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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"

28086 results found.

  1. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  2. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  3. EP250812a: Nickel optical upper limit
  4. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  5. EP250812a: NOT, NTT, and GS observations
  6. GRB 250812A: Swift/UVOT Detection
  7. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  8. EP250812a: Liverpool Telescope upper limits
  9. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  10. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  11. GRB 250812A: EP-FXT counterpart detection
  12. GRB 250807B: Swift-BAT refined analysis
  13. EP 250812a: GOTO optical upper limit
  14. GRB 250812A: Kilonova-Catcher optical afterglow detection
  15. EP250812a: Swift-XRT counterpart detection
  16. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  17. EP250812a: Einstein Probe detection of an X-ray transient
  18. GRB 250812A: Swift-XRT afterglow detection
  19. GRB 250812A: TRT likely optical counterpart detection
  20. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  21. GRB 250809A: Swift-BAT refined analysis
  22. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  23. GRB 250807A: Swift-BAT refined analysis
  24. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  25. GRB 250809A: Swift/UVOT Detection
  26. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  27. Corrected Swift-XRT Refined Analysis of GRB 250809A
  28. GRB 250809A: Swift-XRT refined Analysis
  29. GRB 250809A: LCOGT Optical Upper Limits
  30. GRB 250808A: VLT X-shooter candidate counterpart
  31. GRB 250809A: Swift detection of a gamma ray burst
  32. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  33. GRB 250808A: Fermi GBM Observation
  34. GRB 250808A: Swift-XRT candidate counterpart detection
  35. GRB 250807B: Swift/UVOT Detection
  36. GRB 250807B: Kilonova-Catcher optical afterglow detection
  37. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  38. GRB 250807A: Swift/UVOT Detection
  39. GRB 250807A: Swift-XRT refined Analysis
  40. GRB 250806A: SVOM/MXT refined analysis
  41. EP250807a: NTT z-band optical upper limit
  42. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  43. GRB 250807A: SVOM/GRM observation
  44. GRB 250807A: AstroSat CZTI detection of bright long burst
  45. GRB 250807B: Swift-XRT refined Analysis
  46. EP250807a: EP-WXT detection of a fast X-ray transient
  47. EP 250807.979: GOTO optical upper limit
  48. EP250807a: COLIBRÍ optical upper limit
  49. EP250806a: Upper limit from Fermi-GBM Observations
  50. GRB 250807B: Enhanced Swift-XRT position
  51. GRB 250807A: Enhanced Swift-XRT position
  52. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  53. GRB 250807B: Swift detection of a burst with an optical counterpart.
  54. GRB 250805A: Kilonova-Catcher optical upper limits
  55. GRB 250805A: Swift/UVOT Upper Limits
  56. GRB 250806A: Swift/UVOT U-band detection
  57. EP250806a: Liverpool telescope optical upper limit
  58. GRB 250807A: Swift detection of a burst with an optical counterpart
  59. EP250802a: EP-FXT follow-up observation
  60. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  61. EP250806a: SVOM /VT optical candidate
  62. GRB 250806A: J-band upper limit from WINTER
  63. GRB 250805A: Swift-BAT refined analysis
  64. GRB 250806A: KAIT optical upper limit
  65. GRB 250806A: Swift-XRT counterpart detection
  66. EP250806a: COLIBRÍ optical upper limit
  67. GRB 250806A: Kilonova-Catcher optical upper limits
  68. EP250806a: Einstein Probe detection of an X-ray transient
  69. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  70. GRB 250806A: SVOM/VT optical upper limit
  71. GRB 250806A: SVOM detection of a soft burst
  72. GRB 250805A: SVOM/VT optical counterpart
  73. GRB 250805A: Swift-XRT refined Analysis
  74. GRB 250804B: Swift-XRT observations
  75. GRB 250805A: Enhanced Swift-XRT position
  76. GRB 250805A: TRT optical upper limits
  77. GRB 250805A: Swift-XRT observations
  78. GRB 250804B: SVOM/GRM observation of a short burst
  79. GRB 250804A: Fermi GBM Final Localization
  80. EP250802a: additional Liverpool Telescope upper limits
  81. EP250730a: SVOM/VT optical upper limit
  82. EP250802a: Liverpool Telescope optical upper limits
  83. EP250802a: Global MASTER-Net observations report
  84. EP250802a: GROWTH-India Telescope optical upper limit
  85. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  86. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  87. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  88. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  89. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  90. EP250711a: CrAO and Assy optical observations
  91. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  92. EP250730a: COLIBRÍ optical upper limit
  93. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  94. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  95. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  96. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  97. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  98. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  99. GRB 250727A: EP-FXT follow-up observation
  100. GRB 250725A: PRIME near-infrared observations

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