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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
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4055 results found.

  1. LIGO/Virgo/KAGRA S250211aa: Updated Sky localization and EM Bright Classification
  2. LIGO/Virgo/KAGRA S250211aa: Identification of a GW compact binary merger candidate
  3. LIGO/VIRGO/KAGRA S250206dm: AT 2025bbo spectroscopic observations with NIRES on Keck II
  4. LIGO/Virgo/KAGRA S250206dm: Gemini-North spectroscopic observation of AT2025bbo and its host galaxy
  5. LIGO/Virgo/KAGRA S250206dm: MASTER detection AT2025bbo
  6. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  7. IceCube-250207A: Upper limits from a search for additional neutrino events in IceCube
  8. LIGO/Virgo/KAGRA S250206dm: Global MASTER-Net observations report
  9. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
  10. LIGO/Virgo/KAGRA S250206dm: Observations from WINTER
  11. LIGO/Virgo/KAGRA S250206dm & FRB 20250206A: MASTER observations and possible mother galaxy
  12. LIGO/Virgo/KAGRA S250206dm: Optical observations of candidate AT 2025bbo with Kinder
  13. LIGO/Virgo/KAGRA S250206dm: WFST follow-up observations
  14. LIGO/Virgo/KAGRA S250206dm: FRB 20250206A BOOTES-5 and 2.2m CAHA optical upper limits
  15. LIGO/Virgo/KAGRA S250206dm: further Pan-STARRS observations and one candidate AT2025bbo
  16. LIGO/Virgo/KAGRA S250207bg: Updated NED Galaxies in the Localization Volume
  17. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  18. LIGO/Virgo/KAGRA S250206dm: GECKO Observation with 7DT and KMTNet
  19. LIGO/Virgo/KAGRA S250118az: Updated Sky localization
  20. LIGO/Virgo/KAGRA S250208ad: Updated Sky localization
  21. GRB 250206A: EIRSAT-1 GMOD Detection
  22. LIGO/Virgo/KAGRA S250206dm: (Update-7) NED Galaxies in the Localization Volume
  23. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Observations
  24. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  25. LIGO/Virgo/KAGRA S250206dm: Spectroscopic Classification of AT2025bay and AT2025baz with Keck I/LRIS
  26. LIGO/Virgo/KAGRA S250206dm: Candidates from the Zwicky Transient Facility
  27. LIGO/Virgo/KAGRA S250206dm: ePESSTO+ classification of AT2025bar
  28. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of the DDOTI optical candidates
  29. LIGO/Virgo/KAGRA S250208ad: Identification of a GW compact binary merger candidate
  30. LIGO/Virgo/KAGRA S250206dm: MMT galaxy targeted observations
  31. LIGO/Virgo/KAGRA S250206dm: FRB 20250206A & "Time Machine" Effect.
  32. CHIME/FRB source FRB 20250206A detected less than 1 minute after LIGO-Virgo-Kagra (LVK) S250206dm, however the probability of spatial coincidence is order 0.1%
  33. LIGO/Virgo/KAGRA S250206dm: GOTO counterpart search update - AT2025bar
  34. EP-WXT trigger 01709131361 / LIGO/Virgo/KAGRA S250206dm: FTW optical and NIR observations
  35. LIGO/Virgo/KAGRA S250206dm: ATLAS observations of the skymap
  36. LIGO/Virgo/KAGRA S250206dm: Pan-STARRS survey of the skymap for optical transients
  37. LIGO/Virgo/KAGRA S250206dm: DDOTI Upper Limits
  38. LIGO/Virgo/KAGRA S250207bg: NED Galaxies in the Localization Volume
  39. IGO/Virgo/KAGRA S250206dm: Virtual Telescope Project upper limit for the Neutrino IceCube Candidate
  40. LIGO/Virgo/KAGRA S250207bg: Identification of a GW compact binary merger candidate
  41. LIGO/Virgo/KAGRA S250206dm:GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  42. LIGO/Virgo/KAGRA S250206dm: DDOTI Upper Limit for the Neutrino IceCube Candidate
  43. LIGO/Virgo/KAGRA S250206dm: GOTO observations of optical candidates AT 2025azn and AT 2025azm
  44. LIGO/Virgo/KAGRA S250206dm: SOAR galaxy targeted observations
  45. LIGO/Virgo/KAGRA S250206dm: Pan-STARRS observations of AT2025azm and AT2025azn
  46. LIGO/Virgo/KAGRA S250206dm: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  47. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of the AT 2025azn Optical Candidate
  48. LIGO/Virgo/KAGRA S250206dm: SAGUARO Detection of Two Potential Optical Counterparts
  49. LIGO/Virgo/KAGRA S250206dm: Updated-6 NED Galaxies in the Localization Volume
  50. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  51. LIGO/Virgo/KAGRA S250206dm: Upper limits from Fermi-GBM Observations
  52. LIGO/Virgo/KAGRA S250206dm: Coverage and upper limits from MAXI/GSC observations
  53. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  54. LIGO/Virgo/KAGRA S250206dm: Updated NED Galaxies in the Localization Volume
  55. LIGO/Virgo/KAGRA S250206dm: Two counterpart neutrino candidates from IceCube neutrino searches
  56. LIGO/Virgo/KAGRA S250206dm: Identification of a GW compact binary merger candidate
  57. LIGO/Virgo/KAGRA S250206dm: NED Galaxies in the Localization Volume
  58. LIGO/Virgo/KAGRA S250205ee: Updated Sky localization and Source Classification
  59. LIGO/Virgo/KAGRA S250205ee: Identification of a GW compact binary merger candidate
  60. LIGO/Virgo/KAGRA S250205bk: NED Galaxies in the Localization Volume
  61. LIGO/Virgo/KAGRA S250205bk: Updated Sky localization
  62. LIGO/Virgo/KAGRA S250205bk: Identification of a GW compact binary merger candidate
  63. LIGO/Virgo/KAGRA S250204ax: Updated Sky localization
  64. LIGO/Virgo/KAGRA S250204ax: Identification of a GW compact binary merger candidate
  65. LIGO/Virgo/KAGRA S250202cu: Updated Sky localization
  66. LIGO/Virgo/KAGRA S250202cu: Identification of a GW compact binary merger candidate
  67. LIGO/Virgo/KAGRA S250202ad: Retraction of GW compact binary merger candidate
  68. LIGO/Virgo/KAGRA S250201i: Coverage and upper limits from MAXI/GSC observations
  69. GRB 250128B: Fermi GBM Observation
  70. IPN triangulation of a bright burst from SGR 1E1841-045
  71. LIGO/Virgo S250119cv: Swift XRT observations, 5 X-ray sources
  72. LIGO/Virgo/KAGRA S250119cv: GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  73. LIGO/Virgo/KAGRA S250105bn: 1 counterpart neutrino candidate event from an IceCube neutrino search
  74. LIGO/Virgo/KAGRA S250119cv: Updated NED Galaxies in the Localization Volume
  75. LIGO/Virgo/KAGRA S250119cv: Updated Sky localization and EM Bright Classification
  76. LIGO/Virgo/KAGRA S250119cv: NED Galaxies in the Localization Volume
  77. LIGO/Virgo/KAGRA S250119cv: Identification of a GW compact binary merger candidate
  78. LIGO/Virgo/KAGRA S250119ag: Updated Sky localization
  79. LIGO/Virgo/KAGRA S250118dp: Updated Sky localization
  80. LIGO/Virgo/KAGRA S250119ag: Identification of a GW compact binary merger candidate
  81. LIGO/Virgo/KAGRA S250118dp: Identification of a GW compact binary merger candidate
  82. LIGO/Virgo/KAGRA S250118t: Updated Sky localization
  83. LIGO/Virgo/KAGRA S250118az: Identification of a GW compact binary merger candidate
  84. LIGO/Virgo/KAGRA S250118t: Identification of a GW compact binary merger candidate
  85. LIGO/Virgo/KAGRA S250114ax: Updated NED Galaxies in the Localization Volume
  86. LIGO/Virgo/KAGRA S250114ax: Updated Sky localization
  87. LIGO/Virgo/KAGRA S250114ax: GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  88. LIGO/Virgo/KAGRA S250114ax: NED Galaxies in the Localization Volume
  89. LIGO/Virgo/KAGRA S250114ax: Identification of a GW compact binary merger candidate
  90. LIGO/Virgo/KAGRA S250109bi: Updated Sky localization
  91. LIGO/Virgo/KAGRA S250109f: Updated Sky localization
  92. LIGO/Virgo/KAGRA S250108eo: Updated Sky localization
  93. LIGO/Virgo/KAGRA S250109bi: Identification of a GW compact binary merger candidate
  94. LIGO/Virgo/KAGRA S250109f: Identification of a GW compact binary merger candidate
  95. Fermi Gamma-ray Burst Monitor trigger 758061038/250108855 is not a GRB
  96. LIGO/Virgo/KAGRA S250108ha: Retraction of GW compact binary merger candidate
  97. LIGO/Virgo/KAGRA S250108eo: Identification of a GW compact binary merger candidate
  98. GRB 250107A: Swift/BAT-GUANO arcminute localization of a burst
  99. LIGO/Virgo/KAGRA S250104v: Updated Sky localization
  100. LIGO/Virgo/KAGRA S250104v: Identification of a GW compact binary merger candidate

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