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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"

45668 results found.

  1. GRB 250807A: Swift-XRT refined Analysis
  2. GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522
  3. GRB 250806A: SVOM/MXT refined analysis
  4. GRB 250806A: SVOM/ECLAIRs refined analysis
  5. EP250807a: NTT z-band optical upper limit
  6. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  7. GRB 250804B: Insight-HXMT detection
  8. GRB 250807A: SVOM/GRM observation
  9. Swift GRB250807.45: Global MASTER-Net observations report
  10. GRB 250807A: AstroSat CZTI detection of bright long burst
  11. GRB 250807B: Swift-XRT refined Analysis
  12. GRB 250806A: NOT z-band upper limit and host galaxy candidate
  13. GRB 250807B: NTT optical observations
  14. EP250807a: EP-WXT detection of a fast X-ray transient
  15. EP 250807.979: GOTO optical upper limit
  16. EP250807a: COLIBRÍ optical upper limit
  17. GRB 250807A: SVOM/VT optical observation
  18. EP250806a: Upper limit from Fermi-GBM Observations
  19. GRB 250807B: Enhanced Swift-XRT position
  20. Swift GRB250807.65: Global MASTER-Net observations report
  21. GRB 250807A: Enhanced Swift-XRT position
  22. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  23. GRB 250807B: Swift detection of a burst with an optical counterpart.
  24. GRB 250805A: Kilonova-Catcher optical upper limits
  25. EP250806a:SVOM/VT refined analysis
  26. GRB 250805A: Swift/UVOT Upper Limits
  27. GRB 250806A: Swift/UVOT U-band detection
  28. EP250806a: Liverpool telescope optical upper limit
  29. GRB 250807A: Swift detection of a burst with an optical counterpart
  30. IceCube Alert 250804.84: Global MASTER-Net observations report
  31. GRB 250806A: EP-FXT observation
  32. EP#01709198415/EP250806a: Swift-XRT observations
  33. EP250806a: Global MASTER-Net observations report
  34. EP250802a: EP-FXT follow-up observation
  35. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  36. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  37. EP250806a: SVOM /VT optical candidate
  38. GRB 250806A: J-band upper limit from WINTER
  39. GRB 250805A: Swift-BAT refined analysis
  40. GRB 250806A: KAIT optical upper limit
  41. GRB 250806A: SVOM/VT refined analysis
  42. GRB 250806A: Swift-XRT counterpart detection
  43. EP250806a: COLIBRÍ optical upper limit
  44. GRB 250806A: Kilonova-Catcher optical upper limits
  45. EP250806a: Einstein Probe detection of an X-ray transient
  46. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  47. GRB 250806A: SVOM/VT optical upper limit
  48. GRB 250806A: SVOM detection of a soft burst
  49. GRB 250805A: SVOM/VT optical counterpart
  50. GRB 250805A: ESO/VLT observations
  51. GRB 250805A: Swift-XRT refined Analysis
  52. GRB 250804B: Swift-XRT observations
  53. GRB 250805A: Enhanced Swift-XRT position
  54. GRB 250804C: AstroSat CZTI detection of a long burst
  55. GRB 250805A: TRT optical upper limits
  56. IceCube-250804A - IceCube observation of a high-energy neutrino candidate track-like event
  57. GRB 250805A: Swift-XRT observations
  58. GRB 250805A: Swift detection of a burst
  59. Swift GRB250805.26: Global MASTER-Net observations report
  60. GRB 250804B: Tiled Swift observations
  61. Fermi trigger No 776041355: Global MASTER-Net observations report
  62. GRB 250804B: SVOM/GRM observation of a short burst
  63. GRB 250804A: Fermi GBM Final Localization
  64. EP250802a: additional Liverpool Telescope upper limits
  65. EP250730a: SVOM/VT optical upper limit
  66. Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB
  67. EP250802a: Liverpool Telescope optical upper limits
  68. EP250802a: Global MASTER-Net observations report
  69. EP250802a: GROWTH-India Telescope optical upper limit
  70. EP250802a: Einstein Probe detection of an X-ray transient
  71. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  72. The EP-WXT trigger 01709198251 is likely a flaring star
  73. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  74. The EP-WXT trigger 01709198202 is likely a flaring star
  75. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  76. GRB 250702B: SMA observations
  77. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  78. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  79. EP250711a: CrAO and Assy optical observations
  80. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  81. EP250730a: Global MASTER-Net observations report
  82. EP250730a: COLIBRÍ optical upper limit
  83. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  84. EP250730a: Einstein Probe detection of an X-ray transient
  85. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  86. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm
  87. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  88. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  89. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  90. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  91. GRB 250725A: AstroSat CZTI detection
  92. GRB 250727A: EP-FXT follow-up observation
  93. GRB 250725A: PRIME near-infrared observations
  94. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  95. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  96. GRB: Clarification on Gamma-Ray Burst Naming Convention
  97. GRB 250728A: Swift-XRT observations
  98. GRB 250727A: SVOM/ECLAIRs refined analysis
  99. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  100. GRB 250728A: COLIBRÍ optical upper limit

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