14.018| 0.026|7.94e-07| 1.80e-09|
|WISEA J074306.54-512537.3| 115.77733| -51.42697| G| 775.86| null| null| null| 13.481| 0.165| 12.975| 0.026|1.77e-07| 1.38e-09|
Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S240915b sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D*P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1).