LIGO/Virgo/KAGRA S250328ae
GCN Circular 40455
Isaac McMahon, Sean MacBride, Marcelle Soares-Santos (UZH), Simran Kaur (U. of Michigan/UZH), Lillian Joseph (Benedictine U.), Ken Herner, Tom Diehl (Fermilab), Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ) report on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team, the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), and Subaru Telescope:
At 01:20 UTC April 6th and 00:14 UTC April 25th, the Dark Energy Camera (DECam) began the third and fourth epochs of observations in final response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). The pointings of these observations were identical to the first epoch observations from March 29th, 2025 (GCN 39934). All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~21.3 in r-band, ~21.2 in i-band, and ~21.0 in z-band for the third epoch and ~22.3 in r-band, ~22.1 in i-band, and ~21.6 in z-band for the fourth.
We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts, requiring an autoscan score of at least 0.7 on at least 3 nights of observations. We also match our candidates against the ALLWISE, Milliquas, Quaia, and LQAC-6 AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024, Souchay et al 2024) within the LVK localization volume. Of the 88 AGNs which exhibited transient variability in our observations, none lay within the localization volume.
Of the 25 high confidence candidates reported previously (GCN 39992), 15 were observed by the J-GEM collaboration, using the Subaru Telescope Prime Focus Spectrograph (PFS), and ruled out by spectral identification and redshift (GCN 40221). Another 8 candidates either did not exhibit any further transient activity after the first two epochs or were determined to be likely stellar in origin. The final 2 candidates were not within the footprint observed by J-GEM and thus could not be determined. We report these two candidates and one last candidate which was observed only in the most recent epochs below, all likely of supernova origin.
| TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR |
|---|---|---|---|---|---|---|---|---|---|---|
| SN_LIKE | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 |
| SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | 21.03 | 0.15 | 21.22 | 0.10 |
| SN_LIKE | 2295351 | AT2025kjv | 143.077064 | 7.385021 | 22.3 | 0.10 | 21.81 | 0.07 | 22.86 | 0.44 |
Additionally, J-GEM reported 5 QSOs which had a redshift consistent with the localization volume. We do not find any evidence of any transient variability for any of these QSOs in our observations after the detection of S250328ae. We also do not recover any of the X-ray source candidates reported by Swift XRT (GCN 39972) within their reported error bounds. Thus, apart from the possibility that the three supernova-like candidates reported above are related to S250328ae, we find no suitable optical counterpart candidate for this binary black hole gravitational wave event.
The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. We also thank the J-GEM and Swift XRT teams for their contribution and support.
We are grateful to the staff at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind support in such aspects as finances, contracts, asset managements, and so on. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawaii.
GCN Circular 40221
Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ), Sean MacBride, Isaac McMahon, Marcelle Soares-Santos (UZH), Ken Herner (Fermilab), Simran Kaur (University of Michigan/UZH), Lillian Joseph (Benedictine U.), and Tom Diehl (FNAL) report on behalf of the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), Subaru Telescope, and Dark Energy Survey Gravitational Wave (DESGW) Team:
Between 05:11 and 10:20 UTC on April 3, 2025, we carried out spectroscopic observations with the Subaru/Prime Focus Spectrograph (PFS) following the LVK alert issued for the gravitational-wave event S250328ae (GCN 39898). The Subaru/PFS is a fiber spectrograph capable of observing ~2400 targets simultaneously within a ~1.25 square degree field of view, and covers a wavelength range of 380 nm to 1260 nm with a resolving power of ~2500-5500 (Sugai et al. 2015; Tamura et al. 2024). We observed seven pointings centered on the ICRS coordinates listed below:
| RA [deg] | Dec [deg] |
|---|---|
| 144.130530 | 10.436230 |
| 144.126501 | 11.595492 |
| 145.151367 | 9.856599 |
| 145.151367 | 11.015861 |
| 145.151367 | 12.175123 |
| 146.176234 | 11.595492 |
| 146.180717 | 12.754753 |
These seven pointings cover the ~50% localization region of the S250328ae event.
We observed targets selected from transient candidates of GCN 39934 and 39992 (including candidates before and after vetting), X-ray sources from GCN 39972, and potential host galaxies from GLADE+ (Dálya et al. 2022) and PS1-STRM (Beck et al. 2021) catalogs in our pointings. A total of ~3900 targets were observed with an on-source exposure time of 1800 seconds in six pointings and 900 seconds in one pointing (shortened due to bad weather conditions).
We reduced the data on-site using the quick reduction system based on the PFS Data Reduction Pipeline, and then carried out classification (fitting galaxy, QSO, star, and supernova templates) and visual inspection. After classification and visual inspection, we obtained confident spectroscopic redshifts of ~70% of our targets. Among these sources, five candidates listed below were identified to be the possible electromagnetic counterpart to the gravitational-wave event S250328ae (within the ~90% three-dimensional localization volume partly covered by our pointings). Because these five candidates were originally selected from the GLADE+ and PS1-STRM catalogs that do not contain information of variability, we encourage follow-up observations to confirm their variability.
| ID_PFS | ATNAME | RA [deg] | Dec [deg] | Type_PFS | Redshift |
|---|---|---|---|---|---|
| 761 | AT2019uib | 145.718857 | 12.412288 | QSO | 0.130 |
| 9238 | N/A | 145.412644 | 12.717089 | QSO | 0.096 |
| 13647 | N/A | 144.989553 | 10.636089 | QSO | 0.136 |
| 17165 | N/A | 145.733559 | 11.593362 | QSO | 0.120 |
| 19826 | N/A | 145.351893 | 12.503455 | QSO | 0.136 |
No counterparts to X-ray sources (GCN 39972) are recovered within their reported error bounds by our observations. We do not identify any transient candidates (GCN 39934 and 39992) we observed within the ~90% three-dimensional localization volume of S250328ae. These transient candidates falling outside the ~90% localization volume are listed below.
| ID_ DESGW | ATNAME | RA [deg] | Dec [deg] | Type_ DESGW | Type_PFS | Redshift |
|---|---|---|---|---|---|---|
| 2290036 | AT2025gek | 145.199481 | 10.828527 | SN_LIKE | SN Ic | 0.233 |
| 2290467 | AT2020woa | 144.388798 | 10.255536 | SN_LIKE | SN Ib | 0.050 |
| 2292782 | AT2025geo | 144.928578 | 10.349243 | SN_LIKE | SN Ia | 0.182 |
| 2290334 | AT2025geq | 145.235616 | 12.469694 | SN_LIKE | SN Ia | 0.186 |
| 2290623 | AT2025gen | 144.112464 | 11.641817 | AGN_LIKE | SN II | 0.204 |
| 2291223 | N/A | 146.389563 | 13.131801 | AGN_LIKE | QSO | 0.540 |
| 2293190 | AT2025cvb | 144.191297 | 10.828462 | SN_LIKE | SN Ia | 0.140 |
| 2290143 | AT2025ggv | 146.033906 | 11.088812 | SN_LIKE | QSO | 1.437 |
| 2292040 | AT2025ges | 144.438216 | 9.885617 | AGN_LIKE | SN Ia | 0.434 |
| 2290059 | N/A | 144.679961 | 10.018211 | AGN_LIKE | QSO | 0.209 |
| 2292786 | N/A | 144.037664 | 10.810454 | AGN_LIKE | SN Ia | 0.254 |
| 2293517 | AT2025geu | 145.956024 | 12.381673 | AGN_LIKE | QSO | 0.507 |
| 2295862 | N/A | 145.361115 | 12.521385 | AGN_LIKE | QSO | 0.969 |
| 2290563 | N/A | 145.149074 | 11.756403 | AGN_LIKE | QSO | 0.255 |
| 2289995 | AT2025ggx | 144.57373 | 10.274445 | SN_LIKE | SN II | 0.358 |
We are grateful to the staffs at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind supports in such aspects as finances, contracts, asset managements, and so on.
This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical, and natural significance in Hawaii.
The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations.
GCN Circular 39992
S. MacBride (UZH), I. McMahon (UZH), M. Soares-Santos (UZH), K. Herner (Fermilab), S. Kaur (University of Michigan/UZH), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team:
At 01:46 UTC, March 30th, the Dark Energy Camera (DECam) began the second epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). We observed eight fields centered on the following ICRS coordinates:
| RA | DEC |
|---|---|
| 145.286221 | 10.615360 |
| 145.996500 | 12.108130 |
| 143.786221 | 10.715360 |
| 144.496500 | 12.208130 |
| 144.069167 | 9.115670 |
| 143.344621 | 7.609550 |
| 145.900667 | 13.593470 |
| 142.620092 | 6.103430 |
These pointings are identical to the first epoch observations from March 29th, 2025 (GCN 39934).
All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~22.8 in r-band, ~22.5 in i-band, and ~21.9 in z-band.
We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts, requiring an autoscan score of at least 0.7 on both nights of observations. We also match our candidates against the ALLWISE, Milliquas, Quaia, and LQAC-6 AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024, Souchay et al 2024) within the LVK localization volume.
After candidate selection, we report 25 high confidence candidates listed below. After vetting and identification, 15 candidates are classified as nuclear candidates (likely active galactic nuclei) and 10 candidates as possible supernovae. No candidates from the second epoch of observations match known AGNs within 1 arcsecond. 12 of the 20 candidates in the first epoch are listed here, while the candidates which do not appear did not have a confident detection in the second epoch. We also do not recover any of the X-ray source candidates reported by Swift XRT (GCN 39972) within their reported error bounds.
| TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR |
|---|---|---|---|---|---|---|---|---|---|---|
| SN_LIKE | 2290036 | AT2025gek | 145.199481 | 10.828527 | 20.77 | 0.04 | 20.62 | 0.03 | 20.69 | 0.1 |
| SN_LIKE | 2290467 | AT2020woa | 144.388798 | 10.255536 | 19.87 | 0.02 | N/A | N/A | 20.1 | 0.04 |
| SN_LIKE | 2292782 | AT2025geo | 144.928578 | 10.349243 | 20.92 | 0.04 | 21.07 | 0.04 | N/A | N/A |
| SN_LIKE | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 |
| SN_LIKE | 2290334 | AT2025geq | 145.235616 | 12.469694 | 20.22 | 0.02 | 20.57 | 0.03 | 21.11 | 0.11 |
| AGN_LIKE | 2290623 | AT2025gen | 144.112464 | 11.641817 | 21.4 | 0.04 | 21.3 | 0.08 | 21.37 | 0.12 |
| AGN_LIKE | 2291223 | N/A | 146.389563 | 13.131801 | 20.56 | 0.02 | 20.64 | 0.04 | 20.52 | 0.05 |
| SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | N/A | N/A | 21.22 | 0.1 |
| SN_LIKE | 2293190 | AT2025cvb | 144.191297 | 10.828462 | 20.86 | 0.03 | 20.87 | 0.03 | N/A | N/A |
| SN_LIKE | 2290143 | AT2025ggv | 146.033906 | 11.088812 | 21.26 | 0.05 | 21.46 | 0.07 | 21.47 | 0.13 |
| AGN_LIKE | 2292003 | N/A | 144.007084 | 9.336975 | 21.18 | 0.03 | 21.16 | 0.05 | 21.6 | 0.11 |
| SN_LIKE | 2292854 | AT2025ggw | 142.67125 | 6.637349 | N/A | N/A | 20.75 | 0.04 | 20.72 | 0.06 |
| AGN_LIKE | 2290453 | N/A | 146.299999 | 13.629839 | 21.7 | 0.06 | 21.89 | 0.11 | 22.14 | 0.19 |
| AGN_LIKE | 2292040 | AT2025ges | 144.438216 | 9.885617 | 21.72 | 0.07 | 21.75 | 0.11 | 21.93 | 0.17 |
| AGN_LIKE | 2290059 | N/A | 144.679961 | 10.018211 | N/A | N/A | 20.26 | 0.03 | 21.11 | 0.12 |
| AGN_LIKE | 2290970 | AT2025ger | 142.543835 | 6.090899 | 21.71 | 0.05 | 21.43 | 0.06 | 21.28 | 0.09 |
| AGN_LIKE | 2294074 | AT2025gew | 144.291829 | 8.349302 | 22.23 | 0.1 | 21.85 | 0.11 | 22.28 | 0.15 |
| AGN_LIKE | 2292786 | N/A | 144.037664 | 10.810454 | 22.27 | 0.08 | 22.12 | 0.11 | 22.89 | 0.25 |
| AGN_LIKE | 2293517 | AT2025geu | 145.956024 | 12.381673 | 21.73 | 0.08 | 21.65 | 0.07 | 21.51 | 0.14 |
| AGN_LIKE | 2295862 | N/A | 145.361115 | 12.521385 | 22.44 | 0.11 | 23.33 | 0.36 | 23.47 | 0.46 |
| AGN_LIKE | 2290563 | N/A | 145.149074 | 11.756403 | 23.41 | 0.33 | 22.11 | 0.11 | 22.3 | 0.24 |
| AGN_LIKE | 2290298 | N/A | 144.167668 | 10.985136 | 21.59 | 0.05 | 21.99 | 0.12 | 21.1 | 0.1 |
| SN_LIKE | 2289995 | AT2025ggx | 144.57373 | 10.274445 | 22.62 | 0.19 | 22.31 | 0.14 | 21.7 | 0.22 |
| AGN_LIKE | 2291169 | N/A | 145.423743 | 11.834742 | 22.57 | 0.14 | 23.44 | 0.34 | 22.8 | 0.46 |
| AGN_LIKE | 2293519 | N/A | 143.751725 | 9.714206 | 22.75 | 0.15 | 22.23 | 0.14 | 21.63 | 0.12 |
We encourage followup of the 25 candidates identified herein.
The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations.
GCN Circular 39972
P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC),
R.A.J. Eyles-Ferris (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.G.
Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De
Pasquale (University of Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì
(INAF-IASFPA) , V. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson
University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S. Laha
(NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P. O’Brien (U. Leicester),
M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato (INAF-OAB), B. Sbarufatti
(INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (U Tor Vergata, INAF) report on
behalf of the Swift team:
Swift has carried out 97 observations of the LVK error region for the GW trigger S250328ae
convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9), using the 'BAYESTAR' GW
localisation map. As this is a 3D skymap, galaxy distances were taken into account in selecting
which ones to observe. The observations currently span from 3.0 ks to 38 ks after the LVK trigger,
and the XRT has covered 5.3 deg^2 on the sky (corrected for overlaps). This covers 68% of the
probability in the 'ligo-skymap-from-samples' skymap, and 72% after convolving with the 2MPZ galaxy
catalogue, as described by Evans et al. (2016, MNRAS, 462, 1591).
We have detected 34 X-ray sources. Each source is assigned a rank of 1-4 which describes how likely
it is to be related to the GW trigger, with 1 being the most likely and 4 being the least likely.
The ranks are described at https://www.swift.ac.uk/ranks.php.
We have found:
* 0 sources of rank 1
* 0 sources of rank 2
* 34 sources of rank 3
* 0 sources of rank 4
RANK 3 sources
==============
These are uncatalogued X-ray sources, however they are not brighter than previous upper limits, so
do not stand out as likely counterparts to the GW trigger.
| Source ID | RA | Dec | Err90 | Detection Flag |
| S250328ae_X1 | 09h 37m 34.26s | +11d 00' 47.1" | 8.3" | POOR |
| S250328ae_X2 | 09h 37m 40.59s | +11d 15' 09.3" | 5.4" | REASONABLE |
| S250328ae_X3 | 09h 38m 01.16s | +11d 14' 02.6" | 6.5" | POOR |
| S250328ae_X5 | 09h 38m 05.54s | +11d 24' 32.5" | 6.5" | POOR |
| S250328ae_X6 | 09h 37m 57.28s | +11d 18' 05.4" | 6.5" | POOR |
| S250328ae_X8 | 09h 38m 05.52s | +11d 19' 00.3" | 9.1" | POOR |
| S250328ae_X9 | 09h 38m 34.55s | +11d 14' 28.5" | 6.4" | POOR |
| S250328ae_X10 | 09h 38m 37.34s | +11d 16' 12.5" | 9.9" | POOR |
| S250328ae_X11 | 09h 38m 13.89s | +11d 16' 52.4" | 9.5" | POOR |
| S250328ae_X12 | 09h 37m 35.17s | +10d 47' 58.5" | 6.6" | POOR |
| S250328ae_X13 | 09h 39m 29.53s | +11d 47' 43.2" | 6.0" | POOR |
| S250328ae_X14 | 09h 39m 57.31s | +12d 06' 58.4" | 8.7" | POOR |
| S250328ae_X15 | 09h 39m 31.81s | +12d 06' 34.6" | 7.9" | POOR |
| S250328ae_X16 | 09h 40m 10.28s | +11d 53' 17.1" | 6.7" | POOR |
| S250328ae_X17 | 09h 39m 48.52s | +11d 55' 48.6" | 7.4" | POOR |
| S250328ae_X18 | 09h 39m 45.99s | +11d 54' 42.0" | 7.5" | POOR |
| S250328ae_X19 | 09h 39m 39.79s | +11d 54' 32.3" | 6.6" | POOR |
| S250328ae_X20 | 09h 39m 23.21s | +11d 57' 42.7" | 6.6" | POOR |
| S250328ae_X21 | 09h 39m 41.64s | +11d 53' 24.9" | 13.1" | POOR |
| S250328ae_X22 | 09h 39m 45.64s | +11d 51' 32.9" | 9.1" | POOR |
| S250328ae_X23 | 09h 39m 28.69s | +11d 59' 35.2" | 8.2" | POOR |
| S250328ae_X24 | 09h 39m 51.34s | +11d 52' 24.6" | 6.2" | POOR |
| S250328ae_X25 | 09h 40m 08.46s | +11d 55' 52.5" | 8.9" | POOR |
| S250328ae_X26 | 09h 39m 51.33s | +11d 55' 00.9" | 6.6" | POOR |
| S250328ae_X27 | 09h 39m 34.55s | +12d 01' 50.9" | 7.2" | POOR |
| S250328ae_X28 | 09h 40m 17.23s | +11d 54' 47.3" | 9.7" | POOR |
| S250328ae_X29 | 09h 39m 31.19s | +11d 54' 35.1" | 8.4" | POOR |
| S250328ae_X30 | 09h 39m 39.91s | +12d 04' 29.3" | 15.4" | POOR |
| S250328ae_X31 | 09h 38m 40.15s | +11d 14' 00.3" | 5.7" | POOR |
| S250328ae_X32 | 09h 38m 17.68s | +11d 19' 25.6" | 13.5" | POOR |
| S250328ae_X33 | 09h 39m 18.34s | +11d 59' 40.6" | 8.9" | POOR |
| S250328ae_X34 | 09h 39m 52.80s | +11d 54' 16.5" | 8.0" | POOR |
| S250328ae_X35 | 09h 39m 34.91s | +12d 05' 56.6" | 9.0" | POOR |
| S250328ae_X36 | 09h 39m 29.20s | +12d 02' 51.1" | 10.7" | POOR |
For all flux conversions and comparisons with catalogues and upper limits from other missions, we
assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index (Gamma)=1.7, unless otherwise
stated.
The results of the XRT automated analysis, including details of the sources listed above, are
online at https://www.swift.ac.uk/LVC/S250328ae
This circular is an official product of the Swift XRT team.
GCN Circular 39934
S. MacBride (UZH), I. McMahon (UZH), S. Kaur (University of Michigan/UZH), M. Soares-Santos (UZH), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team:
At 01:43 UTC, March 29th, the Dark Energy Camera (DECam) began the first epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). We observed eight fields centered on the following ICRS coordinates:
(145.286221, 10.615360)
(145.996500, 12.108130)
(143.786221, 10.715360)
(144.496500, 12.208130)
(144.069167, 9.115670)
(143.344621, 7.609550)
(145.900667, 13.593470)
(142.620092, 6.103430)
These pointings cover the 90% localization region of candidate gravitational-wave event S250328ae.
All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~22.7 in r-band, ~22.1 in i-band, and ~21.4 in z-band.
We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts. Candidates were selected by requiring at least two high signal to noise detections. We also require an autoscan score of at least 0.7 on at least one of those detections. We also match our candidates against the ALLWISE, Milliquas, and Quaia AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024) within the LVK localization volume to determine if any correspond to known active galactic nuclei.
After candidate selection, we report the 20 high confidence candidates listed below. After vetting and identification, 8 candidates are classified as nuclear candidates (likely active galactic nuclei), 8 candidates as possible supernovae, and 3 other candidates do not fall in either category. 1 additional candidate (2292763) has been identified as a known AGN WISEA J093710.05+082057.2. We have numerous other transient candidates which require further observation to confidently classify. Further observations are ongoing, and we encourage followup of the 20 candidates identified herein.
| TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR |
| -------- | ------- | --------- | ---------- | ---------- | ----- | ---- | ----- | ---- | ----- | ---- |
| SN_LIKE | 2290892 | AT2025gei | 143.636743 | 9.980209 | N/A | N/A | 20.59 | 0.03 | N/A | N/A |
| OTHER | 2292987 | AT2025gej | 143.183373 | 6.893136 | 21.37 | 0.04 | 21.45 | 0.08 | N/A | N/A |
| AGN_LIKE | 2290036 | AT2025gek | 145.199481 | 10.828527 | 20.77 | 0.04 | 20.62 | 0.03 | 20.69 | 0.1 |
| SN_LIKE | 2290467 | AT2020woa | 144.388798 | 10.255536 | 19.87 | 0.02 | N/A | N/A | 20.1 | 0.04 |
| SN_LIKE | 2290524 | AT2025gel | 144.524917 | 10.199936 | N/A | N/A | N/A | N/A | 20.47 | 0.06 |
| OTHER | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 |
| SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | N/A | N/A | 21.22 | 0.1 |
| AGN_LIKE | 2293190 | AT2025cvb | 144.191297 | 10.828462 | 20.86 | 0.03 | 20.87 | 0.03 | N/A | N/A |
| AGN_LIKE | 2290623 | AT2025gen | 144.112464 | 11.641817 | 21.4 | 0.04 | 21.3 | 0.08 | 21.37 | 0.12 |
| SN_LIKE | 2292782 | AT2025geo | 144.928578 | 10.349243 | 20.92 | 0.04 | 21.07 | 0.04 | N/A | N/A |
| SN_LIKE | 2291779 | AT2025gej | 143.182187 | 6.894174 | N/A | N/A | N/A | N/A | 20.76 | 0.06 |
| OTHER | 2290762 | AT2025gep | 144.259773 | 11.511316 | 21.29 | 0.04 | N/A | N/A | N/A | N/A |
| SN_LIKE | 2290334 | AT2025geq | 145.235616 | 12.469694 | 20.22 | 0.02 | 20.57 | 0.03 | N/A | N/A |
| AGN_LIKE | 2290970 | AT2025ger | 142.543835 | 6.090899 | 21.71 | 0.05 | 21.43 | 0.06 | 21.28 | 0.09 |
| AGN_LIKE | 2292040 | AT2025ges | 144.438216 | 9.885617 | 21.72 | 0.07 | 21.75 | 0.11 | 21.93 | 0.17 |
| SN_LIKE | 2292645 | AT2025get | 144.053408 | 11.422277 | N/A | N/A | 22.67 | 0.21 | N/A | N/A |
| AGN_LIKE | 2293517 | AT2025geu | 145.956024 | 12.381673 | 21.73 | 0.08 | 21.65 | 0.07 | N/A | N/A |
| AGN_LIKE | 2291833 | AT2025gev | 143.241035 | 8.651865 | 22.16 | 0.09 | 21.99 | 0.13 | 22.22 | 0.22 |
| AGN_LIKE | 2294074 | AT2025gew | 144.291829 | 8.349302 | 22.23 | 0.1 | 21.85 | 0.11 | N/A | N/A |
| AGN | 2292763 | AT2025gex | 146.071329 | 11.839902 | 21.89 | 0.11 | 21.92 | 0.12 | 21.05 | 0.1 |
The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations.
GCN Circular 39908
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 S250328ae-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 839 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/S250328ae/4
Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250328ae/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 follow-up 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 J094227.03+110047.4 | 145.61266 | 11.01318 | G | 612.35 | null | null | null | 12.661 | 0.096 | 10.577 | 0.006 | 2.63e-06 | 5.47e-08 |
| WISEA J093435.61+082700.3 | 143.64838 | 8.45010 | G | 507.10 | 0.11 | null | null | 13.186 | 0.203 | 10.854 | 0.006 | 3.85e-06 | 4.28e-08 |
| WISEA J093458.83+094902.6 | 143.74516 | 9.81741 | G | 564.56 | 0.09 | null | null | 14.250 | 0.157 | 10.944 | 0.007 | 2.12e-06 | 2.69e-08 |
| WISEA J093555.60+093752.8 | 143.98169 | 9.63134 | G | 589.67 | 0.08 | null | null | 13.465 | 0.202 | 11.501 | 0.007 | 2.87e-06 | 2.37e-08 |
| WISEA J093938.05+110947.9 | 144.90857 | 11.16332 | G | 482.07 | 0.08 | null | null | 13.597 | 0.141 | 12.972 | 0.014 | 1.58e-05 | 2.25e-08 |
| WISEA J094028.13+111733.4 | 145.11722 | 11.29263 | G | 556.24 | 0.11 | null | null | 13.110 | 0.111 | 12.941 | 0.015 | 9.93e-06 | 1.94e-08 |
| WISEA J094035.77+103104.6 | 145.14905 | 10.51795 | G | 495.66 | 0.07 | null | null | 13.045 | 0.080 | 12.298 | 0.012 | 6.77e-06 | 1.90e-08 |
| WISEA J093657.39+085125.0 | 144.23916 | 8.85696 | G | 557.28 | 0.06 | null | null | null | null | 11.769 | 0.007 | 3.22e-06 | 1.86e-08 |
| WISEA J094109.87+105038.6 | 145.29116 | 10.84407 | G | 439.67 | 0.07 | null | null | 12.109 | 0.080 | 12.120 | 0.012 | 6.55e-06 | 1.70e-08 |
| WISEA J094121.23+112617.1 | 145.33849 | 11.43811 | G | 564.36 | 0.09 | null | null | 13.311 | 0.123 | 13.095 | 0.017 | 9.76e-06 | 1.70e-08 |
| WISEA J094025.05+111347.9 | 145.10441 | 11.23000 | G | 557.91 | 0.09 | null | null | 13.243 | 0.108 | 13.078 | 0.020 | 9.62e-06 | 1.66e-08 |
| WISEA J093619.16+091944.6 | 144.07983 | 9.32906 | G | 588.58 | 0.11 | null | null | 13.919 | 0.167 | 12.015 | 0.007 | 3.16e-06 | 1.62e-08 |
| WISEA J093619.13+091936.4 | 144.07971 | 9.32680 | G | 591.85 | 0.08 | null | null | 12.365 | 0.106 | 12.060 | 0.010 | 3.00e-06 | 1.49e-08 |
| WISEA J093747.49+101024.7 | 144.44789 | 10.17354 | G | 432.26 | 0.05 | null | null | 12.881 | 0.108 | 12.438 | 0.013 | 7.81e-06 | 1.46e-08 |
| WISEA J093417.20+081006.5 | 143.57167 | 8.16848 | G | 347.36 | 0.08 | 21.156 | 0.071 | 13.681 | 0.191 | 10.002 | 0.006 | 1.22e-06 | 1.39e-08 |
| WISEA J094125.76+110548.3 | 145.35737 | 11.09678 | G | 557.02 | 0.07 | null | null | 13.696 | 0.126 | 13.350 | 0.021 | 9.58e-06 | 1.28e-08 |
| WISEA J094051.38+102028.4 | 145.21409 | 10.34125 | G | 444.19 | 0.03 | null | null | 15.275 | 0.145 | 12.091 | 0.007 | 4.61e-06 | 1.25e-08 |
| WISEA J094106.66+105024.2 | 145.27777 | 10.84008 | G | 487.71 | null | null | null | 14.219 | 0.109 | 13.198 | 0.021 | 1.00e-05 | 1.18e-08 |
| WISEA J093537.73+091115.6 | 143.90721 | 9.18768 | G | 552.71 | 0.11 | null | null | 13.648 | 0.222 | 12.528 | 0.013 | 4.10e-06 | 1.16e-08 |
| WISEA J093620.06+092335.0 | 144.08362 | 9.39307 | G | 582.84 | 0.07 | 20.401 | 0.231 | 13.508 | 0.189 | 12.534 | 0.014 | 3.60e-06 | 1.12e-08 |
Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S250328ae 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).
GCN Circular 39900
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 S250328ae (GCN Circular 39898). 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/S250328ae
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 15 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(09h39m, +10d53m, 4.94d, 0.99d, 116.27d)
Marginalized over the whole sky, the a posteriori luminosity distance estimate is 511 +/- 82 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
GCN Circular 39898
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250328ae during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-03-28 05:40:27.419 UTC (GPS time: 1427175645.419). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], MLy [5], PyCBC Live [6], and SPIIR [7] analysis pipelines.
S250328ae 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/S250328ae
After parameter estimation by RapidPE-RIFT [8], 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%. [9] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [9] 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 7%.
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 [10], distributed via GCN notice about 32 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [10], 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 well fit by an ellipse with an area of 22 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(09h39m, +10d34m, 7.42d, 0.95d, 115.70d)
Marginalized over the whole sky, the a posteriori luminosity distance estimate is 492 +/- 91 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] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913
[5] Skliris et al. (2020) arXiv:2009.14611
[6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a
[7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023
[8] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002
[9] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013