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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 241229A: SVOM/VT optical upperlimit
  2. GRB 250103B: Swift-XRT refined Analysis
  3. GRB 250103B: LCO/1m optical afterglow candidate detection
  4. GRB 250103A: Bassano Bresciano Observatory upper limit
  5. GRB 250103B: VLT/X-shooter spectroscopic redshift z = 1.416
  6. GRB 250103A: Swift-XRT observations
  7. GRB 250101A: 1.3m DFOT optical afterglow detection
  8. GRB 241229A: 1.3m DFOT upper limit
  9. GRB 241228B: 1.3m DFOT Optical observations
  10. GRB 241228A: 1.3m DFOT upper limit
  11. GRB 250103A: NOT spectroscopic redshift
  12. GRB 250103B：SVOM/VT optical counterpart
  13. LIGO/Virgo/KAGRA S250104v: Identification of a GW compact binary merger candidate
  14. GRB 250103A: Montarrenti Observatory optical detection
  15. GRB 250101A: further LCOGT optical afterglow observations
  16. GRB 250103A: Redshift 4.01 from OSIRIS+/GTC
  17. GRB 250103A: NOT optical observations
  18. GRB 250103A: TSHAO optical upper limit
  19. GRB 250103A: Fermi GBM Observation
  20. GRB 250103B: LCOGT Optical Upper Limit
  21. IceCube-250102A: Upper limits from a search for additional neutrino events in IceCube
  22. Swift GRB 250103B: Global MASTER-Net observations report
  23. GRB 250103A: SVOM/VT optical counterpart confirmation
  24. EP250101a: Liverpool Telescope optical upper limit
  25. GRB 250103A: Swift ToO observations
  26. IceCube-250101A: Upper limits from a search for additional neutrino events in IceCube
  27. GRB 250101a: Liverpool Telescope optical follow-up
  28. GRB 250103B: SVOM detection of a long burst
  29. GRB 250103B: Swift detection of a burst
  30. GRB 250103A: Xinglong 2.16m Optical Candidate
  31. Fermi GRB 250102A: Global MASTER-Net observations report
  32. GRB 250101B: SVOM/GRM observation
  33. GRB 250103A: GOTO optical upper limit
  34. GRB 250103A: SVOM/C-GFT optical upper limit
  35. GRB 250101A: NUTTelA-TAO / BSTI Optical Limits
  36. IceCube Alert 250102.58: Global MASTER-Net observations report
  37. EP241231b: optical upper limit with the Liverpool Telescope
  38. GRB 250103A: SVOM detection of a long burst (duplicate submission)
  39. GRB 250103A: SVOM detection of a long burst
  40. EP250101a: Xinglong optical upper limit
  41. GRB 250102A: Fermi GBM Final Real-time Localization
  42. LIGO/Virgo/KAGRA S241230bd: Upper limits from Swift/BAT-GUANO
  43. GRB 250101A: Swift-BAT refined analysis
  44. IceCube-250102A - IceCube observation of a high-energy neutrino candidate track-like event
  45. GRB 250101A: further SAO RAS optical observations
  46. GRB 250101A: LCO optical counterpart detection
  47. EP241231b and EP250101a: EP-WXT detection of two X-ray transients
  48. GRB 250101A NUTTelA-TAO / BSTI Early Measurements
  49. GRB 250101A: GMG spectroscopic redshift at z ~ 2.481
  50. GRB 250101A: Swift/UVOT Detection
  51. GRB 250101A: 1.6m Mephisto multi-band optical followup
  52. GRB 250101A: Swift-XRT refined Analysis
  53. Fermi Gamma-ray Burst Monitor trigger 757464861/250101954 is not a GRB
  54. GRB 250101A: Montarrenti Observatory optical observations and rebrightening
  55. IceCube-250101A - IceCube observation of a high-energy neutrino candidate track-like event
  56. GRB 250101A: LCOGT optical afterglow detection
  57. GRB 250101A: OASDG optical observations
  58. Fermi GRB 250101B: Global MASTER-Net observations report
  59. GRB 250101B: Fermi GBM Final Real-time Localization
  60. GRB 250101A: SAO RAS observations of optical brightening
  61. GRB 250101A: BOOTES-4/MET optical afterglow detection
  62. GRB 250101A: AKO Optical Afterglow Detection
  63. GRB 250101A: SAO RAS optical observations
  64. GRB 250101A: Enhanced Swift-XRT position
  65. LIGO/Virgo/KAGRA S250101k: Updated Sky localization and Source Classification
  66. GRB 250101A: Xinglong-2.16m spectroscopic redshift
  67. GRB 250101A: SVOM/C-GFT early optical observations
  68. LIGO/Virgo/KAGRA S250101k: Upper limits from Fermi-GBM Observations
  69. GRB 250101A: MASTER earlier OT observations with SOSS emission features
  70. GRB 250101A: Nanshan/HMT optical observations
  71. GRB 250101A : GIT optical detection
  72. GRB 250101A: GMG Optical Observation
  73. GRB 250101A: Swift detection of a burst with an optical counterpart
  74. Swift GRB250101.56: Global MASTER-Net observations report
  75. GRB 241217a/EP241217b: ATCA Radio Detection
  76. EP241217a: VLA Radio Detection

  77. LIGO/Virgo/KAGRA S241231du: Coverage and upper limit from MAXI/GSC observations
  78. LIGO/Virgo/KAGRA S250101k: Identification of a GW compact binary merger candidate
  79. GRB 241229B: Continued CrAO ZTSh observations
  80. LIGO/Virgo/KAGRA S241231bg: Updated NED Galaxies in the Localization Volume
  81. LIGO/Virgo/KAGRA S241231bg: Updated Sky localization and EM Bright Classification
  82. LIGO/Virgo/KAGRA S241230ev: Updated Sky localization
  83. LIGO/Virgo/KAGRA S241231bg: NED Galaxies in the Localization Volume
  84. LIGO/Virgo/KAGRA S241230bd: Updated Sky localization
  85. GRB 241229A: EP-FXT X-ray afterglow confirmation
  86. GRB 241228B: Multiband optical monitoring with 1.6m Mephisto
  87. GRB 241229B: SVOM/GRM observation
  88. LIGO/Virgo/KAGRA S241231bg: Identification of a GW compact binary merger candidate
  89. EP241217A: J band upper limit by SYSU 80cm telescope
  90. LIGO/Virgo/KAGRA S241230ev: Identification of a GW compact binary merger candidate
  91. GRB 241229B: SAO RAS optical upper limit
  92. GRB 241228B: SAO RAS optical observations
  93. GRB 241229B: CrAO ZTSh possible optical counterpart of SVOM/VT confirmation
  94. GRB 241229A: SAO RAS optical observations
  95. IceCube-Cascade 241228A: Upper limits from a search for additional neutrino events in IceCube
  96. GRB 241229B: SVOM/VT optical candidate
  97. GRB 241229A: Swift-XRT observations
  98. Konus-Wind detection of GRB 241228A
  99. GRB 241229A: EP-FXT afterglow candidates
  100. EP240702a: 7DT Optical upper limits

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