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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"

14824 results found.

  1. GRB 250823A: Swift detection of a burst
  2. GRB 250823A: Fermi GBM Final Real-time Localization
  3. Konus-Wind detection of GRB 250821B
  4. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  5. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  6. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  7. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  8. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  9. IPN triangulation of GRB 250821B (long/bright)
  10. GRB 250821A: GECAM-B detection
  11. GRB 250821C: Fermi GBM Final Real-time Localization
  12. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  13. GRB 250821B: Fermi GBM Detection
  14. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  15. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  16. EP250821a: Swift XRT and UVOT counterpart detection
  17. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  18. GRB 250821A: Swift detection of a burst
  19. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  20. EP250821a: Einstein Probe detection of an X-ray transient
  21. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  22. GRB 250819A: Insight-HXMT detection
  23. GRB 250818B: 10 GHz VLA detection
  24. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  25. IPN triangulation of GRB 250816A (short)
  26. IPN triangulation of GRB 250814C (short)
  27. IPN triangulation of GRB 250804B (short)
  28. GRB 250818B: Kilonova-Catcher optical afterglow detection
  29. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  30. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  31. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  32. GRB 250818A: AstroSat CZTI detection
  33. GRB 250818B: Swift/UVOT Detection
  34. GRB 250820A: Fermi GBM Final Real-time Localization
  35. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  36. GRB 250818B: TRT Optical Observation
  37. GRB 250818B: EP-FXT counterpart detection
  38. GRB 250818C: Fermi GBM Final Real-time Localization
  39. GRB 250818B: Swift-XRT afterglow detection
  40. GRB 250818B: SVOM detection of a short burst
  41. GRB 250818A: Swift detection of a burst
  42. GRB 250818A: Fermi GBM Final Real-time Localization
  43. SVOM/sb25081602: detection of a likely X-ray transient
  44. GRB 250816A: Fermi GBM Final Real-time Localization
  45. GRB 250815A: Fermi GBM Final Localization
  46. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  47. GRB 250812A: SVOM/VT optical continued observation
  48. GRB250814A: TRT optical upper limits
  49. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  50. GRB 250814A: Possible afterglow candidate from P200/WIRC
  51. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  52. GRB 250814B: Fermi GBM Final Real-time Localization
  53. GRB 250813A: AstroSat CZTI detection
  54. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  55. GRB 250813B: EP-FXT counterpart detection
  56. GRB 250813B: Swift-XRT afterglow detection
  57. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  58. GRB 250814A: Fermi GBM Final Real-time Localization
  59. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  60. GRB 250813B: Ondrejov D50 optical afterglow detection
  61. GRB 250813B: SVOM detection of a bright long burst
  62. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  63. GRB 250812A: NTT spectroscopic redshift z = 2.57
  64. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  65. GRB 250812A: Swift/UVOT Detection
  66. GRB 250813A: Fermi GBM Final Localization
  67. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  68. EP250812a: Liverpool Telescope upper limits
  69. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  70. GRB 250812A: EP-FXT counterpart detection
  71. GRB 250812A: Kilonova-Catcher optical afterglow detection
  72. EP250812a: Swift-XRT counterpart detection
  73. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  74. EP250812a: Einstein Probe detection of an X-ray transient
  75. GRB 250812A: SVOM/VT optical afterglow confirmation
  76. GRB 250812A: Swift-XRT afterglow detection
  77. GRB 250812A: TRT likely optical counterpart detection
  78. GRB 250812A: SVOM detection of a faint long burst
  79. GRB 250809A: Swift/UVOT Detection
  80. GRB 250702B: Chandra X-ray Detection
  81. GRB 250809A: Swift detection of a gamma ray burst
  82. GRB 250808A: Swift-XRT candidate counterpart detection
  83. GRB 250808A: SVOM detection of a long burst
  84. GRB 250808A: Fermi GBM Final Real-time Localization
  85. Konus-Wind detection of GRB 250807A
  86. GRB 250807B: Swift/UVOT Detection
  87. GRB 250807B: Kilonova-Catcher optical afterglow detection
  88. GRB 250807A: Swift/UVOT Detection
  89. GRB 250806A: SVOM/MXT refined analysis
  90. GRB 250804B: Insight-HXMT detection
  91. GRB 250807A: AstroSat CZTI detection of bright long burst
  92. EP250807a: EP-WXT detection of a fast X-ray transient
  93. GRB 250807B: Swift detection of a burst with an optical counterpart.
  94. GRB 250806A: Swift/UVOT U-band detection
  95. GRB 250807A: Swift detection of a burst with an optical counterpart
  96. GRB 250806A: EP-FXT observation
  97. EP250802a: EP-FXT follow-up observation
  98. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  99. GRB 250806A: SVOM/VT refined analysis
  100. GRB 250806A: Swift-XRT counterpart detection

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