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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. GRB 250805A: Swift-XRT observations
  2. GRB 250805A: Swift detection of a burst
  3. Swift GRB250805.26: Global MASTER-Net observations report
  4. GRB 250804B: Tiled Swift observations
  5. Fermi trigger No 776041355: Global MASTER-Net observations report
  6. GRB 250804B: SVOM/GRM observation of a short burst
  7. GRB 250804A: Fermi GBM Final Localization
  8. EP250802a: additional Liverpool Telescope upper limits
  9. EP250730a: SVOM/VT optical upper limit
  10. Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB
  11. EP250802a: Liverpool Telescope optical upper limits
  12. EP250802a: Global MASTER-Net observations report
  13. EP250802a: GROWTH-India Telescope optical upper limit
  14. EP250802a: Einstein Probe detection of an X-ray transient
  15. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  16. The EP-WXT trigger 01709198251 is likely a flaring star
  17. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  18. The EP-WXT trigger 01709198202 is likely a flaring star
  19. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  20. GRB 250702B: SMA observations
  21. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  22. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  23. EP250711a: CrAO and Assy optical observations
  24. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  25. EP250730a: Global MASTER-Net observations report
  26. EP250730a: COLIBRÍ optical upper limit
  27. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  28. EP250730a: Einstein Probe detection of an X-ray transient
  29. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  30. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm
  31. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  32. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  33. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  34. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  35. GRB 250725A: AstroSat CZTI detection
  36. GRB 250727A: EP-FXT follow-up observation
  37. GRB 250725A: PRIME near-infrared observations
  38. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  39. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  40. GRB: Clarification on Gamma-Ray Burst Naming Convention
  41. GRB 250728A: Swift-XRT observations
  42. GRB 250727A: SVOM/ECLAIRs refined analysis
  43. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  44. GRB 250728A: COLIBRÍ optical upper limit
  45. GRB 250728A: Fermi GBM Observation
  46. Fermi trigger No 775387550: Global MASTER-Net observations report
  47. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  48. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  49. GRB 250728A: Swift ToO observations
  50. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  51. GRB 250727A: AST3-2 Upper limit
  52. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  53. GRB 250727A: EP-FXT counterpart detection
  54. GRB250727A: SVOM/VT optical upper limit
  55. GRB 250727A: Swift-XRT observations
  56. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  57. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  58. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  59. GRB 250727A: SVOM detection of a burst
  60. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  61. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  62. The EP-WXT trigger 01709195487 is likely a flaring star
  63. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  64. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  65. GRB 250725A: Swift-XRT refined Analysis
  66. GRB 250725A: Fermi GBM Observation
  67. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  68. GRB 250725A: Swift-BAT refined analysis
  69. Konus-Wind detection of GRB 250725A
  70. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  71. GRB 250725A: SVOM/GRM observation
  72. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  73. GRB 250725A: Swift/UVOT Upper Limits
  74. GRB 250725A: Fermi-LAT detection
  75. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  76. GRB 250725A: BOOTES-7 early optical detection
  77. GRB 250725A: SVOM/VT optical candidate
  78. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  79. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  80. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  81. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  82. GRB 250725A: Enhanced Swift-XRT position
  83. GRB 250725A: Swift detection of a burst
  84. Swift GRB 250725A: Global MASTER-Net OT detection
  85. GRB 250725A: Fermi GBM Final Real-time Localization
  86. Fermi GRB 250725A: Global MASTER-Net observations report
  87. Swift GRB 250725A: Global MASTER-Net observations report
  88. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  89. SVOM J195836+32283 is not a real source
  90. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  91. SVOM J195836+32283/sb25072103: Second VT observation
  92. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  93. GRB 250723B: Fermi GBM Final Real-time Localization
  94. GRB 250721A: Fermi GBM Observation
  95. GRB 250723A: Fermi GBM Final Real-time Localization
  96. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  97. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  98. Swift-BAT trigger 1334535 is not a GRB
  99. GRB 250721A: Swift-XRT observations
  100. GRB 250722A: Fermi GBM Final Real-time Localization

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