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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 250108A: Swift/UVOT Upper Limits
  2. EP250108a: Global MASTER-Net observations report
  3. EP250109a: EP-WXT detection of an X-ray transient
  4. LIGO/Virgo/KAGRA S250109bi: Identification of a GW compact binary merger candidate
  5. GRB 250108A: NOT optical upper limit
  6. EP250108a: EP-WXT detection of an X-ray transient
  7. LIGO/Virgo/KAGRA S250109f: Identification of a GW compact binary merger candidate
  8. GRB 250108B: Swift-XRT refined Analysis
  9. Swift GRB 250108B: Global MASTER-Net observations report
  10. Fermi Gamma-ray Burst Monitor trigger 758061038/250108855 is not a GRB
  11. LIGO/Virgo/KAGRA S250108ha: Retraction of GW compact binary merger candidate
  12. GRB 250108B: Gemini-North Candidate Optical Afterglow Detection
  13. GRB 250103A: 1.6m Mephisto optical observations
  14. GRB 250108A: Swift-XRT afterglow detection
  15. GRB 250108A:SVOM/VT optical candidate
  16. LIGO/Virgo/KAGRA S250108eo: Identification of a GW compact binary merger candidate
  17. GRB 250108B: Swift/UVOT Upper Limits
  18. GRB 250103A: Swift-XRT afterglow detection
  19. GRB 250108B: Enhanced Swift-XRT position
  20. GRB 250108B: Swift detection of a burst
  21. GRB 250108A: Swift ToO observations
  22. GRB 250108A: SVOM detection of a soft long burst
  23. GRB 250107A: Fermi GBM Observation
  24. GRB 241228B: Fermi-LAT detection
  25. Fermi GRB 250107B: Global MASTER-Net observations report
  26. GRB 250107A: Swift ToO observations
  27. GRB 250107A: Swift/BAT-GUANO arcminute localization of a burst
  28. GRB 250107B: Fermi GBM Final Real-time Localization
  29. GRB 250106A: SVOM/VT 2nd optical deep observation
  30. GRB 250101A: J band upper limit by SYSU 80cm telescope
  31. GRB 250107A: Fermi GBM Final Real-time Localization
  32. EPWXT01709129925: Xinglong optical observations
  33. GRB 250106A: NOT optical observations
  34. LIGO/Virgo/KAGRA S250104v: Updated Sky localization
  35. GRB 250103B: REM optical/NIR upper limits
  36. GRB 250101A: REM optical/NIR counterpart detection
  37. GRB 250106A: Swift-XRT observations
  38. GRB 250106A: SVOM/VT optical candidate
  39. GRB 250106A: Swift ToO observations
  40. The EP-WXT trigger 01709129925 is likely a flaring star
  41. GRB 250106A: SVOM detection of a long burst
  42. Fermi trigger No 757753930: Global MASTER-Net observations report
  43. GRB 241229A: SVOM/VT optical upperlimit
  44. GRB 250103B: Swift-XRT refined Analysis
  45. GRB 250103B: LCO/1m optical afterglow candidate detection
  46. GRB 250103A: Bassano Bresciano Observatory upper limit
  47. GRB 250103B: VLT/X-shooter spectroscopic redshift z = 1.416
  48. GRB 250103A: Swift-XRT observations
  49. GRB 250101A: 1.3m DFOT optical afterglow detection
  50. GRB 241229A: 1.3m DFOT upper limit
  51. GRB 241228B: 1.3m DFOT Optical observations
  52. GRB 241228A: 1.3m DFOT upper limit
  53. GRB 250103A: NOT spectroscopic redshift
  54. GRB 250103B：SVOM/VT optical counterpart
  55. LIGO/Virgo/KAGRA S250104v: Identification of a GW compact binary merger candidate
  56. GRB 250103A: Montarrenti Observatory optical detection
  57. GRB 250101A: further LCOGT optical afterglow observations
  58. GRB 250103A: Redshift 4.01 from OSIRIS+/GTC
  59. GRB 250103A: NOT optical observations
  60. GRB 250103A: TSHAO optical upper limit
  61. GRB 250103A: Fermi GBM Observation
  62. GRB 250103B: LCOGT Optical Upper Limit
  63. IceCube-250102A: Upper limits from a search for additional neutrino events in IceCube
  64. Swift GRB 250103B: Global MASTER-Net observations report
  65. GRB 250103A: SVOM/VT optical counterpart confirmation
  66. EP250101a: Liverpool Telescope optical upper limit
  67. GRB 250103A: Swift ToO observations
  68. IceCube-250101A: Upper limits from a search for additional neutrino events in IceCube
  69. GRB 250101a: Liverpool Telescope optical follow-up
  70. GRB 250103B: SVOM detection of a long burst
  71. GRB 250103B: Swift detection of a burst
  72. GRB 250103A: Xinglong 2.16m Optical Candidate
  73. Fermi GRB 250102A: Global MASTER-Net observations report
  74. GRB 250101B: SVOM/GRM observation
  75. GRB 250103A: GOTO optical upper limit
  76. GRB 250103A: SVOM/C-GFT optical upper limit
  77. GRB 250101A: NUTTelA-TAO / BSTI Optical Limits
  78. IceCube Alert 250102.58: Global MASTER-Net observations report
  79. EP241231b: optical upper limit with the Liverpool Telescope
  80. GRB 250103A: SVOM detection of a long burst (duplicate submission)
  81. GRB 250103A: SVOM detection of a long burst
  82. EP250101a: Xinglong optical upper limit
  83. GRB 250102A: Fermi GBM Final Real-time Localization
  84. LIGO/Virgo/KAGRA S241230bd: Upper limits from Swift/BAT-GUANO
  85. GRB 250101A: Swift-BAT refined analysis
  86. IceCube-250102A - IceCube observation of a high-energy neutrino candidate track-like event
  87. GRB 250101A: further SAO RAS optical observations
  88. GRB 250101A: LCO optical counterpart detection
  89. EP241231b and EP250101a: EP-WXT detection of two X-ray transients
  90. GRB 250101A NUTTelA-TAO / BSTI Early Measurements
  91. GRB 250101A: GMG spectroscopic redshift at z ~ 2.481
  92. GRB 250101A: Swift/UVOT Detection
  93. GRB 250101A: 1.6m Mephisto multi-band optical followup
  94. GRB 250101A: Swift-XRT refined Analysis
  95. Fermi Gamma-ray Burst Monitor trigger 757464861/250101954 is not a GRB
  96. GRB 250101A: Montarrenti Observatory optical observations and rebrightening
  97. IceCube-250101A - IceCube observation of a high-energy neutrino candidate track-like event
  98. GRB 250101A: LCOGT optical afterglow detection
  99. GRB 250101A: OASDG optical observations
  100. Fermi GRB 250101B: Global MASTER-Net observations report

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