[vsnet-grb-info 24261] LIGO/Virgo S191205ah: SAGUARO observations and identification of an optical candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26360
SUBJECT: LIGO/Virgo S191205ah: SAGUARO observations and identification of an optical candidate
DATE:    19/12/06 06:58:12 GMT
FROM:    Kerry Paterson at Northwestern  <kerry.paterson at northwestern.edu>

Kerry Paterson (Northwestern), Michael J. Lundquist, David J. Sand (UA), Jillian Rastinejad, Wen-fai Fong (Northwestern), Jennifer Andrews (UA), Sam Wyatt (UA), Eric Christensen, Alex Gibbs, Frank Shelly, Greg Leonard (UA/LPL), report on behalf of the SAGUARO collaboration:

We initiated observations of 12 fields (each 5 deg^2, totalling 60 deg^2) within the LVC localization region for the GW trigger S191205ah (LVC Circ 26350) starting on 2019-12-06 at 02:13:30 UT (4.36 hours after the GW trigger) with the 1.5m Catalina Sky Survey (CSS) telescope on Mt. Lemmon, AZ.

Below are the field centers observed.

RA   Dec
349.8120  14.3541
349.9380 12.1458
349.9995 7.72917
349.9995 9.93747
350.0610 5.52081
350.0610 3.3125
350.1210 1.10417
350.1210 -1.10417
352.0755 14.3541
352.1730 12.1458
352.2225 9.93747
352.2225 7.72917

We perform real-time processing and image subtraction (described in Lundquist et al. 2019, ApJL, 881, 2). After discarding known moving objects, stellar sources and known transients (cross-correlating with the Transient Name Server and the ZTF alert stream), we find one candidate with S/N>5:

------------------------------------------------------------------------
Name     | RA (deg)   | Dec (deg)  | Filter | Mag   | Magerr
------------------------------------------------------------------------
SAGUARO19j | 348.98484 | 10.68373 | Gaia G | 20.8 | 0.2
------------------------------------------------------------------------

The last non-detection at the position of SAGUARO19j was on 2019-11-25 UT to a 3-sigma limit of G>19.3 AB mag. We otherwise find no new transients within the 60 deg^2 searched down to a 3-sigma limit of G~21.3 AB mag (calibrated to Gaia DR2) relative to deep CSS reference images.

We obtained V- and R-band imaging observations of SAGUARO19j with the Mont4K imager mounted on the Kuiper 1.5m telescope on Mt. Bigelow, AZ starting on 2019-12-06 at 05:31:46 UT (7.66 hours after the GW trigger and 3.30 hours after the start of our CSS observations). SAGUARO19j is clearly detected in both bands, with analysis ongoing.

We have posted our pointings to the Treasure Map, and encourage others to do the same:
http://treasuremap.space/index?graceids=S191205ah&alert_type=Initial&pointing_status=completed

SAGUARO is supported by the National Science Foundation under Award Nos. AST-1909358 and AST-1908972.