{
  "bibcode": "2019GCN.24767....1K",
  "body": "N. P. M. Kuin (UCL-MSSL), A. A. Breeveld (MSSL-UCL),  C. Gronwall (PSU),\nF. E. Marshall (NASA/GSFC), S. R. Oates (Uni. of Warwick), M.J. Page\n(UCL-MSSL),\nM. de Pasquale (U Istambul), M. H. Siegel (PSU), A. D'Ai (INAF-IASFPA),\nP. D'Avanzo (INAF-OAB), S. D. Barthelmy (NASA/GSFC), A. P. Beardmore (U.\nLeicester),\nD. N. Burrows (PSU), S. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC),\nG. Cusumano (INAF-IASF PA), V. D'Elia(ASDC), P. A. Evans (U. Leicester),\nP. Giommi (ASI), D. Hartmann (Clemson U.), J. A. Kennea (PSU),\nH. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), D. B. Malesani (DARK/NBI),\nA. Melandri (INAF-OAB), J. A.  Nousek (PSU), P. T. O'Brien (U. Leicester),\nJ. P. Osborne (U. Leicester), C. Pagani (U. Leicester), K. L. Page\n(U.Leicester),\nD.M. Palmer (LANL), M. Perri (ASDC), J. L. Racusin (NASA/GSFC), T. Sakamoto\n(AGU),\nB. Sbarufatti (INAF-OAB/PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu\n(PSU),\nand E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team:\n\nThe Neil Gehrels Swift Observatory UVOT and XRT instruments began pointed\ngalaxy-targeted followup of the LIGO/Virgo detected S190425z (LVC GCN.\n24168)\nat 2019-04-25 12:53 UT (T0+274 min), delayed due to a commanding gap.\nThe observations continued until 2019-04-26 20:15 UT, when they were aborted\nto begin followup of S190426c (LVC GCN. 24237).\n\nThe UVOT points at the same sky area as the Swift XRT but with a slightly\nsmaller FOV (17'x17'). As announced in Tohuvavohu et al.\n(GCN Circ. 24353 ), the Swift GW follow up can be seen at\nhttp://www.swift.ac.uk/LVC/.\n\nThe Swift UVOT exposures of around 70s are usually in the u-band (central\nwavelength 350nm) or a UV band when there are bright stars in the FOV. The\nnominal exposure time varies depending on several factors like the slew\ntime.\nThe limiting magnitude can vary but typically is 18.6th magnitude.\n\nEach field is automatically processed by detecting sources in the image,\nmatching them to several catalogs and screening the remaining sources to\nremove artifacts.  A check is made for any remaining candidates against the\nMinor Planet Center list of solar system objects. Candidates are ranked for\nfurther examination. In addition, for each galaxy detected in the UVOT image\nwhich is in the GLADE catalog, a \"postage stamp\" image of a small region\naround\nthe galaxy is produced as well as a comparison \"postage stamp\" from the\nDSS to be used for manual inspection.\n\nAfter the automated processing, potential candidates are all examined\nmanually.\nThis allows for the removal of image artifacts from our candidate lists\nthat\nsometimes get flagged as potential sources. For S190425z the automated\nprocessing\nidentified 21 source candidates which all, except for one, were either\nimage\nartifacts or fast moving objects that passed the screening.\n\nA further examination of the \"postage stamps\" with galaxies is then made as\neffort allows. This is done mainly because the source-finding algorithm\nhas difficulty finding point sources in extended sources such as galaxies.\n\nFor the fields observed for S190425z, 2298 galaxy postage stamp images were\ngenerated. No credible sources were found.\n\nThe candidate source reported in Breeveld et al. (GCN Circ. 24296) was\nidentified\ninitially by the automated processing, and is likely a very red flaring\nobject\n(see also Lipunov et al. GCN Circ. 24326).",
  "circularId": 24767,
  "createdOn": 1559861248000,
  "email": "npkuin@gmail.com",
  "subject": "LIGO/Virgo S190425z: Swift UVOT - no new sources identified, and a summary of the Swift UVOT processing of GW triggers.",
  "submitter": "Paul Kuin at MSSL  <npkuin@gmail.com>",
  "eventId": "LIGO/Virgo S190425z"
}