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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 250101A: further LCOGT optical afterglow observations
  2. GRB 250103A: Redshift 4.01 from OSIRIS+/GTC
  3. GRB 250103A: NOT optical observations
  4. GRB 250103A: TSHAO optical upper limit
  5. GRB 250103A: Fermi GBM Observation
  6. GRB 250103B: LCOGT Optical Upper Limit
  7. IceCube-250102A: Upper limits from a search for additional neutrino events in IceCube
  8. Swift GRB 250103B: Global MASTER-Net observations report
  9. GRB 250103A: SVOM/VT optical counterpart confirmation
  10. EP250101a: Liverpool Telescope optical upper limit
  11. GRB 250103A: Swift ToO observations
  12. IceCube-250101A: Upper limits from a search for additional neutrino events in IceCube
  13. GRB 250101a: Liverpool Telescope optical follow-up
  14. GRB 250103B: SVOM detection of a long burst
  15. GRB 250103B: Swift detection of a burst
  16. GRB 250103A: Xinglong 2.16m Optical Candidate
  17. Fermi GRB 250102A: Global MASTER-Net observations report
  18. GRB 250101B: SVOM/GRM observation
  19. GRB 250103A: GOTO optical upper limit
  20. GRB 250103A: SVOM/C-GFT optical upper limit
  21. GRB 250101A: NUTTelA-TAO / BSTI Optical Limits
  22. IceCube Alert 250102.58: Global MASTER-Net observations report
  23. EP241231b: optical upper limit with the Liverpool Telescope
  24. GRB 250103A: SVOM detection of a long burst (duplicate submission)
  25. GRB 250103A: SVOM detection of a long burst
  26. EP250101a: Xinglong optical upper limit
  27. GRB 250102A: Fermi GBM Final Real-time Localization
  28. LIGO/Virgo/KAGRA S241230bd: Upper limits from Swift/BAT-GUANO
  29. GRB 250101A: Swift-BAT refined analysis
  30. IceCube-250102A - IceCube observation of a high-energy neutrino candidate track-like event
  31. GRB 250101A: further SAO RAS optical observations
  32. GRB 250101A: LCO optical counterpart detection
  33. EP241231b and EP250101a: EP-WXT detection of two X-ray transients
  34. GRB 250101A NUTTelA-TAO / BSTI Early Measurements
  35. GRB 250101A: GMG spectroscopic redshift at z ~ 2.481
  36. GRB 250101A: Swift/UVOT Detection
  37. GRB 250101A: 1.6m Mephisto multi-band optical followup
  38. GRB 250101A: Swift-XRT refined Analysis
  39. Fermi Gamma-ray Burst Monitor trigger 757464861/250101954 is not a GRB
  40. GRB 250101A: Montarrenti Observatory optical observations and rebrightening
  41. IceCube-250101A - IceCube observation of a high-energy neutrino candidate track-like event
  42. GRB 250101A: LCOGT optical afterglow detection
  43. GRB 250101A: OASDG optical observations
  44. Fermi GRB 250101B: Global MASTER-Net observations report
  45. GRB 250101B: Fermi GBM Final Real-time Localization
  46. GRB 250101A: SAO RAS observations of optical brightening
  47. GRB 250101A: BOOTES-4/MET optical afterglow detection
  48. GRB 250101A: AKO Optical Afterglow Detection
  49. GRB 250101A: SAO RAS optical observations
  50. GRB 250101A: Enhanced Swift-XRT position
  51. LIGO/Virgo/KAGRA S250101k: Updated Sky localization and Source Classification
  52. GRB 250101A: Xinglong-2.16m spectroscopic redshift
  53. GRB 250101A: SVOM/C-GFT early optical observations
  54. LIGO/Virgo/KAGRA S250101k: Upper limits from Fermi-GBM Observations
  55. GRB 250101A: MASTER earlier OT observations with SOSS emission features
  56. GRB 250101A: Nanshan/HMT optical observations
  57. GRB 250101A : GIT optical detection
  58. GRB 250101A: GMG Optical Observation
  59. GRB 250101A: Swift detection of a burst with an optical counterpart
  60. Swift GRB250101.56: Global MASTER-Net observations report
  61. GRB 241217a/EP241217b: ATCA Radio Detection
  62. EP241217a: VLA Radio Detection

  63. LIGO/Virgo/KAGRA S241231du: Coverage and upper limit from MAXI/GSC observations
  64. LIGO/Virgo/KAGRA S250101k: Identification of a GW compact binary merger candidate
  65. GRB 241229B: Continued CrAO ZTSh observations
  66. LIGO/Virgo/KAGRA S241231bg: Updated NED Galaxies in the Localization Volume
  67. LIGO/Virgo/KAGRA S241231bg: Updated Sky localization and EM Bright Classification
  68. LIGO/Virgo/KAGRA S241230ev: Updated Sky localization
  69. LIGO/Virgo/KAGRA S241231bg: NED Galaxies in the Localization Volume
  70. LIGO/Virgo/KAGRA S241230bd: Updated Sky localization
  71. GRB 241229A: EP-FXT X-ray afterglow confirmation
  72. GRB 241228B: Multiband optical monitoring with 1.6m Mephisto
  73. GRB 241229B: SVOM/GRM observation
  74. LIGO/Virgo/KAGRA S241231bg: Identification of a GW compact binary merger candidate
  75. EP241217A: J band upper limit by SYSU 80cm telescope
  76. LIGO/Virgo/KAGRA S241230ev: Identification of a GW compact binary merger candidate
  77. GRB 241229B: SAO RAS optical upper limit
  78. GRB 241228B: SAO RAS optical observations
  79. GRB 241229B: CrAO ZTSh possible optical counterpart of SVOM/VT confirmation
  80. GRB 241229A: SAO RAS optical observations
  81. IceCube-Cascade 241228A: Upper limits from a search for additional neutrino events in IceCube
  82. GRB 241229B: SVOM/VT optical candidate
  83. GRB 241229A: Swift-XRT observations
  84. Konus-Wind detection of GRB 241228A
  85. GRB 241229A: EP-FXT afterglow candidates
  86. EP240702a: 7DT Optical upper limits
  87. GRB 240606B: 7DT Optical upper limits
  88. Fermi trigger No 757231333: Global MASTER-Net observations report
  89. LIGO/Virgo/KAGRA S241230bd: Identification of a GW compact binary merger candidate
  90. GRB 241229B: Swift-BAT refined analysis
  91. LIGO/Virgo/KAGRA S241225v: Updated Sky localization
  92. LIGO/Virgo/KAGRA S241225c: Updated Sky localization and EM Bright Classification
  93. Fermi Gamma-ray Burst Monitor trigger 757207662/241229978 (GRB 241229C) is not a GRB
  94. GRB241229B: UVOT upper limits
  95. GRB 241229C: Fermi GBM Final Real-time Localization
  96. GRB 241228B: D50 optical detection
  97. GRB 241228B: Fermi GBM Observation
  98. GRB 241228B: Swift-XRT afterglow detection
  99. GRB 241229B: Fermi GBM Observation
  100. GRB 241229A: Swift ToO observations

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