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GCN Circular 20377

Subject
LIGO/Virgo G268556: ATLAS imaging of the skymap
Date
2017-01-05T23:24:44Z (7 years ago)
From
S. J. Smartt at Queens U Belfast <s.smartt@qub.ac.uk>
J. Tonry, L. Denneau, A. Heinze, B. Stalder,  H. Weiland (IfA), C. W. Stubbs (Harvard), 
K. W. Smith, S. J. Smartt, (QUB), D. R. Young (QUB),  A. Rest (STScI),   
K. C. Chambers (IfA), M. Coughlin (Harvard), M. E. Huber (IfA), D. E. Wright (QUB), 
H. Flewelling,  E. A. Magnier,  A. S. B. Schultz,   C. Waters, R. J. Wainscoat (IfA) 

We report the following observations of the skymap for LIGO/Virgo
G268556 with the ATLAS telescope system ATLAS is a twin 0.5m telescope
system on Haleakala and Mauna Loa (see Tonry et al. ATel 8680 and
Tonry 2011, PASP, 123, 58). The first unit is operational on Haleakala
and is robotically surveying the sky in two filters cyan and orange
(denoted c and o, all mags are in AB system). More information is on
http://www.fallingstar.com

The alert for G268556 was received 6.5 hours after the event, too
close to sunrise for targeted observations on 57757 in Hawaii. The
next night we started observing the LIGO/VIRGO localisation region at
57758.296 (2016-01-05.296 UT) starting at a pointing centre of RA=80,
DEC=-30, moving north and east across the lobe to RA=170,80. A total
of 1250 square degrees were covered.  Sets of dithered 8x30sec
exposures in the cyan filter were taken, at a 5-sigma sensitivity of c
= 19.0 for each exposure.  Difference images are automatically created
with a reference image built during early 2016. These data are currently 
being processed and results will be reported soon. Maps will be 
uploaded to GraceDB.

During the previous night (2016-01-04 UT) ATLAS did its routine survey
of a 20 degree wide declination strip between RA = 334 to 213 deg
(wrapped through 0), and DEC = +15 to +35 deg. This intersected a
small part of the LIGO/VIRGO map (containing 9% of the probability)
between 30mins to 3hrs after the detection time of G268556.  ATLAS
also surveyed this strip four days prior on 57753, but the sky was
partly cloudy. No obvious transient is visible in this 9% region.

Furthermore, ATLAS has been scanning the northern region containing
the highest probability contours during the last three weeks. We
report here bright transients found before the detection of G268556.
They will mostly be still visible on the sky map region, but are 
mostly field supernovae (or CVs) and unrelated to the GW source. 

IAU Name  | ATLAS Name | RA (J2000)  | Dec (J2000) | Disc. MJD | Disc. Date  | Disc Mag |  Notes
AT2016iyx | ATLAS16dzp | 08:43:24.74 | +37:32:45.8 | 57742.47  | 20161220.47 |  17.28 o |        
SN2016izg | ATLAS16eak | 07:53:12.77 | +12:53:56.4 | 57736.47  | 20161214.47 |  17.10 o |  ASASSN-16pb (Ia)
AT2016izk | ATLAS16eaw | 08:49:04.77 | +14:24:49.8 | 57744.57  | 20161222.57 |  16.62 c |   ASASSN-16pc (CV)
AT2016jae | ATLAS16eay | 09:42:34.50 | +10:59:35.3 | 57744.61  | 20161222.61 |  17.42 c |     
AT2016jax | ATLAS16ecb | 08:32:53.76 | +42:08:01.6 | 57746.49  | 20161224.49 |  17.60 c |     
AT2016jaw | ATLAS16ecc | 08:48:21.88 | +24:31:51.9 | 57745.52  | 20161223.52 |  17.98 c |    
          | ATLAS16ecj | 08:50:02.45 | +46:39:49.0 | 57742.48  | 20161220.48 |  18.50 o |        |  
          | ATLAS17aay | 09:34:07.69 | +31:46:25.4 | 57745.55  | 20161223.55 |  18.44 c |        |
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