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GCN Circular 24331

Subject
LIGO/Virgo S190426c: Additional Candidates from the Zwicky Transient Facility
Date
2019-04-28T16:30:41Z (5 years ago)
From
Daniel Perley at Liverpool JMU <d.a.perley@ljmu.ac.uk>
Daniel A. Perley (LJMU), Ariel Goobar (OKC), Mansi M. Kasliwal 
(Caltech), Michael W. Coughlin (Caltech), Adam A. Miller (Northwestern), 
Tomas Ahumada (UMD), Jacob Jencson (Caltech), Harsh Kumar (IITB), David 
Kaplan (UWM), Shreya Anand (Caltech),  Leo P. Singer (NASA GSFC), Igor 
Andreoni (Caltech), Varun Bhalerao (IITB), Danny Goldstein (Caltech), 
Dmitry Duev (Caltech), S. Bradley Cenko (NASA GSFC),  Eric C. Bellm 
(UW), Kishalay De (Caltech),  Rahul Biswas (OKC), Kishalay De (Caltech), 
and Joshua Bloom (UCB) report on behalf of the Zwicky Transient Facility 
(ZTF) and Global Relay of Observatories Watching Transients Happen 
(GROWTH) collaborations:

We continued observations of the gravitational wave trigger S190426c 
(LVC et al. GCN 24237) with ZTF on UT 2019-04-28. We covered 1150 sq deg 
in g-band and r-band with over 54% of the enclosed probability targeted 
based on the latest sky map (LALInference1.fits.gz, GCN 24277). Each 
exposure on the second night was 300s, with a typical depth of 22 mag. 
In total, over both nights, we have covered 4420 sq deg, enclosing 56% 
of the the total probability. See details in Coughlin et al. (GCN 24283) 
for additional details on data processing.

Additional candidates with no detections prior to merger, inside the 90% 
localization area of the LALInference sky map, and not consistent with 
the locations of known AGN or other variable objects, are:

------------------------------------------------------------------------------------------------
ZTF Name     | RA (deg)    | DEC (deg)  | Filt.| Mag.  | Magerr | Notes
------------------------------------------------------------------------------------------------
ZTF19aasmftm | 325.9004479 | 77.8315634 |    g | 21.16 | 0.12   | [rising]
ZTF19aaslvwn | 299.059846  | 46.463559  |    g | 20.83 | 0.12   | [lowb]
ZTF19aasmdir | 300.2360007 |  9.504002  |    g | 20.35 | 0.09   | [lowb] 
[nuc] [agn?]
ZTF19aaslzjf | 320.6262982 | 65.8134516 |    r | 20.54 | 0.09   | [lowb]
ZTF19aassfws | 298.6678611 | 61.2400121 |    r | 21.41 | 0.20   | 
photz~0.07 +/- 0.03 [nuc]
ZTF19aasmddt | 299.25055   |  9.7016748 |    g | 20.00 | 0.08   | 
photz~0.08 +/- 0.04 [lowb]
ZTF19aaslszp | 301.3434628 | 53.3990477 |    g | 20.84 | 0.11   | 
photz~0.062 [lowb] [nuc?]
ZTF19aasmekb | 300.6013987 | 14.2873159 |    g | 18.29 | 0.03   | [lowb] 
[hostless] [fading]
ZTF19aaslolf | 288.7838539 | 79.4357187 |    g | 21.33 | 0.19   | 
photz~0.42+/-0.20 [nuc] [agn?]
ZTF19aaslphi | 297.3809977 | 61.9605925 |    g | 21.24 | 0.17   | 
photz~0.16+/-0.02
ZTF19aaslpds | 306.2625186 |  61.521461 |    r | 20.99 | 0.13   | [lowb]
ZTF19aaslozu | 306.3144981 | 65.1093759 |    r | 20.87 | 0.16   |
ZTF19aasshpf | 315.4768651 | 70.2055771 |    r | 21.42 | 0.18   |
ZTF19aasmzee | 296.8366485 |  5.1534971 |    r | 20.33 | 0.09   | [lowb]
ZTF19aasmzqf | 353.5204911 | 78.9577781 |    g | 20.53 | 0.09   |
----------------------------------------------------------------------------------------------
Notes:
[rising] : Rising light curve
[lowb] : Galactic latitude less than 15 degrees
[agn?] : WISE colors consistent within an AGN within 1" of the transient.
[hostless] : No discernable host galaxy or other counterpart.
[nuc] : Close to the host nucleus.
[fading] : Clear fading is observed over the past two nights, with no 
prior rise.  This may indicate a CV / dwarf nova.

Three candidates (ZTF19aassfws, ZTF19aasmddt, ZTF19aaslszp) are 
interesting given that their photometric redshifts are consistent with 
the LVC error volume.  ZTF19aaslzjf is also in a galaxy that is likely 
nearby, although no redshift estimate is available.  ZTF19aasmftm is 
interesting given a (probable) rising light curve that suggests a young 
object, although its galaxy counterpart is very faint (r=21.2 in PS1). 
Deep upper limits preceding the detections are not available for any of 
these sources, and they could be unrelated SNe.

Additional follow-up and analysis is ongoing.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; 
IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; 
DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, 
Japan; IIT-B, India; IIA, India; LJMU, UK; TTU USA and USyd, Australia. 
ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 
1440341. GROWTH acknowledges generous support of the NSF under PIRE 
Grant No 1545949. Alert distribution service provided by DIRAC@UW 
(Patterson et al. 2019). Alert filtering and follow-up co-ordination is 
being undertaken by the GROWTH marshal system (Kasliwal et al. 2019).













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