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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"

18048 results found.

  1. GRB 250823A: SVOM/VT optical observation
  2. GRB 250823A: Swift/UVOT Detection
  3. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  4. GRB 250823A: Enhanced Swift-XRT position
  5. GRB 250823A: LCOGT Optical Detection
  6. GRB 250823A: Swift detection of a burst
  7. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  8. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  9. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  10. GRB 250821A: Kilonova-Catcher optical upper limits
  11. GRB 250821A: VLT/FORS2 Optical Observation
  12. GRB 250821B: SVOM/GRM observation
  13. EP250821a: SVOM/VT optical observation
  14. GRB 250821A: NOT z-band upper limit
  15. GRB 250821A: KAIT optical upper limit
  16. GRB 250821A: Enhanced Swift-XRT position
  17. GRB 250821A: Swift/UVOT Upper Limits
  18. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  19. GRB 250821A: LCOGT Optical Upper Limits
  20. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  21. GRB 250821A: Swift detection of a burst
  22. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  23. EP250821a: Einstein Probe detection of an X-ray transient
  24. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  25. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  26. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  27. GRB 250814A: Swift/UVOT Upper Limits
  28. GRB 250813B: Swift/UVOT Upper Limit
  29. IPN triangulation of GRB 250816A (short)
  30. IPN triangulation of GRB 250814C (short)
  31. IPN triangulation of GRB 250804B (short)
  32. GRB 250818B: Kilonova-Catcher optical afterglow detection
  33. GRB 250818B: Swift/UVOT Detection
  34. GRB 250818B: SAO RAS optical observations
  35. GRB 250818B: KAIT optical observations
  36. GRB 250818A: Swift/UVOT Upper Limits
  37. GRB 250818A: Enhanced Swift-XRT position
  38. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  39. GRB 250814A: Further GRAWITA TNG NIR observations
  40. GRB 250818B: SVOM detection of a short burst
  41. GRB 250818A: Swift detection of a burst
  42. GRB 250816A: SVOM/GRM observation of a short burst
  43. GRB 250813B: Liverpool Telescope optical upper limits
  44. GRB 250814A: Further COLIBRÍ optical upper limit
  45. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  46. GRB 250814A: GRAWITA TNG NIR observations
  47. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  48. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  49. GRB250814A: TRT optical upper limits
  50. GRB 250814B: SVOM/GRM observation
  51. GRB 250814A: P200/WIRC observations of the afterglow candidate
  52. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  53. GRB 250814A: KAIT optical upper limit
  54. GRB 250814A: Swift-XRT refined Analysis
  55. GRB 250814A: Possible afterglow candidate from P200/WIRC
  56. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  57. GRB 250814A: J-band upper limit from WINTER
  58. GRB 250813B: NOT observations of the optical afterglow
  59. GRB 250814A: COLIBRÍ optical upper limit
  60. GRB 250813A: AstroSat CZTI detection
  61. GRB 250814A: DDOTI Optical Upper Limit
  62. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  63. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  64. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  65. GRB 250813B: SVOM detection of a bright long burst
  66. EP250812a: Nickel optical upper limit
  67. EP250812a: NOT, NTT, and GS observations
  68. GRB 250812A: Swift/UVOT Detection
  69. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  70. EP250812a: Liverpool Telescope upper limits
  71. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  72. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  73. GRB 250812A: Swift ToO observations
  74. EP 250812a: GOTO optical upper limit
  75. GRB 250812A: Kilonova-Catcher optical afterglow detection
  76. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  77. EP250812a: Einstein Probe detection of an X-ray transient
  78. GRB 250812A: Swift-XRT afterglow detection
  79. GRB 250812A: TRT likely optical counterpart detection
  80. GRB 250812A: SVOM detection of a faint long burst
  81. GRB 250809A: Swift/UVOT Detection
  82. Corrected Swift-XRT Refined Analysis of GRB 250809A
  83. GRB 250809A: Swift-XRT refined Analysis
  84. GRB 250809A: LCOGT Optical Upper Limits
  85. GRB 250808A: VLT X-shooter candidate counterpart
  86. GRB 250809A: Swift detection of a gamma ray burst
  87. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  88. GRB 250808A: Fermi GBM Final Real-time Localization
  89. GRB 250807B: Swift/UVOT Detection
  90. GRB 250807B: Kilonova-Catcher optical afterglow detection
  91. GRB 250807A: Swift/UVOT Detection
  92. GRB 250806A: SVOM/ECLAIRs refined analysis
  93. EP250807a: NTT z-band optical upper limit
  94. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  95. GRB 250807A: SVOM/GRM observation
  96. EP250807a: EP-WXT detection of a fast X-ray transient
  97. EP 250807.979: GOTO optical upper limit
  98. EP250807a: COLIBRÍ optical upper limit
  99. GRB 250807B: Enhanced Swift-XRT position
  100. GRB 250807A: Enhanced Swift-XRT position

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