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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"

28062 results found.

  1. GRB 250808A: VLT X-shooter candidate counterpart
  2. GRB 250809A: Swift detection of a gamma ray burst
  3. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  4. GRB 250808A: Fermi GBM Observation
  5. GRB 250808A: Swift-XRT candidate counterpart detection
  6. GRB 250807B: Swift/UVOT Detection
  7. GRB 250807B: Kilonova-Catcher optical afterglow detection
  8. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  9. GRB 250807A: Swift/UVOT Detection
  10. GRB 250807A: Swift-XRT refined Analysis
  11. GRB 250806A: SVOM/MXT refined analysis
  12. EP250807a: NTT z-band optical upper limit
  13. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  14. GRB 250807A: SVOM/GRM observation
  15. GRB 250807A: AstroSat CZTI detection of bright long burst
  16. GRB 250807B: Swift-XRT refined Analysis
  17. EP250807a: EP-WXT detection of a fast X-ray transient
  18. EP 250807.979: GOTO optical upper limit
  19. EP250807a: COLIBRÍ optical upper limit
  20. EP250806a: Upper limit from Fermi-GBM Observations
  21. GRB 250807B: Enhanced Swift-XRT position
  22. GRB 250807A: Enhanced Swift-XRT position
  23. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  24. GRB 250807B: Swift detection of a burst with an optical counterpart.
  25. GRB 250805A: Kilonova-Catcher optical upper limits
  26. GRB 250805A: Swift/UVOT Upper Limits
  27. GRB 250806A: Swift/UVOT U-band detection
  28. EP250806a: Liverpool telescope optical upper limit
  29. GRB 250807A: Swift detection of a burst with an optical counterpart
  30. EP250802a: EP-FXT follow-up observation
  31. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  32. EP250806a: SVOM /VT optical candidate
  33. GRB 250806A: J-band upper limit from WINTER
  34. GRB 250805A: Swift-BAT refined analysis
  35. GRB 250806A: KAIT optical upper limit
  36. GRB 250806A: Swift-XRT counterpart detection
  37. EP250806a: COLIBRÍ optical upper limit
  38. GRB 250806A: Kilonova-Catcher optical upper limits
  39. EP250806a: Einstein Probe detection of an X-ray transient
  40. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  41. GRB 250806A: SVOM/VT optical upper limit
  42. GRB 250806A: SVOM detection of a soft burst
  43. GRB 250805A: SVOM/VT optical counterpart
  44. GRB 250805A: Swift-XRT refined Analysis
  45. GRB 250804B: Swift-XRT observations
  46. GRB 250805A: Enhanced Swift-XRT position
  47. GRB 250805A: TRT optical upper limits
  48. GRB 250805A: Swift-XRT observations
  49. GRB 250804B: SVOM/GRM observation of a short burst
  50. GRB 250804A: Fermi GBM Final Localization
  51. EP250802a: additional Liverpool Telescope upper limits
  52. EP250730a: SVOM/VT optical upper limit
  53. EP250802a: Liverpool Telescope optical upper limits
  54. EP250802a: Global MASTER-Net observations report
  55. EP250802a: GROWTH-India Telescope optical upper limit
  56. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  57. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  58. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  59. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  60. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  61. EP250711a: CrAO and Assy optical observations
  62. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  63. EP250730a: COLIBRÍ optical upper limit
  64. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  65. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  66. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  67. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  68. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  69. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  70. GRB 250727A: EP-FXT follow-up observation
  71. GRB 250725A: PRIME near-infrared observations
  72. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  73. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  74. GRB 250728A: Swift-XRT observations
  75. GRB 250728A: COLIBRÍ optical upper limit
  76. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  77. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  78. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  79. GRB 250727A: EP-FXT counterpart detection
  80. GRB 250727A: Swift-XRT observations
  81. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  82. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  83. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  84. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  85. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  86. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  87. GRB 250725A: Swift-XRT refined Analysis
  88. GRB 250725A: Fermi GBM Observation
  89. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  90. GRB 250725A: Swift-BAT refined analysis
  91. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  92. GRB 250725A: SVOM/GRM observation
  93. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  94. GRB 250725A: Swift/UVOT Upper Limits
  95. GRB 250725A: Fermi-LAT detection
  96. GRB 250725A: BOOTES-7 early optical detection
  97. GRB 250725A: SVOM/VT optical candidate
  98. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  99. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  100. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate

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