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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 250804A: Fermi GBM Final Localization
  2. EP250802a: additional Liverpool Telescope upper limits
  3. EP250730a: SVOM/VT optical upper limit
  4. Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB
  5. EP250802a: Liverpool Telescope optical upper limits
  6. EP250802a: Global MASTER-Net observations report
  7. EP250802a: GROWTH-India Telescope optical upper limit
  8. EP250802a: Einstein Probe detection of an X-ray transient
  9. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  10. The EP-WXT trigger 01709198251 is likely a flaring star
  11. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  12. The EP-WXT trigger 01709198202 is likely a flaring star
  13. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  14. GRB 250702B: SMA observations
  15. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  16. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  17. EP250711a: CrAO and Assy optical observations
  18. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  19. EP250730a: Global MASTER-Net observations report
  20. EP250730a: COLIBRÍ optical upper limit
  21. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  22. EP250730a: Einstein Probe detection of an X-ray transient
  23. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  24. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm
  25. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  26. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  27. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  28. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  29. GRB 250725A: AstroSat CZTI detection
  30. GRB 250727A: EP-FXT follow-up observation
  31. GRB 250725A: PRIME near-infrared observations
  32. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  33. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  34. GRB: Clarification on Gamma-Ray Burst Naming Convention
  35. GRB 250728A: Swift-XRT observations
  36. GRB 250727A: SVOM/ECLAIRs refined analysis
  37. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  38. GRB 250728A: COLIBRÍ optical upper limit
  39. GRB 250728A: Fermi GBM Observation
  40. Fermi trigger No 775387550: Global MASTER-Net observations report
  41. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  42. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  43. GRB 250728A: Swift ToO observations
  44. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  45. GRB 250727A: AST3-2 Upper limit
  46. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  47. GRB 250727A: EP-FXT counterpart detection
  48. GRB250727A: SVOM/VT optical upper limit
  49. GRB 250727A: Swift-XRT observations
  50. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  51. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  52. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  53. GRB 250727A: SVOM detection of a burst
  54. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  55. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  56. The EP-WXT trigger 01709195487 is likely a flaring star
  57. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  58. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  59. GRB 250725A: Swift-XRT refined Analysis
  60. GRB 250725A: Fermi GBM Observation
  61. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  62. GRB 250725A: Swift-BAT refined analysis
  63. Konus-Wind detection of GRB 250725A
  64. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  65. GRB 250725A: SVOM/GRM observation
  66. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  67. GRB 250725A: Swift/UVOT Upper Limits
  68. GRB 250725A: Fermi-LAT detection
  69. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  70. GRB 250725A: BOOTES-7 early optical detection
  71. GRB 250725A: SVOM/VT optical candidate
  72. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  73. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  74. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  75. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  76. GRB 250725A: Enhanced Swift-XRT position
  77. GRB 250725A: Swift detection of a burst
  78. Swift GRB 250725A: Global MASTER-Net OT detection
  79. GRB 250725A: Fermi GBM Final Real-time Localization
  80. Fermi GRB 250725A: Global MASTER-Net observations report
  81. Swift GRB 250725A: Global MASTER-Net observations report
  82. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  83. SVOM J195836+32283 is not a real source
  84. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  85. SVOM J195836+32283/sb25072103: Second VT observation
  86. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  87. GRB 250723B: Fermi GBM Final Real-time Localization
  88. GRB 250721A: Fermi GBM Observation
  89. GRB 250723A: Fermi GBM Final Real-time Localization
  90. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  91. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  92. Swift-BAT trigger 1334535 is not a GRB
  93. GRB 250721A: Swift-XRT observations
  94. GRB 250722A: Fermi GBM Final Real-time Localization
  95. GRB 250713A : SVOM/ECLAIRs refined analysis
  96. GRB 250717B: SVOM/GRM observation
  97. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  98. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  99. GRB 250721A: Tiled Swift observations
  100. GRB 250721A: MAXI/GSC detection

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