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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. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  2. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  3. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  4. GRB 250725A: AstroSat CZTI detection
  5. GRB 250727A: EP-FXT follow-up observation
  6. GRB 250725A: PRIME near-infrared observations
  7. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  8. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  9. GRB: Clarification on Gamma-Ray Burst Naming Convention
  10. GRB 250728A: Swift-XRT observations
  11. GRB 250727A: SVOM/ECLAIRs refined analysis
  12. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  13. GRB 250728A: COLIBRÍ optical upper limit
  14. GRB 250728A: Fermi GBM Observation
  15. Fermi trigger No 775387550: Global MASTER-Net observations report
  16. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  17. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  18. GRB 250728A: Swift ToO observations
  19. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  20. GRB 250727A: AST3-2 Upper limit
  21. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  22. GRB 250727A: EP-FXT counterpart detection
  23. GRB250727A: SVOM/VT optical upper limit
  24. GRB 250727A: Swift-XRT observations
  25. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  26. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  27. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  28. GRB 250727A: SVOM detection of a burst
  29. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  30. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  31. The EP-WXT trigger 01709195487 is likely a flaring star
  32. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  33. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  34. GRB 250725A: Swift-XRT refined Analysis
  35. GRB 250725A: Fermi GBM Observation
  36. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  37. GRB 250725A: Swift-BAT refined analysis
  38. Konus-Wind detection of GRB 250725A
  39. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  40. GRB 250725A: SVOM/GRM observation
  41. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  42. GRB 250725A: Swift/UVOT Upper Limits
  43. GRB 250725A: Fermi-LAT detection
  44. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  45. GRB 250725A: BOOTES-7 early optical detection
  46. GRB 250725A: SVOM/VT optical candidate
  47. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  48. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  49. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  50. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  51. GRB 250725A: Enhanced Swift-XRT position
  52. GRB 250725A: Swift detection of a burst
  53. Swift GRB 250725A: Global MASTER-Net OT detection
  54. GRB 250725A: Fermi GBM Final Real-time Localization
  55. Fermi GRB 250725A: Global MASTER-Net observations report
  56. Swift GRB 250725A: Global MASTER-Net observations report
  57. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  58. SVOM J195836+32283 is not a real source
  59. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  60. SVOM J195836+32283/sb25072103: Second VT observation
  61. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  62. GRB 250723B: Fermi GBM Final Real-time Localization
  63. GRB 250721A: Fermi GBM Observation
  64. GRB 250723A: Fermi GBM Final Real-time Localization
  65. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  66. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  67. Swift-BAT trigger 1334535 is not a GRB
  68. GRB 250721A: Swift-XRT observations
  69. GRB 250722A: Fermi GBM Final Real-time Localization
  70. GRB 250713A : SVOM/ECLAIRs refined analysis
  71. GRB 250717B: SVOM/GRM observation
  72. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  73. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  74. GRB 250721A: Tiled Swift observations
  75. GRB 250721A: MAXI/GSC detection
  76. GRB 250721A: Fermi GBM Final Localization
  77. GRB 250720B: Fermi GBM Final Localization Correction
  78. GRB 250720A: Fermi GBM Final Localization
  79. Fermi trigger No 774730635: Global MASTER-Net observations report
  80. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  81. Fermi Gamma-ray Burst Monitor trigger 774670514/250720094 is not a GRB
  82. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  83. GRB 250717B: COLIBRÍ optical upper limit
  84. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  85. GRB 250717B: Swift-XRT observations
  86. GRB 250718B: Fermi GBM Final Localization Correction
  87. GRB 250718B: Fermi GBM Final Real-time Localization
  88. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  89. Swift Trigger 1334535: a possible GRB 250718A
  90. Swift GRB250718.01: Global MASTER-Net observations report
  91. GRB 250717B: Swift ToO observations
  92. GRB 270713A: Kitab and AbAO Optical Observations
  93. GRB 250717B: Fermi GBM Observation
  94. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  95. Konus-Wind detection of GRB 250716A
  96. GRB 250716A: Swift-XRT afterglow detection
  97. GRB 250717B: Fermi GBM Final Real-time Localization
  98. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  99. GRB 250717A: Fermi GBM Final Real-time Localization
  100. GRB 250716A: Swift ToO observations

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