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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"

21802 results found.

  1. GRB 250818B: Swift-XRT afterglow detection
  2. GRB 250818B: GOTO optical counterpart candidate
  3. sb25081602: Swift-XRT observations
  4. Fermi GRB 250814B: Global MASTER-Net observations report
  5. GRB 250813B: Liverpool Telescope optical upper limits
  6. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  7. GRB 250814A: GRAWITA TNG NIR observations
  8. GRB 250812A: SVOM/VT optical continued observation
  9. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  10. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  11. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  12. GRB 250814A: P200/WIRC observations of the afterglow candidate
  13. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  14. GRB 250814A: Possible afterglow candidate from P200/WIRC
  15. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  16. Fermi trigger No 776818276: Global MASTER-Net observations report
  17. Swift GRB250814.32: Global MASTER-Net observations report
  18. GRB 250814A: J-band upper limit from WINTER
  19. GRB 250813B: NOT observations of the optical afterglow
  20. GRB 250813B: SVOM/VT optical observations
  21. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  22. GRB 250814A: DDOTI Optical Upper Limit
  23. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  24. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  25. GRB 250813B: Ondrejov D50 fast decay
  26. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  27. EP250812a: Nickel optical upper limit
  28. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  29. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  30. EP250812a: NOT, NTT, and GS observations
  31. GRB 250812A: Swift/UVOT Detection
  32. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  33. EP250812a: SVOM/VT optical counterpart
  34. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  35. IceCube Alert 250813.14: Global MASTER-Net observations report
  36. GRB 250812A: Swift ToO observations
  37. EP 250812a: GOTO optical upper limit
  38. GRB 250812A: Kilonova-Catcher optical afterglow detection
  39. EP250812a: Swift-XRT counterpart detection
  40. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  41. GRB 250812A: SVOM/VT optical afterglow confirmation
  42. GRB 250812A: Swift-XRT afterglow detection
  43. GRB 250812A: TRT likely optical counterpart detection
  44. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  45. GRB 250809A: Swift/UVOT Detection
  46. GRB 250702B: Chandra X-ray Detection
  47. EP250807a: Global MASTER-Net observations report
  48. Fermi GRB 250808A: Global MASTER-Net observations report
  49. GRB 250808A: VLT X-shooter candidate counterpart
  50. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  51. GRB 250808A: Swift-XRT candidate counterpart detection
  52. GRB 250807A: SVOM/VT optical continued observation
  53. EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
  54. GRB 250807B: Swift/UVOT Detection
  55. GRB 250807B: Kilonova-Catcher optical afterglow detection
  56. GRB 250807A: Swift/UVOT Detection
  57. GRB 250806A: SVOM/ECLAIRs refined analysis
  58. EP250807a: NTT z-band optical upper limit
  59. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  60. Swift GRB250807.45: Global MASTER-Net observations report
  61. GRB 250806A: NOT z-band upper limit and host galaxy candidate
  62. GRB 250807B: NTT optical observations
  63. EP250807a: EP-WXT detection of a fast X-ray transient
  64. EP 250807.979: GOTO optical upper limit
  65. GRB 250807A: SVOM/VT optical observation
  66. EP250806a: Upper limit from Fermi-GBM Observations
  67. Swift GRB250807.65: Global MASTER-Net observations report
  68. GRB 250805A: Kilonova-Catcher optical upper limits
  69. GRB 250805A: Swift/UVOT Upper Limits
  70. GRB 250806A: Swift/UVOT U-band detection
  71. IceCube Alert 250804.84: Global MASTER-Net observations report
  72. EP#01709198415/EP250806a: Swift-XRT observations
  73. EP250806a: Global MASTER-Net observations report
  74. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  75. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  76. GRB 250806A: J-band upper limit from WINTER
  77. GRB 250806A: KAIT optical upper limit
  78. GRB 250806A: Kilonova-Catcher optical upper limits
  79. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  80. GRB 250805A: ESO/VLT observations
  81. GRB 250804B: Swift-XRT observations
  82. GRB 250805A: TRT optical upper limits
  83. GRB 250805A: Swift-XRT observations
  84. Swift GRB250805.26: Global MASTER-Net observations report
  85. GRB 250804B: Tiled Swift observations
  86. Fermi trigger No 776041355: Global MASTER-Net observations report
  87. EP250802a: Global MASTER-Net observations report
  88. EP250802a: Einstein Probe detection of an X-ray transient
  89. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  90. GRB 250702B: SMA observations
  91. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  92. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  93. EP250711a: CrAO and Assy optical observations
  94. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  95. EP250730a: Global MASTER-Net observations report
  96. EP250730a: Einstein Probe detection of an X-ray transient
  97. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  98. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  99. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  100. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO

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