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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').

24250 results found.

  1. GRB 250321A: Swift-XRT refined Analysis
  2. EP 250321A: Optical counterpart detection by LCO.
  3. EP250321a: Kinder optical follow-up observations
  4. GRB 250321A: Swift/UVOT Upper Limits
  5. GRB 250320B: SVOM/GRM observation of a long burst
  6. EP250321a: LCO optical counterpart detection
  7. EP250321a: Swift-XRT detection of an X-ray source
  8. EP250321A: COLIBRÍ Optical Observations
  9. GRB 250320B: AstroSat CZTI detection
  10. EP250321a: REM optical/NIR afterglow detection
  11. EP250321a: TRT optical counterpart detection
  12. Swift GRB 250321A: Global MASTER-Net observations report
  13. EP250321a: Einstein Probe detection of an X-ray transient
  14. GRB 250321A: GOTO optical upper limits
  15. GRB 250314A: Keck/NIRC2 J-band upper limit
  16. EP250226a/GRB 250226A: KAIT optical observations
  17. GRB 250321A: Fermi GBM Observation
  18. GRB 250321A: Swift detection of a burst
  19. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  20. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  21. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  22. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  23. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  24. GRB 250317D: EIRSAT-1 GMOD Detection
  25. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  26. GRB 250314A: ATCA radio upper limits
  27. GRB 250317B: OHP/T193 continued follow-up
  28. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  29. GRB 250317C: SVOM/GRM observation of a long burst
  30. GRB 250317B: Leavitt Observatory optical upper limit
  31. GRB 250317B: Mondy AZT-33IK Optical Observations
  32. GRB 250317B: NOT optical observations suggest an optical plateau phase
  33. GRB 250317C: GECAM-B detection
  34. GRB 250317B: OHP/T193 optical observations
  35. GRB250312A: Swift/UVOT Upper Limits
  36. GRB 250317B: REM optical/NIR observations
  37. GRB 250317B: Swift-XRT observations
  38. GRB 250316A: Swift/UVOT Upper Limits
  39. GRB 250314A: REM optical/NIR upper limits
  40. GRB 250316A: AbAO AS-32 Optical Upper Limit
  41. EP 250317B: Fading optical counterpart detection by LCO
  42. GRB 250316A: Swift-XRT afterglow detection
  43. GRB 250317B: LCO detection of the fading optical afterglow
  44. GRB250317B: SVOM/VT detection of an optical candidate from VHF data
  45. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  46. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  47. GRB 250317B: SVOM detection of a burst
  48. GRB 250316A: Fermi GBM Observation
  49. GRB 250316A: Swift-XRT observations
  50. GRB 250314A: SVOM/GRM analysis
  51. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  52. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  53. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  54. GRB 250314A: EP-FXT afterglow detection
  55. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  56. GRB 250314A: Swift/UVOT Upper Limits
  57. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  58. GRB 250314A: Swift XRT Detection
  59. EP250315a: optical counterpart candidate detected by Gemini North
  60. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  61. EP250315a: Einstein Probe detection of an X-ray transient
  62. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  63. SVOM/MXT upper limit on GRB 250314A
  64. GRB 250314A: SVOM/VT upper limit
  65. GRB 250314A: NOT near-infrared candidate counterpart
  66. GRB 250313A: Fermi GBM Detection
  67. GRB 250312B: Fermi GBM Observation
  68. GRB 250313A: Swift-XRT observations
  69. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  70. GRB 250314A: SVOM detection of a burst
  71. GRB 250313A: AstroSat CZTI detection of a bright long burst
  72. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  73. GRB 250313A: Fermi-LAT detection
  74. EP250304a: Pan-STARRS r and i-band imaging and photometry
  75. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  76. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  77. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  78. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  79. GRB 250312A: Swift-XRT refined Analysis
  80. GRB 250312A: Enhanced Swift-XRT position
  81. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  82. GRB 250226B: Fermi GBM Observation
  83. GRB 250302A: Fermi GBM Observation
  84. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  85. GRB 250312A: Swift detection of a burst
  86. GRB 241213A: VIRT Optical Upper Limit
  87. GRB 241228A: VIRT Optical Upper Limit
  88. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  89. GRB 250311A: Swift-XRT observations
  90. GRB 230509B: 1.3m DFOT Optical observations
  91. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  92. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  93. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  94. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  95. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  96. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  97. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  98. GRB 250309B: PRIME near-infrared detection
  99. GRB 250225B: Swift-BAT refined analysis
  100. GRB 250311A/EP250311a: TRT optical upper limit

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