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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

8474 results found.

  1. EP250711a: NOT optical counterpart candidate
  2. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  3. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  4. LIGO/Virgo/KAGRA S250629bs: Upper limits from Swift/BAT-GUANO
  5. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  6. IceCube-250708A: No Candidates from WINTER
  7. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  8. IceCube-250708A: Upper limits from a search for additional neutrino events in IceCube
  9. GRB250702 B,D,E / EP250702a: MOSFIRE imaging of the afterglow
  10. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 4-Update Localization Volume
  11. IceCube-250706A: No Candidates from WINTER
  12. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  13. IceCube-250708A - IceCube observation of a high-energy neutrino candidate track-like event
  14. IceCube-250706A: Upper limits from a search for additional neutrino events in IceCube
  15. LIGO/Virgo/KAGRA S250705cb: Updated Sky localization
  16. LIGO/Virgo/KAGRA S250704ab: Updated Sky localization and EM Bright Classification
  17. LIGO/Virgo/KAGRA S250702n: Updated Sky localization
  18. LIGO/Virgo/KAGRA S250701bq: Updated Sky localization
  19. LIGO/Virgo/KAGRA S250701bp: Updated Sky localization
  20. GRB 250702F: radio detection with the VLA
  21. GRB 250706A: SAO RAS optical observations
  22. GRB 250706A: SVOM/C-GFT upper limit in eary phase
  23. GRB250706B: Swift-XRT counterpart detection
  24. IceCube-250706A - IceCube observation of a high-energy neutrino candidate track-like event
  25. GRB 250706B: SVOM/VT optical observation
  26. GRB 250706A: Swift detection of a burst
  27. EP250702a/GRB 250702B,C,D,E: Archival radio observations from ASKAP VAST
  28. LIGO/Virgo/KAGRA S250705cb: Identification of a GW compact binary merger candidate
  29. GRBs 250702B,D,E / EP250702a: fast fading, extremely red counterpart
  30. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 3-Initial Localization Volume
  31. EP250704a / GRB 250704B: Pan-STARRS iz-band imaging and photometry
  32. EP 250704a: BOOTES-5 optical detection
  33. LIGO/Virgo/KAGRA S250704ab: Upper limits from Fermi-GBM Observations
  34. EP250704a / GRB250704B: Swift-XRT counterpart detection
  35. EP250704a / GRB 250704B - REM observations
  36. EP250704a: COLIBRÍ optical counterpart candidate
  37. LIGO/Virgo/KAGRA S250704ab: Coverage and upper limits from MAXI/GSC observations
  38. LIGO/Virgo/KAGRA S250704ab: Identification of a GW compact binary merger candidate
  39. GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
  40. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  41. GRB 250702F: Swift detection of a burst with an optical counterpart
  42. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate
  43. LIGO/Virgo/KAGRA S250701bq: Identification of a GW compact binary merger candidate
  44. LIGO/Virgo/KAGRA S250701bp: Identification of a GW compact binary merger candidate
  45. GRB 250628B: Swift-XRT observations
  46. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  47. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  48. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  49. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate (duplicate submission)
  50. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  51. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  52. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  53. GRB 250628A: Swift detection of a burst
  54. GRB 250625A: Swift detection of a burst
  55. GRB 250617B: Swift detection of a burst with an optical counterpart
  56. EP#01709178975: Swift-XRT counterpart detection
  57. EP-WXT trigger 01709178975: GOTO optical upper limit
  58. GRB 250615A: Swift detection of a burst
  59. IceCube alert 141029_8144692 retraction
  60. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  61. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  62. sb25061218: Swift-XRT observations
  63. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  64. sb25061207: EP-FXT follow-up observation and afterglow candidate
  65. EP250612a: SVOM/VT optical candidate
  66. sb25061207: Swift-XRT observations
  67. sb25061207: SVOM/VT optical counterpart
  68. EP250610a: Upper limit from Fermi-GBM Observations
  69. Fermi GBM Sub-Threshold Detection of GRB 250610B
  70. EP250610a: TNG NIR upper limit
  71. GRB 250610B: OHP/T120 optical counterpart candidate
  72. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  73. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  74. EP250610a: SVOM/VT optical upper limit
  75. EP250610a: REM optical/NIR observations
  76. EP250610a: Swift-XRT counterpart detection
  77. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  78. GRB 250527C: CrAO Optical Upper Limit
  79. GRB 250605A: SVOM/VT optical upper limit
  80. GRB 250605A: Swift detection of a burst
  81. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  82. GRB 250601A: Swift/XRT candidate afterglow
  83. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  84. GRB 250601A: Swift ToO observations
  85. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  86. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  87. EP#01709177494: Swift-XRT counterpart detection of known source
  88. GRB 250530C: BOOTES-7 optical upper limit
  89. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  90. GRB 250530C: Swift detection of a burst
  91. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  92. GRB 250530A: EP-FXT counterpart detection
  93. GRB 250530A: SVOM/VT optical upper limit
  94. GRB 250530A: Swift-XRT counterpart detection
  95. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  96. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  97. EP J1350.0-8622: EP-FXT follow-up observation
  98. GRB 250527C: Swift ToO observations
  99. GRB 250527B: Tiled Swift observations
  100. GRB 250520A: Gemini-South optical afterglow detection

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