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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"

21232 results found.

  1. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  2. GRB 250814A: J-band upper limit from WINTER
  3. GRB 250813B: NOT observations of the optical afterglow
  4. GRB 250814A: COLIBRÍ optical upper limit
  5. GRB 250813A: AstroSat CZTI detection
  6. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  7. GRB 250814A: DDOTI Optical Upper Limit
  8. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  9. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  10. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  11. GRB 250813B: SVOM detection of a bright long burst
  12. EP250812a: Nickel optical upper limit
  13. EP250812a: NOT, NTT, and GS observations
  14. GRB 250812A: Swift/UVOT Detection
  15. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  16. EP250812a: Liverpool Telescope upper limits
  17. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  18. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  19. EP 250812a: GOTO optical upper limit
  20. GRB 250812A: Kilonova-Catcher optical afterglow detection
  21. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  22. EP250812a: Einstein Probe detection of an X-ray transient
  23. GRB 250812A: Swift-XRT afterglow detection
  24. GRB 250812A: TRT likely optical counterpart detection
  25. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  26. GRB 250809A: Swift/UVOT Detection
  27. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  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: SVOM detection of a long burst
  34. Konus-Wind detection of GRB 250807A
  35. GRB 250807B: Swift/UVOT Detection
  36. GRB 250807B: Kilonova-Catcher optical afterglow detection
  37. GRB 250807A: Swift/UVOT Detection
  38. GRB 250807A: Swift-XRT refined Analysis
  39. GRB 250806A: SVOM/MXT refined analysis
  40. EP250807a: NTT z-band optical upper limit
  41. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  42. GRB 250807A: SVOM/GRM observation
  43. GRB 250807A: AstroSat CZTI detection of bright long burst
  44. EP250807a: EP-WXT detection of a fast X-ray transient
  45. EP 250807.979: GOTO optical upper limit
  46. EP250807a: COLIBRÍ optical upper limit
  47. GRB 250807B: Enhanced Swift-XRT position
  48. GRB 250807A: Enhanced Swift-XRT position
  49. GRB 250807B: Swift detection of a burst with an optical counterpart.
  50. GRB 250805A: Kilonova-Catcher optical upper limits
  51. GRB 250805A: Swift/UVOT Upper Limits
  52. GRB 250806A: Swift/UVOT U-band detection
  53. EP250806a: Liverpool telescope optical upper limit
  54. GRB 250807A: Swift detection of a burst with an optical counterpart
  55. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  56. EP250806a: SVOM /VT optical candidate
  57. GRB 250806A: J-band upper limit from WINTER
  58. GRB 250806A: KAIT optical upper limit
  59. GRB 250806A: Swift-XRT counterpart detection
  60. EP250806a: COLIBRÍ optical upper limit
  61. GRB 250806A: Kilonova-Catcher optical upper limits
  62. EP250806a: Einstein Probe detection of an X-ray transient
  63. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  64. GRB 250806A: SVOM/VT optical upper limit
  65. GRB 250806A: SVOM detection of a soft burst
  66. GRB 250805A: SVOM/VT optical counterpart
  67. GRB 250804B: Swift-XRT observations
  68. GRB 250805A: Enhanced Swift-XRT position
  69. GRB 250805A: TRT optical upper limits
  70. GRB 250805A: Swift-XRT observations
  71. GRB 250804B: SVOM/GRM observation of a short burst
  72. EP250802a: additional Liverpool Telescope upper limits
  73. EP250730a: SVOM/VT optical upper limit
  74. EP250802a: Liverpool Telescope optical upper limits
  75. EP250802a: GROWTH-India Telescope optical upper limit
  76. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  77. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  78. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  79. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  80. EP250711a: CrAO and Assy optical observations
  81. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  82. EP250730a: COLIBRÍ optical upper limit
  83. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  84. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  85. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  86. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  87. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  88. GRB 250725A: PRIME near-infrared observations
  89. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  90. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  91. GRB 250727A: SVOM/ECLAIRs refined analysis
  92. GRB 250728A: COLIBRÍ optical upper limit
  93. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  94. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  95. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  96. GRB 250727A: SVOM detection of a burst
  97. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  98. Konus-Wind detection of GRB 250725A
  99. GRB 250725A: SVOM/GRM observation
  100. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.

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