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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"
  1. EP250730a: Global MASTER-Net observations report
  2. EP250730a: COLIBRÍ optical upper limit
  3. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  4. EP250730a: Einstein Probe detection of an X-ray transient
  5. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  6. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm
  7. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  8. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  9. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  10. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  11. GRB 250725A: AstroSat CZTI detection
  12. GRB 250727A: EP-FXT follow-up observation
  13. GRB 250725A: PRIME near-infrared observations
  14. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  15. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  16. GRB: Clarification on Gamma-Ray Burst Naming Convention
  17. GRB 250728A: Swift-XRT observations
  18. GRB 250727A: SVOM/ECLAIRs refined analysis
  19. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  20. GRB 250728A: COLIBRÍ optical upper limit
  21. GRB 250728A: Fermi GBM Observation
  22. Fermi trigger No 775387550: Global MASTER-Net observations report
  23. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  24. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  25. GRB 250728A: Swift ToO observations
  26. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  27. GRB 250727A: AST3-2 Upper limit
  28. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  29. GRB 250727A: EP-FXT counterpart detection
  30. GRB250727A: SVOM/VT optical upper limit
  31. GRB 250727A: Swift-XRT observations
  32. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  33. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  34. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  35. GRB 250727A: SVOM detection of a burst
  36. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  37. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  38. The EP-WXT trigger 01709195487 is likely a flaring star
  39. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  40. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  41. GRB 250725A: Swift-XRT refined Analysis
  42. GRB 250725A: Fermi GBM Observation
  43. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  44. GRB 250725A: Swift-BAT refined analysis
  45. Konus-Wind detection of GRB 250725A
  46. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  47. GRB 250725A: SVOM/GRM observation
  48. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  49. GRB 250725A: Swift/UVOT Upper Limits
  50. GRB 250725A: Fermi-LAT detection
  51. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  52. GRB 250725A: BOOTES-7 early optical detection
  53. GRB 250725A: SVOM/VT optical candidate
  54. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  55. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  56. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  57. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  58. GRB 250725A: Enhanced Swift-XRT position
  59. GRB 250725A: Swift detection of a burst
  60. Swift GRB 250725A: Global MASTER-Net OT detection
  61. GRB 250725A: Fermi GBM Final Real-time Localization
  62. Fermi GRB 250725A: Global MASTER-Net observations report
  63. Swift GRB 250725A: Global MASTER-Net observations report
  64. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  65. SVOM J195836+32283 is not a real source
  66. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  67. SVOM J195836+32283/sb25072103: Second VT observation
  68. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  69. GRB 250723B: Fermi GBM Final Real-time Localization
  70. GRB 250721A: Fermi GBM Observation
  71. GRB 250723A: Fermi GBM Final Real-time Localization
  72. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  73. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  74. Swift-BAT trigger 1334535 is not a GRB
  75. GRB 250721A: Swift-XRT observations
  76. GRB 250722A: Fermi GBM Final Real-time Localization
  77. GRB 250713A : SVOM/ECLAIRs refined analysis
  78. GRB 250717B: SVOM/GRM observation
  79. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  80. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  81. GRB 250721A: Tiled Swift observations
  82. GRB 250721A: MAXI/GSC detection
  83. GRB 250721A: Fermi GBM Final Localization
  84. GRB 250720B: Fermi GBM Final Localization Correction
  85. GRB 250720A: Fermi GBM Final Localization
  86. Fermi trigger No 774730635: Global MASTER-Net observations report
  87. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  88. Fermi Gamma-ray Burst Monitor trigger 774670514/250720094 is not a GRB
  89. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  90. GRB 250717B: COLIBRÍ optical upper limit
  91. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  92. GRB 250717B: Swift-XRT observations
  93. GRB 250718B: Fermi GBM Final Localization Correction
  94. GRB 250718B: Fermi GBM Final Real-time Localization
  95. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  96. Swift Trigger 1334535: a possible GRB 250718A
  97. Swift GRB250718.01: Global MASTER-Net observations report
  98. GRB 250717B: Swift ToO observations
  99. GRB 270713A: Kitab and AbAO Optical Observations
  100. GRB 250717B: Fermi GBM Observation

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