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GCN Circular 36303

LIGO/Virgo/KAGRA S240422ed: Second night Pan-STARRS observations of the skymap
2024-04-25T14:34:28Z (3 months ago)
Ken Smith at Queen's University Belfast <>
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K. W. Smith (QUB), M. Huber (IfA, Hawaii), S. Srivastav (Oxford), S. J. Smartt (Oxford/QUB),  K. C. Chambers, (IfA, Hawaii), D. R. Young, M. Nicholl, M. D. Fulton, A. Aamer, C. R. Angus, M. McCollum, T. Moore, S. Sim, J. Weston, X. Sheng (QUB), P. Ramsden (QUB/Birmingham), L. Shingles (GSI/QUB), J. Sommer (LMU/QUB), J. Gillanders, H. Stevance, L. Rhodes, A. Andersson (Oxford), A. S. B. Schultz, T. de Boer, J. Herman, J. Fairlamb, H. Gao, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii), T.-W. Chen (NCU), A. Rest (STScI), C. Stubbs (Harvard):

We report additional observations of the Bilby.fits skymap of the NSBH merger event S240422ed (The LIGO-Virgo-Kagra Collaboration, GCN 36236) with the Pan-STARRS telescope system (Chambers et al., 2016, ArXiv e-prints, 1612.05560). Observations on MJD 60423 yielded no viable candidates (see GCN 36258 for coverage strategy.)

On MJD 60424 we covered 174 square degrees of the bilby.fits skymap 90% area, and covered a sky region totalling 66% of the event's full localisation. We covered nearly all the 90% region above declination -30 degrees, due to lack of reference frames below that declination. The image quality on MJD 60424 was significantly better than on 60423.

The depths of these stacked images were typically i < 20.54 +/- 0.44 , z < 20.47 +/- 0.41.

Data acquisition began at MJD 60424.23261477 or 2024-04-24 05:34:57 (UTC), 32.0 hrs after the merger event (which was 60422.89946078). The last image was taken at 60424.34269043.

These additional observations yielded the following transient objects. We ran forced photometry on the two day coverage. We do not find any of them to have the right combination of features to be considered a compelling candidate optical counterpart. (+Days = days since GW event). The photometric redshifts (from NED) are either too large or the sources have no lightcurve evolution. We have not yet run historical forced photometry in ATLAS or ZTF to further rule them out as we don’t consider them to be good candidates for the counterpart of S240422ed.

Name    | TNS Name  | RA (J2000)  | Dec (J2000) | +Days | Comment
PS24bxc | AT2024hfu | 08:28:56.91 | -22:40:22.3 | 1.35  | Offset from host, NED photz = 0.092748, lightcurve flat
PS24bxi | AT2024hga | 08:13:52.97 | -24:56:55.9 | 0.38  | Nuclear source, lightcurve flat, no photz, i-z ~ 0
PS24bxj | AT2024hgb | 08:00:18.42 | -30:28:07.4 | 0.35  | NED photz = 0.099940, lightcurve flat
PS24bwz | AT2024hdl | 08:21:53.45 | -30:06:07.7 | 0.35  | DECam discovery,  lightcurve flat
PS24bxk | AT2024hgc | 08:28:11.57 | -21:30:43.7 | 1.35  | On host, no photz, lightcurve flat
PS24bxf | AT2024hfx | 08:19:41.57 | -17:28:07.4 | 1.37  | Rising lightcurve, faint host, i-z ~0, likely higher redshift SN
PS24bxo | AT2024hfo | 08:15:50.35 | -28:40:10.0 | 1.34  | DECam discovery, lightcurve flat, offset from host with no z
PS24bxb | AT2024hft | 08:26:40.13 | -25:57:42.9 | 1.35  | Nuclear, photz = 0.091043 from NED.

The discoveries from this program are a byproduct of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) NEO survey observations. Operation of the Pan-STARRS1 and Pan-STARRS2 telescopes is primarily supported by the National Aeronautics and Space Administration under Grant No. NNX12AR65G and Grant No. NNX14AM74G issued through the SSO Near-Earth Object Observations Program. Data are processed at Queen's University Belfast and are enabled through the STFC grants to Oxford and QUB : ST/Y001605/1, ST/T000198/1, ST/X001253/1.  

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