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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"
body:"GRB"
submitter:"Judith Racusin"

7420 results found.

  1. LIGO/Virgo/KAGRA S250206dm: GOTO counterpart search update - AT2025bar
  2. EP-WXT trigger 01709131361 / LIGO/Virgo/KAGRA S250206dm: FTW optical and NIR observations
  3. LIGO/Virgo/KAGRA S250206dm: ATLAS observations of the skymap
  4. LIGO/Virgo/KAGRA S250206dm: Pan-STARRS survey of the skymap for optical transients
  5. LIGO/Virgo/KAGRA S250206dm: DDOTI Upper Limits
  6. GRB 250207B: Tiled Swift observations
  7. LIGO/Virgo/KAGRA S250207bg: NED Galaxies in the Localization Volume
  8. IGO/Virgo/KAGRA S250206dm: Virtual Telescope Project upper limit for the Neutrino IceCube Candidate
  9. IceCube-250207A - IceCube observation of a high-energy neutrino candidate track-like event
  10. LIGO/Virgo/KAGRA S250207bg: Identification of a GW compact binary merger candidate
  11. LIGO/Virgo/KAGRA S250206dm: DDOTI Upper Limit for the Neutrino IceCube Candidate
  12. LIGO/Virgo/KAGRA S250206dm: Pan-STARRS observations of AT2025azm and AT2025azn
  13. LIGO/Virgo/KAGRA S250206dm: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  14. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of the AT 2025azn Optical Candidate
  15. LIGO/Virgo/KAGRA S250206dm: SAGUARO Detection of Two Potential Optical Counterparts
  16. The EP-WXT trigger 01709131347 is likely a flaring star
  17. LIGO/Virgo/KAGRA S250206dm: Updated-6 NED Galaxies in the Localization Volume
  18. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  19. LIGO/Virgo/KAGRA S250206dm: Upper limits from Fermi-GBM Observations
  20. GRB 250207A: Swift detection of a burst with optical counterpart
  21. LIGO/Virgo/KAGRA S250206dm: Coverage and upper limits from MAXI/GSC observations
  22. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  23. LIGO/Virgo/KAGRA S250206dm: Updated NED Galaxies in the Localization Volume
  24. LIGO/Virgo/KAGRA S250206dm: Two counterpart neutrino candidates from IceCube neutrino searches
  25. LIGO/Virgo/KAGRA S250206dm: Identification of a GW compact binary merger candidate
  26. LIGO/Virgo/KAGRA S250206dm: NED Galaxies in the Localization Volume
  27. GRB 250205A: REM NIR upper limit
  28. LIGO/Virgo/KAGRA S250205ee: Updated Sky localization and Source Classification
  29. GRB 250205A: OHP/T193 optical counterpart candidate
  30. GRB 250205A: Liverpool Telescope optical counterpart candidate detection
  31. LIGO/Virgo/KAGRA S250205ee: Identification of a GW compact binary merger candidate
  32. LIGO/Virgo/KAGRA S250205bk: NED Galaxies in the Localization Volume
  33. LIGO/Virgo/KAGRA S250205bk: Updated Sky localization
  34. LIGO/Virgo/KAGRA S250205bk: Identification of a GW compact binary merger candidate
  35. LIGO/Virgo/KAGRA S250204ax: Updated Sky localization
  36. LIGO/Virgo/KAGRA S250204ax: Identification of a GW compact binary merger candidate
  37. IceCube-250203A - IceCube observation of a high-energy neutrino candidate track-like event
  38. LIGO/Virgo/KAGRA S250202cu: Updated Sky localization
  39. LIGO/Virgo/KAGRA S250202cu: Identification of a GW compact binary merger candidate
  40. LIGO/Virgo/KAGRA S250202ad: Retraction of GW compact binary merger candidate
  41. LIGO/Virgo/KAGRA S250201i: Coverage and upper limits from MAXI/GSC observations
  42. GRB 250129A: GRANDMA/TAROT optical afterglow detection
  43. GRB 250128B: Gemini-North optical extended source detection
  44. GRB 250128B: TNG optical upper limit
  45. GRB 250129A: Swift detection of a burst with an optical counterpart
  46. GRB 250128B: GOTO optical upper limit
  47. GRB 250128B: Swift detection of a short burst
  48. GRB 250127A: Swift ToO observations
  49. EP250125a: Optical upper limit with Kinder observations
  50. EP250108a/AT2025kg: 1.3m DFOT Optical observations
  51. LIGO/Virgo/KAGRA S250105bn: 1 counterpart neutrino candidate event from an IceCube neutrino search
  52. LIGO/Virgo/KAGRA S250119cv: Updated NED Galaxies in the Localization Volume
  53. LIGO/Virgo/KAGRA S250119cv: Updated Sky localization and EM Bright Classification
  54. LIGO/Virgo/KAGRA S250119cv: NED Galaxies in the Localization Volume
  55. LIGO/Virgo/KAGRA S250119cv: Identification of a GW compact binary merger candidate
  56. LIGO/Virgo/KAGRA S250119ag: Updated Sky localization
  57. LIGO/Virgo/KAGRA S250118dp: Updated Sky localization
  58. LIGO/Virgo/KAGRA S250119ag: Identification of a GW compact binary merger candidate
  59. LIGO/Virgo/KAGRA S250118dp: Identification of a GW compact binary merger candidate
  60. LIGO/Virgo/KAGRA S250118t: Updated Sky localization
  61. LIGO/Virgo/KAGRA S250118az: Identification of a GW compact binary merger candidate
  62. LIGO/Virgo/KAGRA S250118t: Identification of a GW compact binary merger candidate
  63. LIGO/Virgo/KAGRA S250114ax: Updated NED Galaxies in the Localization Volume
  64. LIGO/Virgo/KAGRA S250114ax: Updated Sky localization
  65. GRB 250114B: Liverpool Telescope optical upper limit
  66. GRB 250114B : MITSuME Akeno optical afterglow candidate detection
  67. GRB 250114A: GRANDMA/TAROT optical afterglow detection
  68. GRB 250114B: Swift ToO observations
  69. LIGO/Virgo/KAGRA S250114ax: NED Galaxies in the Localization Volume
  70. LIGO/Virgo/KAGRA S250114ax: Identification of a GW compact binary merger candidate
  71. GRB 250114A: Swift detection of a burst with an optical counterpart
  72. EP250111a: Swift/XRT detection and fading
  73. EP250109a/GRB 250109A:SVOM/VT optical counterpart
  74. GRB 250109A / EP250109a: Terskol (INASAN) and SAO RAS observations
  75. GRB 250108A: Swift/XRT afterglow fading
  76. LIGO/Virgo/KAGRA S250109bi: Updated Sky localization
  77. LIGO/Virgo/KAGRA S250109f: Updated Sky localization
  78. LIGO/Virgo/KAGRA S250108eo: Updated Sky localization
  79. GRB 250108B: REM optical/NIR upper limits
  80. EP250109a: SVOM/VT optical candidate
  81. GRB 250108A: Swift/UVOT Upper Limits
  82. LIGO/Virgo/KAGRA S250109bi: Identification of a GW compact binary merger candidate
  83. GRB 250108A: NOT optical upper limit
  84. LIGO/Virgo/KAGRA S250109f: Identification of a GW compact binary merger candidate
  85. LIGO/Virgo/KAGRA S250108ha: Retraction of GW compact binary merger candidate
  86. GRB 250108B: Gemini-North Candidate Optical Afterglow Detection
  87. GRB 250103A: 1.6m Mephisto optical observations
  88. GRB 250108A:SVOM/VT optical candidate
  89. LIGO/Virgo/KAGRA S250108eo: Identification of a GW compact binary merger candidate
  90. GRB 250108B: Swift detection of a burst
  91. GRB 250108A: Swift ToO observations
  92. GRB 250107A: Swift ToO observations
  93. GRB 250106A: SVOM/VT 2nd optical deep observation
  94. GRB 250106A: NOT optical observations
  95. LIGO/Virgo/KAGRA S250104v: Updated Sky localization
  96. GRB 250106A: SVOM/VT optical candidate
  97. GRB 250106A: Swift ToO observations
  98. GRB 250103B: LCO/1m optical afterglow candidate detection
  99. GRB 250103A: Swift-XRT observations
  100. GRB 241228B: 1.3m DFOT Optical observations

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