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GCN Circular 20881

Subject
SUBJECT: LIGO/Virgo G277583: ATLAS coverage and transients over the first 2 days
Date
2017-03-16T17:15:00Z (8 years ago)
From
S. J. Smartt at Queens U Belfast <s.smartt@qub.ac.uk>
S. J. Smartt, K. W. Smith, J. Tonry, L. Denneau, A. Heinze,
B. Stalder, H. Weiland (IfA), C. W. Stubbs (Harvard), A. Rest (STScI),
K. C. Chambers (IfA), T.-W. Chen (MPE), M. Coughlin (Harvard),
M. E. Huber (IfA), D. E. Wright, D. R. Young, E. Kankare (QUB),
H. Flewelling, T. Lowe, E. A. Magnier, A. S. B. Schultz, C. Waters,
R. J. Wainscoat, M. Willman (IfA),


Further to GCN20877, we report ATLAS observations of the skymap
(cWB_plus_LIB.fits) of G277583 (GCN 20860), with event time
2017-03-13 22:40:09.593 == 57825.94498372

We started observing at MJD=57826.54, 14hrs after the LIGO alert and
covered approximately 3600 sq degrees during the first 2 days. This
corresponds to a probability coverage of approximately 60% of the
cWB_plus_LIB.fits skymap (final number currently being refined, map
plot will be available on GraceDB). The limiting magnitude in the 30 sec
exposures in the orange filters is o ~ 18.7

We find the following four transients which are within the 90% contour
for which we have no previous detections. We also list, for reference 
old objects which are within the skymap but discovered before G277583

We apologise for the earlier release of ATLAS17cck in GCN 20877, which
is indeed minor planet Azalea (GCN 20879, Littlefield &
Garnavich). The object passed through our automated positional scatter
and ephemeris filters for removing known and unknown moving objects
and therefore did not trigger automatic rejection. This was due to an
artificial magnitude split introduced into our local version (at QUB)
of the minor planet database, with objects brighter than a threshold
maximum magnitude not being checked. The magnitude calculation was an 
oversimplification, and has been removed. Additional checks have also 
been introduced to prevent leakage of minor planets into the stationary list.


Name        RA            DEC          MJD Discovery Mag   f    PC    Host/Comment                      
ATLAS17cdb  05:14:50.41  -32:09:46.9  57827.25431835 18.55 o    90   orphan                            
ATLAS17byq  17:07:47.34  +09:49:20.8  57826.61285455 17.61 o    90   2MASX J17074707+0949172           
ATLAS17byo  16:33:19.87  +23:43:52.4  57826.58056845 17.43 o    80   z=0.033, SDSS J163319.94+234356.4 
ATLAS17cgg  08:03:55.23  +26:31:12.3  57826.42460955 18.02 o    50   z=0.0217, IC 0491                

f = filter
PC = probability contour within which the object lies 


Old objects from before G277583
Name        RA            DEC          MJD Discovery Mag   f    PC    Host/Comment                      
ATLAS17bza  17:19:36.88  -25:01:04.2  57826.57606615 16.49 o    70     AT2017aby (Gaia17agz), b=7, likely Galactic                         
ATLAS17bkc  15:27:56.20  +11:42:17.0  57816.61101455 18.40 c    80                                                 
ATLAS17bhd  06:26:20.16  -01:22:47.5  57808.37305585 16.55 c    90     b=-6.2, probable CV, faint source in PS1                                            
ATLAS17bib  09:44:23.18  +34:16:03.1  57805.44415665 18.87 c    90     AT 2017blg                        
ATLAS17bkt  15:19:18.86  +28:13:44.4  57817.57088835 16.54 c    90     AT2017cak, ATel 10152                   
ATLAS17cgp  16:32:23.53  -02:36:07.2  57816.65313705 18.30 c    40     AT2017ly                                
ATLAS17bkb  15:20:07.83  +11:52:37.5  57816.61101455 18.25 c    90     AT2017byj, ATel 10148                   
ATLAS17btj  12:14:16.03  -38:05:48.1  57807.56503375 18.66 c    80     AT2017bzg  ATel 10152                   
ATLAS17bhq  08:38:57.62  +28:24:40.0  57805.40020845 19.07 c    60     AT2017bhe
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