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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"

22086 results found.

  1. GRB 250814A: P200/WIRC observations of the afterglow candidate
  2. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  3. GRB 250814A: KAIT optical upper limit
  4. GRB 250814A: Swift-XRT refined Analysis
  5. GRB 250814A: Possible afterglow candidate from P200/WIRC
  6. GRB 250813B: Fermi GBM Observation
  7. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  8. GRB 250814A: J-band upper limit from WINTER
  9. GRB 250813B: NOT observations of the optical afterglow
  10. GRB 250814A: COLIBRÍ optical upper limit
  11. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  12. GRB 250814A: DDOTI Optical Upper Limit
  13. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  14. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  15. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  16. GRB 250813B: SVOM detection of a bright long burst
  17. EP250812a: Nickel optical upper limit
  18. EP250812a: NOT, NTT, and GS observations
  19. GRB 250812A: Swift/UVOT Detection
  20. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  21. EP250812a: Liverpool Telescope upper limits
  22. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  23. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  24. EP 250812a: GOTO optical upper limit
  25. GRB 250812A: Kilonova-Catcher optical afterglow detection
  26. EP250812a: Swift-XRT counterpart detection
  27. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  28. EP250812a: Einstein Probe detection of an X-ray transient
  29. GRB 250812A: Swift-XRT afterglow detection
  30. GRB 250812A: TRT likely optical counterpart detection
  31. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  32. GRB 250809A: Swift/UVOT Detection
  33. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  34. GRB 250809A: Swift-XRT refined Analysis
  35. GRB 250809A: LCOGT Optical Upper Limits
  36. GRB 250808A: VLT X-shooter candidate counterpart
  37. GRB 250809A: Swift detection of a gamma ray burst
  38. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  39. GRB 250808A: Swift-XRT candidate counterpart detection
  40. GRB 250807B: Swift/UVOT Detection
  41. GRB 250807B: Kilonova-Catcher optical afterglow detection
  42. GRB 250807A: Swift/UVOT Detection
  43. EP250807a: NTT z-band optical upper limit
  44. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  45. GRB 250807A: SVOM/GRM observation
  46. GRB 250807A: AstroSat CZTI detection of bright long burst
  47. GRB 250807B: Swift-XRT refined Analysis
  48. EP250807a: EP-WXT detection of a fast X-ray transient
  49. EP 250807.979: GOTO optical upper limit
  50. EP250807a: COLIBRÍ optical upper limit
  51. GRB 250807A: SVOM/VT optical observation
  52. GRB 250807B: Enhanced Swift-XRT position
  53. GRB 250807A: Enhanced Swift-XRT position
  54. GRB 250807B: Swift detection of a burst with an optical counterpart.
  55. GRB 250805A: Kilonova-Catcher optical upper limits
  56. EP250806a:SVOM/VT refined analysis
  57. GRB 250805A: Swift/UVOT Upper Limits
  58. GRB 250806A: Swift/UVOT U-band detection
  59. EP250806a: Liverpool telescope optical upper limit
  60. GRB 250807A: Swift detection of a burst with an optical counterpart
  61. EP250802a: EP-FXT follow-up observation
  62. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  63. EP250806a: SVOM /VT optical candidate
  64. GRB 250806A: J-band upper limit from WINTER
  65. GRB 250806A: KAIT optical upper limit
  66. GRB 250806A: SVOM/VT refined analysis
  67. EP250806a: COLIBRÍ optical upper limit
  68. GRB 250806A: Kilonova-Catcher optical upper limits
  69. EP250806a: Einstein Probe detection of an X-ray transient
  70. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  71. GRB 250806A: SVOM/VT optical upper limit
  72. GRB 250806A: SVOM detection of a soft burst
  73. GRB 250805A: SVOM/VT optical counterpart
  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 250805A: Swift detection of a burst
  79. GRB 250804B: SVOM/GRM observation of a short burst
  80. EP250802a: additional Liverpool Telescope upper limits
  81. EP250730a: SVOM/VT optical upper limit
  82. EP250802a: Liverpool Telescope optical upper limits
  83. EP250802a: GROWTH-India Telescope optical upper limit
  84. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  85. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  86. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  87. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  88. EP250711a: CrAO and Assy optical observations
  89. EP250730a: COLIBRÍ optical upper limit
  90. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  91. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  92. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm
  93. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  94. GRB 250727A: EP-FXT follow-up observation
  95. GRB 250725A: PRIME near-infrared observations
  96. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  97. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  98. GRB 250728A: Swift-XRT observations
  99. GRB 250728A: COLIBRÍ optical upper limit
  100. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst

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