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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"

18114 results found.

  1. GRB 250818B: KAIT optical observations
  2. GRB 250818A: Swift/UVOT Upper Limits
  3. GRB 250818A: Enhanced Swift-XRT position
  4. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  5. GRB 250814A: Further GRAWITA TNG NIR observations
  6. GRB 250818B: SVOM detection of a short burst
  7. GRB 250818A: Swift detection of a burst
  8. GRB 250816A: SVOM/GRM observation of a short burst
  9. GRB 250813B: Liverpool Telescope optical upper limits
  10. GRB 250814A: Further COLIBRÍ optical upper limit
  11. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  12. GRB 250814A: GRAWITA TNG NIR observations
  13. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  14. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  15. GRB250814A: TRT optical upper limits
  16. GRB 250814B: SVOM/GRM observation
  17. GRB 250814A: P200/WIRC observations of the afterglow candidate
  18. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  19. GRB 250814A: KAIT optical upper limit
  20. GRB 250814A: Swift-XRT refined Analysis
  21. GRB 250814A: Possible afterglow candidate from P200/WIRC
  22. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  23. GRB 250814A: J-band upper limit from WINTER
  24. GRB 250813B: NOT observations of the optical afterglow
  25. GRB 250814A: COLIBRÍ optical upper limit
  26. GRB 250813A: AstroSat CZTI detection
  27. GRB 250814A: DDOTI Optical Upper Limit
  28. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  29. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  30. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  31. GRB 250813B: SVOM detection of a bright long burst
  32. EP250812a: Nickel optical upper limit
  33. EP250812a: NOT, NTT, and GS observations
  34. GRB 250812A: Swift/UVOT Detection
  35. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  36. EP250812a: Liverpool Telescope upper limits
  37. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  38. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  39. GRB 250812A: Swift ToO observations
  40. EP 250812a: GOTO optical upper limit
  41. GRB 250812A: Kilonova-Catcher optical afterglow detection
  42. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  43. EP250812a: Einstein Probe detection of an X-ray transient
  44. GRB 250812A: Swift-XRT afterglow detection
  45. GRB 250812A: TRT likely optical counterpart detection
  46. GRB 250812A: SVOM detection of a faint long burst
  47. GRB 250809A: Swift/UVOT Detection
  48. Corrected Swift-XRT Refined Analysis of GRB 250809A
  49. GRB 250809A: Swift-XRT refined Analysis
  50. GRB 250809A: LCOGT Optical Upper Limits
  51. GRB 250808A: VLT X-shooter candidate counterpart
  52. GRB 250809A: Swift detection of a gamma ray burst
  53. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  54. GRB 250808A: Fermi GBM Final Real-time Localization
  55. GRB 250807B: Swift/UVOT Detection
  56. GRB 250807B: Kilonova-Catcher optical afterglow detection
  57. GRB 250807A: Swift/UVOT Detection
  58. GRB 250806A: SVOM/ECLAIRs refined analysis
  59. EP250807a: NTT z-band optical upper limit
  60. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  61. GRB 250807A: SVOM/GRM observation
  62. EP250807a: EP-WXT detection of a fast X-ray transient
  63. EP 250807.979: GOTO optical upper limit
  64. EP250807a: COLIBRÍ optical upper limit
  65. GRB 250807B: Enhanced Swift-XRT position
  66. GRB 250807A: Enhanced Swift-XRT position
  67. GRB 250807B: Swift detection of a burst with an optical counterpart.
  68. GRB 250805A: Kilonova-Catcher optical upper limits
  69. GRB 250805A: Swift/UVOT Upper Limits
  70. GRB 250806A: Swift/UVOT U-band detection
  71. EP250806a: Liverpool telescope optical upper limit
  72. GRB 250807A: Swift detection of a burst with an optical counterpart
  73. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  74. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  75. EP250806a: SVOM /VT optical candidate
  76. GRB 250806A: J-band upper limit from WINTER
  77. GRB 250806A: KAIT optical upper limit
  78. EP250806a: COLIBRÍ optical upper limit
  79. GRB 250806A: Kilonova-Catcher optical upper limits
  80. EP250806a: Einstein Probe detection of an X-ray transient
  81. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  82. GRB 250806A: SVOM/VT optical upper limit
  83. GRB 250806A: SVOM detection of a soft burst
  84. GRB 250805A: SVOM/VT optical counterpart
  85. GRB 250805A: Enhanced Swift-XRT position
  86. GRB 250804C: AstroSat CZTI detection of a long burst
  87. GRB 250805A: TRT optical upper limits
  88. GRB 250805A: Swift-XRT observations
  89. GRB 250804B: Tiled Swift observations
  90. GRB 250804B: SVOM/GRM observation of a short burst
  91. EP250802a: additional Liverpool Telescope upper limits
  92. EP250730a: SVOM/VT optical upper limit
  93. EP250802a: Liverpool Telescope optical upper limits
  94. EP250802a: GROWTH-India Telescope optical upper limit
  95. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  96. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  97. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  98. EP250711a: CrAO and Assy optical observations
  99. EP250730a: COLIBRÍ optical upper limit
  100. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis

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