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Special Notice #287: Request to observe X-ray transient Swift J1910.2-0546

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June 28, 2012: The recently discovered gamma-ray source Swift J1910.2-0546 (Krimm et al., ATel #4139; Barthelmy et al., GCNC #13369; T. Ohshima., vsnet-alert 14674) is optically bright, reaching magnitude CR = 15.7 on 2012 June 14 (R. Pickard, BAAVSS, using the Faulkes Telescope South).  The object was also observed by A. Odasso, using the Sierra Stars Observatory Network (A. Odasso, private communication).  The source was found to be optically bright on 2012 June 18, coincident with the issuance of a GCN Notice (see GCN Circular 13369).  Pickard, along with R. Miles (BAAVSS) and A. Odasso are undertaking a campaign to detect any potential optical periodicities in this new source.

The campaign is being led by Roger Pickard who requests that observers contact him directly via email at We request that observers also submit their observations to the AAVSO for archiving in the AAVSO International Database.

The following message was first posted by Roger Pickard to the BAAVSS-alert mailing list [coordinates of the source were modified from the original as per private communication between R. Pickard and AAVSO]:

 "Following an alert posted via vsnet-alert on 14th June 2012 that Swift/MAXI had detected an X-ray transient with
 a bright optical counterpart I observed the object with the Faulkes Telescope South on the same day at magnitude
 15.7 R. According to ATel 4149, this object is suspected to be a black hole candidate Low Mass X-ray Binary.

  Subsequently Alessandro Odasso, who had also commenced observing it using the Sierra Stars Observatory
  Network, and had been in contact with NASA and the discoverers of the object, contacted Richard Miles and
  we agreed that it may be worth a short observing campaign to try and determine its period.

  It is located at RA 19h 10m 22.82s and Dec -05d 47m 55.8s. [2000.0]

  [NOTE: Coords. corrected as per R. Pickard, private communication - MT]

  Suitable comparison stars are:

         CMC14                 RA             DEC            r'         V
  C1 191023.3-054652 19 10 23.3 -05 46 52.9 14.386 14.930
  C2 191020.7-054658 19 10 20.8 -05 46 58.4 14.056 14.560
  C3 191024.5-054918 19 10 24.6 -05 49 18.4 13.031 13.572
  C4 191028.2-054652 19 10 28.2 -05 46 52.5 13.535 13.762
  C5 191011.7-055026 19 10 11.7 -05 50 26.7 14.050 14.255

  Note that the preferred comp stars are C4 and C5.

  A chart is also available on the VSS web page [click on Swift/Maxi X-ray Transient link].

  Please report reduced observations to me at the email address below using the name
  Swift J1910.2-0546
when I shall analyse them to see if we can find a period.

A second message posted by Pickard 2012 June 28 adds the following information and recommendation:

 "I've now received two sets of data from Arto Oksanen covering June 27 and 28 showing the object
 around 15.8 with an amplitude of less than about 0.1 mag and a probable period of about 2 hours.

 "However, as this object is rather faint I suggest that rather than V or R filters that unfiltered will be
 better to get a better signal to noise ratio - unless you're lucky enough to use a very large telescope.

  Roger Pickard,
  Director VSS "

This AAVSO Special Notice was prepared by M. Templeton.


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