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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 250815A: Fermi GBM Final Localization
  2. GRB 250813B: Liverpool Telescope optical upper limits
  3. GRB 250814A: Further COLIBRÍ optical upper limit
  4. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  5. GRB 250814A: GRAWITA TNG NIR observations
  6. GRB 250812A: SVOM/VT optical continued observation
  7. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  8. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  9. GRB250814A: TRT optical upper limits
  10. GRB 250814B: SVOM/GRM observation
  11. GRB 250814C: SVOM/GRM observation of a short burst
  12. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  13. GRB 250813B: SVOM/GRM observation
  14. GRB 250814A: P200/WIRC observations of the afterglow candidate
  15. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  16. GRB 250814A: KAIT optical upper limit
  17. GRB 250814A: Swift-XRT refined Analysis
  18. GRB 240814A: Fermi GBM Observation
  19. GRB 250814A: Possible afterglow candidate from P200/WIRC
  20. GRB 250813B: Fermi GBM Observation
  21. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  22. Fermi trigger No 776818276: Global MASTER-Net observations report
  23. Swift GRB250814.32: Global MASTER-Net observations report
  24. GRB 250814A: J-band upper limit from WINTER
  25. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  26. GRB 250813B: NOT observations of the optical afterglow
  27. GRB 250813B: SVOM/VT optical observations
  28. Subject GRB 250813B: SVOM/MXT refined analysis
  29. GRB 250814A: COLIBRÍ optical upper limit
  30. GRB 250814B: Fermi GBM Final Real-time Localization
  31. GRB 250813A: AstroSat CZTI detection
  32. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  33. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  34. GRB 250814A: DDOTI Optical Upper Limit
  35. GRB 250813B: EP-FXT counterpart detection
  36. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  37. GRB 250813B: Swift-XRT afterglow detection
  38. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  39. GRB 250814A: Fermi GBM Final Real-time Localization
  40. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  41. GRB 250813B: Ondrejov D50 fast decay
  42. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  43. GRB 250813B: Ondrejov D50 optical afterglow detection
  44. GRB 250813B: SVOM detection of a bright long burst
  45. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  46. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  47. EP250812a: Nickel optical upper limit
  48. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  49. GRB 250812A: NTT spectroscopic redshift z = 2.57
  50. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  51. EP250812a: NOT, NTT, and GS observations
  52. GRB 250812A: Swift/UVOT Detection
  53. GRB 250813A: Fermi GBM Final Localization
  54. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  55. EP250812a: Liverpool Telescope upper limits
  56. EP250812a: SVOM/VT optical counterpart
  57. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  58. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  59. IceCube Alert 250813.14: Global MASTER-Net observations report
  60. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  61. GRB 250812A: EP-FXT counterpart detection
  62. GRB 250812A: Swift ToO observations
  63. GRB 250807B: Swift-BAT refined analysis
  64. EP 250812a: GOTO optical upper limit
  65. GRB 250812A: Kilonova-Catcher optical afterglow detection
  66. EP250812a: Swift-XRT counterpart detection
  67. Fermi Gamma-ray Burst Monitor trigger 776705265/250812644 is not a GRB
  68. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  69. EP250812a: Einstein Probe detection of an X-ray transient
  70. GRB 250812A: SVOM/VT optical afterglow confirmation
  71. GRB 250812A: Swift-XRT afterglow detection
  72. GRB 250812A: TRT likely optical counterpart detection
  73. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  74. GRB 250812A: SVOM detection of a faint long burst
  75. GRB 250809A: Swift-BAT refined analysis
  76. Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB
  77. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  78. GRB 250807A: Swift-BAT refined analysis
  79. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  80. GRB 250809A: Swift/UVOT Detection
  81. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  82. Corrected Swift-XRT Refined Analysis of GRB 250809A
  83. GRB 250809A: Swift-XRT refined Analysis
  84. GRB 250807B: SVOM/VT optical observation
  85. EP250807a: EP-FXT follow-up observation upper limit
  86. GRB 250809A: LCOGT Optical Upper Limits
  87. GRB 250702B: Chandra X-ray Detection
  88. EP250807a: Global MASTER-Net observations report
  89. Fermi GRB 250808A: Global MASTER-Net observations report
  90. Fermi Gamma-ray Burst Monitor trigger 776449964/250809689 is not a GRB
  91. GRB 250808A: VLT X-shooter candidate counterpart
  92. GRB 250809A: Prompt enhanced Swift-XRT position
  93. GRB 250809A: Swift detection of a gamma ray burst
  94. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  95. GRB 250808A: Fermi GBM Observation
  96. GRB 250808A: Swift-XRT candidate counterpart detection
  97. GRB 250807A: SVOM/VT optical continued observation
  98. EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
  99. GRB 250808A: SVOM detection of a long burst
  100. GRB 250808A: Fermi GBM Final Real-time Localization

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